Development of the Sustainable Extraction Procedures of Bioactive Compounds from Industrial Food Wastes and Their Application in the Products for Human Uses

Reducing natural resources caused by the growth of the world’s population, meeting the growing demands of consumers, and preventing environmental pollution requires the development of sustainable and efficient procedures that include the valorization of wastes. Industrial food wastes (bark, seeds, pomace, etc.) are commonly used for the recovery of high value-added bioactive compounds (proteins, vitamins, carotenoids, minerals, carbohydrates, fatty acids, tocopherols, and polyphenolic compounds) that can be further used in the development of supplements and products (food, cosmetic, and pharmaceutical products). The valorization of food wastes is one of the current areas of research that has attracted a lot of attention.

The various conventional extraction techniques, such as maceration, digestion, Soxhlet extraction, etc., are used for the recovery of high value-added bioactive compounds from food wastes. These extraction techniques have some disadvantages, such as low process efficiency, high energy and time consumption, use of toxic solvents, thermal degradation of compounds, negative impact on the environment and obtaining the extracts of inadequate quality [1]. Due to the use of large amounts of plant material during the extraction, these methods are considered uneconomical. Additionally, the used solvents are commonly non-selective, so a product with a high content of ballast substances is obtained. Their presence makes it difficult to isolate sensitive and thermolabile compounds that are present in a small percentage. Having this in mind, there is a tendency to develop sustainable extraction procedures (advanced extraction methods) based on the use of solvents with a minimal negative impact on the environment (“green” solvents), which will allow increasing the extraction efficiency [2]. The ultrasound-assisted extraction (UAE), microwave-assisted extraction (MAE), supercritical fluid extraction (SFE), pressurized liquid extraction (PLE), enzyme-assisted extraction, and their combination belong to the advanced extraction techniques [3]. The mentioned techniques make it possible to reduce or eliminate the use of toxic organic solvents, while increasing the extraction yield and extract quality. They are also known as “cold” extraction techniques, because the temperature during the extraction process is relatively low and does not affect the stability of the extracted compounds. In recent years, the SFE and PLE have attracted attention as a promising alternative to conventional extraction techniques in the recovery of high value-added bioactive compounds from food wastes [4], because it offers numerous advantages. In addition to shorter extraction time, higher extraction yield, use of eco-friendly solvents, these techniques allow the complete removal of the extractant. The main disadvantage of advanced extraction techniques is the high cost of devices and equipment necessary for this process, which is primarily a consequence of working with high pressure. For these reasons, research by many authors was performed only at the laboratory level. In contrast to these extraction procedures, the UAE has a number of advantages, which are reflected in the use of simple equipment, reduced extraction time and reduced solvent consumption. Otherwise, due to these advantages, the UAE is a key technique to achieve the principles of sustainable green extraction. The UAE is reproducible, lasts a few minutes and results in reduced solvent consumption, providing higher extract yields, a higher degree of purity, and eliminating post-treatment of effluents [5]. The efficiency of UAE is affected by many parameters, such as the design of ultrasonic reactors, the shape of the ultrasonic probe [6], solvent choice, liquid-to-solid ratio, temperature and extraction time, which have been studied in detail through numerous studies [7]. Optimal UAE conditions vary depending on the type of compound and material from which it is isolated. The most frequently used ultrasound frequencies are 20–60 Hz, ultrasound power 90–150 W, and extraction time 2–30 min. An increase in temperature leads to better solubility of the desired compounds, which increase in the extraction efficiency. The high temperatures can lead to the degradation of thermolabile compounds. Usually, the UAE is performed at room temperature or at a temperature lower than 60 °C. Due to such operational conditions, the UAE has gained immense importance in the isolation of oils from various plant material. Kumar et al. suggested the optimal UAE conditions for the isolation of oil from sea buckthorn berries (Contribution 1). In order to increase the prince and obtain better quality oil, the authors combined UAE with enzymes. The MAE as a modern extraction technique is characterized by the use of a smaller amount of solvent (sometimes even the absence of solvent because water present in the cells of the plant material is used), shorter extraction time, achieving the higher yield and better quality of the extracted compounds [8]. The main advantages are lower cost and simpler operating equipment compared to the SFE, while the decisive factor is the shorter extraction time compared to the UAE. The potential side effects that may occur due to the action of microwaves are changes in the chemical structure of the targeted bioactive components and/or their degradation, which causes a decrease in the extraction yield. Additionally, the efficiency of MAE can be reduced either if the solvent or target components are non-polar or in the case of choosing highly viscous solvents.

The extraction process has a significant impact on the quality of the obtained extract. This statement was also confirmed by the invited authors for this Special Issue, who in their work studied the influence of different extraction techniques during the recovery of sugars, antioxidants, and antimicrobial compounds from blue agave bagasse from the tequila industry, brewer’s spent grain from craft beer production, raspberries, and blackberries (Contribution 2). The application of extraction technique depends on the desired (further) application of the extract and the compound of interest. In the following paper of this Special Issue, it was shown that the solvent also has an influence on the phytochemical composition and biological activity of the extract (Contribution 3). In that research, the influence of two organic solvents on the phenolic profile of Ruta tuberculata extracts, as well as antioxidant, antidiabetic, and anticholinesterase activities were analyzed.

