Co-fermentation of yeast and microalgae for enhancing single-cell oil production using expired fruit juice as a low-cost substrate

Abstract

Expired fruit juice (EFJ) is a biowaste that causes several environmental issues owing to its high sugar content. A potential solution for solving this problem is to implement a biorefinery that utilizes EFJ as an economical carbon source for the synthesis of value-added chemicals via microorganisms. This work intends to utilize EFJ for the production of microbial biomass and single-cell oil (SCO) through the co-fermentation of oleaginous yeast and microalgae. Monocultures of yeast and microalgae, together with co-cultures of a synergistic yeast and microalgae pair, were cultured in EFJ medium for 7 days, with and without adjustments to pH and inoculation ratio. Cell dry weight, chlorophyll a, total sugar consumption, and pH were monitored throughout the incubation period. The co-culture of Chlorella vulgaris with Cyberlidnera subsufficiens (CV×CS) and C. vulgaris with Rhodotorula mucilaginosa (CV×RM) attained maximum biomass of 3.482 ± 0.455 g·L-1 and 1.431 ± 0.362 g·L-1 on day 7 in unadjusted EFJ, respectively. Simultaneously, CV×CS attained a maximum biomass of 6.823 ± 1.450 g·L-1, whereas CV×RM reached a maximum biomass of 8.549 ± 2.076 g·L-1, both in pH-adjusted EFJ medium with a 1:3 (yeast: microalgae) inoculation ratio. The lipid content obtained in unmodified EFJ was 0.3781 ± 0.337 g·L-1 for CV×CS and 0.714 ± 0.510 g·L-1 for CV×RM, respectively. After adjustment of pH and inoculation ratio, the lipid concentrations were elevated to 0.402 ± 0.229 and 0.887 ± 0.575 g·L-1 for CV×VS and CV×RM, respectively. The findings suggest that EFJ can serve as a cost-effective biowaste substrate for the co-cultivation of yeast and microalgae.