Kenya is home to a variety of traditional fermented milk products such as mursik of the Kalenjin community and kule naoto of the Maasai community. These sour milk products are produced by leaving fresh milk to ferment spontaneously in a smoke-treated gourd for up to two days at room temperature.
Spontaneous fermentation takes advantage of the actions of various species of lactic acid bacteria that occur naturally in milk. Smoking of the inside of the gourd with smouldering acacia twigs is said to increase the milk’s storage life and gives the sour milk its characteristic flavour.
For generations, fermentation has been used as an effective means of extending the storage life of milk in Africa. Cow, goat, sheep or camel milk may be used as the raw material. In some cases, a mixture of milk from different animals may be used.
During fermentation, the lactic acid bacteria in the milk convert the milk sugar lactose into lactic acid, which gives the product a distinct sour taste. Some of the lactic acid bacteria also produce antimicrobial substances called bacteriocins that inhibit the growth of disease-causing bacteria (pathogens).
Microbial safety of raw milk is of concern primarily because milk is a highly nutritious product that readily supports the growth of spoilage microbes. Fermented milk is, however, safer than fresh milk (microbiologically speaking) since the lactic acid and the bacteriocins kill coliforms and other disease-causing bacteria such as E. coli.
In addition to enhanced microbiological safety, regular drinking of fermented milk is said to offer various health-related benefits to the consumer, such as lowering of cholesterol, boosting of the body’s immune system, and protection against diarrhoea and constipation.
The findings of a seminal study by Mann and Spoerry in 1974 suggest that consuming traditional fermented milk can help reduce serum cholesterol levels. These researchers studied a group of Maasai men in Kenya and found that despite their consumption of large amounts of red meat, the level of cholesterol in their serum was low and there were few cases of coronary heart disease. This was linked to their practice of consuming up to five litres a day of fermented milk.
Fermented milk is also easier for lactose intolerant people to digest. Up to 80 per cent of East African adults suffer from lactose intolerance, a condition in which lactose is not completely digested due to a lack of the enzyme lactase.
Lactose intolerance often manifests in uncomfortable sensations in the digestive system like bloating, flatulence and diarrhoea soon after drinking fresh milk. People with lactose intolerance can, however, drink fermented milk without experiencing gastric distress, thanks to the breakdown of lactose by the lactic acid bacteria.
Probiotic foods contain live microorganisms which actively enhance health by improving the balance of intestinal bacteria. The most commonly studied probiotic microorganisms are members of the genera Lactobacillus and Bifidobacterium which are found in probiotic yoghurt and other traditional fermented dairy and vegetable products.
They act by adhering to the lining of the intestine and preventing harmful bacteria from multiplying. The increasing incidence of colon cancer globally has drawn scientific attention to the probiotic effects of the microflora in traditional fermented products, especially among populations whose diets are high in refined foods.
The anticancer properties of the probiotic Lactobacillus acidophilus have been established by microbiological studies carried out in the US in the mid 1980s. In addition to activating the body’s immune system, the organism decreased the levels of the enzymes responsible for converting procarcinogens in the colon into cancer-causing agents. Research continues into conclusive evidence.
Among food microbiologists, there is now renewed focus on gaining a deeper understanding of the nature of traditional fermentations, especially the identity and functional properties of the microorganisms involved.
Results of a study of the functional properties of Lactobacillus species isolated from kule naoto show promise for development of suitable starter cultures. This would offer a useful opportunity to standardize and scale up production of kule naoto and other traditional fermented milk products.
NOTE: This blog post is based on an article I wrote for the Daily Nation newspaper that was published in October 2003. I have revised and edited the text, modified the structure slightly, and added hyperlinks for those interested in reading further on the various topics. If you’d like to read the original article, please leave a comment and I’ll send you a copy.