Effect of Acid Adaptation on the Survival of Listeria Monocytogenes in Pineapple Juice and Guava Juice

Niam, Xin Yi (2016) Effect of Acid Adaptation on the Survival of Listeria Monocytogenes in Pineapple Juice and Guava Juice. Final Year Project (Bachelor), Tunku Abdul Rahman University College.

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Abstract

Stress adaptation of microbial cells enables cells to become more resistant to the subsequent stress exposure and survive better in the severe acid environments. This acid tolerance respond (ATR) has becomes one concerned issue in the food industry since low pH is one of the major factors in the food preservation in order to eliminate pathogens such as Listeria monocytogenes. In this study, the survival of the acidadapted and non-adapted L. monocytogenes in the pineapple juice and guava juice at refrigerated temperature (5˚C) was examined. The acid-adapted cells were obtained by maintaining the log-phase L. monocytogenes in Tryptic Soy Broth (TSB) adjusted to pH 5.5 and pH 7.0 for the non-adapted cells for 1 h. Both of the acid-adapted L. monocytogenes in pineapple juice and guava juice demonstrated higher survival rates, but did not significantly different (p > 0.05) from the non-adapted cells. However, there was a significant difference (p < 0.05) observed between the survival rates of the L. monocytogenes in pineapple juice and guava juice. The acid-adapted cells inoculated in pineapple juice showed significantly higher survival rate as compared to that inoculated in guava juice. Overall, the acid-adapted culture decreased by 2.31 log CFU/mL in pineapple juice and 7 log CFU/mL in guava juice over the 4 h incubation period. The data suggest that the pre-adaptation to the mild acid may increased the acid resistance for L. monocytogenes towards the subsequent lethal acid stress. Keywords: Acid tolerance response; acid adaptation; log phase; Listeria monocytogenes; pineapple; guava.