Oncom: A Nutritive Functional Fermented Food Made from Food Process Solid Residue

Abstract

Food security is one of the critical issues in facing the world food crisis. Utilizing food processing residue waste to make nutritious and healthy functional foods should follow a double-merit approach in facing the world food crisis. Oncom, an overlooked traditional fermented product based on local wisdom, might be an example of potential sustainable food to overcome hunger and support the circular economy programme. This review attempts to portray the existence and role of oncom based on a systematic study of hundreds of reports from different angles, mainly focusing on its processing, the microbes involved, its sensory characteristics, nutritional benefits, and promising bioactivities. Oncom can be produced by various raw materials such as tofu dreg (okara), peanut press cake, and tapioca solid waste, involving various microbes, mainly Neurospora sp. or Rhizopus sp., and various processing steps. The products show promising nutritional values. In terms of sensory characteristics, oncom is sensory-friendly due to its umami dominance. Many bioactivity capacities have been reported, including antioxidants, lowering cholesterol effect, and cardiovascular disease prevention, although some findings are still only preliminary. Undoubtedly, oncom has the potential to be developed as a future functional food with standardized quality and reliable bioefficacy. This kind of solid fermented product, based on agricultural residue wastes, is worthy of further development worldwide with full scientific support to create more reliable functional foods with a modern touch to achieve zero hunger.

1. Introduction

The food crisis has worsened dramatically due to wars and climate change. A breakthrough innovation to a sustainable, climate-friendly, and cost-affordable food system is urgently needed as the food sector must feed at least 9 billion people by 2050 [1,2].

Reducing food waste, particularly food processing residue, has been considered one of the critical approaches to improving world food security. Fermented foods using product residue should provide double or multiple benefits. Residue of agricultural products, if released into the environment without proper disposal, may cause environmental pollution and harm human and animal health. Most agro-industrial waste is untreated and underutilized. The effective use of agro-residue to improve nutritional, functional, and other health-promoting properties by solid-state fermentation like in a food product called “oncom” is a prospective tool to solve the issue [3,4,5] and strengthen the circular economy policy [6].

Solid-state fermentation (SSF) has been used as an effective strategy to convert agro- residues into nutritional food ingredients [4]. SSF is used to produce foods with high or superior nutritional value in common foodstuffs and to preserve these foods without freezing or canning [7,8,9,10]. Fermented foods are the oldest and most traditional version of microbial food, produced through the controlled microbial fermentation of ingredients. This type of food might influence and shape the hundreds of different microbial species in our gut, which in turn will impact our nutritional status and overall health [11,12]. Moreover, according to previous reports, most bioactive compounds are produced in higher quantities through SSF [4,13,14,15]. Increasing demand for functional food ingredients might drive the development of this kind of food source, besides various food products that have been developed from the agro- and food industry residue as consumers are now moving towards natural plant-based food products [16,17].

“Oncom” is one of the prospective uses of the SSF mentioned above, initially made by Sundanese ethnic people from West Java, Indonesia. The raw materials of oncom are mainly the residues of agricultural product processing such as tofu residue (okara) and peanut press cake, and many kinds of oncom are a combination of several moulds and raw materials [3]. Oncom has been a source of nutrition potential for society for many decades due to its affordable price, unique flavour, and meat-like texture, especially “red oncom”. The fermentation process breaks down the complex structure of chemical materials into simpler compounds that are more easily digested and utilized by the human body [18,19,20,21]. Cooked oncom has a flavour reminiscent of minced meat and is rich in protein [22]. The umami substances reported by Andayani et al. (2020) [23] are the other merit. There were also a lot of reports regarding its bioactive compounds [24,25]. Therefore, further information about this solid-state fermentation product and the effective use of agro-residue with improved nutritional, sensory, and other health-promoting properties is of great interest to be developed as one of the sustainable products to answer the challenge of circular economics in the future.

2. What Is “Oncom”?

Oncom is a native Indonesian fermented food made from various agricultural byproducts [4]. Oncom, which is primarily consumed in West Java, is used in various dishes such as pepes oncom, sautéed oncom, fried oncom, sambal oncom, or snacks such as oncom chips, or used as an ingredient in several other cuisines such as added into asinan, laksa, taoge goreng sauce, and as a filler for combro. Crispy fried oncom is the most well-known snack product in the Bandung area under the name of oncom chips and is available in various snack shops throughout West Java [26].

Oncom is typically divided into red oncom (Figure 1A) and black oncom (Figure 1B) based on the different raw materials and moulds. Red oncom is produced using Neurospora sp., namely N. crassa, N. intermedia var. oncomensis, and N. sitophila. Black oncom is produced using Rhizopus oligosporus and various varieties of Mucor sp. [3,21,27]. Red oncom is the fermented product of tofu dreg (okara) or peanut press cake with a thick layer of living conidia. The colour of red oncom might be due to the conidia of the microorganisms that give a brilliant orange hue [3,27]. The economic value of this product increases due to its conidial layer thickness. Oncom is known as the only human food created by Neurospora sp. In contrast to the pink and microscopic macroconidia of the natural N. intermedia, N. intermedia var. oncomensis has vivid yellow macroconidia [21].

The research by Sastraatmadja et al. [3] highlighted the role of ready-to-cook oncom in the fermentation process. The types of inoculum growth in oncom significantly influence its chemical characteristics (

Table 1. Chemical composition of oncom made by pure inoculum after 48 h of fermentation [3].

Fungi Type	Water Content (%) *	Reducing Sugar Content (mg/g) *	Nitrogen Content (%) *
			Total	Dissolved
Neurospora sp.	No significant change	No data	+	++
Mucor sp.	-	++	-	++
Rhizopus sp.	+	+++	No data	+++

* + slightly increased, ++ increased, +++ greatly increased, - slightly decreased.

). For instance, oncom fermented by pure Neurospora sp. shows no significant difference in water content, but the total nitrogen content increases slightly, along with its soluble nitrogen content. Similarly, Mucor sp. leads to a slight decrease in the total nitrogen content of Bandung red oncom, but an increase in the soluble nitrogen and reducing sugar content. Rhizopus sp., on the other hand, increases the reducing sugar and soluble nitrogen content of the product. Rhizopus sp. produced more soluble nitrogen compared to other two fungi types, especially R. oligosporus, which has been reported to have the ability to degrade protein. Soluble nitrogen and reducing sugars were said to contribute to taste, especially in oncom fermented by Rhizopus sp. [3]. It is important to note that oncom is typically made using ready-to-cook oncom from the previous day, a traditional practice that remains relevant in modern research.

As mentioned previously, the raw materials of oncom are mainly the waste of agricultural products, such as peanut press cake, tapioca solid waste, and tofu dreg (okara). The community mostly uses these raw materials as livestock additives or throws them away [26]. This is a pity since the materials still contain a high amount of protein, suitable as a nutrient source [3]. Black oncom is usually made from peanut press cake mixed with tapioca solid waste. In contrast, the materials used to make red oncom vary among regions; for instance, in Subang, West Java, the producers use all three materials and wheat flour to make the red oncom, while in Bandung, only peanut press cake and tapioca solid waste are used [21].

Most traditional food fermentations in Indonesia are carried out naturally or spontaneously. This process, which relies on a variety of advantageous microorganisms from common ingredients and the environment, is a key element of the cultural heritage and authenticity of the product. These fermentations are often prepared on a small scale at home using old techniques that have been passed down from generation to generation. The use of natural fermentation and the lack of sterility mean that pure and single cultures are not engaged, and natural contamination and unstandardized product quality may result [21]. Although oncom is a traditional fermented food, its fermentation uses starter cultures added as a dried starter culture or back slopping using the previous batch of oncom as a starter. As the fermentation is carried out in less sanitary conditions, various microorganisms from the environment and raw material, in addition to the primary mould, are present and grow during oncom fermentation. This contributes to the diversity of microorganisms in oncom as well as its chemical and sensory characteristics. When oncom fermentation involves a soaking step at the start, such as in peanut press cake oncom, natural acid fermentation takes place during soaking.

The steps in the production process of red oncom commonly are as follows: the raw materials are prepared by steaming for 45 to 90 min to cook and reduce the microbial load present in raw materials; the raw materials are then moulded to a thickness of 2 cm; the raw materials are cooled at ambient temperature and then inoculated with mould starter at a concentration of about 2 g for 1 kg of raw materials; and finally, the raw materials are incubated for 24 h at room temperature [28].

Traditional black oncom’s production process generally takes a longer time, approximately three days. Before cooking the peanut press cake, it is soaked overnight. During soaking, acid-producing organisms grow to naturally acidify the cake. It is then steamed for about an hour and drained. Cooked peanut press cakes inoculated by a starter culture are packed into banana leaves or food wrappers and left to ferment. During this time, the mould grows by knitting the cake together and turning it into an oncom. Oncom is usually harvested after about 1–2 days of fermentation [29]. When the fermentation is prolonged, the mould will continue to grow, producing spores, and the oncom will turn blacker.

