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THE EFFECT OF PROCESSING AND SOURING MILK BY THE INDI- GENOUS METHOD By K. S. RANGAPPA, m.sc. (Bom.) (From the Department of Biochemistry, Indian Institute of Science, Bangalore) Heat treatment of milk is a well-known and widely-adopted device for improving the storage life of milk either as such or before souring it. While in the West scalding or the more recent high-temperature short-time method of pasteurization is practised, boiling of milk is the time-honoured custom in India. Srinivasan and Banerjee (private communica- tion) have shown that boiling for 10 minutes is more efficient than pasteurization in bringing down the bacterial count from over 100,000 to less than 100 per c.c. Anantakrishnan and co- workers (1943) have recorded the chemical changes occurring on boiling milk, and reported as a loss the contents of the skin formed on the surface of milk after boiling and cooling. But as the practice stands in the Indian household the skin is invariably utilized for making curd, butter or confectionery. In this paper the chemical changes on boiling milk for 10 minutes without allowing the skin to be formed, and the rise in the bacterial count of the pro- cessed milk with keeping have been recorded. Further, the processed milk has been soured with seed curd, and the multiplication of bacteria June, 1947] EFFECT OF PROCESSING & SOURING MILK : RANGAPPA 321 during the process, and the count of the result- Table I lng butter and buttermilk have been studied. Rise of bacterial count oj processed milk on Experimental keeping In order to study the growth of bacteria in Processed milk on keeping 2 litres of freshly Boiled for 10 minutes Pasteurized drawn buffalo milk were collected in a clean, steamed aluminium can in the dairy farm, Hours Hours to at once in Standard Standard brought the laboratory and plated after plate after plate count c.c. count standard nutrient agar. The milk was then set milking per milking per c.c. to boil in a tinned-brass vessel of 4 litre capacity over a Primus stove, and continuously stirred Wlth a wooden ladle to the formation 1.5 130,000 2 225,000 prevent Boiled and of over of the skin and residue as well as boiling cooled in the After and pasteurization milk. The time lapse between milking same vessel getting the milk to the boil was 1 to 1.5 hours. 275 2.5 he milk was to boiling 9,400 j brought boil, kept Stored at 17?- (95? cooled (bottled) to 96?C.) for 10 minutes and then 25?C. in flask t? room temperature (23? to 25?C.), keeping plugged nvith up the stirring all the time, the total time thus cotton-wool taken for 20 to 25 minutes. processing being 5 4,000 While repeating the experiment it was observed 15,000 that the count of the boiled milk which was 10 22,500 18 121,000 cooled in the open vessel as well as the rate of (returning from of bacteria on the milk multiplication keeping delivery) n'ere considerably higher than those obtained ^'hen the boiled milk was at once into poured Effect of cooling and storing in closed vessel a conical flask, plugged with cotton-wool and then cooled. The was therefore experiment 360.000 repeated both and the milk Fresh ways; processed milk Boiled in tinned- m the a J conical flask was stored in cupboard 2 | brass vessel, and at room temperature (19? to 31?C.). The cooled in flask with standard count was estimated at intervals plugged agar cotton-wool ?f a few hours. The rises in the count on keep- are same the mg given in table I. In the table 2.5 120 results of a similar experiment on pasteurized Stored at 19?- milk (Rep. Marketing of Milk in India and 30?C. are entered for Burma, 1943) comparison. 7.5 1 2,600 In the above experiment the change in com- position due to processing were also estimated by measuring the density (lactometer), fat samples were plated at intervals until the 'Gerber process), total solids, lactose and ash acidity of the curd reached 1.2 per cent. It was ?f milk (Woodman, 1941) before and after then churned in an American bottle churn by processing. The differences are recorded in adding an equal volume of water. The plate table II. counts of the butter and of the buttermilk were The rate of multiplication of bacteria on also estimated. The resulting average counts souring was studied by seeding 2.5 per cent by are recorded in table III. volume of a homogeneously set curd of 1.0 to The standard agar count was always 1-1 cent lactic into a litre of buffalo estimated by the official method described in per acidity ' milk processed as before. The flask was kept The Standard Methods of Examination of in an electric incubator at 40? ? 