Milk has been used to produce fermented milk products as far back as 10,000 B.C. in different regions worldwide. The benefits of fermented milk products include enhanced digestibility, new and unique flavors, added probiotics, vitamins and minerals, and preservation products for food that usually has a concise shelf life.
Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. Fermented milk products are created when milk ferments with specific kinds of bacteria called Lactobacilli or Bifidobacterium. In other words, it can also be said that fermentation is partial digestion by bacteria. The fermentation process increases the shelf life of the product while enhancing its taste and improving the digestibility of its milk
Fermentation – How it works?
- Microorganisms survive using carbohydrates (sugars, such as glucose) for energy and fuel.
- Organic chemicals like adenosine triphosphate (ATP) deliver that energy to every part of a cell when needed.
- Microbes generate ATP using respiration. Aerobic respiration, which requires oxygen, is the most efficient way to do that. Aerobic respiration begins with glycolysis, where glucose is converted into pyruvic acid. When there is enough oxygen present, aerobic respiration occurs.
- Fermentation is similar to anaerobic respiration—the kind that takes place when there isn’t enough oxygen present. However, fermentation leads to the production of different organic molecules like lactic acid, which also leads to ATP, unlike respiration, which uses pyruvic acid.
- Depending upon environmental conditions, individual cells and microbes have the ability to switch between the two different modes of energy production.
- Organisms commonly obtain energy anaerobically through fermentation, but some systems use sulfate as the electron transport chain’s final electron acceptor.
Different Fermented Dairy Products
There are various fermented dairy products in the market. Fermented milk products also known as cultured dairy products are dairy foods which have been fermented by a consortium of lactic acid bacteria (LAB) responsible for the curdling or souring of milk. LAB are best-suited organisms for milk fermentation while preserving the taste and nutritional properties. These bacteria are non-sporulated, mostly anaerobic in nature, and can only grow in rich nutritional conditions that provide growth factors like vitamins, amino acids, and nucleotides. Bacterial members associated with fermented dairy products belong to the genera of Lactobacillus, Lactococcus, Leuconostoc, Pediococcus, Bacillus, Propionibacterium, and Bifidobacterium. Introduction to few fermented dairy products is given below.
Dahi is produced by bacterial fermentation of milk. The bacteria used to make Dahi are known as Dahi cultures. As per the national standards, the minimum requirement for milk fat is 1.5 per cent for double-toned milk and 3.0 per cent for toned milk. For cow milk, the minimum milk fat requirement is 3.2 %.
Shrikhand is a semi-solid, sweetish-sour fermented milk product prepared from Dahi. It is a popular dessert and a part of the meals on festive occasions, especially in Gujarat and Maharashtra. The product has a shelf life of 40 days under refrigeration at 8°C or below.
Buttermilk is a popular fermented dairy drink. This can be salted, without salted and/ or spicy variant. It is manufactured by breaking the curd. The product has a shelf life of 7 days at refrigeration temperature (8°C or below) when packed in Polyfilm.
Cheese is a dairy product made from the curds of milk that have been separated from the whey. The curds form a firm substance that is aged to create added flavor. Cheese making occurs in two main stages: In the first stage, milk is moulded into solid curd and liquid whey by the coagulation of the milk protein, casein. In the second stage, curd is separated containing the casein and milk fat from the whey. Depending on the type of cheese, the curd can be heated, salted, pressed and is moulded into various shapes and sizes.
Originally, it can be done by naturally occurring lactic acid bacteria in the milk. However, today dairy industries usually standardize the process by adding domesticated bacterial cultures, including strains of Lactococcus lactis, Streptococcus thermophilus and Lactobacillus sp.
Industrial production of Fermented Product
One of the fermented products is described below in detail.
Shrikhand is a semi-solid-soft, sweetish-sour fermented dairy product. It is prepared from either cow, buffalo, or mixed milk.
- Select good quality milk and separate it into the cream and skim milk using a centrifugal cream separator. The skim milk should be completely devoid of fat. The cream should preferably be of high fat (70 per cent or above).
- Heat the skim milk to 90° C for ten minutes, followed by cooling to 30°C. Alternatively, a batch pasteurizer can also be used. Simultaneously, pasteurize the required quantity of cream at 85° C for 16 seconds for later use.
- Take the heated skim milk in a pre-sterilized incubation/ storage vat and add 0.5 per cent lactic starter and mix well with the help of a mechanical agitator. Maintain the vat’s temperature at about 30° C with the help of circulation of the warm water.
- Incubate it for about eight hours.
- After the curd has properly set and acidity developed in the range of 0.8 – 1.0 per cent, stop incubation. Separate the whey by centrifuging the curd for 60 minutes using a basket centrifuge (at about 1100 rpm). Thus, chakka is obtained.
- Transfer the known quantity of chakka into a planetary mixer.
- Add the required amount of pasteurized cream (the fat in the final product should be about six per cent) and sugar (about forty-two per cent in the final product) to the chakka.
- Mix the contents by running the mixer at variable speeds. Typically, it takes 40 minutes at 110 rpm for getting a homogenous mass.
- Flavors and other additives may also be added during the mixing of chakka, sugar and cream.
- Cool the final product and fill in the paper cups/ polystyrene cups (100 or 500 gm capacity).
- Store under refrigerated condition.
Fermented dairy products are the economical source of many nutrients. Lactic acid is produced by fermentation of lactose which reduces the pH, affects the casein physical properties, and consequently enhances digestibility. It also meliorates usage of calcium and different other minerals and suppresses the development of potentially injurious bacteria. Fermented dairy products include cheese, buttermilk, yoghurt, kefir, etc. Fortunately, lactobacilli, lactic acid bacteria and streptococci are the dominant bacteria in fermented milk that effectively suppress the pathogenic and spoilage micro-organisms.