Preparation of 5′-GMP-rich yeast extracts from spent brewer's yeast

Spent brewer's yeast was autolysed and used as a raw material for the preparation of 5′-GMP-rich yeast extracts. Malt rootlets were used as a source of 5′-phosphodiesterase. The crude enzyme was extracted from malt rootlets and pretreated to inactivate 5′-nucleotidase. The optimum pretreatment conditions were heating at 65 °C for 30 min or 70 °C for 7 min. The effects of autolysis time, phosphodiesterase concentration and incubation period on 5′-GMP content were examined. The suitable autolysis time was 8 h. The preferable enzyme treatment period was in the range of 8–14 h. Longer autolysis and enzyme incubation periods caused a decrease in the 5′-GMP content from 0.7–0.9% (w/w) to 0.2–0.4% (w/w). The 5′-GMP content in extracts from debittered and non-debittered yeast was similar. The highest 5′-GMP content in yeast extract was 0.93% (w/w), obtained with a phosphodiesterase concentration of 1.6unit/ml of yeast extract (5% solids content).