Microbiological Quality, Shelf Life and Fermentation Activity of Active Dried Yeast

Abstract

Microbiological quality and shelf-life of 10 active dried yeast (Saccharomyces cerevisiae) preparations (ADYP) were determined. Yeasts were tested for total microbial count (TMC), total viable yeasts (TVY), total wild yeasts, total bacterial count (TBC), spore forming bacteria (SFB), Enterobacteriaceae, and lactic acid bacteria, using standard techniques. Shelf-life detn. of the yeasts after 6 months storage at 0, 4, 15, and 25°C was carried out and fermentation activity of rehydrated ADYP in 500 ml Colombar must was examined. Results are tabulated and show that TMC varied from 8.2 × 109 to 5.9 × 1010, and TVY from 1.3 × 109 to 6.1 × 1010, hence all ADYP studied complied with set guidelines of 1 × 109 viable yeast cells/g ADYP. TBC varied from 1 × 102 to 8 × 102, Enterobacteriaceae ranged from 1.3 × 102 to 7.1 × 105, and lactic acid bacteria counts were up to 4.5 × 108. Survival % of TVY after 6 months storage was best at 4°C with figures between 33 and 100% survival, whilst % survival at 15 and 25°C dropped to 1 and 0.1%, resp. Yeast stored at higher temp. had longer lag phases and slower fermentation rates than those stored at lower temp. due to a loss of viability at the higher temp. It was concluded that microbiological quality of ADYP was within recommended guidelines and that TBC of 5 × 106/g ADYP and lactic acid bacteria count of 1 × 106/g ADYP should become accepted norms, with a possible max. of 1 × 103 wild yeasts/g ADYP. Furthermore, ADYP should be stored at low temp. to ensure proper survival.