Protein-rich fungal biomass production on sugarcane vinasse for animal feed applications with concomitant water reclamation

The sugar-to-ethanol production process generates a significant amount of lowvalue residue known as vinasse. Vinasse has a high organic content measured as chemical oxygen demand (COD) of over 100 g/L, and its direct disposal has a negative impact on the environment. This research investigated the feasibility of fungal technology as a cost effective and environment-friendly approach in utilizing the vinasse as a sole substrate for producing a protein-rich edible fungus, Rhizopus microsporus (var. oligosporus) with concomitant wastewater reclamation. Optimization studies showed prolific fungal growth at pH 5.0 on vinasse with nutrient (nitrogen and phosphorus) supplementation. The fungus grew exponentially during the first 24 hours using reducing sugar as a major constituent to support its growth. Ethanol at concentrations greater than 5.0% (v/v) adversely affected the fungal growth through change in mycelial morphology. Fungal fermentation in an airlift bioreactor (2.5-L working volume) under various aeration rates (0.5, 1.0, 1.5, and 2.0 volumeair/volumeliquid/min (vvm)) was investigated for the potential large-scale fungal biomass production. The fungal biomass yield was found to depend on the aeration rate, and the aeration rate of 1.5 vvm resulted in the highest fungal biomass yield of 8.04 ± 0.80 (gbiomass increase/ginitial biomass) with significant reduction in organic content ~ 80% (or 26 g/L) measured as soluble chemical oxygen demand (SCOD). Vinasse-derived fungal biomass contained approximately 50% crude protein with 84% in vitro protein digestibility. Essential amino acids contents of the fungal biomass were comparable to commercial protein sources (fishmeal and soybean meal) for animal feeds, with the exception of methionine and phenylalanine. Importantly, the fungal biomass contained high lysine (~ 8% on protein basis), which is the most critical amino acid required in animal feed. Moreover, fungal biomass had essential fatty acids including linoleic, linolenic, eicosapentaenoic (EPA), and docosahexaenoic (DHA), which could further benefit fungal biomass as an aquatic feed. The integration of innovative fungal technology with sugar-based ethanol production could provide an opportunity for producing food-grade fungal protein for animal feed application with simultaneous wastewater reclamation for in-plant use or for land applications.