For more than six thousand years, mankind has been using fermentation to prepare food and drinks, and still fermented dairy products and other fermented foods are widely consumed for their high nutritional value, pleasing sensory attributes and potential health-promoting properties. Some of these products (such as yogurt) are produced and sold around the world, while others are little known outside of one or a few countries.
Biochemists from the Institute of the Research Center of Biotechnology RAS (Russia) and Durban University of Technology (South Africa) studied the composition and properties of fermented drinks popular in their countries. The research included three milk-based products—kefir and ryazhenka from Russia, and amasi (also known as maas) from South Africa, as well as one corn-based South African product—mahewu (also known as amahewu, mageu).
"Usually, food is considered only as a source for sustenance. However, more and more people start to believe that it also should preserve and improve health. Modern methods of biochemistry, biotechnology, medicine, and pharmacology allow mankind to look differently at the usefulness of traditional, centuries-old foods. Our research focuses on fermented products, which regular consumption can potentially prevent atherosclerosis, hypertension, and thrombosis," says Konstantin Moiseenko, co-author of the study.
Kefir is made from milk using a special starter culture, kefir grains, which contains a large number of different microorganisms, including Lactococcus, Lactobacillus, and Leuconostoc bacteria, acetic acid bacteria, and yeasts. Kefir is native to the Caucasus region, but in the 19th and 20th centuries, it spread to other regions and became one of the most popular sour-milk drinks in Russia.
Ryazhenka is also an extremely popular product in the Russian market. This drink is made from baked milk using traditional yogurt starter that includes the bacteria Lactobacillus bulgaricus (Bulgarian bacillus) and Streptococcus thermophilus.
Amasi is produced in South Africa from cow's milk using bacterial cultures of Lactococcus lactis subsp. lactis, Lactococcus lactis subsp. cremoris, and Leuconostoc mesenteroides subsp. cremoris. The traditional way of making amasi involves fermentation in a calabash or in a gourd. Another typical South African fermented soft drink, mahewu, is made from cornmeal, which begins to ferment when wheat flour or lactobacillus starter is added.
The experiments and their results
Scientists analyzed the content of antioxidants and fatty acids (for fermented dairy products) in the drinks, as well as the volatile organic compounds that determine their taste and smell. In addition, biochemists tested which of the products can inhibit the angiotensin-converting enzyme responsible for increase of blood pressure.
Milk-based products were found to have more antioxidants, but mahewu was better at suppressing the angiotensin-converting enzyme. The composition of fatty acids in kefir and ryazhenka was more diverse than in amasi, and from the point of view of a healthy diet (prevention of atherosclerosis and thrombosis), kefir and ryazhenka are preferable. However, more branched chain fatty acids have been found in amasi; these fatty acids have recently been considered as important bioactive molecules that are beneficial for human health. In particular, some studies showed that branched chain fatty acids have anti-tumor activity.
Kefir and ryazhenka have a more distinct and spicy flavor compared to amasi, which feels creamier. Mahewu has quite plain flavor but acquires additional fruity notes when stored. Acidic components in all these drinks were equal – about a third of all volatile compounds. Kefir was found to have the highest alcohol content (67% of all volatile compounds), while ryazhenka and amasi had only three percent each. Scientists found ketones only in ryazhenka (62%) and kefir (1%), and esters in mahewu (50%) and ryazhenka (6%). This explains the fruity flavor of the first two products and the peculiar flavor of the third. Aromatic alcohol (furfural), formed as a result of the Maillard reaction, was also found in the ryazhenka, which gives the drink a burnt caramel flavor. In addition, acetoin was found in amasi (which makes it creamy), and lactamide was found in mahewu (the source of which seems to be wheat flour added during fermentation).
"Results of our studies will help to update and extend current dietary recommendation for healthy eating. Studying the substances that are responsible for the traditional taste of these foods can help find better combinations for new recipes. There is a hypothesis that foods that share volatile organic compounds are more likely to taste better together," explained scientists.
- This press release was provided by the Federal Research Centre «Fundamentals of Biotechnology» of the Russian Academy of Science