Application of Weibull type distribution of resistances model to thermal resistance of Listeria innocua in vanillin containing orange juice

CHAR, C; GUERRERO, S; ALZAMORA, STELLA MARIS

Río de Janeiro

Congreso; ENPROMER 2005 - 2nd Mercosur Congress on Chemical Engineering - 4th Mercosur Congress on Process Systems Engineering; 2005

Different methods are being explored for the preservation of orange juice for reducing the severity of conventional pasteurization. In order to decrease process temperature and/or time other stress factors must be included to assure food safety. Among natural antimicrobials, vanillin has been shown to be a natural inhibitor for molds and yeasts in fruit products. On the other hand, contamination of commercial products with Listeria monocytogenes has become a major concern for food processors. The purpose of the present work was to evaluate and model the influence of incorporated vanillin and process temperature on Listeria innocua (as surrogate microorganism for L. monocytogenes) survival in orange juice. Inactivation experiments were carried out in a 150 mL- double wall vessel containing orange juice supplemented with non inhibitory levels of vanillin (0, 500, 700, 900 or 1100 ppm). The temperature was controlled to attain 57 °C to 61°C. Samples were taken at regular intervals during .8 minutes and monitored by plate counting and NMP techniques using Triptone Soy Agar supplemented with 1% sodium piruvate in order to detect injured cells. L. innocua log reductions increased exponentially with temperature and vanillin concentration, reaching for some conditions 5 log CFU/ml as required by FDA to assure juice safety. Vanillin effect was more pronounced at higher temperatures. Weibull type distribution of resistances model was successfully fitted to survival curves. Statistic parameters which better explain the observed frequencies: distribution mode, mean, variance, and coefficient of skewness, were calculated. Some combinations of temperature-vanillin were highly effective exhibiting narrow frequency shapes, slightly skewed to the right, with low time media and variance, indicating that the majority of the population died at the beginning of treatment. The results suggest that the use of vanillin combined with mild heat treatment could inactivate L. innocua in minimally processed orange juice.  Listeria monocytogenes has become a major concern for food processors. The purpose of the present work was to evaluate and model the influence of incorporated vanillin and process temperature on Listeria innocua (as surrogate microorganism for L. monocytogenes) survival in orange juice. Inactivation experiments were carried out in a 150 mL- double wall vessel containing orange juice supplemented with non inhibitory levels of vanillin (0, 500, 700, 900 or 1100 ppm). The temperature was controlled to attain 57 °C to 61°C. Samples were taken at regular intervals during .8 minutes and monitored by plate counting and NMP techniques using Triptone Soy Agar supplemented with 1% sodium piruvate in order to detect injured cells. L. innocua log reductions increased exponentially with temperature and vanillin concentration, reaching for some conditions 5 log CFU/ml as required by FDA to assure juice safety. Vanillin effect was more pronounced at higher temperatures. Weibull type distribution of resistances model was successfully fitted to survival curves. Statistic parameters which better explain the observed frequencies: distribution mode, mean, variance, and coefficient of skewness, were calculated. Some combinations of temperature-vanillin were highly effective exhibiting narrow frequency shapes, slightly skewed to the right, with low time media and variance, indicating that the majority of the population died at the beginning of treatment. The results suggest that the use of vanillin combined with mild heat treatment could inactivate L. innocua in minimally processed orange juice.