Isolation and identification of gas-producing spoilage microbes in fermented broad bean paste

- The gas-producing spoilage microbe in broad bean paste was Bacillus licheniformis.
- B. licheniformis was tolerant towards high temperature, low-pH and high salinity.
- B. licheniformis was able to produce gas only when it was thermally treated.
- Heat treatment stimulated the germination of B. licheniformis spores.
- Nisin and salinity could effectively inhibit the growth of B. licheniformis in media.

This study aimed to isolate and identify the spoilage microbes which could produce gas in fermented broad bean paste and to provide an effective method to restrain their growth in media. The gas-producing spoilage microbe was isolated in anaerobic condition and identified as Bacillus licheniformis FHYM 8. B. licheniformis FHYM 8 was resistant to high temperature, low pH and high salinity condition since it could survive after treatment at 100 °C for 10 min and when the pH value was as low as pH3.8. The inhibitory salinity for B. licheniformis FHYM 8 was 15% in aerobic condition while 11% of salinity could completely inhibit its growth in anaerobic condition. Interestingly, B. licheniformis FHYM 8 showed the ability to produce gas when the broad bean paste was sterilized at 66 °C while no gas was produced when B. licheniformis FHYM 8 was inoculated in broad bean paste after the heat treatment process, indicating that heat treatment was the necessary step for B. licheniformis FHYM 8 to produce CO2 in broad bean paste. The inhibition analysis showed that nisin with a minimal inhibitory concentration of 0.02 mg mL−1 was efficient in inhibiting the growth of B. licheniformis FHYM 8 in MRS media when the salinity was 8%. This will provide guidance to broad bean paste manufacturers to further adopt efficient strategies to inhibit the growth of gas-producing microbe in broad bean paste.