Spore inactivation in differently composed whey concentrates

The influence of dry matter (DM) content and composition of reverse osmosis (RO; 12-30% DM), nanofiltration (NF; 12-30% DM) and ultrafiltration (UF; 7.5-8.9% DM) whey concentrates on the heat resistance of spores of Bacillus subtilis was investigated over a wide temperature range (75-140 °C). D-values for spore inactivation in whey concentrates were calculated from linear inactivation kinetics. Heat resistance of the spores was greatly influenced by DM content and composition of the heating medium. In general, the spores showed higher stability in RO and NF concentrates with increasing DM contents between 12% and 30% compared with whey and UF concentrates with 7.5% and 8.1% DM. However, the effect of DM as well as composition was also dependent on the heating temperature. As factors raising the heat resistance of spores of B. subtilis we identified the decreasing aw-value as well as increasing whey protein and lactose concentration.