Field Validation of Predictive Models for the Growth of Lactic Acid Bacteria in Acidic Cheese-Based Greek Appetizers

Abstract

A microbial model was developed for spoilage of two acidic Greek appetizers, namely, tyrosalata (TS) and tyrokafteri (TK), with pH values of 4.34 to 4.50 and 4.22 to 4.38, respectively. The specific spoilage organisms of these products were lactic acid bacteria (LAB), which dominated during storage, while yeasts, whenever present, remained at low levels (1 to 2 log CFU/g). Correlations of LAB populations with changes in pH and sensory characteristics indicated that the spoilage level of LAB ranged from 8.1 to 8.6 log CFU/g for both products. TK showed a relatively higher microbial stability than did TS. The growth of LAB was modeled with the Baranyi model, while their maximum specific growth rates were further modeled as a function of temperature with square-root model and Arrhenius equations for each appetizer. The validation of the model was performed under nonisothermal conditions in the laboratory and in a field validation trial with temperature logging during distribution of individual packages in the chill supply chain, including transportation from the plant to the distribution center, retail display, and household refrigerators. Models for both appetizers showed satisfactory agreement with data, with a slight tendency of overprediction of LAB in TS. The field validation process also confirmed the higher stability of TK over TS. The developed models may serve as a useful tool for monitoring the microbiological quality of such complex products and manage their distribution. Furthermore, depending on the seasonal variation of chill chain conditions, reassessment of shelf life may be performed.