Department of Food Hygiene and Technology, Institute of Health Sciences, University of Burdur Mehmet Akif Ersoy, 15030, Burdur, Turkey.
Department of Food Hygiene and Technology, Faculty of Veterinary Medicine, University of Burdur Mehmet Akif Ersoy, 15030, Burdur, Turkey.
Pol J Vet Sci. 2024 Mar 20;27(1):53-60. doi: 10.24425/pjvs.2024.149333.
The aim of this study was to determine the effects of an ohmic heating (OH) process with different electric field intensities on Listeria monocytogenes inactivation in protein-enriched cow milk. Protein powder was added at rates of 2.5%, 5% and 7.5% in 1.5% fat content milk, and L. monocytogenes (ATCC 13932) strain was then inoculated into the samples. The OH process was carried out in a laboratory-type pilot unit created using stainless steel electrodes, a K-type thermocouple, a datalogger and power supply providing AC current at 0-250 V, 10 A. The inoculated milk samples were heated to 63°C by applying an electric field intensity of 10V/cm and 20V/cm. L. monocytogenes counts, pH, color measurement and hydroxymethylfurfurol levels were then determined. OH applied with an electric field intensity of 10 V/cm caused an average decrease of 5 logs in L. monocytogenes level in the samples containing 2.5% protein and decreased below the detection limit (<1 log) at the 9th minute (p<0.05). Similarly, application of an electric field intensity of 20 V/cm in milk containing 2.5% and 5% protein caused the L.monocytogenes level to decrease below the detection limit (<1 log) at 2 minutes 30 seconds (p<0.05). No change was observed in the L* (brightness) values of the samples but it was determined that there was a slight increase in pH, a* (redness) and b* (yellowness) values compared to the control group. It was observed that the inactivation of L. monocytogenes by OH depends on the duration of the OH process, protein concentration in the milk and the applied voltage gradient.
本研究旨在确定不同电场强度的欧姆加热（OH）过程对富含蛋白质的牛奶中单核细胞增生李斯特菌失活的影响。在 1.5%脂肪含量的牛奶中分别添加 2.5%、5%和 7.5%的蛋白粉，并将单核细胞增生李斯特菌（ATCC 13932）菌株接种到样品中。OH 过程在使用不锈钢电极、K 型热电偶、数据记录仪和提供 0-250V、10A 的交流电的实验室型试验单元中进行。将接种的牛奶样品加热至 63°C，施加的电场强度为 10V/cm 和 20V/cm。然后测定单核细胞增生李斯特菌计数、pH 值、颜色测量和羟甲基糠醛水平。在含有 2.5%蛋白质的样品中，施加 10V/cm 的电场强度导致单核细胞增生李斯特菌水平平均下降 5 个对数级，在第 9 分钟时降至检测限以下（<1 个对数级）（p<0.05）。同样，在含有 2.5%和 5%蛋白质的牛奶中施加 20V/cm 的电场强度导致单核细胞增生李斯特菌水平在 2 分 30 秒时降至检测限以下（<1 个对数级）（p<0.05）。样品的 L*（亮度）值没有变化，但与对照组相比，pH 值、a*（红色）和 b*（黄色）值略有升高。观察到 OH 对单核细胞增生李斯特菌的灭活取决于 OH 过程的持续时间、牛奶中的蛋白质浓度和施加的电压梯度。
