In this study, the effects of heat shock-repair combined with addition of trehalose in lyoprotectant on the freeze-drying resistance and room temperature storage stability of Lactiplantibacillus plantarum LIP-1 were investigated. The results showed that the freeze-drying survival rate of the combined treatment group with heat shock-repair and 4 g/100 mL trehalose addition was 81.65%, which was significantly higher than those of the control group without heat shock-repair treatment (59.92%) and the heat shock-repair treatment group (70.23%) (P < 0.05). The damage degree of cell wall and cell membrane in the combined treatment group was significantly reduced compared with that in the control group. The addition of trehalose maintained a high proportion of unsaturated fatty acids in the cell membrane, reduced cell membrane damage, and significantly enhanced the freeze-drying resistance of the strain while improving its room temperature storage stability. After eight weeks of storage, the survival rate of the combined treatment group was 51.66%, which was significantly higher than those of the control (12.09%) and heat shock-repair (43.79%) groups (P < 0.05), and the intracellular fluorescence intensity was 1 969.23 ± 37.22, which was significantly lower than those in the control (3 475.21 ± 106.56) and heat shock-repair (2 843.95 ± 52.12) groups (P < 0.05). To sum up, the combined treatment could improve the freeze-drying resistance and room temperature storage stability of the strain.

Although the production efficiency of lactic acid bacterial starter cultures can be greatly reduced by using spray drying technology, the low viable count of spray dried starter cultures is a bottleneck currently. Therefore, this paper reviews the effects of different stress treatments on the survival rate of lactic acid bacteria after spray drying. It has been found that stress treatments stress treatments induce lactic acid bacteria to produce stress proteins to repair or degrade damaged proteins, or adjust the membrane fatty acid composition to maintain the stability of the cell membrane and regulate cellular metabolic pathways to enhance resistance, ultimately increasing the survival rate of lactic acid bacteria after spray drying. We believe that this paper will provide a theoretical reference for selecting reasonable stress treatments to improve the survival rate of lactic acid bacteria after spray drying.

Trehalose is a non-reducing disaccharide widely present in organisms. It has unique biological characteristics and plays an important role in protecting cells and biomolecules in many fields such as medicine, agriculture and food. In recent years, as an important microorganism in the food fermentation industry, lactic acid bacteria (LAB) have gradually become a research hotspot. In order to drive further research on the protective mechanism of trehalose on LAB, this article reviews recent studies on the protective mechanism of trehalose on biomolecules and its application in protecting LAB from environmental stress. Four hypotheses explaining the protection mechanism of trehalose on biomolecules have been proposed: water substitution, glass state, priority exclusion and intermolecular synergism. Trehalose can protect LAB from harsh environments such as dehydration stress, high temperature stress, freezing stress and oxidative stress. This article will provide a theoretical basis for applying trehalose as a protective agent to improve the resistance of LAB to adverse environments.

The effect of different concentrations of CaCl2 in the culture medium on the freeze-drying resistance and heat resistance of Lactobacillus plantarum LIP-1, a probiotic strain with hypolipidemic properties, was studied. The viable counts in different hot drinks were compared among freeze-dried cells of strain LIP-1 with or without added Ca2+ and a commercial probiotic. The results showed that the addition of 0.5 mmol/L Ca2+ to the medium not only significantly improved the freezedrying survival rate (P < 0.05) but also increased the heat resistance of the strain compared with the control group. When added to hot drinks, the survival rate of freeze-dried cells of strain LIP-1 with added Ca2+ was significantly higher that of a commercial probiotic. The intrinsic mechanism was investigated, showing that the damage degree of cell membrane and wall in LIP-1 were significantly lower than that in the other groups (P < 0.05). This was accompanied by a significant increase in the unsaturated fatty acid content of the cell membrane. The above results indicated that the addition of Ca2+ to the medium could significantly improve the cold and heat resistance of Lactobacillus plantarum LIP-1.

Lactic acid bacteria (LAB) are an important group of microorganisms used in the fermented food industry. Lactic acid and special flavor substances produced by the metabolism of LAB can impart fermented foods with unique qualities, and LAB have been widely used in the food industry, health care and clinical medicine. Therefore, the preparation and storage of LAB starter cultures are crucial. As the traditional method for producing dried agents, freeze-drying technology has the disadvantages of high cost, long time consumption and high energy consumption. In contrast, spray drying has the advantages of low cost, high efficiency and rapidity, and continuous production. It is a potential alternative to freeze-drying for the production of LAB powder. However, hot air generated during spray drying kills LAB, resulting in a low survival rate after drying. This paper reviews the current status of research on different spray drying process parameters, and it highlights the external and internal factors that may affect the quality and efficacy of spray-dried LAB starter cultures.

The probiotic Lactobacillus plantarum LIP-1 was cultured in modified MRS medium at high cell density to investigate the effect of changes in medium components (the types and amounts of nitrogen source, carbon source and buffer salt, total amount of carbon and nitrogen, and carbon/nitrogen ratio) on the viable cell count and survival rate after freezedrying of this strain. The optimal medium was found to be composed of carbon source (sucrose) 33.35 g/L, nitrogen source (yeast powder, soy peptone and casein peptone, 3:3:5, m/m) 10.80 g/L, and buffer salt (sodium acetate, potassium dihydrogen phosphate and sodium citrate, 2.5:1:1, m/m) 14.85 g/L (namely 0.13 mol/L). The viable cell count of strain LIP-1 cultured in the optimized medium after freeze-drying was 9.767 (lg(CFU/mL)), which was distinctly higher than that cultured in MRS medium. The modified medium allowed high-cell-density fermentation of Lactobacillus plantarum LIP-1 while maintaining its viability during freeze-drying.