BY-PRODUCTS TECHNOLOGY

Module 2. Skim milk and its by-products

Lesson 13
MANUFACTURE OF OTHER CASEINATES

13.1 Introduction

Next to sodium caseinate, calcium caseinate is common and finds use in both pharmaceutical preparations and as a food ingredient. The specifications for this product vary with its end use, but they frequently include a limitation of the calcium content to within the range of 1.0-1.5%. Various countries have prescribed varying specifications for caseinates. In contrast to the translucent, viscous, straw-coloured sodium, potassium and ammonium caseinate solutions, calcium caseinate forms micelles in water, producing an intensely white, opaque, 'milky' solution of relatively low viscosity. Calcium caseinates are much less soluble and have poorer functional attributes than sodium caseinate.

13.2 Calcium Caseinate

Its preparation follows the same general process as that used for sodium caseinate with one or two important exceptions. Calcium caseinate solution is destabilized on heating especially at pH values below 6. This sensitivity decreases with an increase in pH or a decrease in concentration and is manifested as a reversible heat-gelation. During the dissolving process, it has been found that the reaction between acid casein curd and calcium hydroxide (the alkali most commonly used in the production of calcium caseinate) proceeds at a much slower rate than that between curd and sodium hydroxide. The temperature of conversion is a particularly important factor in determining the completeness of solubility (assessed from the amount of sedimentable matter) of the calcium caseinate. Therefore, the dissolving process must be closely monitored to ensure production of calcium caseinate with a good solubility.

The optimum process as recommended by Roeper (1977) is: pass 'soft' casein curd through a mixer to give evenly-sized particles, mix with water to about 25% total solids, pass the mixture through a colloid mill and adjust the temperature to give a milled slurry at 35-40°C; mix the slurry with a metered volume of 10% aqueous calcium hydroxide to give the desired final pH; agitate and recirculate in a low-temperature conversion tank until conversion is complete (>10 min); heat the dispersion in a tubular heat exchanger to 70°C and pump directly to a spray drier (Fig. 13.1). Calcium caseinate then packaged and stored in a cool, dry place.

The common associated problems in the manufacture of calcium caseinate have led to an examination of alternative methods of producing calcium caseinate. Calcium hydroxide is soluble in sugar solutions and may, therefore, be used in this form for reaction with acid casein. In order to increase the rate of reaction between casein and calcium hydroxide, the casein may first be dissolved completely (and rapidly) in ammonia (Fig. 13.2). Calcium hydroxide solution of sugars (sucrose, glucose, galactose, lactose or fructose) is then added and the solution of calcium caseinate dried by means of a roller drier. Most of the ammonia evaporates during processing, leaving a relatively pure calcium caseinate (protein 84%, sucrose 5.8%, moisture 4.5%, calcium 1.0%) with nutritional properties similar to those of the original casein.

13.3 Ammonium/Potassium/Citrated Caseinates

Ammonium and potassium caseinates may be prepared by a method similar to that used for the production of sodium caseinate by substituting NH₄OH or KOH for NaOH. Granular ammonium caseinate may be prepared by exposing dry acid casein to ammonia gas and removing excess ammonia with a stream of air in a fluidized bed degassing system. Citrated caseinate has been prepared by a method similar to that used for the preparation of spray dried sodium caseinate by using a mixture of trisodium citrate and tripotassium citrate in place of NaOH.

13.4 Other Caseinates

Magnesium caseinate is prepared from casein and a magnesium base or basic salt such as magnesium oxide, magnesium hydroxide, carbonate or phosphate or by ion exchange. Compounds of casein with aluminium may be prepared for medicinal use or for use as an emulsifier in meat products. Heavy metal derivatives of casein which have been used principally for therapeutic purposes include those containing silver, mercury, iron and bismuth. Iron and copper caseinates have also been prepared by ion exchange for use in infant and dietetic products.

13.5 Specifications of Caseinates

The quality standards for caseinates vary from country to country. As per FSSAI (2011), edible caseinate means the dry product obtained by reaction of edible casein or fresh casein curd with food grade neutralising agents and which have been subjected to an appropriate heat treatment. It shall be qualified by the name of the cation and the drying process used (Spray or Roller dried). The product shall be white to pale cream or have greenish tinge; free from lumps and any unpleasant foreign flavour, it may contain food additives permitted in these regulations. It shall conform to the microbiological requirements prescribed in Annexure - I. It shall conform to the requirements as given in Table 13.1.

Table 13.1 FSSAI (2011) compositional standards for edible sodium caseinate

The typical chemical composition of caseinates is given in Table 13.2. Within a general pH range of 6.5-7.0, sodium caseinate will usually contain 1.2-1.4% sodium, while the calcium content of calcium caseinate is generally in the range, 1.3-1.6%.

Table 13.2 Typical composition of caseinates

Selected reference

Roeper, J. 1977. N Z J. of Dairy Sci. and Technol., 12: 182.