Dairy At Glance

Chemistry Of Milk In Relation To Manufacture Of Indian Dairy Products

Bimelsh Mann ,Rajesh Kumar,RamBhagat Sangwan and Shilpa Vij*

   Dairy Chemistry Division    *Dairy Microbiology Division

National Dairy Research Institute, Karnal


Milk is an extremely complex biological fluid with scores of nutrient. These nutrient exist in milk in  three physical phases: a dilute emulsion, colloidal dispersion and a solution. The emulsion can be broken by low speed centrifugation and the milk separates into lipid and aqueous phases or compartments, each with a characteristic composition. With ultracentrifugation the casein micelles precipitate, bringing some other proteins such as lactoferrin with them. The supernatant remaining after this process has the characteristics of a true solution. The chemical makeup of milk and its physicochemical behavior provide scientific basis for process of milk and manufacture of products.  In India, milk from buffalo and cow (desi, cross breed and exotic) is commercially important. Depending on its characteristics, each type of milk is eminently suitable for certain types of region specific indigenous traditional milk products. These Indian traditional dairy products can be classified into the following broad categories:

Heat Desiccated Milk Products:

Heat desiccated milk products such as khoa – an intermediate concentrate that is the base for a wider range of mithais including gulabjamun, burfi, peda, kalakand, rabri, kulfi and their variants. The heat processing and accompanying reduction in water activity result in substantial destruction of pathogenic and spoilage micro organisms as well as inactivation of enzymes. Besides, desirable heat induced chemical interactions among milk constituents result in reduction of redox potential and water activity which extend the product shelf life. The desirable flavours, textures and overall acceptability of these products is enhanced by heat processing. The main reaction in the preparation of khoa is the heat denaturation and coagulation of milk proteins. Most of the albumins and globulins are rapidly denatured, the protective properties of the other colloids are destroyed early in the boiling process, and the process is accelerated by the incorporation of air and the frothing during stirring. Total heat coagulation of the proteins occurs when the boiling mixture thickens to a buttery consistency in the pan. Coagulation of milk proteins is brought about by heating to 132-136ºC. Albumin and globulins are coagulated below 100ºC, while casein is coagulated above 100ºC. During desiccation whey proteins are almost fully denatured from colloidal state of non-dispersible state. The factors that influence the heat coagulation are temperature and time of holding, concentration of casein, acidity of milk, salt balance and precise heat treatment.  The color of milk changes from light to a more intense shade of the color due to denaturation and coagulation of protein. Due to vigorous agitation of milk at high temperature the fat globules are appreciately sub-divided. Almost half of the globular fat is released as free fat-the extent of which depend upon the type and fat content of milk and manufacturing process. Usually 44.8 to 62.8 % of fat appears as free fat in khoa. Patel et al (1990) have found a positive and significant correlation in total solids and hardness. The fat level is usually adjusted to 4 % for cow milk and 5 % for buffalo milk. The yield of khoa depends upon the type of milk used when milk is standardized to 4.5 % fat and 8.5 % SNF; its yield is about 20 % for buffalo milk. Khoa from buffalo milk is considered distinctly superior, being whiter in color and having smooth body and granular texture. These characteristics are considered desirable for making high quality sweets.

The quality of khoa is better when made from buffalo milk as khoa from cow milk is inferior due to its moist surface, sticky and sandy texture which is not considered suitable for the preparation of sweetmeats (De and Ray, 1953). The higher emulsifying capacity of buffalo milk fat due to the presence of larger proportion of butyric acid containing triglycerides (50 %) compared to only 37 % in cow milk fat may be responsible for smooth and mellowy texture of its khoa (Sandhu, 1996). Good quality khoa can be prepared from cow milk with the incorporation of whey protein concentrates (5 %) and keeping the total solids of the product low, as higher total solids in WPC containing khoa adversely effect the rheological parameters (Patel et al, 1993). Rajoria et al, 1990 studied the effect of milk quality on the chemical, sensory, rheological properties of khoa. They observed that khoa from slightly soured milk (0.2 % lactic acid) did not have much adverse effect on the flavour of khoa while khoa prepared from excessively sour milk had acidic smell, which has improved but not totally suppressed by neutralization of excessively soured milk had a salt taste. The coarse structure of the khoa is increased with increase in the acidity of milk. Increase in size and hardness of the grain lead to poor body and texture of khoa. Smoothness of khoa was also adversely affected by the developed acidity. The hardness of khoa was observed to increase. Gumminess and chewiness of khoa was also increased due to developed acidity in milk and was reduced by neutralization of the same. Khoa from excessively high acidic milk is sour in taste.

