Modeling growth for predicting the contamination level of guava nectar by Candida pelliculosa under different conditions of pH and storage temperature.

Abstract

The combined effects of temperature (2-46 degrees C) and pH (1.55-6.25) on the growth of Candida pelliculosa isolated from guava nectar produced in Cameroon were studied using a turbidity method, ie measurement of optical density at 630 nm. A quadratic polynomial model was constructed to predict the effects and interactions of these two environmental conditions on the maximal optical density obtained (i2 = 0.97). The relation between optical density and population density of C. pelliculosa (CFU ml-1) was also established using an exponential regression (2 = 0.99). According to the model, maximal growth conditions were 37 degrees C and pH 6.25 for obtaining the maximal optical density of 1.25 corresponding to about 60 x 10(6) CFU ml-1. A good agreement of the model was found between the predicted values and the observed values of maximal optical density. The model was validated by the experimental values of maximal optical density obtained in the growth of C. pelliculosa in commercial guava nectar (pH 3.15).