Utilization of brewer's spent grains and other wastes of the food industry using Aspergillus species

Agro-industrial wastes rich in dietary fiber, starch or fermentable carbohydrates, such as bran, citrus pulps, potato peel and molasses can be treated by bacteria and fungi to obtain protein enriched animal feeds, leading at the same time to creation of added value and reduction of the pollution caused by their disposal. Brewer's spent grain (BSG) slurries, containing 2% starch, were treated with strains of Aspergillus oryzae and A. awamori, at various conditions (pH 4, 6 and 8; initial spore concentrations 9(.)10(5), 10(6) and 2(.)10(6) spores/ml). In the first case, simultaneous biomass production was carried out at 30 degrees C in order to evaluate the possibility of producing a substrate that could be used as protein enriched animal feed. In the second case, various by-products (wastes) of the food industry, such as molasses, orange pulp, blended potato peel and their mixtures, after dilution at suitable densities, were used for fungi growth and enzyme secretion. BSG starch hydrolysis was carried out at 45 degrees C using the produced crude enzyme solutions. This way, transformation of the produced fermentable sugars to fungal biomass was avoided and therefore, the hydrolyzates could be utilized as e.g. raw materials for yeast biomass production within the brewery plant. The hydrolyzed slurries were assayed for residual fermentable sugar (glucose and maltose) and crude protein in order to evaluate the possibility of use as protein enriched animal feed, or as carbon sources for yeast production. Both fungi performed well, although A. oryzae proved more efficient in terms of process times and enzyme stability. In both cases, fermentable sugar production was not efficient (0.24-0.95 g/l and 0.96-1.83 g/l respectively) to support use of the BSG hydrolyzates as substrates e.g. for yeast propagation within the brewery. Alternatively, BSG treated directly with the fungi spores are proposed as protein enriched animal feeds. BSG hydrolyzates were also evaluated as nutritious supplements (e.g. sources of minerals and nitrogen compounds such as peptides and amino acids), which when incorporated into yeast growth media containing mixtures of molasses and orange pulp (as carbon sources), resulted in significantly improved biomass yields.