Caseinates are produced by dissolving precipitated casein by means of sodium hydroxide, sodium phosphate or calcium hydroxide.

Caseinates are typically used as protein source in baby food, 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 production of spray dried caseinates. The type of acid used for the precipitation of the casein (casein precipitates at the isoelectric 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 preferred.

As solutions of sodium casein contain practically only protein, they will 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 redissolved concentrate has to be kept low and is usually in the range of 18-24% depending upon the process.

The dissolution of casein by means of alkaline can be carried out in two different ways:

  • Batch Process
  • Continuous Process

BATCH 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 70C 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 70C) the viscosity increase (age-thickening) is significant. Furthermore, the viscosity increase is intensified, as it takes some time to spray dry a batch. During this time another problem arises, since a discolouring due to the Maillard reaction between remaining lactose and aminoacids cannot be avoided. The final product will thus become light yellow and may even get a gluey taste.

CONTINUOUS PROCESS
Increasing market interest in high quality sodium or calcium caseinate has made it attractive to develop an improved technique of production. Experiments have resultedin 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.

On the basis of the information available in the literature concerning the batch process, the continuous process can be divided into the following stages:

 1. Disintegration of the casein particles
 2. Dosing of the alcaline
 3. Mixing

Apart from these processes, viscosity and temperature of the solution must be controlled.

The stages in the continuous process of dissolution of casein are shown in Fig. 145.

Diagram of a continuous conversion plant
Fig. 145  Schematic diagram of a continuous conversion plant for production of NA-caseinate

Freshly precipitated, well-washed acid casein curd and water are led into the vessel 1 which is 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 1 the casein suspension is pumped by the pump 2 to the colloid mill 3. Here the suspension of casein particles in water is transformed into a thick paste. The size of the casein particles is reduced so much that the following process of dissolving is accelerated considerably.

From the colloid mill 3, the casein paste passes to the mixer 4, and simultaneously a solution of sodium hydroxide of appropriate concentration is added from dosing equipment 5. The addition of NaOH or Ca(OH)2 is controlled by an automatic pH controller.

The sodium caseinate solution leaving the mixer passes to equipment measuring and controlling pH (6), temperature (7), and viscosity (8) of the solution.

The solution of caseinate then enters the feeding tank of the spray drying plant.

The time interval where the casein dispersion during the process of dissolving has a low pH and therefore a very high viscosity is very quickly passed. The pH field 6.6-7.0 is thus reached where the viscosity of the solution is at its minimum (depending upon solids content and temperature it may reach several thousand cps).

By means of the continuous process line it is possible to reduce the reaction time from the moment the casein is dosed with the solution of the hydroxide, until the finished caseinate is available in dry powder from, to 1-2% of the time needed in the batch process.

In this way it is possible partly to counteract the development of taste defects and partly to utilize the relation between temperature and viscosity of sodium caseinate solutions. The higher the temperature (in a shorter time) to which the solution can be heated during the dissolution process and especially immediately before the drying, the higher the solids contents in the solution.

In the continuous process it is possible, because of the short holding time, to handle concentrates with a solids content up to 24% depending on 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.

The main problem is the low solids content resulting in a low particle density and a low bulk density. Special attention should therefore be paid to the powder recovery system, and bag filters used.

In order to increase the particle density, nozzle atomization and two-stage drying is recommended. The moisture content in the powder leaving the chamber can be as high as 10-12%, as caseinates are good water binders. The remaining moisture content is evaporated in Vibro-Fluidizers, in which the fluidization velocity should be kept low to ensure the powder is not carried off with the drying air.

Typical drying conditions are:

Sodium Caseinate 

Calcium Caseinate

Drying temperature:

200-230C

200-250C

Solids content:

20-24%

20-22%

Feed temperature:

80-90C

80-90C

Moisture in chamber fraction:

10-12%

7-9%

Due to the lack of carbohydrates (lactose) as binder, it is almost impossible to agglomerate the caseinates, if they are dried in conventional dryers, even if fines return is used. Only in the Multi-Stage Dryer (see page 203, Fig. 85) it is possible, and if an instant powder is required, it is necessary to use lecithination for reasons as discussed for the 80% WPC powder, see page 269.

The majority of caseinates is used in foodstuffs such as sausages, hams and luncheon meat, where it acts as a fat emulsifier and water binder, thus protecting the product against drying out and keeping it fresh for a longer time at the same time enriching the product with protein.

The emulsifying effect of caseinates is utilized to a great extent in imitation milk products, such as filled milk, imitation milk, coffee whitener, whipped cream, ice-cream, milk-ice, etc.

The high nutritive value of caseinates makes it applicable in other foodstuffs in which the protein content should be enriched, in spaghetti and macaroni, for example.