14C-1 |
Aspergillus flavus and A. parasiticus growth response as affected by solute and acid type at selected water activities and pHs |
E. PALOU, A. López-Malo, and L. C. Coronado. Departamento de Ingeniería Química y Alimentos, Universidad de las Américas-Puebla, Santa Catarina Mártir, Cholula, Puebla, 72820, Mexico Aspergillus flavus and A. parasiticus are common contaminants in several types of foods being responsible for spoilage and possible toxin production, and characterized by resistance to salted, sugared and/or acidic environments. Due to the variety of environments that these molds may spoilage, solute and acid type may affect their response. Mold response in laboratory media formulated at aw 0.99, 0.95 or 0.90, pH 5, 4 or 3 when using sodium chloride, sucrose or glucose to adjust aw, in combination with acetic, citric, phosphoric or tartaric acid to reduced pH was evaluated. For each mold, solid media formulated with each factor combination was inoculated with 103 spores mL-1, and incubated at 27ºC up to 30 days. Periodically during incubation, mold colony diameter was measured, determining if growth or inhibition (growth delay) occurred. An ANOVA demonstrates that individual variables as well as their interactions significantly (p<0.05) affected each mold response (lag time). A. parasiticus was more resistant to the studied combined effects growing in 96 of the 108 evaluated cases. For both molds, acetic acid significantly (p<0.05) inhibit mold growth in more cases than the other evaluated acids, growth was observed in only 15 of the 27 evaluated combinations. When growth was observed, lag time increased as aw and pH decreased. With citric acid growth was observed in all evaluated combinations. The use of sodium chloride to adjust aw in combination with pH 3, promoted growth delay and mold inhibition (no growth after 30 days of incubation). Combinations of low aw and pH causes mold inhibition in more cases when sodium chloride and acetic or phosphoric acid were used. The studied molds not have the same behavior to equal combinations of aw and pH, demonstrating that acid and solute type exhibited an important effect on their response.
Session 14C, Food Microbiology: Food mycology
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