61C-33 |
Inactivation kinetics of Zygosaccharomyces bailii under isothermal conditions |
A. ARGAIZ-JAMET1, M. M. Olmedo-Hernandez, and A. López-Malo. (1) Laboratorio de Microbiologia, Universidad de las Americas - Puebla, A.P. 391, Santa Catarina Martir, 72820, Mexico Zygosaccharomyces bailii is commonly implicated in the deterioration of many foods, mostly those in which factors such as water activity (aw), pH reduction, and antimicrobials are used in combination with pasteurization. In these foods it would be important to know how yeasts have been inactivated. In this experiment the effects of aw (0.97 o 0.99) ajusted with glucose or sucrose, pH (3 o 4), in combination with the presence or absence of potassium sorbate (KS, 500ppm) on the inactivation kinetics of Z. bailii were studied using linear temperature increments from 30 to 70°C. Sabouraud broths were formulated for each combination of factors and inoculated with 10exp6 CFU of yeasts per mL. The treatments were done in a double-walled container conected to a ciculating bath. Samples were taken at preselected times and the number of survivors determined. From the survivor curves the inactivation parameters were determined and the results analyzed through multiple linear regression and ANOVA. Multiple linear regression demonstrated that for all inactivation factors combinations inactivation was first order, and from it the activation energies (Ea) and the frequency factors could be determined. Ea values were smaller when glucose was used instead of fructose to adjust aw. For aw 0.99 higher Ea values were observed in the presence of KS and low pH. A reduction of aw to 0.97 resulted in an increase in the resistance of the yeast but made the interpretation of the interactions with low pH and presence of KS difficult. en un incremento en la resistencia de la levadura pero dificult. Thermal inactivation was favored at aw 0.99, low pH and the presence of KS. ANOVA demonstrated a significant effect (p<0.05) of each factor and their interactions on the inactivation of the yeast.
Session 61C, Food Microbiology: General I
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