Heat resistance of Monascus ruber ascospores isolated from thermally processed green olives of the Conservolea variety

Abstract

A heat-resistant fungus identified as Monascus ruber was isolated from thermally processed green olives of the Conservolea variety. Thermal death parameters of the ascospores were determined using Baranyi's primary predictive model in phosphate buffer (pH 7.0), citrate buffer (pH 4.0) and brine (pH 3.8) at two different NaCl levels (5.6% and 10.5%). The decimal reduction times ( D values) at 70, 75 and 80 °C in phosphate buffer (pH 7.0) were 37.31, 7.14 and 1.66 min, respectively, and the calculated z value was 7.4 °C. In citrate buffer (pH 4.0), the relative D values were 38.61, 7.83 and 2.10 min and the z value was 7.9 °C. In brine, the D 70 °C, D 75 °C and D 80 °C values increased from 46.08, 4.91 and 0.88 min to 72.99, 7.98 and 1.04 min, respectively, as the level of NaCl in brine increased from 5.6% to 10.5%, indicating a protective effect in ascospore inactivation. This effect was more pronounced at lower heating temperatures. It was concluded that a thermal process of F 80 °C=5 min could be considered as an effective thermal processing treatment. Results from this research could assist the table olive industry in designing an effective pasteurization plan to eliminate the fungus in thermally processed table olives.