Valorization of agro-starchy wastes as substrates for oleaginous microbes

Highlights: • Production of lipid using starchy wastes and oleaginous yeasts and fungi explored. • Activity of amylase, xylanase, FPase and inulinase in all yeast and fungal strains. • These enzymes facilitate lipid production by enhancing the production of monomeric sugars. • Promising combinations of yeast-starchy biomass identified for high lipid production. • Cost and resource-effective alternative for energy intensive extraction process for biodiesel. -- Abstract: Different types of agro-industrial or household food processing wastes were assessed for their suitability as growth substrates using a set of oleaginous yeasts, for maximizing the production of lipids and useful enzymes under submerged fermentation (SmF). Minimal medium (pH 5.0) containing different wastes (10% w/v) were inoculated with different yeast strains and incubated at 30 °C for 8 days in an incubator shaker (120 rpm). The processing wastes (potato peel, banana peel, cassava peel, corn residue, rice husk, wheat bran, yam peel and barley husk) utilized, without any pre-treatment, were found to support both microbial growth and lipid production. Lipid productivity was observed to be higher in Cryptococcus curvatus as compared to Rhodotorula mucilaginosa, Saccharomyces pastorianus, Trichosporon cutaneum, Lipomyces starkeyi and Rhodotorula glutinis. Among the different substrates, wheat bran proved to be the best substrate for C. curvatus, as it resulted in the production of 16.0 g lipid/g starch, followed by banana peel yielding 14.3 g lipids/g starch. Interestingly, all the cultures (yeast and fungal) were found to exhibit activity of cellulases, as well as amylase and inulinase, which illustrates the novelty of the study and the viability of the technology for lipid production. Positive correlation between lipid productivity and enzyme activities further highlights the promise of these strains. These research findings illustrate the environmental friendly and alternate use of agro-industrial and household food processing wastes, towards their valorization as substrates for commercial single cell oil production.