Thermal Inactivation of Conidia from Aspergillus flavus and Aspergillus parasiticus

Abstract

Conidiospores from one strain of Aspergillus flavus and two of Aspergillus parasiticus were thermally inactivated in menstrua at pH values of 3.5, 4.5, 5.5, and 6.0. These values were obtained with the following buffering systems: sodium acetate and acetic acid, citric acid and Na2HPO4, potassium acid phthalate (KHP)-HCl and KHP-NaOH, and KH2PO4 and NaOH. Heating of conidia in a menstruum adjusted to pH 7.0 with KH2PO4 and NaOH served as the control. Use of the sodium acetate and acetic acid buffering system resulted in an increase in the rate at which conidia were inactivated when the pH was decreased. Use of the citric acid and Na2HPO4 buffering system resulted in increased thermal resistance for the conidia as the pH was decreased; however, the degree of increased thermal resistance was strain dependent. When the KHP-HCl and KHP-NaOH buffers were used, conidia were inactivated more rapidly than in the control at the higher pH values and more slowly than in the control at the lower pH values. An increase in amount of sodium chloride, sucrose, or glucose in the menstruum was accompanied by a decrease in the rate at which conidia were inactivated. Generally, sodium chloride was markedly protective to conidia at aw values of less than 0.94, whereas the sugars were markedly protective at values below 0.95. Greatest protection at these values was afforded by sucrose.