Microbial population and chemical changes during fermentation of Plaa-som, a Thai fermented fish product(Thai)

Abstract

An investigation of microbial population and chemical changes during fermentation of plaa-som was conducted. The pH was found to decrease from 6.47 initially to 5.24 on day 3. Total acidity increased gradually from an initial value of 1.04% (w/w) reaching a peak on day 3 at 4.76 % (w/w). The total acidity then decreased from day 3 descending to 2.88 % (w/w) on day 8. Lactic acid and acetic acid were found to continually increase from day 0 to 26.77 and 16.21 mg/g on day 3, respectively. This indicates that both acids were produced during the fermentation. Their amounts correlate with total acidity and inversely with pH during the first 3 days of fermentation. The number of acid producing bacteria exhibit a direct relationship with pH and total acidity. The acid producing bacteria count increased gradually from 2.0 x 107 CFU/g on day 0 to 7.9 x 108 CFU/g on day 3. They then declined to 4.8 x 107 CFU/g on day 8. The number of total bacteria counts from both aerobic and microaerobic incubation conditions were found to decrease from 5.5 x 108 CFU/g and 4.6 x 108 CFU/g on day 0 to 1.9 x 108 and 2.3 x 108 CFU/g on day 3, respectively. After day 3 the total aerobic bacteria count gradually increased to 4.4 x 108 CFU/g. After day 4, the total microaerobic bacteria count gradually decreased from 3.9 x 108 CFU/g to 5.7 x 107 CFU/g on day 8