Practices that Lead to Microbial Contamination of Milk in Zimbabwe’s Informal Dairy Sector
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A recent study provided insight into the on-farm hygiene characteristics that affect the contamination of milk produced at informal dairy farms in Zimbabwe. The research was led by the Zimbabwe Ministry of Health and Childcare’s Department of Food and Microbiology, in collaboration with Midlands State University, the University of Venda, and the National Food Institute at the Technical University of Denmark.
Specifically, the study looked at the microbiological safety level profiles (MSLPs) of dairy workers' hands and milking containers, and the influence of hygiene and handling practices on MSLPs of raw and cultured milk, from six informal dairy farms in Zimbabwe. Interviews and direct observations were conducted to assess hygiene and handling practices, and a total of 192 environmental swabs and milk samples were taken to be analyzed for the presence of microbes. The researchers sampled and swabbed raw milk, cultured milk, the dairy workers' hands, and milking containers, which were analyzed for total bacterial and coliform counts, Escherichia coli, Salmonella, Listeria monocytogenes, and Klebsiella pneumonia.
None of the six farms included in the study received maximum MSLP scores from the researchers, due to factors like utilizing plastic containers, using unsafe water sources such as wells, milking in open areas with bare hands, a lack of cold rooms, and generally not having established food safety management systems (FSMS).
Regarding the microbiological assessment of environmental swabs and milk samples, the researchers found that raw milk from all six farms contained unacceptably high total bacterial and coliform counts, exceeding legal limits. The poor microbial quality of the milk was mostly linked to poor sanitation and hygiene of the farm environment, milking, and storage equipment, as well as personnel hygiene. Additionally, E. coli levels in raw milk were a concern at four farms, indicating fecal contamination; although milk contaminated by E. coli is illegal to sell in Zimbabwe, the raw milk produced by these farms was still sold to consumers. The study’s authors use this case as an example of why milk pasteurization is crucial.
Cultured milk did not fare much better, with samples from all farms except one containing enough microbes to earn low MSLP scores. Cultured milk sold at informal, small-scale dairy farms in Zimbabwe is produced by natural fermentation under rudimentary and uncontrolled conditions. Although cultured milk, because of its metabolites and low pH, is expected to inhibit the growth and survival of bacteria, the recorded pH of the samples from this study ranged from 4.6–4.9, which allows the growth of most microbes, including E. coli.
On a positive note, Salmonella and L. monocytogenes were not detected in the collected samples and swabs, suggesting that the handling and hygiene procedures at the six farms successfully kept these pathogens under control, even with the observed subpar facilities and practices. Additionally, no indicator organisms or pathogens were detected in the swabs from dairy workers' hands and milking containers. Still, the total bacteria count range for dairy workers' hands was 2.0 colony forming units per square centimeter (CFU/cm2)–log 6.1 CFU/cm2, and for milking containers, 2.3 CFU/cm2–log 4.3 CFU/cm2. Total bacteria count on hands and surfaces that come into contact with food should be less than log 2 CFU/cm2. The high total bacteria count for swabs from dairy workers' hands and milking containers could be attributed to inadequate personal hygiene, the use of unsafe well water, and milking in open spaces with bare hands.
The farm that achieved the highest MSLP score was able to reduce the risk of raw and cultured milk contamination through procedures like cleaning the milking parlor with detergents after each milking session, using municipal water, storing milk in stainless steel cans in a cold room, and minimizing the amount of time it took to store milk (less than 30 minutes). The farm also had documentation of a food safety program, despite its implementation being inadequate according to globally accepted FSMS standards (ISO 22000).
The risk variables identified in the study can serve as a foundation for microbial contamination prevention strategies in Zimbabwe's informal dairy sector. Infrastructure development and training are required to improve the quality of milk and milk products that are produced and marketed through this value chain.
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