Table 2. Characteristics of red and black oncom [3,20,21,30,31,32,33].

Parameter	Red Oncom	Black Oncom
Fungi type	Neurospora	Rhizopus and Mucor
Materials	A mixture of peanut press cake, tapioca solid waste, and tofu dreg (okara)	Peanut press cake
Regions of production in Indonesia	Bandung, Sumedang, Subang, and Bogor	Bogor and Jakarta
Production scale	Small and medium-sized industries	Home industry

shows the summary of red and black oncoms’ unique characteristics. Oncom’s characteristics can be different depending especially on its fungi type, materials, region of production, and production scale. This diversity and complexity in the traditional oncom production process will intrigue those interested in the rich culinary heritage of Indonesia. Red oncom is easily found in the areas of Bandung, Sumedang, Subang, and Bogor, while black oncom is mostly produced only around Bogor and Jakarta. The materials used can vary depending on the region and culture in which it is made [30].

Moreover, different from Indonesia’s other traditional fermented foods such as tauco, soy sauce, tempeh, tape ketela, and tape ketan, which are produced by using a modernized technique that uses inoculum, as mentioned above, oncom is mainly produced on a small-scale home industry basis without using a specific inoculum, although it is more common for red oncom to be produced at a bigger scale of production compared to black oncom. Still, the quality of the oncoms is occasionally unstable and cannot be guaranteed [3]. Even so, the utilization of waste, such as okara and peanut press cake, can enhance nutritional and functional properties, for example improving protein and fat content.

3. From Waste to a Nutritious Food

Various food products have been created from waste in the agricultural and food industries as customers seek more natural and plant-based foods [5]. The successful use of agricultural byproducts with enhanced nutritional, functional, and other health-promoting qualities through solid-state fermentation is becoming of great interest [4,34]. As previously mentioned, oncom can be made from several different agricultural wastes such as peanut press cake, tapioca solid waste, or tofu dreg (okara), depending on the type of oncom.

3.1. Nutrition Composition of Oncom

Each ingredient shows different characteristics and nutritional leftovers, which influence the nutrient quality of the oncom. Tofu dreg (okara), or ampas tahu in Indonesian, is an agro-industrial byproduct of soy products, including tofu and soymilk. It is estimated that seven metric tons of soymilk and two metric tons of okara are generated from 1 metric ton of soybeans [35]. Tofu dreg (okara) is an insoluble component of the soybean shell, hull, or husk that can be white or yellowish [36]. Although it has undergone significant changes due to heating treatment applied during manufacturing, tofu dreg (okara) may contain protein similar to tofu and soy [3]. It has been established that tofu dreg (okara) still contains a significant amount of protein because not all the protein content is used up during tofu production [37]. Tofu dreg (okara) often has a protein content of up to 25.4–28.4% (dry basis), which makes it highly nutritious and has a high protein efficiency ratio, all of which indicate that it may be a source of vegetable protein for human consumption [38,39]. This high protein content makes oncom a valuable addition to a healthy diet.

To support the production of fermented products, the amount of peanut press cake is crucial. For example, peanut processing generates a significant residue release in India in the form of peanut press cake. This cake is not wasted but is successfully utilized as a stable substrate for the growth of microorganisms that produce useful enzymes such as amylase, glucosidase, xylanase, and lipase. Its contribution to food production is invaluable and deserves recognition [20].

Other than okara and peanut press cake, solid waste from tapioca is usually added to the mixture which is known as “onggok” [40]. Onggok still contains protein and carbohydrates, which makes it suitable for use as a food ingredient. Onggok improves the texture of oncom by increasing the tenderness when added. The approximate composition of oncom’s ingredients can be seen in

Table 3. Approximate composition of oncom ingredients [8,40,41,42,43].

Type of Ingredient	Moisture (%w/w wb) 1	Ash (%w/w db) 2	Crude Proteins (%w/w db)	Fats (%w/w db)	Carbohydrates (%w/w db)
Tofu dreg (okara)	14.79	3.98	24.93	12.77	43.53
Peanut press cake	4.31–6.2	3.33–4.8	33.31–44.90	8.8–9.2	35.30–35.87
Tapioca solid waste	14	1.2	1.57	0.26	72.49–85.99

¹ Values are percentages by mass, wet basis. ² Values are percentages by mass, dry basis.

.

The approximate configuration of tofu dreg (okara), peanut press cake, and tapioca solid waste as oncom ingredients is represented in Table 3. Tapioca solid waste (72.49–85.99%) had the highest carbohydrate content, followed by tofu dreg (okara) (43.53%) and peanut press cake (35.30–35.87). Tofu dreg (okara) had a higher moisture content than peanut press cake. There was a notable difference in ash content. Peanut press cake had a higher protein content than the other two, while the fat content of tofu dreg (okara) was the highest [8,40,41,42].

This is supported by the study of Nuramalia et al. [33], which discussed the effect of raw ingredients used in the oncom itself. Higher ash content was seen in red oncom, although the addition of tapioca solid waste could make it lower. The use of peanut press cake and the soaking method in the process could reduce the ash content in black oncom. Whereas black oncom had similar levels of fat, protein, and carbohydrates, red oncom had over 90% of protein and carbs. Nearly 70% of black oncom’s ingredients were fat and protein, with peanut press cake serving as the primary raw material. The amount of fat and protein in peanut press cake was considerably higher [33].

Confirmed by the research of Wikanta [26], black oncom showed superior and higher nutritional value compared to red oncom. According to various studies, the chemical composition of oncom is summarized in

Table 4. Chemical composition of red and black oncoms reported by several researchers [3,20,23,26,29,44,45,46].

Composition	Red Oncom	Black Oncom
Moisture (%w/w wb) 1	80.56	52.98
	39.11–66.11	na 2
	na 2	70.51
	67.4–72.0	56.7–68.6
Ash (%w/w db) 3	4.14	2.38
	0.27–0.98	na 2
	na 2	6.53
Crude proteins (%w/w db) 3	24.16	40.60
	20.67–22.77	na 2
	na 2	28.87
	2.78	1.88
	55.2	54.4
	4.6	8.6
Fats (%w/w db) 3	16.10	40.47
	0.8–24.18	na 2
	na 2	31.07
	2.31	1.9
	2.0	1.6
	2.3	3.6
Carbohydrates (%w/w db) 3	55.56	16.55
	12.15–23.83	na 2
	na 2	33.53
	25.5	27.0
Calcium (mg/100 g db) 3	na 2	123.55
Zinc (mg/100 g db) 3	na 2	3.29
Iron (mg/100 g db) 3	na 2	9.90

¹ Values are percentages by mass, wet basis. ² na is an abbreviation for “not available”. ³ Values are percentages by mass, dry basis.

. Despite Oncom’s nutritional value varying wildly due to the influence of raw ingredients and the microbe’s diversity, both oncoms show a promising nutrient composition.

In the study of Firoh et al. [30], it is described that oncom’s components and processing methods can change depending on the area and culture. For instance, tapioca and okara wastes are used to make Bogor’s red oncom. In the Bandung area, tapioca waste, okara, and peanut press cake are used to make red oncom [30]. Another illustration is the Subang region’s Dawuan red oncom, which is created from a blend of okara and peanuts [47].

It has been claimed that the raw materials utilized had a significant impact on the variations in oncom processing. Oncoms that use peanut press cake undergo a soaking process before adding okara, but those that use okara do not. Soaking peanut cakes is intended to separate the remaining cakes. The usage of tapioca solid waste was another distinction. Both Bandung and Bogor craftsmen employ tapioca solid waste; however, only Bandung craftsmen carry out the soaking procedure. The craftsmen of Bandung red oncom claimed that soaking tapioca solid waste is intended to get rid of any remaining filth. Perhaps because of the low quantity of tapioca solid waste contributed, Bogor craftsmen do not soak it [30].

Oncom is known as a food for the lower class because the essential ingredients mostly use food and agricultural waste but still retain a significant quantity of nutrition [3]. Using R. oligosporus, N. sitophila, and Mucor sp. in fermentation, oncom is transformed into “a classy product” with high nutritional content significantly [48,49]. In addition, the effect of fermentation on oncom produces products that are richer in protein (52.64–55.35%) depending on the type of microorganism and conditions during the fermentation process [50]. The protein content is higher than the protein content on a dry basis of tofu dreg (okara) (16.1–33.4%) [51] and peanuts (20.7–25.3%) [52], but it has a lower fat content [46]. The nutrient composition of oncom is based on the formal data published by the Indonesian Ministry of Health in 2018, which can be seen in

Table 5. Nutrition composition of oncom per 100 g [53].

