Valorization of spent Brewers yeast in the integrated production of the fungal exopolysaccharide (1 → 6)-β-D-glucan (lasiodiplodan) and single-cell protein

Abstract

Spent Brewers yeast was studied as a low-cost alternative feedstock for sustainably producing a high value-added microbial β-D-glucan (lasiodiplodan). The potential of using the mycelial biomass (single-cell protein, SCP) generated in the production of β-glucan was also evaluated as a strategy of an integrated biorefining. Five cell lysis protocols were studied to obtain a yeast cell lysate rich in nutrients. Mineral supplementation of the fermentation medium was assessed, and the SCP produced was characterized by the nutritional composition, amino acid, and lipid profiles. Lasiodiplodia theobromae MMPI was effective in the co-production of lasiodiplodan ((1 → 6)-β-D-glucan)) and SCP in a cell lyzate-based medium. Enzymatic lysis with Alcalase promoted more significant cell rupture and release of soluble intracellular components. Highest production of lasiodiplodan (2.12 gL-1) and mycelial biomass (9.95 gL-1) resulted from Alcalase-treated cell lysate-based medium (7 gproteinL−1) supplemented with sucrose (60 gL-1). Under these conditions, volumetric productivities of lasiodiplodan and mycelial biomass: 0.029 gL−1h−1 and 0.138 gL−1h−1, respectively, were obtained. Mycelial biomass generated in this cultivation was rich in protein and contained all essential amino acids, especially high concentrations of leucine (69 mgg−1protein), lysine (62.2 mgg−1protein), valine (44.2 mgg−1protein), threonine (43.2 mgg−1protein). Co-production of lasiodiplodan and SCP could be an economically promising bioprospecting alternative.