Purpose: The objectives of this study were to investigate the response of heat-resistant fungal spores of Neosartorya pseudofischeri isolated from contaminated blueberry juice to various heat treatments, establish heat treatment time and temperature combinations to inactivate this fungus, and elucidate the mechanism(s) of heat resistance.
Methods: The 15 and 30 days old heat-resistant fungal spores were collected and inoculated into the blueberry juice at 104 spores/ml. Blueberry juice was then subjected to heat treatments at 80, 85, 90, 93, 95, 96 and 99°C for different duration. Mold counts were conducted and survivor curves were plotted. D- and z-values were determined and compared using ANOVA. Proteomic approach was used to investigate protein changes of N. pseudofischeri subjected to heat treatment at 93°C for 0, 1, and 8 min.
Results: The 30 days old fungal spores had significantly higher thermal resistance than that of the 15 days old spores (P < 0.05). Practical heat inactivation data were generated for different heat time and temperature combination. The D-values of 30 days old spores of N. pseudofischeri at 85, 90, 93, 96 and 99°C were 53.8, 12.2, 2.03, 0.98 and 0.42 min, respectively. The z-value calculated from the thermal death time curves was 6.32°C. Protein profile of the fungal spores was determined using LC/MS/MS.
Significance: The results established by this study may be used by fruit (blueberry) processors to prevent losses due to spoilage caused by the heat-resistant microorganisms and establish appropriate thermal process schedules for fruit (blueberry) products.