Nutrition Composition	Red Oncom	Black Oncom
Water (g)	80.9	65.0
Energy (kcal)	76	132
Protein (g)	5.2	12.7
Fat (g)	1.8	3.8
Carbohydrate (g)	10.6	13.7
Fibre (g)	2.2	3.1
Ash (g)	1.5	4.8
Calcium (mg)	215	133
Phosphorus (mg)	66	355
Fe (mg)	12.5	34.4
Total carotene (mcg)	268	10
Vitamin B1 (mg)	0.11	0.08
Vitamin B2 (mg)	na 1	0.20
Niacin (mg)	na 1	0.7

¹ na is an abbreviation for “not available”.

.

Black oncom, made of peanut press cake, is a nutritional powerhouse, delivering more energy than the red oncom made of tofu dreg (okara). Red oncom, on the other hand, has the highest moisture content. Black oncom (13.7 g) has a higher carbohydrate content than red oncom (10.6 g), showcasing its nutritional superiority. There is a notable difference in protein content, further emphasizing the nutritional benefits of black oncom. The quality of nutritional content data for various types of food is influenced by many factors, one of which is the use of food ingredients and the place or area where the plants grow [54]. In this study, it could affect the oncom samples used for analysis, which might be reflected by the difference seen in Table 4 and Table 5.

As shown in Table 5, black oncom and red oncom contain a lot of mineral elements, namely calcium, phosphorus, and iron, as much as 133 and 215 mg/100 g, 335 and 66 mg/100 g, and 34.4 and 12.5 mg/100 g, respectively [53]. Both oncoms contain vitamins, such as B1, but only black oncom contains vitamin B2 and niacin. Red oncom has more fibre and calcium due to its primary ingredient, soybeans, having about 9.3 g of fibre and 277 mg of calcium per 100 g of raw soybeans, while peanuts have only 8.5 g and 92 mg per 100 g, respectively [55]. Other than that, black oncom made of fermented peanut meal contains as much as 39 mg of unsaturated fatty acids and 42.40–52.48 g of amino acids per 100 g, with essential amino acids being 12.06 g/100 g [20,29,56].

Proteins and carbohydrates were the two basic building blocks of red oncom, with a 2:1 ratio of the two, while the main components of black oncom, which were present in equal amounts, were proteins and lipids. Due to its distinct raw ingredients, black oncom had an almost two times higher crude protein level than red oncom. Compared to red oncom, created from solid waste from processing tofu, black oncom’s raw ingredient, peanut press cake, includes more proteins.

It appears that oncom significantly enriches the diet with protein in the region where it is produced and consumed, both quantitatively and qualitatively [57]. Because crude protein might rise after 36 h of fermentation, protein is raised [58]. Fermentation’s proteolysis process results in the production of peptides and amino acids, producing more soluble proteins [59,60]. Compared to R. oligosporus NCIM 1215, the peanut press cake fermented by N. sitophila NCIM 899 exhibits a greater reduction in total carbohydrates (3.1%) than the latter (1.6%). However, R. oligosporus NCIM 1215 also shows a more significant reduction in total protein (4.4%) and lipids (1.2%) than does N. sitophila NCIM 899 (protein 3.6%, lipids 0.8%). Research has shown that N. sitophila NCIM 899 uses more carbohydrates during fermentation than R. oligosporus NCIM 1215, but R. oligosporus NCIM 1215 uses more protein and lipids [20].

Based on Rohimah et al. [46], black oncom has complete amino acids, including essential (L-lysine, L-Leucine, L-Isoleucine, L-Methionine, L-Phenylalanine, L-Threonine, L-Valine, and L-Histidine) and non-essential (L-Tyrosine, L-Arginine, L-Alanine, L-Aspartic acid, Glycine, L-Proline, L-Glutamic acid, and L-Serine), where L-Glutamic acid is the amino acid with the highest content (3.85 g/100 g dry basis), and the lowest is L-Methionine (0.17 g/100 g dry basis). Black oncom has a higher nutritional composition than red oncom, particularly in terms of protein content [46]. Interestingly, red oncom contains less fat than black oncom [59,60]. Controlled fermentation of black oncom produced higher calcium (60.54% mg/100 g dry basis) and zinc content (74.25% mg/100 g dry basis) than traditional black oncom [46].

One crucial point that has not been discussed here is the nutrient merits of the carotenoid content of red oncom, which is not found in black oncom. Carotenoids such as beta and alpha carotenes are known as pro-vitamin A. Reliable studies on this topic are still ongoing.

Oncom can also be made using different kinds of legumes. Lupine, peanut, and velvet beans have been used in making red oncom [44]. Research has shown that use of different raw materials affected the moisture content of oncom. Moulds responsible for oncom fermentation produce amylase, protease, and lipase, causing physical and chemical changes in the components of peanut press cake, such as nutritional content [20]. During oncom fermentation, some functional substances with bioactivities are released as explained in the sections below. Consuming oncom as a fermented product has multiple health benefits, including increased nutrient digestibility, increased antioxidant activity, reduced cholesterol, and prevented cardiovascular disease.

3.2. Oncom and Nutrient Digestibility

Soybeans, as the raw material of oncom, are known to contain antinutrient factors such as phytic acid, trypsin inhibitors, lectin, and soybean oligosaccharides (SBOSs) [29,61], which reduce the digestibility of nutrient and mineral absorption [62]. Soybean oligosaccharides (SBOSs) are soluble oligosaccharides in soy or other legumes [63,64]. SBOSs consist mainly of raffinose, stachyose, and sucrose [64]. Raffinose and stachyose are the major bioactive components of SBOSs [63,65], used in fermentation in soybean fermented products such as oncom, tempeh, and soy sauce [9].

Oncom is a source of potential nutrition for society, since during fermentation, complex chemical components will break down into simpler chemicals that are easier for the body to digest and utilize [56,66,67]. Raffinose and stachyose may be hydrolysed during fermentation, thus contributing to increased digestibility. It was found that within the first 21 h of fermentation, N. sitophila, the mould most frequently employed to ferment peanut press cake in making oncom, almost eliminated sucrose and the intestinal gas-forming sugars raffinose and stachyose. The enhanced digestibility of oncom that has been suggested may be caused by N. sitophila utilizing carbohydrates that cause flatulence [68]. Because of the fermenting process, it has a higher protein digestibility (89.9%) than peanuts [69].

Antinutrients are reduced or inactivated by soaking, boiling, and fermentation methods, mainly controlled fermentation [29,62]. During fermentation, lactic acid bacteria (LAB)-mediated fermentation reduces phytates, trypsin inhibitors, and lectins [70]. R. oligosporus has vigorous phytase activity to reduce phytic acid content during the oncom fermentation process for 72 h of oncom fermentation [19]. Stodolak et al. [71] reported that fermentation with A. oryzae and N. intermedia increased protein digestibility by 24–47% depending on the optimum length of the fermentation period and the type of mould (N. sitophila and R. oligosporus). The moulds produce proteolytic enzymes that can hydrolyse proteins of raw products into peptides and free amino acids during fermentation [23]. Free amino released from the amino acids can then bind to antinutrients [46]. In addition, the moulds can produce the invertase enzyme, which can break down sucrose into fructose and glucose, and also produce the enzyme alpha-galactosidase, which can break down raffinose and stachyose into galactose and sucrose [56], which can then enhance nutrient and mineral digestibility and bioavailability [62,72]. However, the effect of these two fungi in degrading SBOSs still needs further investigation.

The moulds involved in the oncom manufacturing process produce lipase and protease enzymes to degrade the starch into sugar during fermentation [56]. Ali et al. [73] reported that R. oligosporus has been found to produce lipases in solid-state fermentation and has the highest productivity of lipases among other mould samples.

4. Microbiology of Oncom

Moulds are the main microorganisms responsible for oncom fermentation. The black oncom’s principal mould is R. oligosporus, while in oncom merah (red oncom), it is N. intermedia var. oncomensis. The moulds of red oncom were previously identified as N. sitophila and N. crassa, but lately, it has been suggested that the mould was N. intermedia var oncomensis [74]. The molecular method used to identify the red oncom mould also revealed that the red oncom mould was identified as N. intermedia [75]. Although those two moulds are the main oncom, other moulds have also been reported to be part of mould fermentation in black oncom, such as Mucor, and its presence could produce high-quality oncom [3].

A recent study on the microbiology of oncom produced by household industries in Bogor revealed that based on the morphology of the mould isolates, moulds present in black oncom also include Rhizopus sp., Neurospora sp., Geotrichum sp., and Penicillium sp. In contrast, those in red oncom include Neurospora sp., Mucor sp., Acremonium sp., and Cladosporium sp. [76]. Previously, Hartanti et al. [77] found R. arrhizus var. delemar (R. delemar), R. arrhizus var. tonkinensis (R. oryzae), and R. microsporus var. chinensis in black oncom.

