Thermal Resistance of Xerophilic Fungi in Low-Water-Activity (0.70 to 0.80) Confectionery Model Foods.

Consumers are increasingly searching for preservative-free and "natural" food options. Confectionery products with low water activity (a) are typically considered resistant to contamination with filamentous fungi; however, several xerophilic fungi can cause considerable economic losses due to spoilage. Very few studies have been published addressing filamentous fungi that are tolerant to low a in food products containing all nutrients essential for filamentous fungi growth, including sugars, carbohydrates, proteins, and fats, but not preservatives. The objective of this study was to evaluate the effect of a on the thermal tolerance and survival of one strain of Aspergillus pseudoglaucus and two strains of Aspergillus fischeri. The decimal reduction time ( D-value) and the temperature needed for a 1-log change in D-value ( z-value) in a low-acid (pH 6) confectionary model comprising evaporated milk and fructose adjusted to a of 0.70, 0.75, and 0.80 were determined by creating thermal death time curves. Experiments were performed in triplicate. A. fischeri had higher thermal tolerance than did A. pseudoglaucus. An interaction between a and temperature was found; however, it was not linear with respect to a. A. fischeri had the highest thermal tolerance for 0.75 a at 90°C ( D-values of 11.5 to 34.8 min) compared with 0.70 and 0.80 a, for 0.80 a or 0.75 a depending on the strain at 92°C (4.3 to 17.1 min), and for 0.75 a at 94°C (2.4 to 7.7 min). A. pseudoglaucus had the highest thermal tolerance for 0.70 a at 78°C ( D-value of 4.9 min), 80°C (1.7 min), and 82°C (0.8 min). The data from this study will be useful for determining parameters for thermal processing of low-a confectionary products to control the growth of xerophilic fungi.