Environmental adaptation of probiotic lactobacilli towards improvement of performance during spray drying

The potential of environmental adaptation as a survival mechanism enabling a human-derived probiotic Lactobacillus strain to withstand heat stress and spray drying was investigated. Heat-adapted (52degreesC for 15 min) L. paracasei NFBC 338 exhibited 300- and 700-fold greater thermotolerance (survival at a lethal temperature of 60 C) compared with controls, in MRS and reconstituted skim milk (RSM), respectively. The level of thermal protection in RSM by pre-adaptation in hydrogen peroxide (0.003 M), salt (0.3 M NaCl) and bile salts (0.1% w/v) was also examined. Although not as efficient as the homologous stress, the levels of cross protection were in the order heat>salt>hydrogen peroxide>bile. Viability of the heat-adapted L. paracasei NFBC 338 in RSM was enhanced 18-fold during spray drying at outlet temperatures of 95-105degreesC, while salt-adapted cultures exhibited 16-fold greater viability than controls. These results highlight the potential of preconditioning treatments for maximizing survival of probiotic bacteria during development of probiotic functional foods. The cross protection afforded by salt against thermal stress may indicate that certain common protective mechanisms are induced by both heat and salt stress. (C) 2002 Published by Elsevier Science Ltd.