Thermal inactivation of talaromyces flavus ascospores in pineapple juice as influenced by temperature, soluble solids, and spore age

Abstract

The ascospores of Talaromyces species can survive pasteurization and grow in high acid fruit juices. In this study, the thermal inactivation of Talaromyces flavus ascospores in pineapple juice was carried out and the log reductions were counted. First, the effect of temperature (T: 80-90°C), soluble solid content (SS: 10-30°Brix), and spore age (30-60 days) on the viability of ascospores were investigated. Then, the first-order kinetic parameters (D and z-values) were determined from the log survivor curves. Results of the thermal processes showed that higher log reductions for higher temperatures (5.2 log for 90°C vs. 0.89 log for 85°C and 0.28 log for 80°C) were obtained at 10°Brix after 15 min heat treatments. Lower spore reductions were observed at higher SS (1.5 log for 30°Brix vs. 2.4 log for 20°Brix and 3.0 log for 12°Brix after 9 min at 90°C). Longer time needed to inactivate the older spores (53.8 min for 30 day-old-spores vs. 67.1 min for 60 day-old-spores). The log survivors are better described by the first-order kinetics at 80-90°C. The estimated D-values in 12°Brix juice were 63.8 min, 16.9 min and 2.89 min for 80, 85 and 90°C, respectively, with z-value of 7.9°C. This result emphasizes the importance of temperature, SS, and ascospore age on the heat resistance of T. flavus ascospores in high acid fruit juice.