How to find out the precipated agglomaration from milk is casein?
Answers
Casein is the major protein in cows’ milk, and comprises about 80 % of the total protein content of which the rest,
some 20 %, are the whey or serum proteins.
Casein is the basic component of ordinary cheese. In the cheese-making process, casein is precipitated by the action of rennet enzymes, and a coagulum is formed consisting of casein, whey proteins, fat, lactose and the minerals of the milk.
Commercial casein is made from skim milk by one of two general methods – precipitation by acid or coagulation by rennet. As much of the fat, whey proteins, lactose and minerals as possible must be removed by multistage washing in water, as they reduce the quality of the casein as well as its keeping quality. Dried, properly produced casein has a relatively good keeping quality and is used mainly in the food and chemical industries.
TYPES OF CASEIN
Casein is usually divided into the following types:
Rennet casein, obtained by enzymatic precipitation
Acid casein, obtained by acidifying skim milk to the isoelectric point (pH 4.6 – 4.7)
In addition to these two main types, there are other commercially available casein products of importance, such as:
Co-precipitate, made by heating skim milk to a high temperature and then precipitating the casein/whey protein complex, usually with calcium chloride.
The co-precipitate also contains whey proteins and calcium.
Caseinates, commonly sodium caseinate, obtained from acid casein dissolved in sodium hydroxide
INFLUENCE OF RAW MATERIAL
In order to produce high-quality casein, the raw material, skim milk, must be of good quality. If bacteria have had time to act on the protein in the milk as a result of a change in acidity, this will affect the colour and consistency of the casein, which will acquire a greyish colour and a smoother consistency. Excessive heating of the milk before precipitation will not only cause assorted interactions among the lactose, casein and whey protein constituents, but it will also give the casein a yellow or at worst a brownish colour.
In order to produce casein of good bacteriological quality, without high heat treatment of the skim milk, the pasteurization plant may also contain a microfiltration (MF) plant. To satisfy the high demands on the quality of casein intended for use in the food industry, not only must the production line be carefully planned right from the reception of the milk, but the treatment and handling of the raw material prior to this stage must also be carefully controlled.
RENNET CASEIN
Skim milk, normally pasteurized at 72 °C for 15 – 20 seconds, is used for the production of rennet casein, as well as other types of casein. Small amounts of fat are detrimental to the quality. It is therefore important that the milk has been separated efficiently.
Figure 20.1 shows the various stages of rennet casein production. Renneting takes place with the help of the enzyme chymosin in the rennet. The milk is heated for a short period of time and then cooled to about 30 °C. Then the rennet is added. A gel forms after 15 – 20 minutes. It is cut and the coagulum is stirred while being heated to about 60 °C. The high temperature is needed to deactivate the enzyme. Cooking time is around 30 minutes.
Fig. 20.1
Process line with countercurrent washing of rennet casein.
Vat for casein production
Decanter
Washing tank
Heater
Drying
Milling, sieving and bagging
You can dissolve casein in 50mM potassium phosphate buffer, pH 7.5.
Then gradually increase the temperature upto 80 degree C. for 10 minutes until homogenous solution is achieved.
Do not boil the solution. Then adjust pH by HCl or NaOH.