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- MakaleYalnız künye2026Scopus SJRQ1Thermal inactivation kinetics of Listeria monocytogenes in fat/water emulsions and fat tissue – effect of fat content
Ozturk, Samet; Huang, Lihan; Hwang, Cheng-An; Sheen, Shiowshuh
Significantly increased thermal resistance was found in Listeria monocytogenes inoculated to beef tallow. However, how the relative compositions of fat and water in emulsions affect bacterial survival during heating has not been evaluated. This study aimed to evaluate the effect of fat levels in solid fat/water (SF/W) emulsions on thermal resistance of L. monocytogenes. SF/W emulsions, containing 0, 25, 50, 60, and 75 % of tallow by weight, were prepared by mixing tallow with soybean lecithin and Tween 80 in 0.1 % peptone water using an ultrasonic processor. A 4-strain cocktail of L. monocytogenes was inoculated to the emulsions and subjected to isothermal heating between 55 and 65 °C. The survival curves were analyzed to estimate the kinetic parameters and evaluate thermal resistance. Linear survival was observed in emulsions with fat below 50 %. However, increased thermal resistance, evidenced by the increasing D and z values with the fat content, was observed. For example, the average D values in SF/W emulsions at 60 °C are 0.54, 1.04, and 2.53 min, respectively, with 0, 25, and 50 % fat. For SF/W emulsions with 60 and 75 % fat and in beef trim fat (BTF, 86.9 % fat), the survival curves became convexly nonlinear and could be described with the Weibull model. The exponents of the Weibull model range between 0.45 and 0.456, suggesting almost identical convexity of the survival curves. The convex survival curves indicate initial sensitivity to heat but the resistance increases with time at each temperature. The estimated time to a 5-log reduction becomes 11.9 and 26.4 min in 60 and 75 % SF/W emulsions, respectively, and 36.5 min in BTF at 60 °C. The study demonstrates the effect of fat levels on thermal resistance of L. monocytogenes in SF/W emulsions and BTF. The results of this study may help the food industry to properly kill L. monocytogenes in fat-containing meat products during thermal processing.
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İncele - MakaleAçık Erişim2024Scopus SJRQ1Thermal resistance of Listeria monocytogenes, Escherichia coli O157:H7 and Salmonella in animal fat – Kinetic analysis and mathematical modeling
Ozturk, Samet; Huang, Lihan; Hwang, Cheng-An; Sheen, Shiowshuh
The objective of this study was to evaluate the effect of fat on thermal resistance of L. monocytogenes, E. coli O157:H7, and Salmonella spp. A 4-strain cocktail of each microorganism was inoculated to beef tallow and heated isothermally at temperatures between 55 and 80℃. All survival curves did not follow the 1st-order inactivation kinetics but conformed to a two-stage linear pattern. The first stage was markedly less heat-resistant than the second, as manifested by significantly lower D values. The z values of E. coli O157 H7 and Salmonella spp. were 11.8 °C and 12.3 °C in the first stage (z1) but increased to 23.7 °C and 20.8 °C in the second stage (z2), respectively. For L. monocytogenes, while the z values were similar for both stages (z1 = 19.6 °C and z2 = 18.5 °C), the second stage D values are 3.6–5.9 times of those in the first stage. One-step analysis was used to fit the nonlinear curves to the Weibull model, yielding < 1 exponents for the model (0.495, 0.362, and 0.282, respectively, for L. monocytogenes, E. coli O157:H7, and Salmonella spp.), suggesting gradually increased thermal resistance during heating. The experimental results showed that these microorganisms could resist heating for longer time and at higher temperatures in tallow than they do in regular meats containing lower levels of fat. The kinetic models can be used to develop thermal processes to properly inactivate pathogens contaminated in the fat portions of meat products or other high fat products.
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