Potential of Conversion of Cassava Processing Residues by Yeasts to Produce Value-Added Bioproducts

Cassava is a major starch crop in Africa, generating substantial amounts of solid (peels and fibres) and liquid (process press water) residues that remain underutilised, particularly in smallholder and semi-industrial processing units. In Mozambique, where cassava is a staple and processed primarily by local farmer associations, these residues—readily available and low-cost feedstocks—have significant potential for value-added applications. This study evaluated the potential of enzymatically hydrolysed cassava residues—peel and fibre hydrolysates—as substrates for independent yeast fermentations targeting microbial lipid and ethanol production. Rhodotorula toruloides CBS 14 efficiently converted sugars from both hydrolysates, producing up to 17.14 g L−1 of cell dry weight (CDW) and 35% intracellular lipid content from the peel hydrolysate, and 16.5 g L−1 CDW with 50% lipids from the fibre hydrolysate. Supplementation with ammonium sulphate accelerated sugar utilisation and reduced fermentation time but did not significantly increase the biomass or lipid yields. Saccharomyces cerevisiae J672 fermented the available sugars anaerobically, achieving ethanol yields of 0.45 ± 0.03 g g−1 glucose from peels and 0.37 ± 0.06 g g−1 glucose from fibres. These findings highlight the regional relevance of valorising cassava processing residues in Mozambique and demonstrate a dual-product valorisation strategy, whereby the same feedstocks are converted into either microbial lipids or ethanol through independent fermentations. This approach supports the sustainable, low-cost utilisation of agro-industrial residues, contributing to circular bioeconomy principles and enhancing the environmental and economic value of local cassava value chains.