S. Y. Thompson

Effects of gamma-irradiation on the vitamin content of diets for laboratory animals

Practical-type diets for chicks, guinea-pigs and cats, and a chick diet of purified ingredients, were assayed for their vitamin content before and after gamma-irradiation at doses ranging from 2 to 5 Mrad. Irradiation of guinea-pig and chick diets resulted in small losses of vitamin A (in this investigation, 6 and 12 per cent respectively). Losses of vitamin E were larger (24 and 65 per cent) but were much less (11 per cent) when the diets were vacuum-packed before irradiation. Vitamins were less stable in the purified chick diets, the most susceptible being vitamins A, E, B6 and thiamine. Vitamin destruction was greatly increased when antioxidants were incorporated into this diet, and also when its moisture content was high. Vitamin A and β-carotene were almost completely destroyed in the cat diet, where there was also some loss of thiamine and folic acid.

326. The effect of temperature of pre-heating, of clarification and of bacteriological quality of the raw milk on the keeping properties of whole-milk powder dried by the Kestner Spray Process

(1) Increasing the pre-heating temperature of the milk from 165 to 190° F. before spray-drying greatly improved the resistance of the powder to the development of tallowy ‘off’-flavours on storage. From the results of accelerated tests at 47 and 37° C. a storage life (in air) of the order of 2 years could safely be predicted for the powders from milk pre-heated at the higher temperature. Confirmation has now been obtained by storage of the powders for 2½ years at 15° C. and at room temperature. (2) Improvement in the bacteriological quality of the milk supply, and more careful control during its passage through the plant, produced some improvement in the keeping properties of powders prepared from milk pre-heated at the lower temperature, but had relatively little effect on the keeping properties of the powder when the higher preheating temperature was used. (3) The shapes of the deterioration curves for the various powders showed that the effect of the higher pre-heating temperature and of improvement in the milk supply was to extend the induction period which precedes rapid deterioration. The protective effect of both factors was greater when measured at the ‘slightly tallowy’ or ‘fairly good’ stage than when comparison was made at a more advanced stage of decomposition.

578. The composition of the milk of the blue whale

The detailed composition of samples of milk from three blue whales (Balaenoptera sibbaldi) is reported in terms of total solids, fat, solids-not-fat, total protein, casein, soluble proteins, non-protein nitrogen, lactose, chloride, ash, calcium, phosphorus, sodium, potassium, magnesium, vitamin A, thiamine, biotin, riboflavin, nicotinic acid, vitamin B6, pantothenic acid and vitamin B12.The composition of the milk of the whale is compared with that of other species.

THE COMPOSITION OF RABBIT'S MILK.

As part of a project on hand-rearing baby rabbits, it was necessary to know the composition of rabbit’s milk so that a suitable milk-substitute diet could be prepared. The gross chemical composition of rabbit’s milk has been studied in some detail by Folin, Denis & Minot (1919), Bergman & Turner (1937) and Neumeister & Krause (1956), but little is known about its vitamin content. We have therefore analysed samples of milk taken from New Zealand White and Chinchilla rabbits at different stages in the lactation cycle and report here their chemical composition and vitamin content. EXPERIMENTAL Milk samples Samples of milk were obtained from one Chinchilla and seven New Zealand White rabbits. Litters were removed from the lactating does on the evening before the sample was taken. The following morning each doe was given 2.5 i.u. oxytocin by injection into the ear vein and milk was expressed by gently massaging the mammary tissue. Milk flow usually began about 3 min after the injection and continued for about 15 min. Up to the 20th day of lactation volumes of 1-35 ml per doe were obtained, the average being about 20 ml; only very small quantities of milk could be expressed from does in later stages of lactation. Samples of colostrum were taken within 24 h of the birth of the litter. For full chemical and vitamin analysis of some of the samples, the milks from two rabbits at similar stages of lactation were bulked. In this way two mixed samples representing the 1st and 3rd weeks of lactation were obtained. Other samples were analysed individually. A portion of each sample (usually 5 ml) was set aside for chemical analysis. The remainder was weighed and centrifuged and the cream layer was removed, weighed and used for the measurement of vitamin A. The fat content of the cream, and thus of the whole milk, was determined. The water-soluble vitamins were measured microbiologically in the skim milk, but the results were recalculated in terms of whole milk.

The Vitamin B1 and Riboflavin of Milk. Part II. The Different Forms of Vitamin B1 in Milk.

Part I 1. A method for the estimation of vitamin B 1 in milk by a modified Jansen test involving takaphosphatase treatment is described in detail. Part II 2. It is shown by ultra-filtration experiments, by treatment with pepsin and takaphosphatase, with trichloroacetic acid and with fullers earth that vitamin Bx is present in milk unesterified and phosphorylated and that both forms may be freely diffusible or combined with protein either loosely or by firmer bonds. Part III 3. The effect of the stage of lactation on the amounts and partition of vitamin B 1 in milk has been studied. Samples of colostrum and early milk were found to contain large amounts of cocarboxylase (up to 80 % of the total). Hardly any cocarboxylase was present in mid or late lactation milks. The total vitamin B 1 content was 60–100μg./100 ml. for colostrum, up to 60μg./100 ml. for early milk and 30–40μg./100 ml. for mid and late lactation. 4. A marked negative correlation exists between the cocarboxylase content of cows and goats milk and their alkaline phosphomonoesterase titre. As this enzyme cannot dephosphorylate cocarboxylase it is probably accompanied in milk by other enzymes more suited to this process. 5. The suggestion is put forward that the vitamin B 1 of milk is mostly derived not directly from the blood but from the secretory cells of the mammary gland.

