Upgrading brewer's spent grains by treatment with Aspergillus species

Abstract

Hydrolysis of brewer's spent grains (BSG) starch was examined using Aspergillus oryzae and A. awamori, at various conditions (pH, spore concentrations). Both fungi performed well, although A. oryzae proved more efficient in terms of process times and enzyme stability. BSG slurries were either treated directly with spore suspensions at 30?C, or with crude enzyme solutions at 45?C. In the first case, simultaneous biomass production and starch hydrolysis occurred, but in the second, transformation of sugars to biomass was avoided. In both cases, fermentable sugar production was not efficient (0.24-0.95 g/l and 0.47-1.83 g/l respectively) to support the use of the BSG hydrolyzates (BSGHs) as substrates e.g. for yeast propagation within the brewery. Alternatively, BSG treated directly with fungi could be proposed as protein enriched animal feeds. BSGHs were also evaluated as nutritious supplements in yeast growth media containing mixtures of molasses and orange pulp (as carbon sources), resulting in significantly improved biomass yields.