Induction of stress tolerance in Lactobacillus delbrueckii ssp. bulgaricus by the addition of sucrose to the growth medium

Abstract

The lactic acid bacteria (LAS) play an important role in the production of fermented foods. The development of concentrated cultures of LAS, for inoculating the production vat directly (bulk starters), has eliminated many problems traditionally involved in their preparation and maintenance by the food industry. For industrial use, LAS are often preserved in a frozen or dried form, the latter preparations having lower transport and storage costs (Kets et aI. 1996). Dried cultures, however, lose viability/activity during storage, especially when kept at room temperature (Champagne et aI. 1991; Teixeira et aI. 1995a, b; Castro et aI. 1996). Attempts to improve the survival of LAS during drying have already been tried (Linders et aI. 1997b; Gardiner et aI. 2000). Previous results indicated a direct relationship between the presence of compatible solutes in LAS and their ability to survive drying conditions. Such solutes include amino acids, amino acid derivatives, quaternary amines, sugars and tetrahydropyrimidines (Kets & De Sont, 1994; Kets et aI. 1994, 1996). It has been reported for severa I strains of lactobacilli that these organisms are probably unable to accumulate compatible solutes during the very short period of the drying process, and therefore they should be accumulated prior to the drying process (Kets & De Sont, 1994; Leslie et aI. 1995; Kets et aI. 1996; Linders et aI. 1997b). The aim of the present work was to investigate the effect of adding sucrose to the growth medium of Lactobacil/us delbrueckii ssp. bulgaricus on its survival during heating, spray drying and during the time of storage.