The study by Damayanti [76] showed that yeast, lactic acid bacteria (LAB), and Enterobacteriaceae were also present in considerable amounts (>7 log CFU/g). Meanwhile, bacterial spores were present to a lesser extent. A considerable amount of LAB and yeast (up to >7 log CFU/g) was also found in tempeh gembus, using tofu dreg (okara) as the raw material similar to red oncom but fermented by R. oligosporus [78]. Some Bacillus species, such as B. thuringiensis and B. megaterium [79], B. pumilus [80], and B. licheniformis [81], have been isolated from red oncom. B. cereus, B. thuringiensis, and B. tequilensis have also been isolated from tempeh gembus [79]. The researchers also showed that other bacteria, such as Staphylococcus carnosus and S. hominis, were present in red oncom.

Studies on microbiology of oncom were mostly based on culture-dependent, enumerating or isolating viable microorganisms in fully fermented oncom. A recent study deploying culture-independent methods revealed differences in microbial community composition between red oncom and black oncom samples from Indonesia as well as between oncom producers [82]. The study revealed that Neurospora was the main fungus detected in all red oncom samples, while Rhizopus was the main fungus in black oncom. The study also confirmed that N. intermedia is the major fungal species in red oncom. In contrast to the culture-dependent method, the culture-independent method did not detect Bacillus in all oncom samples. Although other microorganisms are present during oncom fermentation, research on the characteristics of microorganisms during oncom fermentation has focused on the role of the principal moulds. R. oligosporus of black oncom is similar to that for tempeh fermentation. This mould produces several extracellular hydrolases, such as amylase, protease, lipase, and polygalacturonase [74]. R. oligosporus has the highest protease activity among Rhizopus strains [20] and produced at least two proteolytic systems with pH optima of 3.0 and 5.5 [83]. The cell-wall-bound proteases were primarily responsible for proteolysis [84].

R. oligosporus is also an active lipase producer, hydrolysing triglycerides to produce free fatty acids. In soy fermentation, the mould’s utilization of oligosaccharides depends on the presence of enzyme α-galactosidase and β-fructosidase [74]. Worthington and Beuchat [68] showed that N. sitophila had a definite α-galactosidase activity with a decrease in raffinose and stachyose content of ferments, while strains R. oligosporus showed varying results. A recent study conducted by Maini Rekdal et al. using transcriptomic, metabolomic, and phylogenomic analysis showed that N. intermedia of oncom utilizes pectin and cellulose degradation during fermentation [82].

The enzyme activity during oncom fermentation contributes to the chemical, biochemical, and sensory characteristics of oncom. The α-galactosidase activity increased the digestibility of oncom as N. sitophila utilized the flatulence-causing sugars such as raffinose and stachyose during the first 21 h of fermentation [68]. When tofu dreg (okara) is used as a substrate for fermentation, extracellular enzymes, especially proteases and carbohydrates, might facilitate the hydrolysis of tofu dreg (okara) protein that yielded antioxidative amino acids and peptides, as well as the release of isoflavones-derived components [85]. Their research showed that fermentation of tofu dreg (okara) with R. oligosporus yield enhanced antioxidant activity 2.6-fold.

Similar to R. oligosporus, N. sitophila is also an active lipase producer [74]; however, the proteolytic activity was lower than that of R. oligosporus, as shown by a study applying both moulds as a starter culture for fermentation of peanut press cake, which revealed that oncom produced with R. oligosporus had higher soluble nitrogen compounds than that with N. sitophila [3]. As a raw material for black oncom, peanuts contain anti-nutritional factors such as phytic acid. R. oligosporus and N. sitophila reduced phytic acid after 72 h of fermentation, with the highest reduction by R. oligosporus (decreased from 1.4% on a dry basis to 0.5%); meanwhile, that with N. sitophila contained 0.7% [19]. N. sitophila produces carotenoids in its spores. Five carotenoids have been identified, including lycopene, neurospheres, g-carotene, β-carotene, and phytoene [75]. The presence of carotenoids may contribute to the availability of nutrition in red oncom.

The safety consideration of using peanuts is aflatoxin, which may be present in peanut press cake as a raw material for black oncom. Fermentation has been reported to reduce aflatoxin. N. sitophila and R. oligosporus could decrease the aflatoxin content of peanut press cake by 50–70% during fermentation [74]. N. intermedia of oncom origin did not encode mycotoxins [82]. Moulds such as R. oligosporus, R. oryzae, Aspergillus oryzae, some osmophilic yeasts, and lactic acid bacteria have been reported to be capable of reducing aflatoxin [86]. Adding about 0.2% of R. oligosporus starter to the mixture significantly decreased the aflatoxin content, such as aflatoxin B1 and total aflatoxin, compared to the peanut cake [29]. L. plantarum added during soaking of peanut press cake and mould fermentation reduced aflatoxin by 87.3% [87].

The role of other microorganisms in oncom fermentation has yet to be well elucidated, apart from the possibility of yeast and LAB contributing to the safety of the oncom, which is primarily related to the reduction in aflatoxin [86]. However, in tempeh fermentation, yeast and LAB play a role in flavour development and chemical substrate modification [88]. A similar role may also be played in oncom fermentation. Feng et al. [89] showed that the addition of yeast, such as Saccharomyces cerevisiae, S. boulardii, Pichia anomala, and Kluyveromyces lactis, in tempeh starter culture did not inhibit the growth of R. oligosporus and contributed to increased ergosterol content. Co-culture of R. oligosporus and yeast Yarrowia lipolytica in tofu dreg (okara) fermentation enhanced the flavour, digestibility, and nutritional value, primarily related to the significant increase in antioxidant activities [90]. Similarly, the addition of LAB did not affect the growth of R. oligosporus [91].

LAB may be involved during the soaking of peanut press cake and the mould fermentation stage, which also happens for tempeh fermentation. LAB lower the pH of the peanut press cake, are suitable for mould growth, and inhibit the growth of spoilage and pathogenic bacteria. In tempeh fermentation, LAB are essential for the acidification of soybeans, in which the pH of soybean-soaking water decreases from pH 7 to pH 4.4–4.9, which is essential for the growth of Rhizopus [92]. The acidification of peanut press cake and the addition of sodium chloride and tapioca solid waste enhanced the growth of N. sitophila and its protease production [18]. The presence of LAB also contributes to the safety of oncom, usually produced under less sanitary conditions. LAB isolated from black and red oncom showed antibacterial activity against some pathogenic bacteria such as B. cereus, Salmonella typhimurium, and Escherichia coli [93]. LAB isolated from tempe gembus (fermented tofu dreg by R. oligosporus) inhibited the growth of mycotoxin-producing fungi such as A. parasiticus and P. citrinum [78].

In contrast to LAB, Enterobacteriaceae considerably relates to the less hygienic condition of establishment and practices during oncom fermentation and may pose a food safety risk. In tempeh fermentation, Enterobacteriaceae in raw materials survived the process [94]. The culture-independent method showed the presence of Enterobacter, Chronobacter, and Klebsiella that belong to the family Enterobacteriaceae in most red oncom and black oncom samples taken from Indonesia [82]. The role of these bacteria during fermentation remains unclear as the bacteria are not considered to be a major player in food fermentation [82], and their presence is considered to be as a contaminant. Bacillus sp., being present in oncom [79,80], may contribute to the undesirable sensory characteristic as the bacteria are highly proteolytic [88,92] and cause a bitter taste in tempeh [92]. Apart from their effect on the sensory characteristics, some Bacillus present in oncom and tempe gembus can potentially be used as protease producers, including fibrinolytic protease, to prevent thrombosis and other related diseases [80].

5. Sensory Characteristics of Oncom: Oncom as an Alternative to Meat

As mentioned, increasing consumer interest in products of plant origin and non-waste causes food producers to develop various food products from the agri-food industry; waste must be allowed [5,14]. Oncom is a good example, both the fermented tofu dreg (okara), called red oncom [95], and black oncom from fermented peanut press cake (FPPC), waste from the production of peanut oil [14].

Both types of oncom are not just valuable sources of protein [14,95]; they also hold the potential to revolutionize the food industry as a substitute for meat. Black oncom, for instance, is already being consumed in Indonesia as a cheap, protein-rich meat alternative [20]. It is eaten as an indigenous dish usually served deep-fried or cooked with native dishes [20]. Another way to prepare oncom is to roast it, cut it into pieces, and serve it with ginger sauce, or cook it in boiling water and season it with salt and sugar [96]. The versatility of oncom in various culinary applications further underscores its potential as a meat substitute.

