Characteristics of isolated lactic acid bacilli bacteria from black glutinous rice (Oryza sativa L.) tapai and its antimicrobial activity in mung bean (Vigna radiata L.) milk

Tapai is a traditional Indonesian fermented food that contains various microorganisms, including lactic acid bacteria (LAB). These LAB are probiotic microorganisms that can confer health benefits for the host consuming them. In this study, four LAB isolates –TM1, TM2, TM3 and TM4 – were isolated from the tapai liquid. The four isolates could grow at 30–40°C, pH 2.5–5.0, and 0.25–2.0% of bile. Antimicrobial screening using the plug agar method against E. coli, P. aeruginosa, B. subtilis, K. rhizophila and S. aureus showed that the growth of all tested bacteria could be inhibited only by TM1 and TM2, with the index of antimicrobial activity being higher for the latter. Antibiosis assay of TM2 cell-free filtrate in MRSB using the cylinder diffusion method also showed a zone of inhibition against all bacterial tested. Molecular identification based on 16S rRNA sequences revealed that the TM2 isolate was closely related to Lactiplantibacillus plantarum. TM2 cell-free filtrate of fermented mung bean milk was also able to inhibit all bacteria tested. Using a scanning electron microscope, observations of E. coli and S. aureus as representative bacteria showed disintegration and hollow bends on the cell wall. According to these results, mung bean milk can be fermented using TM2 as a potential isolate for as a probiotic agent to ferment mung bean milk.