Antimicrobial activity of indigenous plants used by pastoral communities for milk preservation in Kilosa District, Tanzania

MSc. DissertationMilk is an important part of the diet among pastoral communities in Kilosa district, Tanzania. Its production and consumption derives much food security and economic benefits to the rural people in the district. However, Milk has a complex biochemical composition and its high-water activity and nutritional value serves as an excellent medium for growth and multiplication of many kinds of microorganisms. This shortens the shelf-life of milk. In the framework of research to improve the shelf-life and safety of milk, this study was conducted to explore the indigenous knowledge on milk preservation and antimicrobial activity of the commonly used plants in milk preservation. A survey was conducted on the use of herbs in milk in Parakuyo and Mbwade villages in the district, after which leaves, stems and roots of two plant species of Dalbergia melanoxylon and Combretum imberbe were collected for laboratory analysis. Biological activity using minimum inhibitory concentration (MIC) serial dilution assay against six milk spoilage bacteria and titratable acidity were determined. The common methods for preservation of milk were boiling, fumigation of milk containers using dried stems and roots of selected plant species and fermentation. Ethanol extracts of the plant parts showed antimicrobial activity against Escherichia coli, Salmonella typhi, Pseudomonas aeriginosa, Staphylococcus aureus, Streptococcus agalactiae and Proteus spp. Stem extract of D. melanoxylon showed highest activity with an MIC of 3.125 mg/ml. The difference in biological activity among the extracts was not statistically significant. Furthermore, there was no statistical difference in lactic acid production between milk samples treated with extracts and non-treated fresh milk samples. The results of this study give credence to the traditional use of Dalbergia melanoxylon and Combretum imberbe and expand our knowledge on the biological activity of their extracts as potential natural preservatives