Yeast enrichment facilitated lipid removal and bioconversion by black soldier fly larvae in the food waste treatment

Food waste can be converted into insectile fatty acids (FAs) by the larvae of black soldier fly (BSFL), Hermetia illucens, for use in the feed sector or as a source of biodiesel. However, waste oil was less decomposed than carbohydrate or protein in frass due to the limitation of larval lipid metabolism. In this study, 10 yeast strains were screened, corresponding to six species, to examine their capacity of improving lipid transformation performance by BSFL. The species of Candida lipolytica was superior to the other five species, which exhibited significantly higher lipid reduction rate (95.0-97.1 %) than the control (88.7 %), and the larval FA yields achieved 82.3-115.5 % of the food waste FA matters, suggesting that BSFL not only transformed waste oil but also biosynthesized FAs from waste carbohydrate and other substances. Further, the CL2 strain of Candida lipolytica was examined for treating food waste containing high lipid content (16-32 %). The lipid removal rate was found improved from 21.4 to 42.3 % (control) to 80.5-93.3% in the waste containing 20-32 % lipid. The upper limit of lipid content that could be endured by BSFL was ≈16 %, and the CL2-enrichment elevated the upper limit to ≈24 %. Fungal community analysis indicated that Candida spp. accounted for the lipid removal improvement. The Candida spp. CL2 strain may facilitate the lipid reduction and transformation by BSFL through microbial catabolizing and assimilation of waste FAs. Altogether, this study suggests that yeast enrichment is feasible in improving lipid transformation by BSFL especially for food waste exhibiting high lipid content.