Thanks to the high nutritional value, constant availability and competitive price, interest is growing for the use of by-products of the food industry as an alternative source for obtaining bioactive compounds (environmental ingredients) with potential market value for the pharmaceutical, cosmetic, and food industries.

Application of agro-industrial residues according to Ajila et al. [9] is divided into six different groups, namely:

• As food ingredients,
• As a source of carbon for the growth of microorganisms during the production of chemicals and enzymes,
• In the production of fertilizers,
• In energy production,
• When returning products with added value,
• As metal adsorbents (environmental pollutants).

In this Special Issue, the application of recovered bioactive compounds in food, cosmetic, and pharmaceutical products is reviewed. Among the by-products of the food industry are defatted cakes, obtained after the extraction of oil from plant materials. It was found that cakes are an excellent source of protein, carbohydrates, minerals, polyphenols, phytosterols, carotenoids, tocopherols, and fatty acids [10]. Additionally, they can be a good source of antimicrobial agents [11], which is important for the food, cosmetic, and pharmaceutical industries. Some proteins from defatted cakes are considered ideal supplements in the human diet, and they are also used as a food ingredient. The defatted cakes are used in the bakery industry for fortification [12]. In cosmetic products, the defatted cakes have a hydrating effect and maintain the epidermal barrier [13], which is very important in the prevention of eczema. Additionally, they can be used as substrates for various biotechnological processes: fermentative production of enzymes, antibiotics, vitamins, antioxidants, fertilizers, for growing mushrooms, as biosorbents in the removal of acid colors during wastewater treatment. In one of the papers of this Special Issue, the physical–chemical and functional properties of plum seed cake were discussed, for which there are scarce data in the literature (Contribution 4). The analyzed cakes were obtained after their defatting by a Soxhlet extractor using organic solvents of different polarities. It has been shown that plum seed cakes contain proteins and raw fibers in a high percentage so that they can be used in human and animal nutrition. Due to their gelling ability, the cakes can be used in formulations where gelation is the ultimate goal. The ethanol extracts of analyzed cakes contain polyphenols, especially phenolic acids, which have expressed antioxidant activity. Due to that, it can be used as a substitute for synthetic antioxidants in food, cosmetic, and pharmaceutical products.

Among the most frequently isolated bioactive compounds from industrial waste are phenolic compounds, which are known to exhibit the different biological activities, such as antioxidant, antimicrobial, anticarcinogenic, anti-inflammatory, antidiabetic, cardioprotective, etc. [14]. Due to these properties, phenols have found wide application in various products with market value. For instance, by-product phenols can be used in the food industry in the production of beverages, dairy products, pastries, meat as natural antioxidants and colors [15]. Additionally, they can extend the shelf life of food products, inhibit the development of microbes and reduce the oxidative processes responsible for the deterioration of the sensory and nutritional quality of the product [16]. In addition to direct application in the food product, phenolic compounds can be incorporated into the packaging material and thus additionally affect the improvement of product quality [17]. Invited authors in this Special Issue discuss the application of oregano extract in bread production (Contribution 5). They showed that the addition of this extract increased the content of antioxidant compounds in bread from 30% to more than 138%. The presence of antioxidants in a high percentage in bread can have a positive effect on human health. The taste and odor of the developed bread with oregano extract was sensory acceptable.

In the pharmaceutical industry, phenolic compounds of agro-industrial byproducts can be used to make various pharmaceutical products (oral, topical and other formulations) intended for the prevention or treatment of many diseases [18]. Phenols can also be used in the development of new high value cosmetic products [19].

List of Contributions

• Kumar, T.A.; Pareek, S.; Kaur, R.; Sagar, N.A.; Singh, L.; Sami, R.; Aljuraide, N.I.; Elhakem, A.; Alsharari, Z.D.; Alruwais, R.S.; et al. Optimization of ultrasonic-assisted enzymatic extraction of freeze-dried sea buckthorn (Hippophae rhamnoides L.) berry oil using response surface methodology. Sustainability 2022, 14, 10849.
• Casas-Godoy, L.; Campos-Valdez, A.R.; Alcázar-Valle, M.; Barrera-Martínez, I. Comparison of extraction techniques for the recovery of sugars, antioxidant and antimicrobial compounds from agro-industrial wastes. Sustainability 2022, 14, 5956.
• Saidi, A.; Hambaba, L.; Bensaad, M.S.; Kadi, I.E.; Bensouici, C.; Sami, R.; Alharthi, S.; Elhakem, A.; Alsharari, Z.D.; Baty, R.S.; et al. Phytochemical analysis using cLC-DAD, Nutritional importance and assessment of antioxidant, antidiabetic and anticholinesterase activities of Ruta tuberculata Forssk organic extracts. Sustainability 2022, 14, 10451.
• Savic, I.M.; Savic Gajic, I.M. Determination of physico-chemical and functional properties of plum seed cakes for estimation of their further industrial applications. Sustainability 2022, 14, 12601.
• Mikołajczak, A.; Ligaj, M.; Kobus-Cisowska, J. Temperature optimization by electrochemical method for improving antioxidant compound extraction efficiency from Origanum vulgare L. and its application in a bread production. Sustainability 2022, 14, 2801.