Valorization of Food Processing Wastewater for Astaxanthin Production by the Mixotrophic Fermentation of Microalgae: A Review

Food processing wastewater (FPW) poses significant environmental risks due to its high nutrient load yet offers untapped potential as a low-cost feedstock for high-value compound production. This review critically evaluates the valorization of FPW for astaxanthin production through the mixotrophic fermentation of microalgae. Key microalgal species (e.g., <i>Haematococcus pluvialis</i> and <i>Chromochloris zofingiensis</i>) effectively remediate nutrients (nutrients removal of up to 100%) while synthesizing astaxanthin under stress-inducing conditions, such as nutrient starvation, salinity, and oxidative stress. Advanced strategies, such as two-stage cultivation, nutrient profile adjustment, and microbial co-cultivation, which could enhance astaxanthin yields and wastewater treatment efficiency were reviewed comprehensively. The resulting astaxanthin-rich biomass demonstrates multifunctional benefits in animal feed, improving meat quality, immunity, growth, and shelf life. However, this review identifies some challenges, including wastewater management risks, low digestibility of microalgae biomass, and astaxanthin instability during feed processing, which should be addressed properly in real-world applications. This integrated approach aligns with circular bio-economy principles, transforming FPW from an environmental liability into a resource for sustainable biotechnology.