**3. Food Waste Valorization for Food and Feed Production**

Feedstock and food waste, mostly represented by agricultural sources, can be used in single cell protein (SCP) production and are suitable as protein supplements in either food or

feed [21]. Single cell protein technology carried out by microorganisms is designed to solve worldwide protein shortages, and it has shown a great advantage because it is independent of climate, soil characteristics and, not the least, on available land [28]. Moreover, concerns regarding the ethical and environmental implications of meat consumption have increased the demand for meat substitutes. Recently, the use of filamentous fungi as a commercial food product has gained considerable attention, due to its high protein content, the presence of essential amino acids and easy digestibility [29].

A solid-state fermentation (SSF) process carried out by the edible fungus *Neurospora intermedia* using bread waste as feedstock for the production of a protein-rich food product has been investigated by Brancoli et al. [30]. The study proposed the SSF process to be implemented as a stand-alone business, or on-site in small-scale bakeries to recover their otherwise discarded surplus bread and has integrated environmental considerations of the development of a fungal food product, showing which scenario has the best environmental performance and highlighting trade-offs and the parts of the process that are hotspots and should be in focus when optimizing the process. The research can contribute to a sustainable way to handle wasted bread, consistent with a circular economy, and it provides a broader base for the developers of the technology to make sustainable decisions during process optimization [30].

Food waste valorization is also addressed to their bioconversion in animal feed. Tropea et al. [14] reported a fermentation process using non-sterilized fish wastes, supplemented with lemon peel as a filler and prebiotic source, carried out by combined starter cultures of *Saccharomyces cerevisiae* and *Lactobacillus reuteri* for bio-transforming these byproducts into a high protein content supplement, rich in healthy microorganisms, for aquaculture feeds. The final fermented product, low in spoilage microorganisms and rich in healthy microorganisms, showed a content of protein and lipids suitable for aquafeed, reducing the problem of a lack of protein sources for aquaculture by encouraging the conversion of fish waste and lemon peel into feed [14].

An interesting review on the utilization of pomaces, waste generated from the pressing of fruits and olives to obtain juices and olive oil, was reported by Munekata et al. [31], where the valorization of this waste as a feed supplement for animal production was deeply investigated. The advances in incorporating and optimizing the use of pomaces in animal feed by generating silages and feeds that improve animal health represent a relevant alternative to using fermented pomaces. Growth performance can be affected, whereas animal health status can be improved. The absence of negative effects and the improvement in the nutritional quality of the foods obtained from animals fed with fermented pomaces is another favorable characteristic to support this strategy [31].

The evaluation of the effects of the feed obtained via fermentation on final consumers was investigated by Panyawoot et al. [32]. Their study has been evaluated the effect of fermented discarded durian peel, a seasonal fruit growing widely in tropical countries, with *Lactobacillus casei*, cellulase, and molasses separately or in combination in total mixed rations on feed utilization, digestibility, ruminal fermentation, and nitrogen utilization in growing crossbreed Thai Native–Anglo-Nubian goats. The study showed that the discarded durian peel fermented with a combination of molasses and *L. casei* had significantly greater nutrient digestibility and propionate concentration, while estimated methane production, the acetate-to-propionate ratio and urinary nitrogen decreased when compared with untreated discarded durian peel. Therefore, a combination-treated discarded durian peel with molasses and *L. casei* could add 25% of dry matter to the diet of growing goats without a negative impact [32].
