a b s t r a c t
The aim of this study was to derive new starter culture variants that are unable to grow below pH 4.6, the
desirable pH of the Thai fermented pork sausage, Nham, specified by Thailand Food Standard, and apply
them in Nham fermentation. Several acid-sensitive mutants of one of the commercial Nham starter
cultures, Lactobacillus plantarum BCC 9546, were isolated as spontaneous neomycin-resistant mutants.
The growth of three representative mutantswas characterized in MRS broth, which revealed that their cell
numbers and acid production were lower than that of the wild-type. The Hþ-ATPase activities of the
three mutants were found significantly lower than that of the wild-type under either neutral or acidic
conditions. Consequently, internal pH values of the mutants appeared to be lower, especially in acidic
environment (pH 5). The most acid-sensitive mutant was applied in experimental Nham production and
the pH of Nham fermented with the mutant had significantly higher pH at the end of fermentation (3 days)
and after an additional 4 days of storage at 30 C. These results indicate that the use of acid-sensitive
L. plantarum as starter culture can reduce the severity of post-acidification and increase the shelf life of
Nham at ambient temperature.