**4. Crude Enzymes, Nutrient Supplements and Biopolymers Production from Food Waste**

Agricultural or animal food wastes, thanks to their natural composition, can represent an important substrate to be used as a source of enzymes, food-grade pigments, nutrient supplements, or biopolymers. Munekata et al. [31] reported an interesting review on the use of pomace from food processing for the production of high-addedvalue products via fermentation processes as a strategy applied to obtain carotenoids, fatty acids, linolenic acid, and polyphenols. The authors reviewed, in terms of industrial processes, the production of high-added value products, in particular from grape, apple, and olive, such as enzymes and organic acids for application in food processing as well as in other areas of relevant application such as the development of functional foods or the production of volatile compounds for improving the aroma of food products. The review also highlights the limitations in terms of industrial application and the additional studies that are required to define strategies for using the high-added value compounds obtained from the fermentation/biotransformation of pomaces in the development of food products [31].

The ability of "generally recognized as safe" (GRAS) microorganisms to secrete enzymes extracellularly along with featuring properties, such as high catalytic activity and reaction rate, has been demonstrated in the study of Lappa et al. [33]. The study indicates the successful development of a novel cheese whey valorization approach within the concept of circular bio-economy. A two-stage operation was established to generate crude enzymatic consortia via fungal solid-state fermentations with *Aspergillus awamori*. Fermentation conditions were optimized, and a novel biocatalyst was effectively secreted, and subsequently implemented to hydrolyze whey lactose, formulating a nutrient substrate for fermentative bioconversions. Bacterial cellulose production was also conceptualized as a transitional compound for subsequent functional food formulations, along with the protein fraction, to complement the sustainability and circularity of the process [33].

Another interesting study aimed to promote an integrated bio-refinery approach fully exploiting discarded whey from buffalo milk has been carried out by Alfano et al. [34]. In their work, they evaluated the permeate and retentate of ultra-filtered whey, both provided by a local dairy factory in the Campania region, where cheese manufacturing is one of the main industrial activities in the food sector. The permeate was further processed to investigate a potential downstream approach for obtaining reusable water with a low organic load. The retentate was evaluated to identify further potential biotechnological applications of buffalo milk whey. In particular, it was investigated as the main substrate for the growth of a probiotic strain showing several potential biomedical usages, *Lactobacillus fermentum*. Furthermore, it was investigated for the identification of active molecules for tissue repair induction by using wound healing assays on mammalian cells. The study pointed out that the concentrated ultra-filtered retentate could represent suitable support for the growth of probiotic strain, *Lactobacillus fermentum*, having an adequate sugars and proteins content; moreover, it was demonstrated to stimulate epidermis (keratinocyte) regeneration and therefore meaning potential applicability as an ingredient in skincare products [34].

The production of microbial pigments as bio-pigments for the food industry has been gradually increasing, and the evaluation of whey as an alternative low-cost sustainable fermentative substrate has been investigated by Mehri et al. [35]. The study refers to the production of red colour pigment by *Monascus purpureus* suitable for the food industry, using raw, demineralized and deproteinized whey as substrates by simultaneous hydrolysis and fermentation. The authors carried out interesting research on the evaluation of several factors affecting pigment production, such as fermentation pH, initial lactose concentration, monosodium glutamate (MSG) concentration as the nitrogen source, inoculation ratio, mycelial development, and pigment synthesis kinetics of the microorganism employed. This study pointed out that demineralized whey is a sustainable substrate in the fermentation process of the *M. purpureus* red pigment [35].

The use of a biosurfactant produced by *Bacillus cereus* as an additive in a cookie formulation, evaluating the nutritional benefits of its addition, the non-toxicity, the antioxidant potential and the effects on the physicochemical properties as well as the texture of the product has been reported by Durval et al. [36]. The study demonstrated that the biosurfactant produced by *B. cereus* grown in a medium containing waste frying oil has the potential to be used as a bioemulsifier in food systems. The addition of the biosurfactant in the formulation

of cookies showed no drastic changing in the final product as the biosurfactant-containing formulations showed energetic and physical characteristics similar to those of the standard formulation. The biosurfactant was non-toxic and showed considerable antioxidant activity. Moreover, it demonstrated promising results as an ingredient for a flour-based product in terms of the physical, physicochemical, and textural properties of the cookies formulated, also ensuring good preservation [36].

Asimakopoulou et al. [18] carried out a study by assessing wheat straw from Greek agricultural residues as a feedstock for the growth of the heterotrophic microalga *Crypthecodinium cohnii* and the accumulation of polyunsaturated omega-3 fatty acids (PUFAs), more specifically docosahexaenoic acid (22:6n-3,DHA). The work reports an efficient, holistic approach for the integrated valorization of all sugar-containing fractions of biomass towards the production of this valuable product through fermentation, representing the first report demonstrating, as a proof of concept, the valorization of all sugar streams towards the production of omega-3 fatty acids from non-edible sources [18].

Food waste valorization through fermentation processes represents an interesting way of obtaining new value-added products in the cosmetic and pharmaceutical fields also. Ferracane et al. [37] carried out a study aimed to produce and evaluate the different ripening stages of soaps produced with non-edible fermented olive oil (NEFOO soap), evaluating the pH, color, and solubility. The results obtained were compared with those obtained from soaps produced with extra virgin olive oil (EVOO soap). The study pointed out an innovative method to produce "alternative" olive oils on a large scale, exploiting non-edible drupes currently used to produce fodder, natural fertilizer, and energy biomass [37].

The glucan and pectin contents detected in the green husks of walnuts grown in two different soil and climate areas of Southern Italy (Montalto Uffugo e Zumpano) were investigated for potential use in food, cosmetics, and pharmaceutical fields by La Torre et al. [38]. The authors reporteda biovalorization of this waste material in their study and also investigated the spectroscopic, morphological and thermal characterizations of the extracted high-value compounds in order to evaluate if the different pedoclimatic conditions of the two areas could affect both the content of glucans and pectins and their functional uses [38].

Finally, a new perspective on the bioremediation of industrial effluents was demonstrated by Costa et al. [39]. In the study, the authors reported the implementation of *Aspergillus oryzae*, a fungal strain widely exploited as an amylase producer, for the bioremediation of starch in industrial paper mill wastewater by carrying out submerged fermentation technologies (SmF) and solid-state fermentation (SSF). *A. oryzae* was found to grow on non-conventional media such as paper mill wastewater. The SSF of *A. oryzae* was performed on rice hulls. In the bioremediation of paper mill wastewater, for removing starch, the fungus maintains its amylase activity and uses reducing sugars as metabolic substrates [39].

**Funding:** Not applicable.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The author declares no conflict of interest.