Heat and Acid Coagulated Products

Paneer and Chhana are the two important heat and acid coagulated products. Paneer, the indigenous variety of cheese is obtained by acid coagulation of the heated milk. The phenomena of coagulation involve the physical and chemical changes in casein brought about by the combined heat and acid treatment. This treatment leads to formation of large structural aggregates of casein from normal colloidal dispersion of discrete casein micelle in which milk fat and coagulated serum proteins are entrapped together with whey. During formation of coagulum, major changes include the progressive removal of tricalcium phosphate from the surface of casein and its conversion into monocalcium phosphate. Further calcium is progressively removed from calcium hydrogen caseinate to form soluble calcium salt and free casein. When the pH of the milk system drops, the colloidal particles become isoelectric i.e. the net charge becomes zero with the formation of zwitter ion. Under such circumstances the dispersion is no longer stable; the casein gets precipitated and forms a coagulum. Good quality paneer is characterized by a white color, sweetish, mildly acidic, nutty flavor, spongy body and close knit texture. Buffalo milk paneer is of good quality as it has all these attributes. On the other hand cow milk paneer is of inferior quality as it is too soft, fragile and its pieces loose their identity on cooking (Sachdeva et al 1985). The lesser proportion of solid fat due to lower proportion of casein in the micelle state, smaller size of casein micelles and fat globules and lower content of calcium in it, particularly in colloidal state, may be responsible for inferior quality of paneer from cow milk. The cow and buffalo milk mixed in the ration of 50:50 having a fat percent of 5 yields a superior product than cow milk alone. Acidic milk having a titratable acidity of 0.2-0.3 % lactic acid yields a product with inferior quality. The COB positive milk with normal acidity is also not suitable for paneer making due to weak body and texture, more moisture and acidic milk (Vishweshwaraih and AnantKrishnan, 1985).

Chhana , a base product for a large variety of Indian delicacies namely rasogolla, chhana gaja, sandesh, cham cham, rasmalai, pantoha, raj bhog, chhana murki etc is also a heat acid coagulated product. It differs from paneer as no pressure is applied to drain the whey and its pH is slightly higher. Scanning electron microscopy of defatted sample of chhana revealed a conglomerated compact protein matrix with numerous small uniformly distributed pores. The coalesced, smooth protein bodies are joined with thick bridge in which fat globules embodied in coalesced casein micelles with some whey filled space at edge. The agglomerated large casein particles formed continuous thick strands joined together with numerous spaces in between (Adhikari et al, 1992). Cow milk is better suited for chhana making because it produces chhana with soft body and smooth texture which is better for sweets. Higher concentration of casein more in the micelle state with bigger size of the cells, harder  fat due to larger proportion if high melting triglycerides in it with bigger size of globules and higher content of calcium more in the colloidal state in buffalo milk (Sindhu and Singhal, 1988) may be responsible for harder and less cohesive chhana.

De and Ray (1954) and Tagtiani et al, 1960 observed that cow milk chhana was soft bodied with small grainy smooth texture and more cohesive compared to hard bodied with granular and hard textured chhana from buffalo milk. Boghra, etal (1988) found that chemical quality of chhana retained less moisture and lactose but higher total solids as compared to cow milk chhana. Retention of minerals (Ca, Mg, P, Citrate, Fe and Zn) was also higher in buffalo milk chhana. On the other hand, it had less Na, K and Cl compared to cow milk chhana. The hardness of chhana is directly related to calcium content of milk. Addition of calcium and magnesium chloride produces hard chhana while sodium chloride, sodium acetate and sodium citrate did not affect the body and texture of chhana. Chhana prepared from cow milk (4-5 % fat) is most suitable for rassogolla. Lower fat content below 3 % produces chhana unsuitable for rassogolla. Adulteration of milk with starch produced a gelatinous mass while the presence of colostrums in milk led to pasty texture. Both of these products were unsuitable for sweet making (Ray and De, 1953). Fresh milk is preferred for chhana production. Acidic milk produces undesirable sour smell and bitter taste in chhana. When acidity is neutralized with sodium carbonate the chhana prepared can be used for sandesh only.

Although buffalo milk is not preferred for production of quality chhana required for making sweets, it can be used in the following ways:

  1. A mixture of buffalo milk and cow milk in the ratio of 1:3 yields chhana with soft body and smooth feature making it suitable for preparing both rassogolla and sandesh.
  2. Adding to the buffalo milk with a mixture of sodium diphosphate and disodium phosphate or sodium citrate at 0.01-0.02 % and storing the hot milk for some time before precipitation produces a soft chhana. Addition of sodium citrate converts some of the insoluble calcium into soluble salts in the buffalo milk and this helps in the production of softer chhana similar to that produced from cow milk.

Sanyal et al, 2006 indicated that addition of carrageenan to buffalo milk before coagulation considerably improved the quality of sandesh as compared to control.

