Purpose: This study aimed to determine the physiological characteristics and potential health benefits of the isolated LAB.
Methods: Cooked taro skins were obtained from four poi manufacturers in Hawaii. After natural fermentation, LAB isolates were obtained on MRS agar and identified by 16S rDNA gene sequencing. Representative LAB strains were tested for their acid and bile tolerance and antimicrobial activity. We also explored the production of bacteriocins by the LAB isolates.
Results: A total of 159 isolates belonging to 11 different LAB species were obtained, of which 40% were Leuconostoc mesenteroides. Four LAB isolates exhibited high tolerance to low pH and bile. Salmonella Typhimurium and Listeria monocytogenes died in their culture supernatants within 2 h and 8 h, respectively. Proteinase K treatment reduced the inhibition zone of certain supernatants against L. monocytogenes. After neutralization, only the supernatant of isolate #137 Lactococcus lactis still retained the bactericidal activity against L. monocytogenes. In PCR test, two bacteriocin structural genes were amplified by primers NisZ and Bac147 from its genomic DNA. #137 is the first Lactococcus lactis strain reported to carry these two bacteriocin genes simultaneously. The anti-Listeria bacteriocins produced by the strain were heat-stable but sensitive to proteinase K and pronase E treatments.
Significance: Both organic acids and bacteriocins may account for the antimicrobial activity of the LAB isolates. These isolates could potentially be used as probiotics to fight bacterial infections and confer other health benefits in humans and animals. Bacteriocins produced by the isolates would offer a promising biocontrol tool for the inhibition of pathogenic bacteria in food.