Investigation of a tunnel pasteurizer for “Nocellara del Belice” table olives processed according to the “Castelvetrano method”

The influence of pasteurization temperature and time of treatment on the flesh firmness and the evolution of microbial communities was studied for table olives Cv. Nocellara del Belice, packed in glass jars and processed with a tunnel pasteurizer. The experiment was preliminarily carried out at laboratory level in order to select the optimal combination of pasteurization time/temperature to obtain the right compromise between consistency of the pulp and microbiological quality of the final product. Pasteurization at industrial scale was then carried out within a tunnel pasteurizer applying the treatment at 75 °C for 8 min in the thermal center of the jars. Besides flesh firmness and microbial evolutions, pH, total titratable acidity (TTA) and colour were evaluated for the table olives during storage at 6, 12 and 15 months from packing. Table olives showed a high stability and an acceptable flesh firmness for the entire period under observation. Specifically, olive pulp texture decreased during the storage period, but the softening was most evident in the deeper layers of the pulp. The results indicated that the storage period should not exceed 6 months; although the hygiene is preserved, after this period the firmness might compromise the acceptability by consumers.