Use of a logistic model to assess spoilage by Byssochlamys fulva in clarified apple juice.

The percentage P (%) of spoiled bottles (n=40) of clarified apple juice due to Byssochlamys fulva, was modeled by using a logistic model: P = P(max)/1 + exp (k(tau-t)) where P(max) (%) the maximum percentage of spoiled bottles, k (h(-1)) a slope parameter and tau (h) the time for P=P(max)/2. Bottles of pasteurized apple juice were inoculated with B. fulva IOC 4518 ascospores for low and high initial loads, 4.8+/-2.3 ascospores/100mL and 19.3+/-4.6 ascospores/100mL respectively and incubated at 21 degrees C and 30 degrees C. P(max) was not significantly different from 100% except for a low initial load at 21 degrees C. Model parameters were estimated with a good accuracy, RMSE in the range 3.89-7.50. Then the model was used to determine the time for 10% bottles spoiled, t(10%). This time was greater at low initial loads, 57.4 and 104 h at 30 and 21 degrees C respectively, than at high initial loads 23.9 and 75.1h at 30 and 21 degrees C respectively. This study demonstrated that even at a very low initial contamination, clarified apple juice can be easily spoiled by B. fulva highlighting the importance of controlling critical control steps of fruit juice processing (i.e., fruit washing, juice filtration and pasteurization).