One of the most exciting properties of both fermented products (oncom) is their umami flavour [23]. This unique taste, often described as savoury and rich, results from the biochemical transformations during fermentation. The fact that oncom retains its umami flavour even after frying [20,96] makes it a promising ingredient for many dishes (

Table 6. Sensory characteristics of red and black oncom [3,20,22,23,33,96,97].

Sensory Characteristics	Red Oncom	Black Oncom
Colour	Shiny orange colour, reddish yellow, salmon pink, golden yellow, brownish yellow, blackish brown, orange, red	Greyish black colour, black with white hyphae, greyish black, ash grey
Odour	Minced meat when cooked, beany, musty, fermented, sour	Pleasant fruity odour, musty, nutty aroma
Taste and flavour	Savoury/umami, bland, bitter, sourness, lower intensity of umami taste than in black oncom	Umami taste, higher intensity of umami taste than in red oncom
		Flavour of minced meat when fried, or almonds
		Fruity, alcoholic flavour
Aftertaste	Bitterness, sourness, and tartness	Bitterness
Texture	Compact and soft texture (Bandung red oncom), juicy, soft, fibrous, chewiness, has high springiness, cohesiveness, less hardness	Thick, has a semi-solid and homogeneous texture, high hardness
Acceptability	Taste and texture are accepted by consumers (Bandung red oncom); red oncom is more preferred than their original waste without fermentation, with a stronger preference for red oncom, driven by its umami taste and red than black colour	Black oncom was rated as more acceptable than red oncom

), especially as a plant-based alternative to meat.

The umami fractions obtained by ultrafiltration and chromatography of red oncom and black oncom, which are responsible for the umami taste, were studied by Andayani and colleagues [23]. Fractions of red oncom with a molecular weight (MW) less than 3000 Da and black oncom with a molecular weight (MW) greater than 3000 Da obtained during ultrafiltration were characterized by an intense umami taste. Using gel filtration chromatography combined with flavour dilution analysis for further fractionation identified umami fractions in which free glutamic acid, free phenylalanine, and peptides containing their amino acid residues were present [23].

The umami flavour intensity of the water-soluble extract (WSE) of black oncom was twice as high (DF = 1.024) as that of red oncom (DF = 512). The intensity of the umami taste was determined by soluble proteins, which were twice as numerous in black oncom as in red oncom [23].

In addition to its umami taste, the flavour of black oncom is also described by some authors as slightly alcoholic and fruity [96], which depends on the fermentation process and mould activity. It also has a pleasant fruity odour [20]. On the other hand, when fried, oncom takes on the flavour of minced meat [20] or an almond flavour [96].

Both types of oncom are prepared from different raw materials but also using different moulds, such that black oncom is prepared using R. oligosporus and red oncom using N. sitophila [3]. The enzymes amylase, protease, and lipase, produced by moulds, cause physicochemical changes in the carbohydrates, proteins, and lipids that make up both types of oncom, increasing its digestibility, nutritional value, and flavour [20]. The biochemical transformations taking place in them shape not only their characteristic taste but also their colour [3]. The fermented products are called red oncom because of the shiny orange colour of the microbial conidia. In the case of black oncom, its surface is not fully covered by mycelia, giving a grey-black colour on the surface [3]. These unique sensory characteristics of black and red oncom make them a fascinating subject of study and experimentation (Table 6).

The red oncom study conducted by Li and colleagues shows that the fermented tofu dreg (okara) was dark in colour, with more red and yellow pigments, and contained more red and yellow pigments than the unfermented product [8]. Red oncom, with its diverse varieties like Bandung red oncom and Bogor red oncom, and the unique black oncom, also known as oncom hitam, offer a fascinating array of flavours and textures. The preparation of these oncoms, using tofu dreg (okara) for Bogor red oncom and a blend of peanut press cake and tapioca solid waste for Bandung red oncom, adds to their distinctiveness [3].

Black oncom, made from peanut press cake, is often mixed with tapioca solid waste or cassava powder, i.e., tapioca, to obtain a better texture and more excellent softness [81]. Oncom from fermented peanut press cake (black oncom) is thick and has a semi-solid and homogeneous texture similar to tempeh [20].

Acceptability and preferences of red and black oncom depends on many factors. For example Bandung red oncom and Bogor red oncom, with their unique textures and flavours, have been well received by consumers, as indicated by the research conducted by Sastraatmadja et al. [3]. The acceptance of these fermented products over their original waste without fermentation [81] underscores their market potential. While both types of oncom have a typical taste, one study indicates that black oncom was rated as more acceptable than red oncom [3,23], further highlighting their consumer appeal. In other research, Nuramalia et al. surveyed 80 consumers about the acceptability of three types of red and black oncoms, revealing a stronger preference for red oncom, driven by its umami taste and red colour, than black oncom [33].

Kurnia et al. [97] analysed the sensory profile and physicochemical properties of roasted red oncom obtained from different manufacturers in Bogor Regency, focusing on understanding the impact of variations in production methods and raw materials. Using the rate-all-that-apply (RATA) method, five samples were tested by 30 panellists who rated the intensity of 18 sensory attributes. The panellists identified key sensory attributes for evaluation during an initial focus group discussion (FGD). The chosen attributes for the red oncom evaluation include aroma (beany, musty, fermented, and sourness), colour (golden yellow, brownish yellow, and blackish brown), texture (juicy, chewiness, soft, and fibrous), taste (savoury/umami, bland, bitter, and sourness), and aftertaste (bitterness, sourness, and tartness). Each red oncom sample was roasted without seasoning and presented to panellists in a randomized order to minimize bias. The samples were rated on a five-point scale, with “1” indicating very weak and “5” very strong attribute perception. Results obtained by Kurnia et al. showed that sensory intensity varied significantly among samples, influenced by factors such as microorganisms, fermentation conditions, pH, and water activity. Sample 259 received the highest consumer preference, primarily due to lower intensities of bitter and sour flavours and aromas. Additionally, a consumer survey revealed differences in oncom consumption patterns, notably by environmental conditions and emotional states, with notable distinctions based on age and gender. The study demonstrated that while production differences affect sensory qualities, red oncom can maintain consumer acceptance, particularly when bitterness and sourness are minimized [97].

The sensory profile of oncom was also evaluated by Nuramalia and coauthors [33]. They analysed both red and black oncom produced with different materials and process conditions by three Indonesian producers from Bogor. The QDA method was used to evaluate their sensory profile. Eight trained panellists came up with a list of 15 attributes for evaluation. For red oncom, there were colour (orange and red), aroma (musty and beany), texture (hardness, springiness, cohesiveness, and juiciness), and taste (bitter and umami) and sour aftertaste, while for black oncom, there were colour (white and brown), aroma (musty and nutty), texture (hardness, springiness, cohesiveness, and juiciness), and taste (bitter and umami) and aftertaste (bitterness). They found that the sensory characteristics of red and black oncom were significantly influenced by differences in the raw materials used to produce oncom, the mould used, and the fermentation process carried out. The profile of black oncom exhibited the greatest hardness, whereas red oncom demonstrated the highest levels of springiness, cohesiveness, and redness. Red oncom was characterized by its orange and red colour, along with a beany aroma and umami taste. Conversely, black oncom was primarily defined by its brown colour, a nutty aroma, and umami taste. The characteristic umami taste in red and black oncom was attributed to the presence of the amino acids glutamic acid and aspartic acid [33].

In a study by Setiawan et al. [69], the physical, sensory, and nutritional properties of cookies made from sorghum flour substituted for wheat flour, with the addition of black oncom or peanut flour, were examined. Using a hedonic scale, 40 semi-trained panellists evaluated biscuit formulations for sensory preferences, rating taste, aroma, texture, aftertaste, and overall on a nine-point hedonic scale. The results showed that sorghum-based black oncom biscuits (SOBs) had a similar level of acceptance as wheat-based black oncom biscuits (WOBs) but received lower ratings than both sorghum-based (SPBs) and wheat-based (WPBs) peanut biscuits. The panellists expressed a slight dislike for SOBs due to their gritty and slightly bitter aftertaste, though the flavour was generally acceptable. Peanut-based biscuits achieved higher preference scores, as they offered a more pleasant texture, aroma, and taste, consistent with previous research on peanut-based products. These findings suggest that sorghum flour can effectively replace wheat flour when combined with peanut or black oncom flour, enhancing sensory acceptance, especially with the inclusion of peanut flour [69].

