Composition and nutritional evaluation of microbial biomass grown on whiskey distillery spent wash

Abstract

Microbial biomass produced from malt whiskey distillery spent wash, composed of a mixture of the filamentous fungus Geotrichum candidum and the yeasts Hansenula anomala and Candida krusei, had crude protein contents of 48 and 52 g 100 g⁻¹ and ‘true protein’ contents of 38 and 42 g 100 g⁻¹ when grown in batch and continuous culture respectively. Analyses of amino acid composition showed that the essential amino acid content was between 45 and 49 g 16 g⁻¹ N and the essential amino acid index between 0.66 and 0.70. The sulphur‐containing amino acids were limiting, being between 49 and 59% deficient compared with the requirements of the growing rat. In rat feeding trials the biomass had a biological value of 0.53, a net protein utilisation value of 0.40 and a digestibility of 0.75 based on its crude protein content. Supplementation of the biomass with methionine and admixture in a ratio of 1:9 with distillers spent grains raised the NPU values to 0.49 and 0.55 respectively. Comparison of the composition and nutritional quality with that of distillers' dark grains demonstrated that the biomass was of a higher quality, and when either supplemented with methionine or mixed with distillers' spent grains was comparable with soya‐bean meal.