Mechanism Of Physiological Damage To Lactobacillus By Spray Drying

Spray drying is an important way to produce Lactobacillus starter culture.However,physiological damage and decreased survival rate of Lactobacillus can be caused by high temperature and rapid dehydration.Thus,Lactobacillus is not currently suitable for commercial production.The mechanism of damage to Lactobacillus caused by spray drying has not yet been fully elucidated.Three strains of Lactobacillus were used for spray drying.The physiological damage mechanism was determined by assessing cell morphology,acid production capacity,metabolic pathway enzyme activity,and cell membrane changes.The mechanism was verified by transcriptomics and protectants were screened.The main results are as follows:1.Three strains Lactobacillus were used for spray drying.The rate of acid production and the acid production capacity of Lactobacillus decreased after spray drying.The morphology of the cells was investigated by scanning electron microscopy.A large number of dents and wrinkles were observed in their structures after spray drying.After adding the protective agent,the morphology of the cells was observed to be full and round.The cell membrane fluidity of Lactobacillus was determined by fluorescence birefringence.Fluorescence polarization of Lactobacillus was 0.8 times of that of the control.The microviscosity was 0.46 times of that of the control after spray drying,which indicated that the cell membrane fluidity was significantly decreased.The cell membrane integrity of Lactobacillus was observed by laser confocal microscopy and was found to be greatly affected by spray drying.The ratio of intact and damaged cell membrane was 1:12.Three strains of Lactobacillus were used to measure the critical enzyme activity.Enzyme activity of experimental group was lower than the control,indicating that the enzyme activity of Lactobacillus was decreased by spray drying.Dehydrogenase and pyruvate kinase were selected as critical enzyme3.The physiological damage and protective mechanism of spray drying on Lactobacillus were confirmed by transcriptomics.Based on the analysis of the functional enrichment of GO and the analysis of KEGG metabolic pathway,genes that were down-regulated were implicated in the glycolytic pathway and phosphotransferase system after spray drying.When protective agents were added,genes that were up-regulated were mainly involved in the PTS and JNK pathways.4.The compound protective agent exerted considerable protective effects based on acid production capacity and critical enzyme activity,followed by trehalose,sodium glutamate,sucrose,and skim milk.In the present work the physiological damage mechanism of spray drying on Lactobacillus was investigated from multiple perspectives.A method of screening protective agents was devised These results provide a theoretical foundation for the industrial production of Lactobacillus starter culture.