Abstract
Liquid-state fermentation (LSF) and solid-state fermentation (SSF) are two forms of industrial production of lactic acid bacteria (LAB). The choice of two fermentations for LAB production has drawn wide concern. In this study, the tolerance of bacteria produced by the two fermentation methods to acid stress was compared, and the reasons for the tolerance differences were analyzed at the physiological and transcriptional levels. The survival rate of the bacterial agent obtained from solid-state fermentation was significantly higher than that of bacteria obtained from liquid-state fermentation after spray drying and cold air drying. However, the tolerance of bacterial cells obtained from liquid-state fermentation to acid stress was significantly higher than that from solid-state fermentation. The analysis at physiological level indicated that under acid stress, cells from liquid-state fermentation displayed a more solid and complete membrane structure, higher cell membrane saturated fatty acid, more stable intracellular pH, and more stable activity of ATPase and glutathione reductase, compared with cells from solid-state fermentation, and these physiological differences led to better tolerance to acid stress. In addition, transcriptomic analysis showed that in the cells cultured from liquid-state fermentation, the genes related to glycolysis, inositol phosphate metabolism, and carbohydrate transport were down-regulated, whereas the genes related to fatty acid synthesis and glutamate metabolism were upregulated, compared with those in cells from solid-state fermentation. In addition, some genes related to acid stress response such as cspA, rimP, rbfA, mazF, and nagB were up-regulated. These findings provide a new perspective for the study of acid stress tolerance of L. paracasei Zhang and offer a reference for the selection of fermentation methods of LAB production.
Highlights
In daily life, people always come into contact with lactic acid bacteria (LAB) and corresponding products
We used solid and liquid media prepared from bran and soybean meal as substrate to culture Lacticaseibacillus paracasei Zhang, prepared the powder by cold air drying and spray drying, we detected the survival rate of powder bacterial agent prepared by the two methods
The results showed (Figure S1) that the survival rate of the powder bacterial agent prepared by solid-state fermentation (SSF) and cold air drying (32.93%) was significantly higher than that prepared by liquid-state fermentation (LSF) and cold air drying (22.13%)
Summary
People always come into contact with lactic acid bacteria (LAB) and corresponding products. Due to their safety [1,2], they are widely used as probiotic products to improve the balance of human intestinal microbiota and promote human health [3,4,5,6,7,8]. The production of LAB is mainly divided into liquid-state fermentation (LSF) and solid-state fermentation (SSF). Liquid-state fermentation is widely used in food industry, medicine and health industry because of its high fermentation density and low contamination by miscellaneous bacteria [14,15].
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