Survival During Simulated Digestion, Bacteriocin Production, and Bile Salt Hydrolase Activities of Lactic Acid Bacteria in Poi, a Fermented Hawaiian Food

Abstract

ObjectivesPoi, a paste from pounded, cooked taro corms, is culturally significant in Hawaii. This study aimed to investigate the probiotic properties of lactic acid bacteria (LAB) in poi.MethodsNaturally fermented poi was subjected to simulated oral, gastric, and intestinal digestions in vitro. The LAB count of poi after each digestion step was determined. After in vitro digestion, ten LAB colonies were randomly isolated. Poi from three different batches were tested independently. Thirty LAB isolates were differentiated using RAPD-PCR with M13, P4, and P7 primers. Strains with unique band patterns were identified by 16s rRNA sequencing. Overnight cultures of representative LAB isolates were collected for cell-free supernatant (CFS) and neutralized to pH 6.5. Antimicrobial properties of CFS were determined against Listeria monocytogenes using agar well diffusion method. Strains that produced CFS forming inhibition zones were identified as bacteriocin positive. Bile salt hydrolase (BSH) activities were assessed by spotting the LAB cultures on MRS agars containing 0.5% sodium salts of taurodeoxycholic acid (TDCA) or glycodeoxycholic acid (GDCA) and 0.037% CaCl2. Strains that formed white precipitation zones were identified as BSH positive, which is associated with bile acid resistance and cholesterol reduction ability.ResultsThe LAB counts of poi before digestion, and after simulated oral, gastric, and intestinal digestions were 10.67, 9.59, 6.55, and 7.15 log CFU, respectively. After digestion, 14 unique LAB strains (A1-A14) were identified from poi, among which nine strains (A1, A2, A4, A5, A7, A8, A10, A11, and A14) belonged to Leuconostoc lactis, two strains (A3 and A6) belonged to Lactococcus lactis, two strains (A12 and A13) belonged to Weissella confuse, and one strain (A9) belonged to Leuconostoc pseudomesenteroides. Strain A13 showed bacteriocin-producing activity against L. monocytogenes. Strains A2, A3, A4, A6, A7, A8, A9, A12, and A13 showed TDCA hydrolase activities. Strains A3 and A6 showed GDCA hydrolase activities.ConclusionsApproximately 0.03% of LAB in poi survived human digestion conditions. Some surviving LAB strains showed probiotic properties including bacteriocin-producing and bile salt hydrolase activities, which warrant further analysis.Funding SourcesUSDA-Hatch, USDA-ARS.