Milk preservation is closely related with its microbiological quality. The spoilage may
occur at any stage from production, during processing and till consumption. Many
potent antimicrobials were discovered recently but, it is important to test their efficacy
against undesirable bacteria inside the food materials that help to improve food safety
and validity. Our research was focused on comparative antibacterial activities between
chitosan, lysozyme and their different mixtures against different undesirable bacterial
strains by agar well diffusion assay. Then apply the selected antibacterial substances in
raw cow milk contaminated with food borne pathogens and spoilage bacteria then
monitoring the bacterial growth or inhibition. Our preliminary investigation showed
that, chitosan 0.5% exhibited the largest inhibition zones diameter followed by
lysozyme hydrolysates with chitosan complex against Salmonella enteritidis and
Bacillus subtilus in-vitro by agar well diffusion method. During application in raw cow
milk, lysozyme hydrolysates and chitosan complex exhibited powerful bactericidal
effect followed by chitosan especially against Clostridium perfringens, Staphylococcus
aureus and Listeria monocytogenes after 24h from cooling storage of raw cow milk. The
bactericidal activity of lysozyme and lysozyme hydrolysates were greatly enhanced
upon their combination with chitosan. But, the bactericidal activity of lysozyme
hydrolysates with chitosan complex exhibited great killing power than the conjugation
between lysozyme with chitosan complex at same concentrations. This may be
attributed to chitosan oligomers and lysozyme peptides acting in a synergistic manner in
penetrating and killing the undesirable bacteria. Although chitosan was effective in
inhibiting the growth of spoilage microorganisms but, it is induce changes in raw milk
pH. Accordingly, we suggest lysozyme hydrolysates with chitosan complex will be a
promising antibacterial additive to produce a highly safe raw milk with recommendation
further future studies to explore its antibacterial mechanism. |
