Effect Of Metal Ions On The Heat Resistance Of Lactobacillus Plantarum Lip-1 Based On The Heat Shock-repair Treatment

Spray drying technology not only has low cost,but also can achieve high efficiency and continuous production.Howerer,but in the preparation of probiotics powder,the survival rate of the strain is often greatly reduced due to high temperature.In order to solve this bottleneck problem,this study started from improving the heat resistance of the strain itself,we took Lactobacillus plantarum LIP-1 as the research object,and measured the subcellular structure damage during lethal thermal treatment(75?,30 s)and determined the main damage sites.On this basis,the effects of heat shock-repair treatment and addition of metal ions in growth medium or heat shock medium on the improvement of the heat resistance of the strain were evaluated,and the related mechanisms were investigated.The results showed that cell wall and cell membrane of the strain were damaged by lethal thermal treatment,compared with the blank group without heat shock-repair treatment,the damage degree of cell wall and cell membrane was significantly reduced by heat shock-repair treatment(p<0.05).In the process of heat shock repair,the strain mainly used heat shock protein to repair cell wall and membrane,and stabilized membrane lipid conformation by increasing the proportion of the membrane unsaturated fatty acids.When 15 mmol/L Ca²⁺was added to heat shock medium and treated with heat shock-repair,the viable cell count after lethal thermal treatment was about 9.61 log CFU/m L,which was dramatically higher than that in growth medium supplemented with Ca²⁺(p<0.05).Compared with adding Mg²⁺in heat shock medium,adding 20 mmol/L Mg²⁺in growth medium had significant protective effect on cell wall and cell membrane(p<0.05),and the viable cell count after lethal thermal treatment was 9.55 log CFU/m L.When 20 mmol/L Mg²⁺(growth medium)and 0.5 mmol/L Ca²⁺(heat shock medium)were added,the viable cell count after lethal thermal treatment was 9.64 log CFU/m L,which was higher than that of single metal ion addition group,and the damage degree of cell membrane and cell wall were significantly decreased(p<0.05).The co-existence of Ca²⁺and Mg²⁺could increase the ratio of unsaturated fatty acids to saturated fatty acids in cell membrane,which might be an important mechanism to improve the heat resistance of the strain.In conclusion,the damage of cell wall and cell membrane was the main cause of the death of the strain,and heat resistance of the strain could be significantly improved by heat shock-repair treatment and adding appropriate amount of metal ions(p<0.05);The decrease of damage degree of cell wall may be related to heat shock protein and Ca²⁺,and the decrease of damage degree of cell membrane is mainly due to the repair of heat shock protein and the adjustment of the relative proportion of unsaturated fatty acids in cell membrane,which reduces the damage degree of cell membrane.This study provides theoretical guidance for improving the ability of strain to deal with high temperature stress.