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Vitamin C Content of Milk of Cows and Buffaloes
EXPERIMENTAL
(a) Plan of work
This work was done with a view to determine the vitamin C content of the
milk of cows and buffaloes and the effects of various factors on it. The animals
selected for the purpose included Sindhi, Gir, Crossbred and Ayrshire cows
and Murrah buffaloes. The animals concerned were fed on a controlled ration
consisting of Guinea grass, Rhodes grass, Ragi straw and a grain mixture fed
at the rate of 1 lb. for every 2 lb. of milk produced. It was decided to determine
the effects on the vitamin C content of the milk obtained from these animals in
its relation to the breed, temperature of heating and storage, exposure to
sunlight, kind of metal of the containers, etc.
(b) Method of estimating vitamin C
(i) Reagents used. The 2 : 6-dichlorophenol indophenol solution used for
the purpose was prepared by grinding the dye in a mortar with pre-boiled
glass distilled water until the solution was complete [Manaker and Guerrant,
1938]. The solution was then standardized by adding 1 gm. of potassium
iodide and 1 ml. of 25 per cent sulphuric acid to 15 ml. of the dye solution
and titrating the liberated iodine with 0 . 01 N sodium thiosulphate solution,
1 ml. of which is equivalent to 0.88 mg. of ascorbic acid. This method
of standardization of the dye solution is based on the quantitative conversion
of the potassium iodide into iodine.
(ii) Estimation of reduced ascorbic acid. To 25 ml. of milk taken from
the representative sample, were added 15 ml. of 25 per cent trichloroacetic
acid. The mixture was allowed to stand for a few minutes after shaking
and was then filtered. Five ml. of the clear resultant filtrate were titrated
from a microburette with 2 : 6-dichlorophenol indophenol reagent until a
faint pink colour, which persisted for about half a minute, was obtained.
(iii) Estimation of total ascorbic acid. Through the remainder of the
filtrate a moderate stream of hydrogen sulphide was passed for about 15
minutes. The container was then stoppered and the saturated solution was
allowed to stand in the dark for about 15 hours. At the end of this period,
the solution which became cloudy on standing was filtered and the hydrogen
sulphide was removed by passing a current of carbon dioxide until the
emergent gas failed to stain moist lead acetate paper. This took on an
average about 10 minutes. The filtrate was then titrated against 2 : 6-
dichlorophenol indophenol reagent. The hydrogen sulphide treatment was
employed to reduce the reversibly oxidized ascorbic acid. The titrations
were carried out in a semi-dark room with the help of an artificial light. The
water used for preparing the solutions and for the dilutions and rinsing of
the apparatus, was obtained by distilling the ordinary distilled water in a
glass apparatus. In the course of the estimation of vitamin C no metal was
allowed to come in contact with the milk.
(c) Factors studied
(i) Effect of breed on the vitamin C content of milk. Animals beyond the
first month of lactation were selected for estimating the vitamin C content
of milk. Samples were taken both morning and evening for a period of two
weeks from 12 animals from every breed of cows and Murrah buffaloes,
with the exception of the Ayrshire breed, of which only two animals were