Milk Safety

Photo: Matt Rosen

Food safety and agriculture are issues that can limit the quality of life in the developing world. In Kenya, where much of the milk is not pasteurized and refrigeration is not common in rural areas, the spoilage of milk presents a problem for dairy farmers. Dairy farmers in Kenya often transport their milk for long distances, over poor roads to deliver it to market for sale. Once at market, the milk must be sold quickly, or it will spoil. The combination of long transport time and the quick spoilage of unpasteurized milk results in wasted milk. This leads to financial loss for farmers and a limit to the amount of milk available to the Kenyan people. Seasonal shortages of milk occur regularly in Kenya, depriving dairy farmers of their source of income and wellbeing and depriving people of the nutritional benefits of milk. These problems have lead Intellectual Ventures Laboratory to take an interest in developing alternative milk transportation and pasteurization systems for use in rural areas of the developing world with limited access to pasteurization, refrigeration, and energy sources.

Photo: Mogan Fowler

Milk is a complex biological fluid which is composed of a variety of proteins and lipids. These biological macromolecules are a food source for many microorganisms.  Degradation of the proteins and lipids by the microorganisms that grow in milk causes milk spoilage. Killing the microorganisms in milk can thus extend the shelf life of the milk. Since its suggestion by Franz von Saxhlet in 1886, the pasteurization process has been used extensively to kill microorganisms and preserve milk in the developed world.

Photo: Matt Rosen

Normally, pasteurized milk is refrigerated after heat treatment to inhibit growth of microorganisms that survived the pasteurization process.  Refrigeration requires electricity, which is limited in rural areas of the developing world. One alternative, Ultra-high temperature (UHT) milk pasteurization coupled with sterile handling and packaging allows milk to be stored at room temperature for 6-9 months. Sterile handling and packaging are a challenge in the developing world, where often there are no facilities or equipment for aseptically transferring and storing milk.  UHT processing is expensive and not a product that is usually consumed by people in rural Kenya. Given these challenges, preservation of milk by alternative pasteurization systems could provide a viable method for preserving milk in rural areas of the developing world.

Development of an effective pasteurization system requires knowledge of the types of microorganisms that need to be killed. Many microorganisms can be pathogenic causing illness in humans. The pasteurization process is complex due to the microorganisms wide range of optimal growth temperatures and heat tolerances. The microbial content of milk varies with geographic location, likely being dependent upon local environmental microorganisms and cattle feed.

Since the microbial content of Kenyan milk is not well documented, a base knowledge of microorganisms in Kenyan milk was needed to understand if potential pasteurization systems would be safe and effective for Kenyan milk. Our Applied Chemistry and Biology Group conducted a broad study of Kenyan bovine milk to determine the microbial content.

Samples of bovine milk were collected from 20 locations throughout Kenya including dairy farms, dairy bars, and dairy cooperatives. These samples were subjected to a range of thermal profiles that mimic potential alternative pasteurization methods. Culturable microorganisms were grown and isolated from these 20 samples before, during, and after the heat treatments. Total Viable Cell (TVC) numbers were calculated to determine the efficacy of the pasteurization.  Isolates from each sample were selected based upon colony morphology. The selected isolates were then identified using Sanger sequencing of the 16s ribosomal RNA (rRNA) gene to determine if there were any pathogenic microorganisms present.

Dairy Bar; Photo: Matt Rosen

In this study the result of the TVC showed that the raw milk samples had cell numbers ranging from  10^5 – 10^7 CFU/ml. The heat treatments reduced TVC to less than  10^3 CFU/ml which is acceptable by the standards set by the Kenyan Bureau of Standards for pasteurized milk (3 x  10^4 CFU/ml). A total of 226 isolates were identified using the 16s rRNA sequence. The sequence identification of the microorganisms isolated from the milk samples showed a total of 78 bacterial species across 36 genera. Of these, 30% were Bacillus species, which are commonly isolated from milk even in the US. Many of the remaining species were other commonly occurring milk bacteria. Additionally, there were many common soil and water bacteria, as well as mammalian skin bacteria.

Photo: Intellectual Ventures

The microbial content of Kenyan milk showed microorganisms that were readily inactivated by the heat treatments employed. The diversity showed many expected and unexpected microorganisms. With an understanding of the microbial composition of Kenyan milk, IV Lab can use this information to assess appropriate methods for milk preservation in this part of the developing world.

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