This study investigated the growth of Propionibacterium cyclohexanicum in orange juice over a temperature range from 4 to 40 °C and its ability to multiply in tomato, grapefruit, apple, pineapple and cranberry juices at 30 and 35 °C. Survival after 10 min exposure to 50, 60, 70, 80, 85, 90 and 95 °C in culture medium and in orange juice was also assessed.
In orange juice the organism was able to multiply by 2 logs at temperatures from 4 to 35 °C and survived for up to 52 days. However, at 40 °C viable counts were reduced after 6 days and no viable cells isolated after 17 days. The optimum growth temperature in orange juice over 6 days was 25 °C but over 4 days it was 35 °C.
The growth of P. cyclohexanicum was monitored in tomato, grapefruit, cranberry, pineapple and apple juices at 30 and 35 °C over 29 days. Cranberry, grapefruit and apple juice did not support the growth of P. cyclohexanicum. At 30 °C no viable cells were detected after 8 days in cranberry juice or after 22 days in grapefruit juice while at 35 °C no viable cells were detected after 5 and 15 days, respectively. However, in apple juice, although a 5 log reduction occurred, viable cells could be detected after 29 days. P. cyclohexanicum was able to multiply in both tomato and pineapple juices. In tomato juice, there was a 2 log increase in viable counts after 8 days at 30 °C but no increase at 35 °C, while in pineapple juice there was a 1 log increase in numbers over 29 days with no significant difference between numbers of viable cells present at 30 and 35 °C.
The organism survived at 50 °C for 10 min in culture medium without a significant loss of viability while similar treatment at 60, 70 and 80 °C resulted in approximately a 3–4 log reduction, with no viable cells detected after treatment at 85 or 90 or 95 °C but, when pre-treated at intermediate temperatures before exposure to higher temperatures, some cells survived. However, in orange juice a proportion of cells survived at 95 °C for 10 min without pre-treatment and there was no significant difference between numbers surviving with and without pre-treatment.
The results from this study demonstrate that P. cyclohexanicum is able to grow in a number of juices, other than orange juice, and able to survive a number of high temperature procedures. Therefore, if initially present in the raw materials P. cyclohexanicum might survive the pasteurization procedures used in the fruit juice industry, contaminate and consequently spoil the final product