Lactobacillus , Bifidobacterium and Lactococcus response to environmental stress: Mechanisms and application of cross‐protection to improve resistance against freeze‐drying

The review deals with lactic acid bacteria in characterizing the stress adaptation with cross-protection effects, mainly associated with Lactobacillus, Bifidobacterium and Lactococcus. It focuses on adaptation and cross-protection in Lactobacillus, Bifidobacterium and Lactococcus, including heat shocking, cold stress, acid stress, osmotic stress, starvation effect, etc. Web of Science, Google Scholar, Science Direct, and PubMed databases were used for the systematic search of literature up to the year 2020. The literature suggests that a lower survival rate during freeze-drying is linked to environmental stress. Protective pretreatment under various mild stresses can be applied to lactic acid bacteria which may enhance resistance in a strain-dependent manner. We investigate the mechanism of damage and adaptation under various stresses including heat, cold, acidic, osmotic, starvation, oxidative and bile stress. Adaptive mechanisms include synthesis of stress-induced proteins, adjusting the composition of cell membrane fatty acids, accumulating compatible substances, etc. Next, we reveal the cross-protective effect of specific stress on the other environmental stresses. Freeze-drying is discussed from three perspectives including the regulation of membrane, accumulation of compatible solutes and the production of chaperones and stress-responsive proteases. The resistance of lactic acid bacteria against technological stress can be enhanced via cross-protection, which improves industrial efficiency concerning the survival of probiotics. However, the adaptive responses and cross-protection are strain-dependent and should be optimized case by case.