Isolation, characterization and identification of lactic acid bacteria from atsarang kangkong (Ipomoea aquatica Forsk.), a traditional fermented vegetable product of Bulacan

Three (3) different fermented vegetable products of the Province of Bulacan, namely, atsarang dampalit, atsarang ampalaya (Duhat Kasipag and homemade) and atsarang kangkong were microbiologically analyzed for the presence of lactic acid bacteria. Atsarang ampalaya and atsarang kangkong gave as high as 109 cfu/gram of sample analyzed while atsarang dampalit gave as low as 102 cfu/gram. High counts of acid producing bacteria and availability of the procedure for the preparation of homemade atsarang kangkong allowed the isolation of LAB from mixture fermented at different time intervals; characterization and identification of the viable and stable LAB. A total of 106 acid-producing isolates were obtained from mixture of atsarang kangkong at different fermentation time; 54 of which were Gram-positive, catalase negative rods and considered as putative LAB. In litmus milk assay, only 44 isolates produced acid as revealed by the change in the color of litmus milk from purple to pink. Glucose fermentation of the 46 isolates showed that 19 were heterofermenters and 27 were homofermenters. Only nine (9) out of 54 putative LAB isolates were further subjected to phenotypic and genotypic characterizations due to viability and stability of the LAB isolates. All of the nine (9) isolates were Gram-positive and catalase negative rods that grow well in MRS broth with pH of 2.8 to 10.7; can tolerate NaCl concentration between 0.85 and 7.5% and with an optimum growth temperature of 37°C. The LAB isolates remained viable when stored at 4°C for 24 hrs and restored its activity when grown at 37°C. The LAB isolates tested did not produce antibacterial activities against Listeria innocua. The biochemical characterization of the LAB isolates using the API 50 CHL led to the identification of the isolates as Lactobacillus plantarum. However, the genotypic characterization using 16S rRNA sequencing did not confirm all isolates as L. plantarum. Instead, it identified LAB isolates 0-2, 14-3 and 14-15 as Weissella confusa. The difference in the identities of the three LAB isolates using phenotypic and genotypic characterizations reveals the limitation of each tests used. This study is the first that isolated and identified the LAB present in atsarang kangkong. Results revealed the presence of L. plantarum and W. confusa as the LAB responsible for the fermentation of atsarang kangkong and remained present after 14 days of fermentation