Barley grain as carbon substrate for fungal protein production in a farm process

Abstract

AbstractA simple, non‐aseptic, submerged aerobic fermentation was sought in which microbial protein could be synthesised from non‐protein nitrogen, at the expense of barley carbohydrate, to supplement the protein content of barley grain for non‐ruminant feeding. Screening of 23 isolates of fungi in shake flask cultures showed that microbial protein could be successfully produced by a number of different species in a medium containing barley as a source of carbohydrate. Protein synthesis was markedly affected by the addition of different sources of non‐protein N to the fermentation; and (NH4)2SO4 or urea proved to be good N sources in this respect. Aspergillus oryzae was selected as the most suitable species for protein synthesis, based on its performance when supplemented with the various N sources. The growth rate of A. oryzae in stirred culture was such that high yields of mycelial protein could be achieved within 24 h from a culture inoculated with a spore suspension. Under the conditions of growth used in these experiments there appeared to be little advantage in adding more than 2% barley to the medium. Higher yields of protein could be achieved at barley concentrations in excess of 2%, but only if the incubation period was extended. The tolerance of A. oryzae to low pH values was exploited to enable fungal cultures to be grown under non‐aseptic conditions. Good yields of protein were obtained in 40 litre cultures grown at pH 3.5 in a modified domestic washing machine. Although protein yields were poor, non‐aseptic growth was also sucesssful at pH 3.5 in 1000 litre cultures grown in an agricultural feed‐mixing vessel.