Survey on the level of Listeria monocytogenes infection on gotu kola and fresh gotu kola juice in Nha Trang, Khanh Hoa province

Gotu kola is often used to make fresh juice without heating. In Nha Trang, gotu kola drinks are usually prepared and refrigerated while being traded. Listeria monocytogenes is a bacterium capable of growing at cold temperatures; whereas the pathogenicity is low, mortality rate can be up to 25 - 30%. Therefore, the assessment of the level of L. monocytogenes contamination on raw gotu kola and in gotu kola juice during cold storage is crucial to ensure food safety and hygiene. This study has shown that the prevalence of L. monocytogenes infection on raw gotu kola cultivated in Nha Trang accounted for 15% of the samples with an average infection density of 24.2 MPN/g, in which gotu kola grown in wastewater field had the highest density of bacteria. Soaking raw vegetables in a solution of potassium permanganate 10 ppm/10 minutes has appeared to reduce the amount of L. monocytogenes by 56%. During the first 6 hours of storage, the amount of L. monocytogenes in gotu kola juice was stable at low level. After 24 hours of storage, the number of bacteria increased tenfold (on gotu kola juice without sugar) and twentyfold (on gotu kola juice with sugar) depending on storage temperature. Noticeably, the addition of sugar in gotu kola juice may have increased the growth of bacteria. Test results of forty-five samples of gotu kola juice sold on the streets of Nha Trang have revealed that the infection rate of L. monocytogenes was 6.67% and the average bacterial density was 5.43 MPN/mL. Thus, consumers need to pay attention to the origin and the manufacturing process of crude materials and should not use this herbal beverage from 6 hours after storage to reduce the possibility of disease caused by L. monocytogenes.