Low thermal inactivation of Escherichia coli ATCC 25922 in pineapple, orange and watermelon juices: Effect of a prior acid‐adaptation and of carvacrol supplementation

Abstract

AbstractPast research on the association of natural antimicrobials and low temperatures for fruit juices pasteurization has not targeted acid‐adapted strains which are yet the most relevant strains in these products. We found that previously acid‐adapted Escherichia coli ATCC 25922 cells exhibited an increase of their resistance to thermal inactivation at 55 °C for 5 min both in the presence and absence of carvacrol (30 µL/L). The inactivation of E. coli was more intense in pineapple (pH 3.25) and orange (pH 3.61) juice, than in watermelon juice (pH 5.4). Supplementation of juices with carvacrol decreased the survival of both acid‐adapted and non‐adapted bacterial cells. Our results suggest that the supplementation of fruit juices with natural antimicrobials, such as carvacrol, may contribute to counteract the mild thermal tolerance developed by acid‐adapted bacteria. Given the different properties of fruit juices, such combined treatments need to be developed specifically for each fruit product.Practical applicationsSupplementation of fruit juices with natural antimicrobials has been described to increase the efficiency of microbial mild thermal inactivation treatments. However, its effect on the thermal resistance of acid‐adapted cells has not previously been addressed. We observed that acid adaptation enhances mild thermal tolerance. Our results suggest that natural antimicrobials can effectively counteract the mild thermal tolerance of acid‐adapted cells. The combination of mild temperature treatments and natural antimicrobials is a firm alternative to conventional pasteurization to ensure the safety of fruit juices without affecting their nutritional properties. Moreover, this combined strategy does not require expensive novel technologies or high energy consumption.