Certain foods have been associated with health benefits for many years. Fermented milk and yoghurt are typical examples.
Fermented milk has been an important component of nutrition and diet. In addition to yoghurt, there are numerous types of fermented milk manufactured in different parts of the world.
The different types are classified according to the methods of fermentation or processing, which are related to the microorganisms involved.
Each type of fermented milk involves use of specific microorganisms, based on the optimum growth requirements of the starter cultures (that is, mesophilic, a low temperature starter culture and thermophilic, a heat loving culture that is activated by high temperatures).
Originally, the primary function of fermenting milk was to extend its shelf life.
Together with this came numerous advantages, such as an improved taste and enhanced digestibility of the milk, as well as the manufacture of a wide variety of products.
Fermentation of milk generally involves the metabolism of lactose to lactic acid – a characteristic common to all fermented milk—by lactic acid bacteria (LAB). This results in reduction of pH with or without coagulation.
The starter microorganisms should be viable, active and abundant in the product to the date of its durability.
Fermented milk products are classified into three different types: Products of lactic fermentation, where strains of mesophilic or thermophilic LAB are used; products obtained through alcohol-lactic fermentation, involving yeast and LAB; and products where, in addition to the two types of fermentation above, there is mold growth. All products are the result of fermentation of lactose into mainly lactic acid.
There are two types of lactic fermentation based on the incubation temperature, namely, mesophilic fermentation, employing mesophilic starters, and thermophilic fermentation, involving thermophilic starters, composed solely of LAB.
Cultured milk, maziwa lala or mala as it is popularly known in Kenya, is a type of product obtained through mesophilic fermentation of milk, while yoghurt is obtained as a result of thermophilic fermentation of milk.
The health properties of these dairy products were a part of tradition until the concept of probiotics emerged, and the study of fermented milk and yoghurt containing probiotic bacteria became more consistent.
Inappropriate nutrition leads to lack of achievement of genetic potential, reduced mental and physical performance and increased susceptibility to disease.
In searching for effective dietary intervention strategies, a new class of food, functional food, has evolved rapidly and new terms such as probiotic and prebiotic have emerged.
Functional foods are defined as foods, or food ingredients, with positive effects on a person’s health and well-being beyond their nutritional value.
Fermented milk comply with the requirements of functional food. The milk contain all the nutrients of unfermented milk; however, several components are modified during fermentation by lactic acid bacteria, mainly in a positive way as far as nutrition is concerned. For example:
The digestibility of fat is improved during fermentation. Milk fat is known for its high proportion of saturated fatty acids. However, at least one-third of the fatty acids are unsaturated, with a cholesterol-lowering tendency.
The fermented milk contain components with protective, hypocholesterolemia effects; these include calcium, linoleic acid, conjugated linoleic acid (CLA), antioxidants and lactic acid bacteria or probiotic bacteria.
LAB degrades protein in milk resulting in some free amino acids and bioactive peptides. These peptides are involved in immunomodulation, anti-microbial activity, anti-thrombotic activity, blood pressure regulation, and mineral or vitamin binding.
Fermented milk is also a rich source of whey proteins, which studies have shown to demonstrate biological effects ranging from anti-carcinogenic activity to different effects on the digestive function.
Lactose, the sugar in milk, is fermented to lactic acid; this reduces pH, influences the physical properties of casein, a milk protein, and thus promoting digestibility, improving the utilisation of calcium and other minerals, and inhibiting the growth of potentially harmful bacteria.
Due to its lower lactose content, fermented milk can be tolerated by people with lactose intolerance. By adding probiotic bacteria and prebiotics, fermented milk can become more of a functional food.
Probiotics are live micro-organisms that have a beneficial effect on the human body; they improve intestinal microbial balance.
Prebiotics are non-digestible food ingredients that can also selectively stimulate the growth and activity of one or a limited number of bacteria in the colon.
The human gastrointestinal tract possesses a complex microbial ecosystem that can influence various physiological functions of the intestine and, ultimately, general human health.
A number of beneficial roles played by probiotic bacteria have been reported.
These include protection against gastrointestinal infections; re-establishment of balanced intestinal microflora; reduction of lactose intolerance; cholesterol reduction; stimulation of the immune system; suppression of allergic reactions in food hypersensitivity; and protection against cancer.
Scientific evidence confirms the fact that the risk for many of chronic diseases such as cancer, osteoporosis, coronary heart disease and hypertension can be diminished by the regular consumption of fermented milk and fermented milk supplemented with probiotics and prebiotics.
Faith Ndungi, Department of Human Nutrition, Egerton University