Determination of hydration properties and thermal behavior of Paecilomyces variotii by differential scanning calorimetry

Abstract

Due to the structure and the composition of Paecilomyces variotii, the mycelia of this fungus could have potential applications as ingredients in wettable foods. For this use, drying could be employed, justifying the study of thermal behavior of P. variotii. The objectives of this work were to perform a study of thermal behavior of P. variotii isolates, to evaluate the hydration properties of these mycelia and to analyze the effect of different technological parameters on the latter properties. Wet cultures exhibited a wide endothermic transition, with mean values of peak temperature of 61°C and denaturation enthalpy of 4 J/g dry matter. Ini tial (50°C) and final (80°C) temperatures of the endothermic transition were used to dry the mycelia. Freeze drying was also assayed. For all dried mycelia, a decrease in denaturation enthalpy between 40 and 50% was observed for drying at 50°C and freezedrying, and a drastic decrease of almost 100% for drying at 80°C. According to the hydration properties, wet mycelia exhibited water holding capacity (WHC) value of 45 g water/g dry matter. Significant differences among dried mycelia, resulting WHC values in order: 50°C > freezedried > 80°C (p < 0.05) were revealed for each P. variotii strain. Fungi obtained by drying at 50 C and by freezedrying, showed a rapid water absorption (t1/2 < 0.1 min). Ionic strength, pH and particle size of dried mycelia influenced the hydration properties.