Is curd a probiotic?

Published in The Hindu on May 30, 2012

Curd - R. Prasad

According to a 2002 study published in the European Journal of Clinical Nutrition, the amount and strain of useful bacteria in curd vary from place to place.The number of different Lactobacillus bacteria isolated from curd preparations in India is as high as 250 species. But can curd and yoghurt be technically called as probiotics?

Dr. Neerja Hajela, who is the Head – Science at Yakult Danone India Pvt. Ltd, in an email to R. Prasad, dwelt in detail on the contentious issue.

Can curd and yoghurt be called as probiotics?

No. Curd and yoghurt cannot be called as true probiotics.

What is the reason for this?

According to the 2001 definition of probiotics by FAO/WHO, it is important that for any strain/product to be classified as a probiotic it must be or must contain live microorganisms (generally numbering one billion) which are resistant to gastric acid, bile and pancreatic juices and reach the target site (small intestine/large intestine) in numbers sufficient enough to elicit a beneficial effect. It should be scientifically validated through well controlled clinical trials.

Curd is defined as a product obtained by souring boiled or pasteurized milk naturally, by harmless lactic acid bacteria or other bacterial cultures. It may contain a wide variety of bacteria, which are not defined qualitatively/quantitatively. The number and type of bacteria also vary from home to home.

Yoghurt, on the other hand, is obtained by lactic acid fermentation of milk by Lactobacillus delbrueckii subspecies bulgaricus and Streptococcus thermophillus, which are not true probiotics as per the definition.

While one cannot undermine the nutritional benefits that these products bestow, it still remains to be determined whether these products contain organisms that are defined in terms of number, viability at the target site and whether scientifically validated for health benefits (all these criteria as per the universally accepted probiotic definition). Hence, products that are standardised in terms of the strain of bacteria, viable count and scientifically proven health benefits are different from these natural products.

A 2002 study published in the European Journal of Clinical Nutrition which had also used Indian dahi found it to be effective in significantly reducing the duration of diarrhoea. Your comments.

I am not so sure of the study design, but the probiotic (Actimel) was more effective in terms of reducing the duration of diarrhoea (0.6 days versus 0.3 days) as compared with curd. The curd used in the study was a standardised preparation with defined viable count.

Should a product contain a certain number and specific beneficial bacterial species to be called a probiotic?

Yes, it is important that a food item/product contains a specific number of beneficial bacteria for it to be called a probiotic. The benefits are strain specific, and therefore vary from strain to strain.

Which are the Lactobacilli species present in curd and yoghurt?

Curd may contain a wide variety of bacteria like Lactobacillus acidophilus, Lactococcus lactis, Lactococcus lactis cremoris etc, whereas yoghurt contains Streptococcus thermophillus and Lactobacillus bulgaricus.

Can the number of bacteria present in curd and yoghurt be increased through natural fermentation?

Yes, the number of bacteria can be increased by natural fermentation. However, prolonged fermentation tends to render the product very sour because of excess amount of acetic/lactic acid that is produced during the process. Moreover, the exact bacterial count cannot be determined in a process that has not been standardised.

It has been a traditional practice to provide buttermilk to children suffering from diarrhoea. If it is not a probiotic, is buttermilk just keeping the children hydrated?

Curd and buttermilk, apart from being a part of our diet, are also taken by people who are lactose intolerant — cannot digest lactose since they lack the enzymes that are needed to break down lactose, the milk sugar.

In fermented products like curd and buttermilk, most of the lactose is converted to lactic acid/acetic acid by the enzymes that are found in fermenting bacteria. Hence these products are easier to digest.

The role of buttermilk in treating diarrhoea has not been scientifically proven. But it is given during diarrhoea to rehydrate, and hence it imparts some benefit.