Modeling the effect of temperature on survival rate of Listeria monocytogenes in yogurt

Abstract

The aim of the study was to (i) evaluate the behavior of Listeria monocytogenes in a commercially produced yogurt, (ii) determine the survival/inactivation rates of L. monocytogenes during cold storage of yogurt and (iii) to generate primary and secondary mathematical models to predict the behavior of these bacteria during storage at different temperatures.The samples of yogurt were inoculated with the mixture of three L. monocytogenes strains and stored at 3, 6, 9, 12 and 15 o C for 16 days. The number of listeriae was determined after 0, 1, 2, 3, 5, 7, 9, 12, 14 and 16 days of storage. From each sample a series of decimal dilutions were prepared and plated onto ALOA agar (agar for Listeria according to Ottaviani and Agosti).It was found that applied temperature and storage time significantly influenced the survival rate of listeriae (p<0.01). The number of L. monocytogenes in all the samples decreased linearly with storage time. The slowest decrease in the number of the bacteria was found in the samples stored at 6 o C (D-10 value = 243.9 h), whereas the highest reduction in the number of the bacteria was observed in the samples stored at 15 o C (D-10 value = 87.0 h). The number of L. monocytogenes was correlated with the pH value of the samples (p<0.01). The natural logarithm of the mean survival/inactivation rates of L. monocytogenes calculated from the primary model was fitted to two secondary models, namely linear and polynomial. Mathematical equations obtained from both secondary models can be applied as a tool for the prediction of the survival/inactivation rate of L. monocytogenes in yogurt stored under temperature range from 3 to 15 o C, however, the polynomial model gave a better fit to the experimental data.

Antimicrobial Effects of Berries on Listeria monocytogenes

“…bulgaricus and Streptococcus salivarius ssp. thermophilus added to milk as a starter culture, as well as the production of organic acids, mainly lactic acid [4] [48] [49]. The researchers found that lag phase and growth rate of Listeria were affected not only by storage temperature but also by lactic acid concentration and pH of product ranged from 5.2 do 5.8.…”

“…In the European Union (EU), 1763 confirmed human cases of listeriosis were reported in 2013 by 27 member states. The EU notification rate was 0.44 cases per 100,000 population which represented an 8.6% increase compared to 2012 [4]. In 2013, there were 191 deaths caused by listeriosis in the EU.…”

A 100-Year Review: Yogurt and other cultured dairy products

“…Choi et al (1988) found that L. monocytogenes will survive 13 to 27 d in vanilla-flavored yogurt after inoculation of 10 4 to 10 5 cells, whereas Tirloni et al (2015) reported that L. monocytogenes with a starting concentration of either 2 or 5 log cfu/g was still detected in 25-g samples of unflavored and strawberry yogurt at 68 d of storage. Szczawiński et al (2016) developed linear and polynomial models to describe the inactivation rate of L. monocytogenes in yogurt as a function of temperature and found D-values (decimal reduction time) ranging from 87.0 h at a storage temperature of 15°C to 243.9 h at a storage temperature of 6°C when calculated from linear models.…”

Modelling the growth rate ofListeria monocytogenesin cooked ham stored at different temperatures

“…A linear decrease in the number of these bacteria was observed during storage (34,35). This phenomenon was mainly explained by the low pH of the samples (range 4.1-4.4), because the pH value of about 4.6 is generally considered as the minimum enabling the growth of L. monocytogenes (7,28).…”

“…Certain food categories are no longer under a zero tolerance regime but have a specified maximum allowed concentration of 100 CFU/g or ml for products placed on the market during their shelf-life. Therefore, many studies on modelling the effects of various factors on the growth of L. monocytogenes have been published in recent years (5,18,22,23,35). This research allows the behaviour of L. monocytogenes in RTE meat products to be predicted.…”