Effect of natural antimicrobials on shelf-life of raw milk

Abstract

Milk has an outstanding nutritional quality but it is an excellent medium for bacterial growth and an important source of bacterial infection when consumed without pasteurization. On the basis of morphology and utilization of carbon source three frequently available microbial contaminants have been isolated from eight different raw milk samples of Kolkata. The organisms were partially characterized. Attempt has been made to inhibit those bacteria and to increase the shelf-life of raw milk using six different natural antimicrobials, Aloe vera juice, Syzygium aromaticum (clove) oil, aquatic extract of Ocimum (tulsi) and Curcuma longa (turmeric), raw honey, and whey of Lactobacillus yogurt. Honey was used directly whereas others were applied as their lyophilized extract (1/10 volume reduced). The inhibition of microorganisms was determined following agar cup assay and the extent of efficacy of antimicrobial agents appeared as clove> honey> tulsi> whey >turmeric> aloe for all, except the Type II bacteria. The antibiotic resistant Type I, Type II and Type III bacteria revealed growth inhibition 64.75, 69.49 and 83% respectively, in NB with clove oil (0.1%, v/v) after 10h. The bactericidal activity of clove oil (0.1%) and diluted filter sterilized honey (1%, v/ v) were comparable with those of ampicillin (100-200 g/ml) and streptomycin (100 g/ml) against the contaminants in filter sterilized raw milk.