Valorization of the green seaweed Ulva rigida for production of fungal biomass protein using a hypercellulolytic terrestrial fungus

Abstract

The green macroalgae biomass accumulated in eutrophicated coastal waters has negative ecological and economic impacts. Green macroalgae have an interesting nutritional profile that can be exploited for production of feeds. Bioconversion of green seaweed by microbial fermentation allows the production of microbial biomass protein. This research aimed to study the saccharification and fermentation of green macroalgae biomass by a cellulolytic fungus to provide a product with a nutritional added-value. For this purpose, green seaweed Ulva rigida was directly saccharified and fermented in batch using the filamentous fungus Trichoderma reesei Rut-C30. The fermentation product obtained from the growth of T. reesei Rut-C30 on Ulva rigida as the sole carbon source in 72 h was called fungal biomass protein (FBP) from fermented Ulva rigida. FBP from fermented Ulva rigida contained all essential amino acids and compared favorably with the FAO guideline profiles. Besides, the content of limiting amino acid methionine of FBP from Ulva rigida increased 4-folds compared to the raw alga (from 0.65% to 3% of the total protein content) and was similar to the methionine levels of ovalbumin protein. The in vitro digestibility of FBP from fermented Ulva rigida increased from 71% to 94% compared to the raw alga, and was higher than that of leguminous seeds and similar to that of soybean meal. The results of our work demonstrate that Ulva rigida can be saccharified and fermented in a single step by a terrestrial fungus in 72 h under submerged fermentation to provide high-quality proteins suitable to produce feeds.