Effect of soluble solids concentration on Neosartorya fischeri inactivation using UV-C light.

Ascospores of Neosartorya fischeri are heat-resistant and can survive thermal commercial treatments normally applied to the juices, as apple juice. Non-thermal processing of food such as exposure to ultraviolet light (UV-C) is reported to induce minimal quality changes while reduces microbial load. The main objective of this study was to determine the effect at different soluble solids concentration (12, 25, 30, 40, 50, 60 and 70 °Brix) on N. fischeri ascospores inactivation in apple juice, using UV-C light intensity (38 W/m2). Weibull model was fitted to experimental data. Then, a secondary model was used to describe how the inactivation kinetic parameters varied with the changes in soluble solids concentration. Results showed that the UV-C light had influence on N. fischeri ascospores inactivation in apple juice even at the highest soluble solids concentrations used, reaching approximately 4 log reductions at all concentrations used. The inactivation parameters, obtained by Weibull model, were δ (dose for the first decimal reduction) and p (the shape factor). Exponential model was chosen to describe the influence of soluble solids concentration on δ and p parameters. It can be concluded that UV-C light is a promising treatment with a drastic impact on the loads of N. fischeri, especially when low soluble solids concentration is used and a model was obtained to describe Brix effect.

Modeling the growth of Byssochlamys fulva and Neosartorya fischeri on solidified apple juice by measuring colony diameter and ergosterol content.

Byssochlamys fulva and Neosartorya fischeri are heat-resistant fungi which are a concern to food industries (e.g. apple juice industry) since their growth represents significant economic liabilities. Although the most common method used to assess fungal growth in solid substrates is by measuring the colony's diameter, it is difficult to apply this method to food substrates. Alternatively, ergosterol contents have been used to quantify fungal contamination in some types of food. The current study aimed at modeling the growth of the heat-resistant fungi B. fulva and N. fischeri by measuring the colony diameter and ergosterol content, fitting the Baranyi and Roberts model to the results, and finally establishing a correlation between the parameters of the two analytical methods. Whereas the colony diameter was measured daily, the quantification of ergosterol was performed when the colonies reached diameters of 30, 60, 90, 120 and 150 mm. Results showed that B. fulva and N. fischeri were able to grow successfully on solidified apple juice at 10, 15, 20, 25 and 30 °C, and the Baranyi and Roberts model showed good ability to describe growth data. The correlation curves between the parameters of colony diameter and ergosterol content were obtained with satisfactory statistical indexes.

Modeling the Growth of Byssochlamys fulva on Solidified Apple Juice at Different Temperatures

The aim of this study was to establish primary and secondary models to describe the growth kinetics of Byssochlamys fulva on solidified apple juice at different temperatures. B. fulva was inoculated on solidified apple juice at 10, 15, 20, 25 and 30 °C. Linear-with-breakpoint, Baranyi and Roberts, and Huang primary models (without upper asymptote) were fitted to the data, and they showed good ability to describe the growth kinetics. B. fulva showed longer adaptation time on apple juice than on culture medium, but growth rates were similar as reported in the literature. The dependence of µmax and λ parameters on temperature was described with Square Root and Arrhenius-Davey secondary models, respectively. These models were important to establish process/storage conditions and apple juice shelf life.