3.0 Cultured/Fermented Products:

Chakka, Shrikhand, Dahi, Misti dahi and lassi are the fermented indigenous dairy products manufactured and consumed in India. Chakka is the semi-solid curd mass obtained by the removal of whey from dahi (curd) is commonly known as chakka which is the base material for making Shrikhand. Chaka has a milky white color, smooth texture and mild acidic flavour. Increase in the temperature of heating the milk before coagulation led to an increase in yield due to complete denaturation of whey protein and precipitation with casein (Aneja et al, 1977).

Shrikhand with its distinct taste richness delicacy, diversity and fairly log shelf life is very popular in India, particularly in states like Gujarat and Maharashtra. Beside fresh milk , other products like diluted condensed milk, reconstituted milk, buttermilk, skim milk and condensed milk have been used for preparation of Shrikhand. However quality of Shrikhand obtained from these products is inferior (Patel and Chakraborty, 1985b). Buffalo milk prepared for making Shrikhand due to higher yield and better quality of the finished product obtained from it (Kadan et al, 1984). Boghra 1988 found that buffalo milk Shrikhand is rich in minerals including calcium, magnesium, phosphorous, copper, iron and zinc compared to cow milk Shrikhand. However sodium, potassium and chloride were less in buffalo milk Shrikhand. Similarly, higher proportions of dissolved proportions of calcium, magnesium, phosphorous were found in buffalo milk Shrikhand than cow milk Shrikhand.

Dahi is an indigenous dairy product obtained by lactic acid fermentation of milk. A good quality dahi is of firm and smooth consistency with sweet aroma and pleasant taste. The composition of dahi is similar to the milk from which it is produced. Dahi from buffalo milk is superior in body and texture than cow milk dahi. Higher total solids, fat and proteins in buffalo milk, higher proportions of casein, more so in the micellar state in the form of larger micellar, higher solid fat due to larger proportion of high melting triglycerides in the form of larger fat globules and higher content of calcium more so in colloidal state milk (Sindhu,1996) may be responsible for better dahi from buffalo milk. During fermentation of milk, lactic acid bacteria is the culture hydrolyse the lactose into lactic acid as a major  product, which contribute to more than 90 % to the acidity of dahi. Diacetyl is the major flavour compound. A portion of lactic acid combines with calcium to form calcium lactate. The casein devoid of calcium is coagulated on reaching its isoelectric point. The fermentation is accompanied by gelling of solids, principally the protein and synersis manipulated by appearance of thin exudates of clear whey on the surface of the product. Decrease in charge on the fat globules brings them together and the raises to the surface.

In the eastern region of India sweet variety of dahi known as Misti dahi is popular. It is produced with the addition of 6-6.5% sugar to milk either during boiling or at setting stage. Prolong heating of sweetened milk at low temperature leads to milk solid concentration and development of brown color. A characteristic cooked and caramelized flavour and firm body develops after setting the curd. The ultra structure of misti dahi shows a clear protein matrix with uniform distribution of lactic acid bacteria, thus forming clusters and chains entrapping whey in between. The extent and inetrlinakges of casein appeared to determine the phenomenon of wheying off which subsequently affect the lactic acid bacteria in matrix. The lactic acid bacteria are spotted in pockets distributed in the protein matrix of coagulum (Gupta et al, 2000).

4.0 Fat Rich Products:

In the traditional Indian dietary regimes, milk fat in the form of malai (cream), makkan (freshly churned butter) and ghee contributes significantly towards nourishment of people of almost all age groups. Buffalo milk is better suited for the manufacture of fat rich dairy products as compared to cow milk due to its higher fat, bigger size of the globule and higher proportion of sold fat leading to the higher yield, lesser loss of fat in butter milk or skim milk, easier preparation of cream or butter and better texture (Sindhu, 1996). The fatty acid composition of buffalo ghee is different from cow ghee. On the other hand short chain concentration of poly unsaturated fatty acid (PUFA) is higher in buffalo ghee compared in cow ghee leading to lower oxidative stability. Moreover buffalo ghee is poor in dienoic and trienoic fatty acids. Based on the crystallization behavior, the separation of triglyceride into higher melting triglyceride (HMT), medium melting triglyceride (MMT) and low melting triglyceride (LMT) revealed that buffalo ghee contains a higher proportion of 9-12 % of MMT than 5-6 % of cow ghee leading to the bigger grain formulation and better texture of ghee. Buffalo ghee has higher melting point, density, specific gravity and saponification value but lower BR reading, refractive index, R.M. value and Polenske value than cow ghee is also higher than buffalo ghee.

The buffalo ghee is whitish with greenish tinge due to the presence of tetrapyragole pigments-biliverdin and bilirubin which is released from the protein during the preparation of ghee. On the other hand cow ghee is golden yellow in color due to the presence of caroteniods in it. Keeping quality of ghee from cotton seed fed animal is better due to the presence of gossypol – a phenolic substance present in cotton seed which act as antioxidant.


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Posted Date : 31/03/2015 Posted By : Admin