Modeling the influence of water activity and ascospore age on the growth of Neosartorya fischeri in pineapple juice

The ascospores of resistant fungi, Neosartorya fischeri, can survive commercial pasteurization, diminishing the shelf life of these products. The time that the ascospores remain in the environment and the effect that they can cause on mold growth are still unknown. This study is aimed to evaluate the influence of water activity (a_w) from 0.90 to 0.99 and the ascospore age (I) from 30 to 90 days of vitro incubation on the growth of N. fischeri in pineapple juice by mathematical modeling. The growth parameters on pineapple juice: adaptation phase (λ), maximum specific growth rate (μ_max) and maximum diameter reached by the colony (A) were obtained by fitting Modified Gompertz and Logistic models to the experimental data. Both models were able to describe microbial growth in pineapple juice, but the Modified Gompertz model presented a slightly superior performance based on statistical indices (correlation coefficients (R²), mean square error (MSE), Bias Factor and Accuracy Factor). The minimum values of λ and A, calculated by the Modified Gompertz model, were 64.7 h and 6.3 mm, while the maximum values were 178.2 h and 20.8 mm, respectively. The result showed that ascospore age did not influence the growth but a_w was statistically significant to the growth parameters λ and A.