Potential Next-Generation Probiotics Isolated from Romaine Lettuce (Lactuca sativa L. var. longifolia) Fermented Brine

Abstract

Nowadays, the search for potential probiotics from lactic acid bacteria continues to develop exclusively for pharmaceutical applications. This study aimed at evaluating the potency of lactic acid bacteria (LAB) isolated from fermented brine of romaine lettuce as next-generation probiotics. The study began with romaine lettuce fermentation in a 10% salt solution for four days at room temperature in the dark. The LAB from the fermentation liquid were grown on MRS agar supplemented with CaCo3 then purified. Purified colonies were identified using Gram-staining, catalase test, and 16S rRNA gene marker, and tested for their ability to be developed as the next-generation probiotics which included the following criteria: antibacterial activity, cholesterol assimilation, and their survival at pH3. The cholesterol-lowering ability was evaluated by incubating the bacteria in MRS agar supplemented with 0.5% taurodeoxycholic acid (TDCA). Well diffusion method was used to assess the antibacterial activity. Their ability to withstand acid environment at pH 3 was also evaluated. This study showed that all isolates (AS1, AS2, AS3, and AS4) survived at pH 3 for 2 hours and grew until the fifth day. Isolates AS2, AS3, and AS4 inhibited the growth of Staphylococcus aureus, while AS1, AS3, and AS4 inhibited the growth of Escherihia coli. All isolates had the ability to lower cholesterol. Isolate AS3 was molecularly identified as Enterococcus faecium. This isolate was chosen to be identified as it showed the best characteristics among all the isolates tested. We concluded that AS3 can be further developed as next-generation probiotic.