The influence of temperature and gas mixtures on the growth of the intrinsic micro-organisms on cut endive: predictive versus actual growth

Abstract

Effects of temperature and carbon dioxide concentration on the growth of mesophilic aerobic count (MAC), psychrotrophic, Gram-negative bacteria, pseudomonads and lactic acid bacteria were investigated in a case-study of minimally processed endive. When plotting population density against time, a distinct lag time was not observed. In a temperature range from 4.3–16.1°C, both combined Arrhenius–Ratkowsky-restricted growth models were used to model growth of these groups of micro-organisms. Temperature dependence of the growth rate constant for pseudomonads and psychrotrophic, Gram-negative bacteria were similar, whereas the growth rate constant of the MAC was much more temperature dependent. A combined exponential (CO 2)–Arrhenius (temperature)-restricted growth model was selected to model the number of pseudomonads and an exponential (CO 2)–Ratkowsky (temperature)-restricted growth model was selected to model the growth of MAC on cut endive. The restricted growth model was differentiated with respect to time to obtain a dynamic restricted growth model. Temperature shift-up and shift-down experiments were performed. Use of the Arrhenius equation for the temperature dependence of the growth rate constant and parameter estimates obtained under constant CO 2and temperature conditions only partially allowed us to predict the microbial evolution of minimally processed endive under dynamic conditions. Especially under temperature shift-down conditions, a systematic underestimation of growth was observed.