Isolation of Acid-Sensitive Lactobacillus plantarum and its application as starter in Nham production to prevent over-fermentation

Abstract

Acid-sensitive mutants of L. plantarum BCC 9546 were isolated from spontaneous neomycin-resistant mutants with potential to be used as starter to reduce the post-acidification in Nham during storage at ambient temperature. In MRS broth, their growths and acid productions (at 30 o C for 48 h) were lower as well as their culture broth pH were higher than the wild-type strain. Three representative acid-sensitive mutants had reduced H+ -ATPase activity in acidic condition (pH 5) corresponding to their lower internal pH than the wild-type strain. Besides, the arginine deiminase activities of the wild-type and mutant strains were also investigated and they were found not significantly different from each other. Finally, Nham fermentation trial was carried out for 3 weeks and Nham fermented with the wild-type strain had significantly higher amounts of released water than Nham fermented using one of the mutants until one week but no significant difference in color was observed, while the total biogenic amine content was higher in mutant fermented Nham. In conclusion, Nham fermented with mutant had longer shelf-life and less post-acidification with a consistent product pH about 4.6 compared to Nham fermented by wild-type.