In milk, Casein is the most important protein component, both nutrition-wise and quantity-wise, accounting for almost 80 % of milk’s total nitrogen. It can be defined as the protein which get precipitated from the milk at a pH of 4.6. It is a rich source of essential amino acids. Cow’s milk has the major quantity of casein and comprises almost 80% of the total protein content, while the rest 20% is whey or serum proteins. Casein has an industrial use – in the production of paper, textiles, paint, and leather-based industries.
The two methods from where commercial casein can be manufactured from skimmed milk – The first one would be through precipitation by acid and the other one would be through coagulation by rennet. As much of the fat, whey proteins, lactose, and other minerals should be removed through multi-stage washing in water as they can reduce the quality of the finished casein as well as the storage quality. After drying, finished casein have relatively good storage quality and can be used in the food and chemical industries.
Casein protein is derived from milk, just like whey protein. Milk has both protein in a 4:1 ratio, in fact, the composition of milk is 80% casein and 20% whey but there would be a major difference in the absorption rate of both these proteins. Casein is basically slow digesting and will stay in the bloodstream for a few hours, this provides a constant supply of the essential amino acids required for a human body. Casein has actually cemented its importance and identity in the supplement and medication industry for genuine reasons.
Amount of casein in different categories of milk.
Casein powder processing flow chart
2. Separation of Casein
Easy separation is possible for casein from milk by increasing the acidic value of milk. Milk can be made more acidic by simply adding acid to it or by the addition of bacteria (such as Streptococcus thermophiles, Lactobacillus, acidophilus, and Lactobacillus bulgaricus) which will produce lactic acid. These bacteria use a process called as Fermentation process in which they will take energy from lactose (milk-based sugar). The byproduct i.e, lactic acid will make the milk more acidic. As a result, Curd (casein protein) will be formed in the form of lumps. That casein protein can be collected and can be turned back into solution form by adding sodium hydroxide or any other alkali, this re-dissolved solution is known as Caseinate which can be sold as it is in the markets or can be processed further in milk or dairy processing plants.
Dry casein powder
Typical levels of the major colloidal and soluble components in bovine whole milk.
3. Dry Casein Production
Two types of caseins are there; Rennet casein and Acid casein.
Acid casein can be easily formed by making the skimmed milk acidic until it reaches the isoelectric point (pH± 4.6). For Rennet casein, the process used will be enzymatic coagulation. Both of these products are created by the effect of a reaction between the acid casein curd and acid casein powder with alkali (sodium hydroxide).
Caseinate is used more often in comparison to casein when it comes to its use in food industries because casein is less soluble than caseinate.
3.1- Acid Casein
- For Acid casein production low-fat skimmed milk will be used because the shelf life of casein depends upon the amount of fat in the milk.
- Low-fat milk should be skimmed properly because the microorganisms present in the milk can directly affect the consistency and also the color of casein that’s why the quality of raw skimmed milk matters a lot.
- The milk should not be heated too much. Due to this, the chances of unwanted chemical reactions can take place within the components of milk which can lead to dark casein.
- To get good quality casein and to prevent these things from happening, the milk should be microfiltered besides being pasteurized.
The raw skimmed milk should be pasteurized for 15-20 seconds at a temperature of 72deg.c.
To reach the isoelectric point of casein through acidification, that point lies between pH 4 and 4.8. The hydrogen ions present will lift the negatively charged ions of casein micelles, as a result, coagulation of casein micelles will find a place.
The acidification can take place in two ways:
(a)- Inorganic Acidification
Later on, Skimmed milk will be cooled down to about 32°C after pasteurization. pH value of the skimmed milk will be lowered between 4.3 and 4.6 by the addition of hydrochloric acid. Then, the mixture formed will be heated up with the help of a heat exchanger at a temperature of 40°C to 45°C and will be kept on hold at the same temperature for about 120 seconds. Within this period of time, the casein aggregates are formed.