1?C., and Dairy Products' (Amer. Pub. Health Assoc., Table II Changes in composition of milk due to boiling for 10 minutes of Lactose, Sample Vo!"me Acidity, Density, Total solids, Fat, Ash, milk, c.c. per cent 20?C. per cent per cent per cent per cent Raw milk 1,100 0.09 1.0294 14.42 5.3 4.4 0.71 Boiled milk 875 0.11 1.0370 17.77 6.5 5.34 0.73 Boiled milk after correcting for 1,100 14.14 5.2 4.26 reduction in volume. 322 THE INDIAN MEDICAL GAZETTE [June, 1947 1941). The standard agar count of each Summary sample was averaged from 5 plates incubated Milk boiled for 10 minutes and preserved is at 37? ? 0.5?C. for 48 hours. a closed vessel not only brings down the bacterial count more than does Table III efficiently pasteurization, but the rate of growth of Rise in bacterial count milk on of souring organisms on keeping it is considerably less at 40?C. than in pasteurized milk. The simplicity and efficiency of the method perfectly suits the small- Hours Standard scale in India. after plate Acidity, village producer count c.c. per cent The rise in the count of boiled milk on milkinir per plate souring has also been studied. On churning the curd almost all the organisms pass into the ! in 2 Fresh milk 566,000 0.1 buttermilk leaving a very, small number 2.5 Boiled for 1.80 0.11 butter. 10 minutes. 2.5 Boiled milk + i 2,240,000 My thanks are due to Mr. B. N. Banerjee and seed curd. Professor V. Subrahmanyan for their kind interest in 5.5 Curd 84,000,000 0.78 these investigations. 8.5 Do. 256,GOO,000- 1.19 Curd was churned into butter REFERENCES Butter 52.000 | American Public Health Standard Methods Exani- Buttermilk 'at 1 : 100.000.000 of Teeming Association Products. dilution (1941). ination of Dairy American Public Health Association, New York. Discussion Anantakrishnan, C. P.. Indian J. Vet. Sci, and Dastur, N. N., and Animal Husbandry, 13, It is clear from the figures in table I that Kothavalla, Z. R. 297. bacterial destruction in milk is not only much (1943). more efficient with boiling for 10 minutes than Gould, I. A. (1945) ./. Dairy Sci., 28, 367. with pasteurization but the rate of multiplica- Grimes, M. (1923) .. Ibid., 6, 427. tion of organisms on keeping is considerably Hammer, B. W., and Iowa State Colleges Res. Nelson, J. A. (1940). Bull, No. 137. less in the former case. The bacterial quality and 62. of milk its is Kieferle, F., Gloetzl, Milschw. Forsch., 11, and, therefore, keeping quality, J. (1930). further the boiled milk improved by transferring G oodman, A. G. (1941). Food Analysis. Macgraw at it. once into a closed vessel and then cooling Hill, Inc., New York. The ease of operation and the needlessness of any elaborate or specialized equipment makes this method eminently suited for conditions obtaining in this country, where small-scale production in rural areas is the rule. This type of processing, it will be observed from table II, reduces the volume by about 20 per cent, and raises the total solids by about 3.3 per cent, fat by 1.2 per cent and lactose by 1.1 per cent. The allowance is, however, made for the reduction in volume, a loss of 0.28 per cent of total solids, 0.1 per cent fat and 0.14 per cent lactose is observed. Kieferle and Gloetzi (1930) have similarly noted a slight loss in lactose and proteins on boiling milk for 30 minutes. Gould (1945) has recorded a destruc- tion of 25 to 30 per cent of lactose on still more rigorous (2.5 hours at 116?C. or 8 hours at 100?C.) processing. In table III, apart from the quick rise in bacterial count with the progress in souring, the most significant fact is the uneven distribution of the bacterial population of curd between butter and buttermilk on churning : almost all the organisms pass into buttermilk leaving a a very small fraction in butter, fact also observed by Grimes (1923) and Hammer and Nelson (1940) in the creamery process. The low count butter produced by the indigenous method as described above compares very favourably with that produced under the best of conditions by the creamery process. .

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