Dahi – Indian Curd – Nutrition Meets Food Science

Dahi, a popular fermented milk product is consumed across the country in different forms as curd, lassi, chhaas or other products made from dahi, like misti doi and shrikhand.

Conversion of milk to dahi is an important intermediate step to manufacture butter and ghee so it can be safely assumed that around 40% of the total milk produced in India is converted to dahi. (1)

Definition of Dahi/ Curd

According to FSSAI, dahi or curd is the product obtained from pasteurized or boiled milk by souring, natural or otherwise, by a harmless lactic acid or other bacterial culture. Dahi may contain additional cane sugar. It should have the same percentage of fat and solids-not-fat as the milk from which it is prepared. Where dahi or curd, other than skimmed milk dahi, is sold or offered for sale without any indication of the class of milk, the standards prescribed for dahi prepared from buffalo milk shall apply.

Dahi is traditionally made at Indian homes by first boiling the milk, then cooling it to ambient temperature followed by inoculation with previous day’s “dahi culture”. It is allowed to set at room temperature for a couple of hours. Once set it can be refrigerated and stored. During winter months the inoculated milk should be kept in a warm place for the dahi to set properly. The actual process is the bacterial fermentation of milk where the milk sugar lactose is converted to lactic acid by several probiotic microorganisms (present in the dahi culture). Almost all starter cultures are members of a group of bacteria known as Lactic Acid Bacteria (LAB). These bacterial species for fermentation could vary depending on the temperature and humidity of the environment and may include Lactococcus lactis, Streptococcus diacetylactis, Streptococcus cremoris, Lactobacillus delbrueckii subsp. bulgaricus, Streptococcus thermophilus and lactose fermenting yeasts. Lactobacilli, may be predominating strain in sour dahi, while streptococcus strain may be responsible for slightly sweet dahi. (2)

Production of curd has so far been predominantly unorganised but considering the nutritional and economic benefits of curd efforts are being taken to standardize the manufacturing process by bringing it under the organized sector of The Indian Dairy Industry.

According to the Bureau of Indian Standards, dahi is

What is the difference between homemade curd and Industrial curd?

Dahi made at home has non standardized starter cultures, which vary from region to region and even between houses, as a result of which the taste and texture may vary. In the industries all the processes are standardized, even the starter cultures are predefined to maintain consistency in the texture, taste and flavour of the dahi. Industrial curd is firmer due to its higher Solid Non- fat content (SNF). The milk at home is either fresh from the dairy farm or branded milk that is already standardized, pasteurized and homogenized, this is directly inoculated with the culture, while in the industry the milk is subjected to pre-treatments with quality checks at each stage before being inoculated with predefined culture.

Industrial processing of dahi can be explained briefly in the following steps (3)

Good quality milk is preheated and standardized to maintain the fat content between 0-5% and solid non- fat between 11-13%.Milk is the homogenized to evenly distribute the fat globules, followed by pasteurization to destroy pathogenic bacteria, yeasts and moulds. Next step is preheating to ~45⁰C and then inoculation with specific starter cultures (The culture used in the commercial production of curd is monoculture of a single cloned bacterium or it may be a mixture of some specific bacteria) and packed in polyethylene, polypropylene, polystyrene packaging material and plastic cups and kept in crates and allowed to ferment at 37⁰C. When dahi attains pH of 4.4-4.5 the dahi is rapidly cooled for proper setting. The fully set dahi is stored at below 5⁰C.

National Collection of Dairy Cultures (NCDC), National Dairy Research Institute, Karnal, National Dairy Development Board (NDDB) and other research centres and universities provide starter cultures for commercial purpose. (4)

Nutrients present in Curd (5)

Dahi is a good source of methionine and contains 12% protein. Like all dairy products dahi is good source of calcium and phosphorous and loaded with riboflavin, Vitamin A, Vitamin B6, Vitamin B12, and pantothenic acid. Lactic acid present in curd helps in absorption of nutrients, and micro minerals and stimulates the functioning of digestive glands.

Health Benefits of curd

Curd contains Calcium, Vitamin D, protein and healthy gut bacteria. Like all dairy products it helps in making the bones and teeth strong. Curd is good source of healthy bacteria which help fight infections and boosts immunity. It is good for digestion as it helps neutralise the effect of eating spicy food. During curd formation the milk sugar lactose is broken down, it is easy to digest and ideal for young children, elderly people and for people who are lactose intolerant.

There are also reports which claim that curd bestows a cosmetic effect by keeping the skin and hair healthy.

In India dahi is exclusively prepared from cow or buffalo milk. Curd from buffalo milk appears thicker as buffalo milk has higher fat content. Health benefits can be obtained from both varieties of curd and the consumer has to choose the appropriate variety based on their requirement and health condition. Dahi can be prepared from whole milk or skim milk to meet the requirements of the consumers.

Dahi vs Yoghurt vs Probiotic Curd

As discussed above dahi contains mainly Lactobacillus species either as single strain or multiple strains, the strength of which is variable depending on how and where the curd is set. Dahi is considered to be natural probiotic but depending on the strains used in starter culture the amount of good bacteria may vary, and if the bacterial count is low it may not reach the intestine and so may not produce the required digestive or other benefits.

Yoghurt may look and to some extent also taste like curd but the difference lies in the starter cultures used. For yoghurt Streptococcus thermophilus and Lactobacillus bulgaricus are the major strains used during fermentation. The process is more homogenous and standardized so levels of good bacteria may be alive and sufficient to reach the gut and make the gut healthy. Unlike dahi yogurt is available in both natural as well as fruit flavours.

Further research to improve the gastrointestinal health resulted in probiotic curd.

Probiotic curd – Probiotic is a term that loosely refers to microbes having some health benefits. The microbes have to be proven safe and beneficial, along with the ability to withstand, survive and lodge in the intestine to provide the health benefits, before being formally defined as a probiotic. Hence it follows that probiotic curd needs to have a specific strain of live bacteria that is resistant to bile, pancreatic and intestinal juices. So they remain unaffected until they reach the intestine and provide the maximum benefit.

Curd market is anticipated to reach INR 2,782.9 Billion by 2027owing to hectic lifestyles leading to increased demand for packaged curd and also due to the introduction of innovative and healthier curd variants by the key players, such as low-fat and high-protein product variants with diverse flavours. (6).

Curd, yoghurt and probiotic curd may be different but they all have some health benefits. It is worthwhile to try and include them in the diet, depending on the individual health condition and take advantage of their benefits.