Quantitative characterization of high-pressure inactivation of E. coli and Salmonella in fruit purees enhanced by acid exposure and delayed sampling

Abstract

This study aimed to quantitatively characterize the inactivation kinetics of Escherichia coli (CECT5947 & CTC1029) and Salmonella (GN001 & CIP106188) during high-pressure processing (HPP, from 300 to 600 MPa) in apple (pH 3.6) and banana (pH 4.2) purees. The impact of a 24 h-acid exposure before HPP and delayed sampling after HPP were addressed, as relevant scenarios for the food industry. Primary and secondary kinetic parameters were estimated by two- and one-step model fitting. HPP efficacy was both strain- and product-dependent, with greater inactivation in apple puree due to its higher acidity compared with banana puree. After 2 min at 400 MPa, E. coli CECT5947 was reduced 3.21 Log (apple) and 0.55 Log (banana), while CTC1029 strain showed reductions of 5.91 Log (apple) and 0.65 Log (banana). Salmonella CIP106188 was reduced by 4.2 Log (apple) and 1.5 Log (banana), while GN001 strain decreased 3.1 Log (apple) and 0.3 Log (banana). Our findings indicate that the inactivation during pressure come-up time should be considered when modelling the HPP bacterial inactivation. According to the model, pressure showed a quadratic effect on the inactivation during come-up time. Remarkably, acid exposure and a delayed sampling after HPP significantly enhanced the inactivation of both microorganisms. This study highlights the need of product-specific predictive models for setting tailored HPP conditions suitable to meet the 5 Log reduction performance criterion. The results emphasize that for validation and verification purposes, sampling for microbiological analysis can be performed 24 h after HPP to avoid underestimation of HPP efficacy in acid food matrixes.