6. A Potential Functional Food? Health-Promoting Properties of Oncom

Researchers are exploring novel, highly nutritious alternatives to traditional food components, driven by the continuous quest for functional food ingredients [4]. Oncom, a traditional fermented soybean product, has gained attention for its exceptional health benefits. The nutritional profile of oncom is enriched through fermentation, which increases the bioavailability of essential nutrients and introduces beneficial compounds. Studies have shown that oncom contains significant amounts of protein, dietary fibre, and phytoestrogens, which are known to mimic oestrogen and may contribute to various health benefits, including improved reproductive health [25]. The fermentation process also enhances the antioxidant capacity of oncom, making it a valuable source of natural antioxidants that can combat oxidative stress in the body [98,99]. Furthermore, the presence of bioactive compounds such as isoflavones in oncom has been linked to various health benefits, including anti-inflammatory and anti-cancer properties [98]. Research indicates that these compounds can play a crucial role in reducing the risk of chronic diseases, such as cardiovascular diseases and certain types of cancer [100]. Additionally, the fibrinolytic activity of microorganisms isolated from oncom suggests potential applications in managing cardiovascular health by preventing blood clot formation [80]. The fermentation of oncom also contributes to its functional food status by enhancing its flavour and preservation qualities. The specific moulds used in the fermentation process, such as N. intermedia, not only improve the sensory attributes of oncom but also ensure safety by inhibiting the growth of harmful pathogens and mycotoxins [101]. This aspect is particularly important in the context of food safety, as traditional fermented foods are often associated with lower risks of contamination compared to their non-fermented counterparts [102].

6.1. Reproductive Health Benefits of Oncom

Oncom is known for its rich isoflavone content, particularly daidzein and genistein, which are related to reproductive health and menopausal symptoms [103,104]. Studies on reproductive-age white rats showed that the consumption of black and red oncom prolonged their oestrous cycles, indicating elevated oestrogen levels compared to the control group [25]. Isoflavones, a class of phytoestrogens predominantly found in soy products such as oncom, exhibit significant biological activity due to their structural similarity to oestrogen. This similarity allows isoflavones to bind to oestrogen receptors (ERs) in the body, particularly ER-alpha and ER-beta, thereby exerting oestrogenic or anti-oestrogenic effects defending on the physiological context [105,106].

The mechanism through which isoflavone exerts its effects involves several pathways. Firstly, isoflavones can act as selective oestrogen receptor modulators (SERMs), meaning they can mimic oestrogen in tissues where oestrogen is beneficial while blocking its effects in tissues where oestrogen may be harmful [105,107,108]. For instance, in postmenopausal women, isoflavones have been shown to alleviate menopausal symptoms such as hot flashes, providing a non-hormonal alternative to hormone replacement therapy [103]. This is particularly important as many women seek alternatives due to the risks associated with traditional hormone therapies [109,110]. The preference for such alternatives is growing due to the associated risks of traditional hormone therapies [111].

The metabolism of isoflavones in the human body also plays a crucial role in their efficacy. Upon ingestion, isoflavones are metabolized by gut microbiota into more bioactive forms such as equol, which has been shown to have a higher affinity for oestrogen receptors and greater antioxidant activity than its parent compounds [112,113]. This conversion is variable among individuals, with some populations exhibiting a higher capacity for equol production, which may influence the health benefits derived from dietary isoflavones [114]. This variability highlights the importance of individual differences in gut microbiota composition in determining the effectiveness of isoflavones.

The presence of free and residual glutamic acid in oncom plays a significant role in its flavour profile and nutritional value. Glutamic acid, an amino acid, is known for its contribution to the umami taste. This characteristic is indicative of rich amino acid content [23]. These nutrients are crucial for maintaining hormonal balance and supporting reproductive functions in both men and women [115,116]. Nakamura et al. demonstrated that amino acids play critical roles in the synthesis of hormones and neurotransmitters, which are essential for reproductive functions [117]. Furthermore, Penttinen-Damdimopoulou et al. emphasized that dietary sources of amino acids can modulate responses to oestrogen, thereby influencing reproductive health and hormonal regulation [118].

6.2. Antioxidant Activity of Oncom

Free radicals are highly reactive, unstable chemical compounds with one or more unpaired electrons that can cause harm to cell components [119,120]. Proper enzymatic activity or natural antioxidants are the body’s defence systems against the harmful effects of free radicals [119]. However, an imbalance will develop if the number of free radicals outweighs the number of antioxidants [10]. An imbalance between oxidants and antioxidants in the body results in oxidative stress, leading to cell death and chronic diseases, including cardiovascular disease, cancer, immune deficiency disease, and ageing [10]. Dietary factors with oxidants and antioxidants are responsible for altering the operating system and improving the host’s antioxidant defence system [10].

The fermentation process significantly enhances antioxidants levels in oncom [4,25,121], a fermented product typically produced with moulds like Neurosposa intermedia, which not only ferment the substrate but also improve its nutritional and bioactive qualities [98,122]. This fermentation promotes the breakdown of complex carbohydrates and proteins, releasing phenolic compounds, carotenoids, and isoflavones known antioxidants [4]. Total phenol, flavonoids, and antioxidant activity all rise directly to the lengthening of the fermentation process [10]. Most bioactive compounds with antioxidant activity are aromatic polyphenol compounds, including flavonoids and isoflavones [13,119,123]. These compounds can delay oxidation and protect biological systems from oxidation processes, preventing the oxidative deterioration of lipids and preserving food quality [13]. The mechanisms underlying the antioxidant activity of these compounds can be attributed to their chemical structures, which typically include electron-donating groups that enhance their radical scavenging capabilities [124].

The antioxidant and anti-cancer properties of red oncom’s flavonoid concentration were reported by Mustarichie et al. [120] and Stodolak et al. [71] using F-CRS (Folin–Ciocalteu reaction substance) and ABTS (2,2′-azino-bis 3 (ethylbenzothiazoline-6-sulfonic acid)) radical scavenging activities to quantify total phenolics and determine the antioxidant activity of SSF with A. oryzae and N. intermedia. The fermentation with A. oryzae and N. intermedia increased the level of F-CRS in the material, resulting in higher accumulation of phenolic compounds and increased antiradical activity.

The antioxidant activity of flavonoids in red oncom can be attributed to their chemical structure, which typically includes hydroxyl groups that can donate electrons to free radicals, stabilizing them and preventing cellular damage [82,125]. The presence of these compounds not only contributes to the health benefits of red oncom but also enhances its potential as a functional food in cancer prevention strategies. For instance, flavonoids have been shown to inhibit the proliferation of cancer cells and induce apoptosis, thereby exerting protective effects against tumour development [126,127]. Moreover, the relationship between the antioxidant properties of red oncom and its anti-cancer effects can be further understood through the lens of the mechanisms by which flavonoids exert their activity. Research indicates that flavonoids can modulate various signalling pathways involved in cell growth and apoptosis, including the inhibition of nuclear factor kappa B (NF-κB) and the activation of p53, a tumour suppressor gene [122,128]. These interactions suggest that the consumption of red oncom may not only provide antioxidant benefits but also contribute to the regulation of cellular processes that are critical in cancer prevention. In addition to their direct effects on cancer cells, flavonoids in red oncom may also enhance the body’s overall antioxidant defence system. By increasing the levels of endogenous antioxidants such as glutathione and superoxide dismutase, these compounds can improve the body’s ability to combat oxidative stress [129,130]. This synergistic effect underscores the importance of dietary sources of flavonoids, such as red oncom, in maintaining health and preventing disease.

Many researchers have reported that red oncom mould (Neurospora sp.) produces carotenoids, primarily neurosporaxanthin (a xanthopyll) and torulene (a carotene), which are responsible for its characteristic orange-to-red pigmentation [131,132,133,134,135]. Carotenoids, such as astaxanthin, are known for their superior antioxidant properties, outperforming β-carotene and vitamin E due to their unique molecular structure, which enhances interaction with cell membranes and efficiently quenches reactive oxygen species (ROS) [136,137,138]. These hydrophobic antioxidants neutralize free radicals, reducing oxidative stress and protecting cellular structures from damage [98,122]. Carotenoids also function as chain-breaking antioxidants, halting the propagation of oxidative damage by interrupting free radical chain reactions [139]. This protective role is crucial in preventing diseases such as cancer and heart disease by maintaining cellular integrity and function [100]. The carotenoids produced by Neurospora sp. may provide similar or even greater health benefits by acting as effective free radical scavengers and contributing to overall oxidative stress reduction.

