Home
  >  
Section 26
  >  
Chapter 25,976

The vitamin B1 and riboflavin of milk. I. The application of Jansen's thiochrome test to the estimation of vitamin B1 in milk. II. The different forms of vitamin B1 in milk. III. Effect of stage of lactation and of season on the vitamin B1 and riboflavin content of milk. Henry, K. M., Houston, J., Kon, S. K. and White, P. IV. Comparison of chemical and biological methods of estimation of vitamin B1

Houston, J.; Kon, S.K.; Thompson, S.Y.

Jour Dairy Res 11(2): 145-183

1940


Accession: 025975937

Since the thiochrome test gives lower values for B1 than biological assay, cocarboxylase may be present in a combined form perhaps with protein. When milk was digested with pepsin or trypsin to bring about hydrolysis of cocarboxylase the fluorimetric assay indicated variable increases of 5-6 ng. per 100 cc. milk. Incubation of milk with takaphosphatase (takadiastase) at pH4 for 3 hrs. practically doubled the original values. The highest values followed peptic digestion and incubation with takaphosphatase; the latter reaction proceeded best at pH 4-5, with maximum increase in 4-6 hrs. II. Up to 50% of the original B1 did not pass through cellophane, somewhat more through collodion. Since aneurin completely passed through these membranes and since adsorption is not involved, this portion of non-filtrable B1 is combined with proteins. In colostrum or early milk the B1 content increased appreciably after incubation with takaphosphatase, indicating that in normal milk cocarboxylase is bound to larger complexes. Trichloroacetic acid extracts B1 from milk with a 10% loss; some of the vit. goes with the precipitated protein. Trichloroacetic acid extracted some of the B1 retained by ultra-filters. The protein fraction of milk ultra-filtrates contained from 6 to 9 [mu]g. of B1 before incubation; the values were markedly increased by digestion and incubation. Cocarboxylase in full lactation milk was found in combination with protein although apparently less firmly bound than B1. III. Immediately after parturition the "free" B1 content was relatively high; it decreased abruptly by the 2d or 3d day and later gradually increased. Values for total and "free" B1 became closer as lactation progressed. The "free" B1 content varied with the phosphomonoesterase content throughout lactation. Alkaline phosphomonoesterase paralleled enzymes capable of complete dephosphorylation of cocarboxylase at the normal pH of milk. Late lactation milk rich in phosphomonoesterase and containing little or no cocarboxylase, rapidly dephosphorylated added cocarboxylase. In early lactation milk, high in cocarboxylase and low in phosphomonoesterase, the natural cocarboxylase was not dephosphorylated. In goat milk the alkaline phosphomonoesterase was a guide to the conc. of enzymes capable of splitting cocarboxylase. Frequent milking showed that enzymic de-phosphorylation of cocarboxylase may take place in the udder. The riboflavin content was 3-4 times as great in colostrum as in later milk, with rapidly decreasing values. Pasture feeding increased the riboflavin content of milk over indoor feeding. IV. When "free" B1 was measured fluorimetrically the biological method gave higher values for raw, sterilized, spray- and roller-dried and evaporated milks. When total B1 content was detd. at the lower levels of feeding, with autoclaved liver to supply the B2 complex, comparison between the two methods was satisfactory for all excepting evaporated milk. Discrepancy at higher levels of feeding may be due to a deficiency of some essential factor in the basal diet or perhaps to the beneficial effects of major constituents of milk.

PDF emailed within 1 workday: $29.90