The proteins in milk consist of casein, from which cheese is made, and serum or whey proteins. However, casein can also exist in pure form by acidifying milk to the isoelectric point at pH 4.6 by either lactic acid or mineral acid. The resulting casein is washed to remove as much of the acid whey as possible, after which it is passed through a decanter and then dried in a special type of ring dryer.
Caseinates are produced by dissolving the precipitated casein by means of sodium hydroxide or calcium hydroxide. Caseinates are typically used as protein source in coffee-whitener, emulsifier and foam stabilizer in ice-cream and desserts, and emulsifier/water-binder in meat products.
Freshly precipitated acid casein curd is the best starting material for the production of spray dried caseinates. The type of acid used for the precipitation of the casein (casein precipitates at the iso-electric point corresponding to a pH of 4.6) does not matter. However, if the end-product is to be used for animal or human consumption, a lactic acid fermented/precipitated skim milk is the optimal choice.
As solutions of sodium casein practically only contain protein, they have a high viscosity. The viscosity will increase with increasing solids content but also if the concentrate is kept at a high temperature for a long time. Also the pH plays a role and the viscosity is lowest in the pH range of 6.6-7. Because of the high viscosity, the solids content in the re-dissolved concentrate has to be kept low and is usually in the range of 18-24 % depending upon the process.
Dissolution of casein by means of alkaline can be carried out in two different ways:
- Batch process
- Continuous process
In the batch process, the casein curd leaves the casein press at a solids content of 48-50 % solids. The curd is dispersed in warm water in a steam-jacketed vat. The dispersion is slowly heated to 70°C during continuous agitation and addition of a NaOH solution to a pH of 6.6-7. As the reaction between the casein and NaOH or Ca (OH)2 takes some time (10-15 min., during which the temperature is 70 °C), the viscosity increase (age-thickening) is significant. During this time another problem arises, since a discoloring cannot be avoided due to the Maillard reaction between remaining lactose and amino acids. The final product will thus become light yellow and may even get a gluey taste.
Increasing market interest in high quality sodium or calcium caseinate has made it attractive to develop an improved technique of production. Experiments have resulted in a continuous process line for dissolution of acid casein suspensions into caseinate solutions. From a technical point of view the task is simple; the difficult point is to find appropriate equipment that can work reliably with a viscous material.
- Disintegration of the casein particles
- Dosing of the alkaline
Freshly precipitated, well-washed acid casein curd and water are led into a vessel, provided with a stirrer. The quantity of water is controlled, so that the solids content of the casein suspension is kept at the desired value. From the vessel, the casein suspension is pumped to a colloid mill. Here, the suspension of casein particles in water is transformed into a thick paste. From the colloid mill, the casein paste passes to a mixer and simultaneously a solution of sodium hydroxide of appro-priate concentration is added. The addition of NaOH or Ca(OH)2 is controlled by an automatic pH controller.
The caseinate solution leaving the mixer passes to equipment measuring, temperature, and viscosity of the solution. The solution of caseinate then enters the feeding tank of the spray drying plant. Because of short holding time, it is possible to handle concentrates with solids content up to 24% depending on the type of alkaline.
Spray drying of caseinates
Spray drying of caseinates does not present any difficulties and is usually carried out using high drying temperatures. For an agglomerated product, the Multi Stage Dryer MSD™, equipped with a bag filter, or an Integrated Filter Dryer IFD™ dryer is recommended.
The majority of caseinates are used in foodstuffs such as sausages, hams and luncheon meat, where it acts as a fat emulsifier and water binder. It protects the product against drying out and keepis it fresh for a longer time - at the same time enriching the product with protein.
The high nutritive value of caseinates makes it applicable in other foodstuffs in which the protein content can be enriched, i.e. in spaghetti and macaroni.