Prevalence of Listeria species in raw milk, ice cream and yogurt and effect of selected natural herbal extract on its survival

Abstract

Objective: This study aimed to detect the prevalence of Listeria species in raw milk, ice cream and yogurt, and to evaluate the effect of extract of clove, thyme and pomegranate peel on such organism.

Design: Descriptive study.

Procedures: One hundred and fifty samples of milk, ice cream and yogurt were examined for isolation, identification and molecular identification of Listeria spp. Extraction of natural plant extract as clove, thyme and pomegranate peels and detection of their inhibitory effect on Listeria spp.

Results: The prevalence of Listeria spp. in milk was 36% where 14% as L. monocytogenes, 6% L. innocua and 16% and other Listeria spp. was 16%. In yogurt, Listeria spp. was 6% as L. innocua was 2% and other Listeria spp. was 4%, while no L. monocytogenes was detected. In ice cream, Listeria spp. was 8% where L. monocytogenes was 2% and other Listeria spp. was 6% while no L. innocua was detected. The concentration of plant extract was 2.5% which showed high reduction rate on L. innocua and L. monocytogenes during shelf life of soft cheese.

Conclusion and clinical relevance: Listeria is widely isolated from milk than from ice cream and yogurt. Plant extracts play role in food preservation and consider as a natural antimicrobial agent where most effective one was clove extract.