6.3. Oncom and Cholesterol Reduction

Oncom, a “plant-based food”, provides bioactive compounds like phytosterol, flavonoid and soluble fibre that can reduce blood cholesterol through a number of processes, such as promoting the elimination of bile acids and inhibiting intestinal absorption [140,141]. Because they have structural similarities with cholesterol, phytosterols compete with it for intestinal absorption. Fermented soy products have been shown to reduce the serum concentrations of total cholesterol, low-density lipoproteins (LDLs), and triglycerides if consumed instead of animal protein [142]. According to Crimarco et al., substituting plant-based meat for animal meat significantly reduces blood levels of LDL cholesterol [143]. Diets high in soy protein selectively reduced blood cholesterol in proportion to the degree of hypercholesterolemia [121]. Some bioactive compounds with cholesterol-lowering effects include phytosterol [9], flavonoids, and soluble fibre. Bioactive compounds in food can help lower cholesterol levels by inhibiting cholesterol absorption in the gut and increasing the excretion of bile acids [144]. Phytosterols (plant sterol) can promote cholesterol balance by reducing uptake, transport, metabolism, plasma concentration, and activation of the liver X receptor CPY7A1-mediated bile acids excretion pathway and influencing the transformation and metabolism of cholesterol [9]. Even though it is made from tofu dreg (okara), oncom contains isoflavones [120], particularly genistein, which has been linked to health benefits [123]. The presence of phytosterols, flavonoids, and soluble fibre, combined with the benefits of fermentation, positions oncom as a valuable dietary option for individuals seeking to manage their cholesterol levels and reduce the risk of cardiovascular diseases. Future research should continue to explore the specific mechanisms by which these compounds interact and their potential long-term effects on cardiovascular health.

Isoflavones, a class of flavonoids primarily found in soybeans, are recognized for their significant health benefits, particularly concerning lipid metabolism and cholesterol management. Isoflavones are mainly in the form of glycosides (daidzein and genistein) [121,145]. Upon ingestion, these compounds undergo extensive metabolism, resulting in various metabolites that can be detected in biological fluids such as blood and urine [146]. Genistein and daidzein have cholesterolaemic effects by inhibiting hepatocyte apoB secretion through several mechanisms, including inhibition of cholesterol synthesis and esterification, inhibition of MTP activity and expression, and increase in LDL receptor expression [147]. Genistein was more efficient than daidzein at reducing blood triglycerides [148]. Daidzein reduced serum and hepatic cholesterol levels in female rats, but genistein did not; equol may be responsible for the hypocholesterolemic effect [146]. The varying impacts of these isoflavones highlight the complexity of their mechanisms and the need for further research to elucidate their specific roles in cholesterol management. Daidzein and genistein levels in fresh oncom were 6.6 and 3.1 mg/100 g wet weight, respectively [149]. These levels, while modest, contribute to the overall intake of isoflavones when oncom is included in the diet. The incorporation of oncom into a balanced diet may thus provide a source of these beneficial compounds, potentially aiding in cholesterol reduction.

The cholesterol-lowering effects of soy isoflavones have been supported by various studies. For instance, a meta-analysis indicated that soy protein, particularly when combined with isoflavones, can lead to significant reductions in total cholesterol and LDL cholesterol levels [150]. However, some studies have suggested that the lipid-lowering effects may not be solely attributable to isoflavones, as other components of soy protein may also play a role [151]. This notion is further reinforced by findings that indicate similar cholesterol-lowering effects from soy protein, regardless of isoflavone content [152]. Moreover, the synergistic effects of isoflavones and other soy components suggest that the health benefits of soy foods may arise from a complex interplay of various bioactive compounds rather than from isoflavones alone [153]. This complexity is particularly relevant in the context of dietary interventions aimed at managing hypercholesterolemia, where a holistic approach that considers the entire food matrix may be more effective than focusing on individual components.

Defatted soy oncom (DSB-oncom), a soy product fermented with N. intermedia significantly reduced plasma cholesterol and increased faecal steroid excretion in rats fed cholesterol-free diets due to its combination of pepsin-resistant protein, isoflavone aglycones, and short-chain fatty acids (SCFAs) producing dietary fibre (DF). This effect is probably the result of the phytosterols and isoflavones found in oncom working together to enhance lipid profiles. The promise of DSB-oncom as a functional food for the management of hypercholesterolemia has been further supported by the considerable decreases in total and LDL cholesterol levels that have been linked to its inclusion in the diet [154]. These findings are important for the larger picture of cardiovascular health as well as for dietary therapies targeted at lowering cholesterol levels. By including foods high in bioactive chemicals, such as those in oncom, people can improve their dietary strategies to fight hypercholesterolemia and the hazards that come with it. Additionally, eating oncom and other fermented soy products can help create a healthier and more sustainable diet, which is in line with current dietary recommendations that prioritize plant-based diets [155].

O-miso, made from soybean oncom and tofu dreg oncom (9:10), has higher tocopherol, isoflavone-aglycone, GSH-Px, hepatic catalase, TBARS, and cholesterol-lowering effects [156]. O-miso, a fermented product derived from a combination of soybean oncom and tofu dreg oncom, has been shown to possess enhanced nutritional and antioxidant properties compared to traditional soybean miso. Specifically, O-miso exhibits higher levels of tocopherols, isoflavone-aglycones, glutathione peroxidase (GSH-Px), and hepatic catalase, along with lower levels of thiobarbituric acid reactive substances (TBARSs) and cholesterol [156]. These components are critical in the context of antioxidant activity, as they contribute to the overall redox state and lipid peroxidation processes within the body. The antioxidant properties of O-miso can be attributed to its rich content of isoflavones, particularly in their aglycone forms, which are known for their potent antioxidant capabilities. Isoflavones, such as genistein and daidzein, have been demonstrated to scavenge free radicals and modulate oxidative stress by enhancing the activity of antioxidant enzymes like GSH-Px and catalase [157]. This enzymatic activity is crucial for detoxifying reactive oxygen species (ROS) and preventing cellular damage, which is often linked to chronic diseases such as cardiovascular disorders and cancer [157]. In addition to its antioxidant properties, O-miso has been associated with cholesterol-lowering effects. The reduction in serum cholesterol levels observed in studies indicates that the bioactive compounds in O-miso may influence lipid metabolism, potentially through the modulation of bile acid excretion and the inhibition of cholesterol absorption [156,157]. This dual action of O-miso—acting as both an antioxidant and a cholesterol-lowering agent—highlights its potential as a functional food that can contribute to cardiovascular health. Moreover, the reduction in TBARS levels, which are indicative of lipid peroxidation, suggests that O-miso may effectively mitigate oxidative stress and its associated risks [156]. This is particularly relevant in the context of dietary interventions aimed at reducing oxidative damage and promoting overall health. The antioxidant mechanisms of O-miso, therefore, not only enhance its nutritional profile but also position it as a valuable component in dietary strategies aimed at improving health outcomes.

Lactic acid bacteria (LAB) are considered beneficial probiotics or a type of “good” bacteria that can provide a variety of health benefits [158]. LAB are commonly found in fermented foods and are intentionally added or obtained by a process. LAB are also present in oncom [93]. LAB can synthesize different polysaccharides, e.g., exopolysaccharides (EPSs), which may play a role as prebiotics. LAB-based EPSs can affect the gastrointestinal microbiome and reduce cholesterol [93]. Regarding the hypocholesterolaemic effect of probiotic bacteria, the potential mechanisms responsible include deconjugation of bile salts, modulation of lipid metabolism, and decreased absorption of intestinal cholesterol through co-precipitation of intestinal cholesterol with the deconjugated bile salts, incorporation and assimilation of cholesterol in the cell membrane of the probiotics, intestinal conversion of cholesterol in coprostanol, and inhibition of the expression of the intestinal cholesterol transporter Niemann-Pick C1-like 1 (NPC1L1) in the enterocytes [159]. LAB can incorporate cholesterol into their cell membranes, effectively lowering the amount of free cholesterol available for absorption [82,125]. This process is complemented by the conversion of cholesterol into coprostanol, a sterol that is less readily absorbed by the body [126]. Additionally, LAB have been shown to inhibit the expression of the intestinal cholesterol transporter Niemann-Pick C1-like 1 (NPC1L1), further reducing cholesterol uptake in enterocytes [127]. Research has demonstrated that specific strains of LAB, such as Lactobacillus fermentum and L. plantarum, possess significant cholesterol-lowering properties [122,128]. For instance, L. fermentum has been characterized for its ability to lower cholesterol levels in animal models, suggesting its potential as a probiotic for managing hypercholesterolemia [129]. The mechanisms by which these LAB strains exert their effects are multifaceted and warrant further investigation to fully elucidate their roles in lipid metabolism. Moreover, the consumption of LAB-rich foods like oncom can lead to beneficial changes in the gut microbiome, promoting a diverse and balanced microbial community. This balance is crucial for maintaining metabolic health and preventing dyslipidaemia, which is often associated with chronic diseases such as cardiovascular disease [160]. The interplay between LAB, their metabolic byproducts, and the host’s microbiome highlights the importance of dietary interventions that include fermented foods.

