I found the article on Kefir by Lucy Goodchild van Hilten (2015, Microbiologist 16, 42) interesting and I thought some members of the Society might like to learn of our experience with kefir in Ireland.
Kefir grains are called buttermilk plants in Ireland and some housewives traditionally use them to produce sour milk, which is an essential ingredient in making soda bread in the home. The sour milk is made exactly as described in the article, except that the incubation period is usually 2-3 d at room temperature or 1-2 d at slightly higher temperatures at the back of a solid fuel cooker, e.g., a Rayburn or Aga. The higher temperatures result in shorter incubation times. The kefir grains are collected from the sour milk by straining and are washed with cold running water before using them to produce the next batch of soured milk. The kefir grain itself is very complex containing yeast, various lactic acid bacteria, including lactococci, leuconostocs and lactobacilli, and acetic acid bacteria, held together in an insoluble matrix of the polysaccharide, kefiran. As far as I am aware the reconstitution of a kefir grain by growing the microorganisms found in it together in milk has never been successful which begs the question, how did it arise first day?
Our interest in the kefir grain was as a potential source of new strains of Lactococccus lactis, the traditional starter culture used in Cheddar cheese production. Lc. lactis is notoriously sensitive to attack by bacteriophage, which inhibits the ability of the starter to produce lactic acid during cheese manufacture resulting in poor quality cheese. One is, therefore, always looking out for new strains of starter. In the laboratory at that time we did not have any source of kefir so a letter to the Irish farming newspaper, the “Farmers Journal”, elicited 49 samples, one of which was of Russian origin and another which had been in the same family for more than 100 years. It is possible that some of the grains were related to each other as they had probably been shared with other housewives over the years. The kinetics of growth of the different microorganisms and the production of lactate, acetoin, acetate and ethanol in six of these kefir grains have been reported (Rea et al 1996 J. Appl. Microbiol. 81, 83).
We isolated 361 strains of Lc. lactis from the kefir grains. Unfortunately, only two strains were good acid producers and neither produced good flavoured cheese (Cogan et al. 1997 J. Dairy Res. 64, 409). However, another strain produced a potent, broad spectrum, bacteriocin, called lacticin 3147, which had several interesting and disparate properties. It is lantibiotic, containing the amino acid, lanthionine, and unlike the well known lantibiotic, nisin, is comprised of two peptides. It is effective in curing mastitis in dairy cows, in controlling the growth of Listeria monocytogenes in cheese, is stable enough to be added to toothpaste as a potential inhibitor of dental caries and inhibits the development of non-starter lactic acid bacteria (NSLAB) in cheese (for a review see Suda et al 2012 Current Protein and Peptide Science, 13, 193). NSLAB are adventitious contaminants of raw milk, some of which withstand pasteurisation and grow to high numbers (~108 cfu/g) in all ripening cheeses. Such high numbers probably have a role in cheese ripening but this is still unclear despite extensive study. The bacteriocin may have some role in determining the health benefits of kefir. Interestingly, lacticin was produced by strains isolated from different kefir grains suggesting that the kefirs from which they were isolated were related to each other.
Tim Cogan, Ballyduff Upper, Co. Waterford, Ireland.
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