The indirect conductimetric method for detecting yeast activity in foods was modified to increase sensitivity and rapidity for detecting yeast activity in preserved beverage concentrates and carbonated beverages. Nine strains of Zygosaccharomyces and Brettanomyces were isolated from spoiled beverage concentrates and carbonated beverages. A 10 fold dilution of inoculated beverage concentrate in 0·5% tryptone glucose yeast extract broth supplemented with 0·1% Tween 80, followed by pre-incubation under constant aeration at 25°C for 24 h before subjecting to conductimetric assay, significantly (P < 0·05) decreased the total time necessary for detecting these yeasts. Initial viable yeast populations in the range of 10-1-10o cfu ml-1 in beverage concentrates can be detected within 72-144 h. The threshold limit for detection is in the range of 104-105 cells ml-1. Low populations (one per 10 ml) of yeasts in carbonated beverages can be detected by collecting cells by filtration before subjecting to conductimetric assay, thus facilitating application of the technique for analysing large volumes of product.
ASJC Scopus subject areas
- Food Science