6.4. Oncom and Preventing of Cardiovascular Disease (CVD)

Plant-based foods, including oncom, have been associated with modulation of inflammatory responses, reducing the risk of cardiovascular disease (CVD) [161]. Chronic inflammation is increasingly recognized as significant risk factor for CVD, with research indicating that the consumption of fermented foods is associated with lower levels of inflammatory markers such as C-reactive protein (CRP) [162], a well-known biomarker of inflammation and a predictor of cardiovascular risk [163]. The mechanisms underlying these benefits are multifaceted, involving the modulation of immunological and inflammatory processes through dietary components, particularly those found in plant-based diets.

The role of probiotics in fermented foods is critical in enhancing the immune response and reducing the immune response, which contributes to overall cardiovascular health [164,165]. Probiotics are live microorganisms that confer health benefits to the host, particularly by improving gut microbiota balance. This balance is essential for maintaining a healthy immune system and reducing inflammation, which is crucial in preventing CVD [166]. The consumption of fermented foods like oncom can positively influence gut microbiota composition, leading to improved metabolic outcomes [167]. A healthy gut microbiome enhance the fermentation of dietary fibres, leading to the production of short-chain fatty acids that have been associated with improved lipid profiles and reduced inflammation [167].

The consumption of plant-based diets has been linked to various health benefits, including a lower incidence of obesity, type 2 diabetes, and hypertension, all of which are risk factors for CVD [168]. Zarantonello and Brunori highlighted that a whole-food plant-based diet could delay the progression of chronic kidney disease, further emphasizing the systemic benefits of such dietary patterns [169]. The high fibre content and low calorie density of plant foods contribute to improved glycaemic control and insulin sensitivity, which are vital for reducing chronic inflammation and, consequently, the risk of CVD [170]. Moreover, the bioactive compounds present in plant-based foods, such as polyphenols, flavonoids, and carotenoids, have been shown to exert anti-inflammatory effects. These compounds can modulate various signalling pathways involved in inflammation, thereby reducing the risk of chronic diseases [101,124]. For instance, flavonoids have been associated with beneficial effects on endothelial function and vascular health, which are critical in preventing atherosclerosis and other cardiovascular conditions [122]. The antioxidant properties of these compounds also play a role in mitigating oxidative stress, which is a contributing factor to inflammation and CVD [171].

Regular consumption of soy products, such as oncom, has been linked to a reduction in lipid profiles and improved high-density lipoprotein (HDL) levels, further lowering the risk of coronary heart disease [172]. Alfaddagh et al. reported that the consumption of fermented products can lead to significant reductions in LDL cholesterol levels, which is crucial for preventing atherosclerosis and other cardiovascular condition [173] by reducing lipid profile [174]. A diet containing 25 g of soy daily may lower the risk of coronary heart disease and associated risks. Soy protein-containing isoflavones may be associated with reduced total cholesterol, LDL-c, triacylglycerols, and increased serum HDL cholesterol [174]. The mechanism by which isoflavones reduce lipid profile has yet to be fully understood. However, it has been suggested that isoflavones may inhibit cholesterol absorption in the intestine and increase the excretion of bile acids. Additionally, isoflavones may increase the activity of enzymes involved in the metabolism of lipids [172].

High protein content in oncom is a promising substrate for producing fibrinogenolytic protease derived from microorganisms. Fibrinolytic enzymes, along with probiotics present in fermented foods, can also modulate the gut microbiota, promoting a healthy microbial balance, which is crucial for cardiovascular health [80,102]. Research by Afifah et al. and Stephani et al. [81,175] successfully isolated B. licheniformis RO3 and Stenotrophomonas sp. from oncom, respectively, which can secrete fibrinolytic enzymes due to their ability to break down fibrin, a key component of thrombosis diseases caused by fibrin aggregation in blood vessels. Thrombosis leads to myocardial infarction or other cardiovascular diseases (CVDs). It has been a significant cause of death worldwide in recent years. Microbial fibrinolytic enzymes, especially those from food-grade microbes, are more effective than classical thrombolytic agents due to their affordability and effects for the treatment of cardiovascular disease and other related diseases and have the potential to be developed as functional food additives and medications as a viable alternative to thrombolytic treatment medications and other related diseases [176,177]. Unlike traditional thrombolytic treatment, which can costly and carry significant risks, microbial-derived enzymes offer a safer and more accessible option for managing thrombolytic conditions [81,175].

The prolonged fermentation process not only increases the abundance of proteolytic bacteria but also enhances their enzymatic activity, leading to higher yields of fibrinolytic enzymes [170]. Tempe gembus and oncom, with their prolonged fermentation, are excellent sources of protease-producing bacteria and various strains that can secrete fibrinolytic enzymes. Nine food-grade protease-producing bacteria were successfully isolated, according to Sulistyaningtyas et al. [79], five of which came from oncom, specifically Bacillus thuringiensis, B. amyloliquefaciens, B. megaterium, Staphylococcus carnosus, and S. hominis, and four from tempe gembus with prolonged fermentation. This indicates that oncom is a rich substrate for enzyme production [81,175].

The mechanism by which fibrinolytic enzymes exert their effects are multifaceted. These enzymes can cleave fibrinogen, leading to the dissolution of fibrin clots, thereby reducing the risk of thrombosis [124]. Moreover, the presence of probiotics in fermented foods like oncom can further support cardiovascular health by improving gut microbiota balance, which is increasingly recognized as a critical factor in overall health [101]. The interplay between dietary components, microbial activity, and gut health highlights the importance of fermented foods in disease prevention and health promotion.

In addition to their fibrinolytic properties, the bioactive compounds released during fermentation, such as peptides and isoflavones, contribute to the antioxidant capacity of oncom [122]. These compounds can mitigate oxidative stress, which is often linked to the pathogenesis of cardiovascular diseases [171]. The synergistic effects of fibrinolytic enzymes and antioxidants present in oncom may provide a comprehensive approach to cardiovascular health, addressing both thrombotic and oxidative-stress-related issues.

Despite the promising potential of oncom as a substrate for producing fibrinogenolytic proteases, further research is needed to optimize fermentation conditions and characterize the specific enzymes produced. Understanding the biochemical properties and mechanism of action of these enzymes will be crucial for their application in functional foods and therapeutic context [178]. Additionally, exploring the health benefits of oncom in clinical settings will help establish its efficacy as a dietary intervention for cardiovascular disease.

6.5. Clinical Studies of Oncom

The literature on oncom research in vitro and in vivo is quite scarce due to the small number of oncom investigations undertaken. On the other hand, oncom includes bioactive and functional substances that have been demonstrated to have anti-inflammatory, anti-cancer, and antimutagenic activities in test animals and cancer cells.

Table 7. Clinical studies of oncom and oncom derivative products [25,56,120,156].

Type and Amount of Oncom	How Oncom Was Applied	Duration of Use	Study Group	Effect Observed
Black and red oncom 0.005 g/g (w/w)	Orally feeding extract	14 days	Twenty-one three-to-four-month-old fertile female rats	Influence the length of oestrous cycle and endometrium thickness
Black and red oncom	Orally feeding formulated feed	35 days	One hundred (unsex) twenty-day-old Lohmann broilers	Positive result on broiler intestinal properties
Red oncom	Ethanol extract of oncom	3 days	In vitro test used breast cancer (MCF-7)	Antioxidant, anti-inflammatory, and anti-cancer properties
O-Miso with 9:1 soy oncom–okara oncom	Orally feeding formulated feed with O-miso	14 days	Ten 4-week-old male Wistar ST rats	High antioxidative activity and antimutagenicity

shows the research’s executive summary.

7. Conclusions and Future Development

The scientific reports showed that oncom is a fermented food that transforms agricultural processing residue into nutritious, functional food using simple technology at an affordable cost. It delivers a lot of potential prospects that can be developed further. The challenges are bringing oncom to mass production with a standardized processing method to produce reliable quality according to consumer demand. The economic analysis supported by valid data and marketing research should be conducted and implemented in varied communities, not only in the Sundanese area. An abundance of innovative ideas can be derived from this product. A comprehensive study and mutual research collaboration on oncom is crucial to creating a lot of innovations.

The previous generation’s brilliant idea of oncom production invention may bring much intellectual knowledge and technical breakthroughs to overcome future food supply obstacles not only in Indonesia but also in global inquiry. Considering the circular economic concept, making such functional food ‘from nothing to something valuable, sustainable and simultaneously reducing the environmental problem’ is worth being notified about and exploring further. The abundance of agricultural residue wastes and diversity of microbes, particularly in tropical areas, plus the proper climate, can support the development of similar products with more benefits. However, the urgency lies in the need for more scientific data to support this promising foodstuff’s superiority and limitations before this traditional local wisdom vanishes with the change of generation. A comprehensive study and mutual research collaboration on oncom is crucial to creating many innovations.