Monitoring Lactobacillus plantarum BCC 9546 starter culture during fermentation of Nham, a traditional Thai pork sausage

The use of Lactobacillus plantarum BCC 9546 (LpBCC9546) as a starter culture for Nham, a traditional Thai fermented pork sausage ensures product quality and consistency. However, no direct evidence has confirmed the growth of this starter during Nham fermentation. In order to investigate its role during Nham fermentation, LpBCC9546 was genetically modified to distinguish it from the natural microflora in Nham. LpBCC9546 was transformed with a recombinant plasmid pRV85 to produce the recombinant strain LpG11, which is resistant to erythromycin and emits green fluorescence. LpG11 was used as a starter culture for Nham fermentation, and its growth was monitored by plating on a selective medium and assay of fluorescent activity. During Nham fermentation the numbers of LpG11 increased ten fold during the first 12 h of fermentation, reaching maximum numbers of between 107 and 108 cfu g− 1 after 24 h, and then declining after 60 h to 105 cfu g− 1 at 168 h. The growth of LpG11 starter culture during Nham fermentation was very similar to that of the untransformed LpBCC9546, although after a prolonged period of fermentation the recombinant LpG11 bacteria appeared to lose the plasmid, or were outgrown by naturally present L. plantarum. The acidity, texture and color of fermented Nham inoculated with recombinant LpG11 or untransformed LpBCC9546 were similar. These results indicated that the recombinant L. plantarum strain LpG11 is a suitable starter culture for Nham fermentation, and that the ability to monitor its growth directly during Nham fermentation could be exploited to further improve Nham production.