(b)- Biological Acidification
In this process, skimmed milk will be cooled down to about 25°C after pasteurization. A non-gas-forming mesophilic starter is added, which basically ensures a desired decrease in the pH value in approximately 15 hours. This acidification process should progress too fast, as this may lead to uneven quality and a reduced yield. After reaching the desired pH value, the mix is stirred then heated up using a heat exchanger and kept on hold at a temperature of 50°C to 55°C.
Decanter and Washing
A decanter centrifuge separates solids from one or two liquid phases in one single continuous process. This is done using centrifugal forces that can be well beyond 3000 times greater than gravity. A decanter centrifuge separates solids from one or two liquid phases in one single continuous process. This is done using centrifugal forces that can be well beyond 3000 times greater than gravity.
Here in casein processing, a decanter will be used to remove the whey before starting the washing process so that less water is required. In the next step, the casein will be washed at a temperature of 35°C to 60°C in a three step-counter washer using water to remove whey proteins, lactose, and salts. After each step, a part of the washing water is separated into the decanter of the casein. And in the last step, the centrifugation process produces casein with a dry matter content of about 45 percent and now the product we got, is ready to be sent to the dryer.
With the application of using hot air, the casein will be dried until the moisture content gets reduced to 12 percent. The drying process for casein can be done in several ways. In the two-stage drying process, the temperature of the first step is between 50°C to 55°C and in the second stage, the temperature will be increased up to 65°C.
When the casein gets totally dried, the casein will be ground into a powder with a particle size of about 0.32mm, 0.42mm or 0.64mm.
Caseinate can be made from acidic casein, acidic casein curd, or powder. But preference is given to the acid casein curd, regardless of the raw material being used. By adding water, the content of dry matter is reduced between 18 to 24 percent. Otherwise, the viscosity of the solution goes too high, because it consists of only protein.
The process of wet-grinding is done at a temperature below 45deg.c because if the temperature would be on the higher side then there are chances of causing re-agglomeration. The slurry formed will be connected in a tank equipped with a mixer of higher scale. Akali is been added to the slurry very carefully to reach the 6.7 pH value. This pH value is the viscosity of the solution at its lowest.
Which caustic solution is used depends on the product that has to be produced.
- Sodium Caseinate
For the production of Sodium caseinate, a 10% aqueous sodium hydroxide solution is used. For this specific purpose, Sodium Bicarbonate or Sodium Phosphate solution can be used. After reaching the desired pH, the whole should be warmed as quickly as possible to 60 to 75°C. The viscosity would otherwise increase too much. The dissolving of the lye takes 30 to 60 minutes to complete.
- Calcium Caseinate
Dissolving a Calcium Hydroxide solution is much more time-consuming compared to the caustic soda solution. That is why casein is often first dissolved in ammonia. Then, in sucrose, dissolved calcium hydroxide is added and the calcium caseinate mixture is wash dried. Most of the ammonia evaporates during the drying process.
To make the Caseinate solution that will be suitable to be sprayed, it has to be first preheated at a temperature between 80 to 90°C. By this, the viscosity of the solution is kept as low as possible and can be worked with a solution having a dry matter content of up to 24%.
The preference is given to nebulize using a nozzle because the dry matter content of the product to be dried is low. It is recommended to complete the dryer process in two steps. The sodium caseinate has to be dried in a spray-drying tower at an air temperature between 200deg.c to 230deg.c to a moisture content of 10% to 12%, the rest of the extra moisture content is reduced using a fluidized bed-type dryer.
- Food safety and Hygienic Design
Most dairy processes take place at a relatively high pH and under wet conditions, which create an ideal environment for a variety of micro-organisms to grow – such as disease-causing micro-organisms. It is therefore important that the entire system is built according to hygienic design standards – so it is cleanable to a microbial level. After the cleaning process, disinfection can kill off any remaining vegetative microorganisms.
In case, the machinery cannot be emptied fully, the equipment will lose its clean status, even after it has been cleaned but was set aside for a certain period of time. The machinery has to be thoroughly cleaned and disinfected before the production process can start again.