Growth of Eurotium Chevalieri in Milk Jam: Influence of Ph, Potassium Sorbate and Water Activity

Milk jam (dulce de leche) is a typical Argentine sweet spread prepared by milk evaporation to about 70% w/w total solids at atmospheric pressure with added sucrose, glucose and vanillin. Growth of xerophilic molds represents a severe problem in this type of intermediate moisture product. This study evaluated the growth response of Eurotium chevalieri in milk jam with different potassium sorbate (KS) concentrations (0, 500, 1,000, 1,500 and 2,000 ppm) at selected water activity ( a w ) values ( ≅ 0.80 and 0.85) and two pH levels ( ≅ 5.5 and 6.0) stored at room temperature (25C) for 90 days. Growth curves were characterized by the modified Gompertz model, and the effect of the independent variables on the estimated parameters (maximum specific growth rate, v m , and lag time, λ) was analyzed through polynomial equations. Growth of E. chevalieri was prevented for at least 90 days when the addition of 1,000 ppm KS was combined with a decrease in a w to 0.80 and ph 5.5. The boundary between growth and nongrowth of E. chevalieri as a function of a w , pH, KS and storage time was also predicted by means of the probabilistic model using logistic regression, which provided a wide range of formulation possibilities depending on the targeted shelf life.