**1. Introduction**

Color introduces data to the class of products and particular brands, creating effective visual recommendations to show attractiveness, tastes, distinction, and novelty in packages. Food producers have preferred to use natural pigments instead of artificial pigments in response to the developing consumer perception that natural pigments are safer. Plant-originated pigments have some disadvantages, such as low solubility in water, being unstable against heat and light [1,2], and high prices along with the required large agricultural areas. However, microbial pigments have many advantages such as being independent of seasonal changes, use of low-cost raw materials, being biodegradable, having different color tones depending on the conditions of culture and higher efficiency compared to chemical synthesis [1,3]. Thus, microbial pigments identified as bio-pigments are the safer preference for the food industry. The production of microbial pigments has been gradually increasing since health concerns such as carcinogenicity and teratogenicity are related more to the synthetic pigments [4]. Furthermore, environmental policies are other main drivers for the diffusion of biopigments in the market.

Among the various pigment-producing organisms, *Monascus purpureus,* is a fungus that is isolated from red-fermented rice in Indonesia [5]. This filamentous fungus has been extensively preferred in the production of fermented foods in Asian countries, southern China, Japan, and Southeastern Asia [6]. *Monascus* pigments (MPs) as secondary metabolites have many therapeutic effects such as antioxidant, anti-inflammatory, antimicrobial, anticarcinogenic

**Citation:** Mehri, D.; Perendeci, N.A.; Goksungur, Y. Utilization of Whey for Red Pigment Production by *Monascus purpureus* in Submerged Fermentation. *Fermentation* **2021**, *7*, 75. https:// doi.org/10.3390/fermentation7020075

Academic Editors: Giuseppa Di Bella and Alessia Tropea

Received: 18 April 2021 Accepted: 5 May 2021 Published: 10 May 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

and antimutagenic [7]. The main color pigments produced by *Monascus* spp. in polyketone structure are red, orange and yellow. The red ones of those six major pigments are called rubropunctamine (C21H26NO4) and monascorubramine (C23H27NO4); orange ones are called rubropunctatin (C21H22O5) and monascorubrin (C23H26O5) and yellow pigments are called as monascin (C21H26O5) and ankaflavin (C23H30O5) [8,9].

*Monascus* pigments are used as food additives, color thickener, or nitrite substitute in different types of foods (red wine, tofu, surimi, sausage, ham, different sauces, noodle products, ready meals, meat products, etc.) especially in East Asian countries. There are also application areas in the dairy, textile and cosmetics industries [1,4,10–12].

The wastes generated by the food industry cause serious environmental pollution and global warming. The major criteria of sustainable industrial production is the recovery and reuse of these wastes as a resource within the cycle of circular economy [13]. Hence, researchers in recent years have concentrated on studies about the use of food industry wastes in the production of high value biotechnological products. The utilization of wastes containing carbon and nitrogen in the bioprocesses is important in terms of reducing environmental pollution and also building low cost, robust and sustainable production schemes.

Various food industry wastes were used to produce *Monascus* pigments in the literature. These are; hydrolyzed rice straw [14], waste beer [15], brewer's spent grain [9], orange peels [16], chicken feather [17], sugarcane bagasse [18,19] bakery wastes [20], rice water based medium [21], sweet potato [22], corn cob [23,24], potato powder [1], the grape pulp [10], corn step liquor [25], Jack fruit wastes [26], wheat [5] and prickly pear juice [27].

Whey, which is a by product of cheese, casein and yogurt manufacturing, is considered as waste of the dairy industry [28]. When processed further, whey becomes a high value by product that is used as substrate in microbial fermentations utilizing lactose. However, it is defined as an ecologically harmful and most polluting waste when released directly into water receiving bodies [29]. With the rapid industrialization observed in the last century [30] and the growth rate of milk production (around 2.8% per annum), dairy processing is usually considered as the largest industrial food wastewater source, especially in Europe [31,32]. Depending on cheese type and production method, 150–200 kg of cheese is produced from a ton of milk, while 800–850 kg of whey is generated. Approximately 180–190 million tons of whey are produced annually in the world. It is a great threat to the environment [33] due to its very high biological oxygen demands (BOD > 35,000 ppm) and chemical oxygen demands (COD > 60,000 ppm) along with its low pH [34]. For a long time in the 20th century, the industry worked on an inexpensive removal strategy for whey, which included release into waterways, the ocean, municipal sewage treatment works, and/or onto fields. Today, these disposal methods are prevented by strict environmental regulations. Treatment and/or recovery of whey for its use in the production of valueadded products have become a major concern. Since whey contains 4.5–5.0% lactose, 0.6–0.8% protein, 0.4–0.5% lipid, vitamins and minerals, there are many studies on its use as substrate in bioprocesses [34–36]. Since some microorganisms can not utilize lactose in whey as the carbon source, some bioprocesses require the hydrolysis of lactose into its monomers, glucose and galactose by the enzyme β-galactosidase.

The aim of this study is to investigate whey as an alternative low-cost sustainable substrate in the fermentation of *Monascus purpureus* CMU 001 strain to produce red color pigment for the food industry. Raw, demineralized, deproteinized whey as a substrate, fermentation pH, initial lactose concentration, monosodium glutamate (MSG) concentration as the nitrogen source, inoculation ratio, mycelial development and pigment synthesis kinetics of *Monascus purpureus* were studied. In contrast to the production of red pigments from different waste resources as a fermentation substrate, to the best of our knowledge no previous study in the literature has systematically investigated the simultaneous hydrolysis and fermentation of whey for the production of red pigment by *Monascus purpureus* from the point of sustainable resource recovery.
