Recently, microalgae have attracted attention as a natural source of healthier bioactive molecules, especially carotenoids, because human bodies lack the ability to synthesize them, and their intake is necessary for human nutrition. Microalgae can produce various classes of these natural products, distinguished by their health benefits. In food sectors, microalgae are available as whole cells or as a source for extracting a specific carotenoid. This review summarizes recent knowledge of the biosynthesis pathway and the factors affecting carotenoid content, as well as strategies for increasing microalgae synthesis of various carotenoids. New uses of carotenoid-rich microalgae in food are highlighted, along with the main challenges and suggested solutions for using microalgal-carotenoids in the foodstuff. Carotenoids, particularly β-carotene and astaxanthin, face significant challenges in terms of bioavailability and stability when included in foods. Although many solutions were proposed, more research is required to determine the stability of other carotenoids under various food processing techniques. Furthermore, future studies should focus on improving bioavailability and accessibility after digestion in order to benefit from all added carotenoids. Modern technology and a fast-paced lifestyle necessitate the inclusion and acceptance of microalgal carotenoids, particularly for the most vulnerable populations, children, and pregnant women.

This study was aimed to reduce the production cost of fungal exopolysaccharides by increasing the yield and extracting chitosan from the fungal wastes produced simultaneously. Aspergillus quadrilineatus was isolated as well as identified morphologically and by molecular analyses (GenBank Accession No. MT742630.1). One-variable-at-a-time method was combined with response surface methodology to explore the effects of medium components and fermentation conditions on both exopolysaccharide and biomass yields. Sucrose and the inorganic nitrogen (NH4)2SO4 had the greatest stimulating effect on biomass and exopolysaccharide production. The highest biomass and exopolysaccharide production were found after 14 and 4 days of fermentation, respectively. Statistical analyses of Plackett–Burman experimental design indicated that the models were significant, in particular, (NH4)2SO4, K2HPO4, tween 80, CaCl2.2H2O, sucrose, and the incubation interval were the most significant for exopolysaccharide production and biomass. Responses of the central composite design for biomass and exopolysaccharide production cleared the strong similarity between the experimental and predicted values. The optimized medium boosted the exopolysaccharide by 329.73% and the biomass by 31.44% of the primary yield. The waste fungal biomass, obtained after production of the enhanced exopolysaccharide, was used to extract chitosan, yielding 3.52 mg/g with about 88.84% deacetylation degree (DD).