252. The effect of commercial pasteurization and sterilization on the vitamin B 1 and riboflavin content of milk as measured by chemical methods

1. Fluorimetric tests applied to commercially pasteurized and commercially sterilized milk showed that in the former some 10% and in the latter up to 50% of vitamin B 1 was destroyed in the course of the heat treatment. 2. Riboflavin withstood both treatments without loss. 3. These findings are in satisfactory agreement with the results of earlier biological tests.

Studies on lipid digestion in the preruminant calf. The source of lipolytic activity in the abomasum

1. Lipolytic and proteolytic activities and pH values were determined in secretions collected from innervated abomasal pouches and in abomasal contents from preruminant calves given liquid diets. 2. No lipolytic activity was detected in pouch secretions collected during 1 h after feeding, though lipolytic activity was present in abomasal contents; pepsin (EC 3.4.23.1) and renin (EC 3.4.23.4) were present in both pouch secretions and abomasal contents. The pH values of pouch secretions ranged from 1-2 to 1-8 and those of abomasal contents from 4-2 to 5-9. 3. When diet was placed directly into the abomasal pouch soon after feeding, the pH values of pouch and abomasal contents decreased similarly (i.e. from 6-3 to approximately 5). Protease activity (U/ml) of pouch contents ranged from 0-1 to 0-8 and that of abomasal contents from 0-1 to 0-2. No lipolytic activity was detected in pouch contents, though abomasal contents contained 0-6 to 1-2 U/ml and when the diet contained milk-fat as the dietary fat source considerable lipolysis of triglycerides containing shorter-chain fatty acids was found. 4. It is concluded that there is no significant secretion of lipolytic enzymes by the fundal mucosa and that the lipolysis of triglycerides in the abomasum of the preruminant calf is due predominantly to a lipolytic enzyme in saliva.

The passage of vitamin A from mother to young in the rat.

In studying the vitamin A content of human milk Kon & Mawson (1950) noted that many of the women whose milk was examined had taken a supplement of vitamin A during pregnancy but not after the birth of the child. Although these women presumably had higher liver reserves of vitamin A than those that had taken no supplement, the difference was not reflected in the vitamin A content of their milk. Dann (1932, 1934u, b) and Baumann, Riising & Steenbock (1934) studied the effect of the liver reserves of the mother rat on the stores of the newborn young and of the young at weaning. They did not analyse the milk; at that time methods of measuring vitamin A were not sufficiently sensitive for the purpose. Nevertheless, a comparison of Dann’s values for the newborn with those for the weanling indicates that large differences in maternal reserves must have been reflected in small differences in the vitamin A content of the milk. The work with rats now described was undertaken to study further the relationship between the maternal reserves of vitamin A, the vitamin A content of the milk, and the stores of vitamin A present in the young at birth and amassed during suckling. The mother rats received vitamin A either preformed or as /3-carotene.

315. The effects of commercial processing and of storage on some nutritive properties of milk. Comparison of full-cream sweetened condensed milk and of evaporated milk with the original raw milk

1. Full-cream unsweetened condensed milk (evaporated milk) and full-cream sweetened condensed milk (condensed milk) were prepared simultaneously on several occasions each time from a common bulk of raw milk. Heat treatment in the preparation of evaporated milk is, of course, much more severe than with condensed milk. (a) There was no loss of vitamin A, carotene or riboflavin in either of the processes. (b) The mean loss of vitamin C as compared with the raw milk was 10% for condensed and 60% for evaporated milk. (c) The vitamin B 1 losses were 3·5 and 27% respectively. (d) Tests on rats showed that the biological values and true digestibilities of the proteins of the raw, condensed and evaporated milks were respectively 85·6 and 94·2, 84·6 and 98·8, 84·1 and 93·7. The differences in biological value are without statistical significance but the digestibility of the condensed milk was significantly higher than that of the other two milks.

258. The Vitamin B 1 and Riboflavin of Milk

Part I 1. A method for the estimation of vitamin B 1 in milk by a modified Jansen test involving takaphosphatase treatment is described in detail. Part II 2. It is shown by ultra-filtration experiments, by treatment with pepsin and takaphosphatase, with trichloroacetic acid and with fullers earth that vitamin Bx is present in milk unesterified and phosphorylated and that both forms may be freely diffusible or combined with protein either loosely or by firmer bonds. Part III 3. The effect of the stage of lactation on the amounts and partition of vitamin B 1 in milk has been studied. Samples of colostrum and early milk were found to contain large amounts of cocarboxylase (up to 80 % of the total). Hardly any cocarboxylase was present in mid or late lactation milks. The total vitamin B 1 content was 60–100μg./100 ml. for colostrum, up to 60μg./100 ml. for early milk and 30–40μg./100 ml. for mid and late lactation. 4. A marked negative correlation exists between the cocarboxylase content of cows and goats milk and their alkaline phosphomonoesterase titre. As this enzyme cannot dephosphorylate cocarboxylase it is probably accompanied in milk by other enzymes more suited to this process. 5. The suggestion is put forward that the vitamin B 1 of milk is mostly derived not directly from the blood but from the secretory cells of the mammary gland.