Object: Diarrhea is a global problem, and the most common cause of bacterial diarrhea is a dysbiosis of the bacterial community caused by pathogenic bacteria. Probiotics can prevent and treat diarrhea by maintaining the balance of Gut microbiota. Adding probiotics with specific functions to specific foods is currently a trend in the development of functional foods, and dairy products, especially yogurt, are the best carriers for probiotics to enter the human body. Lactobacillus is currently the most widely developed and utilized source of probiotics. Therefore, this study aims to screen excellent strains with anti diarrhea pathogenic bacteria ability from human lactobacilli, and conduct multi strain combination testing to screen out lactobacilli combinations with good anti diarrhea ability, and further apply them to yogurt production. By optimizing various indicators of yogurt, the impact of probiotic strain combinations on yogurt quality is analyzed, laying the foundation for the development of anti diarrhea functional fermented dairy products..
Methods: In this study, Lactobacillus isolated from human lactic acid bacteria was selected as the research object, and the strains with obvious antibacterial ability were initially screened out, and the representative strains were identified by groEL gene sequence analysis. Lactobacillus with excellent antibacterial ability was obtained by acid resistance, bile salt resistance, simulated gastroenteric fluid, self-aggregation, hydrophobic combination of carbohydrates, and further multi-strain combination test was carried out to screen lactobacillus combination and applied in the preparation of yogurt. The pH value, titrated acidity, acetaldehyde content, diacetyl content, water retention and texture characteristics of different yogurts were studied and the optimal combination was selected by sensory evaluation. The single factor method combined with response surface was used to optimize the yoghurt fermentation process of the optimal combination strains, and the influence of the optimal combination on yoghurt flavor was further studied.
Results: (1) 36 strains of lactic acid bacteria with antibacterial ability were screened. Based on the results of groEL sequence sequencing, the 36 strains of lactic acid bacteria included 22 strains of Lactobacillus plantarum and 14 strains of Lactobacillus rhamnosus. Combined with the analysis of the results of probiotic properties and other indicators, 22 strains could be obtained for follow-up experiments, including 10 strains of Lactobacillus rhamnosus and 12 strains of Lactobacillus plantarum;
(2) The metabolism experiments of galactose oligosaccharide, glucose, fructose and lactose were conducted by 1:1 combination of 10 strains of Lactobacillus rhamnosus with excellent bacteriostatic effect and 12 strains of Lactobacillus plantarum with excellent bacteriostatic effect. 35 excellent combinations of 4 kinds of carbon sources were selected for the subsequent screening of bacteriostatic combination strains. The 35 combinations were tested by the Oxford Cup method, and 5 combinations (YLH2L47-16 and YLH2L85-1; YLW2L83-22 and YLH1L12-14; YLW2L83-22 and YLW2L63-9; HTb28X11-4 and YLH1L12-14) were used to prepare yogurt in the follow-up experiment;
(3) The optimal combination (YLW2L83-22 and YLW2L63-9) was selected through the determination of pH value, titration acidity, acetaldehyde content, diacetyl content, water retention, texture properties and other indicators combined with sensory evaluation. Single factor and response surface design experiments were carried out, and the optimal conditions of the mixed bacterial combination fermentation were as follows: sucrose addition of 8%, strain inoculation amount of 3%. The inoculation ratio of strains to coccus: Bacillus is 1:1. After 14 days of storage, the number of viable bacteria was still greater than 107, which met the requirements of the national standard. Finally, SPME combined with GC-MS was used to determine the volatile flavor substances of the yoghurt in the combination and control group, and 25 volatile substances were detected in the control group. Compared with the control group, 27 kinds of volatile substances were detected in yoghurt samples. The alcohols in yoghurt samples were significantly increased, and the aldehydes were produced, which contributed to the richer flavor of yoghurt. The results showed that Lactobacillus plantarum YLW2L63-9 and Lactobacillus rhamnosus YLW2L83-22 had a good effect on the flavor of yogurt.
Conclusion: The combination of Lactobacillus rhamnosus YLW2L83-22 and Lactobacillus plantarum YLW2L63-9 has strong antibacterial activity against diarrhea pathogens, can enrich the flavor quality of yogurt, and maintain a high survival rate (107 CFU/mL or more), which is expected to be applied in the development of functional yogurt.
谷歌
火狐
