Kathleen M. Henry

368. Deterioration on storage of dried skim milk

1. Three spray-dried separated milk powders with moisture contents of 2·9, 4·7 and 7·3% (3 hr. air oven) or 3·0, 5·0 and 7·6% (20 hr. vacuum oven) were packed in air and in almost pure nitrogen, in gas-tight cans, and stored at 20·0, 28·5 and 37° C, for a period of nearly 2 years. 2. The powders were examined at intervals for palatability, colour, pH, equilibrium relative humidity (indicating crystallization of the lactose), conversion of β-lactose to α-lactose hydrate, decrease in total soluble lactose, absorption of oxygen, production of carbon dioxide, solubility in water at 20 and at 50 or 60° C, changes in the distribution of soluble nitrogen, reducing power towards potassium ferricyanide, base-binding capacity, formol titration, weight of the undialysable fraction, free amino-nitrogen by the Van Slyke method, sugar attached to the protein, and bacterial content.

A study of the composition of sow's milk.

Most of the scanty literature on the major constituents of sow’s milk is old, and nothing has to our knowledge been published on its vitamin composition, with the exception of the fragmentary information about vitamins A and C mentioned below. Probably the main reason for this relative lack of information is the difficulty of obtaining satisfactory samples of sow’s milk. This difficulty is stressed in every paper published on the subject, and is connected with the mechanism of the ‘let down’ o f . milk over which the sow appears to have complete control. It is well known that milk cannot be obtained from the sow by milking in the way normally effective with other large animals. Small samples of milk have been obtained mainly by subterfuge. For this purpose a piglet had to be quietly removed while the sow was suckling her litter and the vacated teat quickly milked by hand. Elly & Petersen (1941) have lately devised a method for inducing the ‘let down’ of milk in the cow by the injection into her blood stream of the oxytocic principle of the pituitary. We have applied their technique to the sow with very satisfactory results, and have been able to obtain with ease from a number of sows large samples of milk at intervals throughout lactation. These samples have been analysed for major constituents and also for certain vitamins. We also obtained colostrum from the same sows in a way previously described (Braude, Kon & Thompson, 1945-6) for comparison of its composition with that of the milk. The investigation has covered the winter as well as the summer feeding of the SOW, and has included a study of the effect of season and fodder on the composition of colostrum and milk. Biological tests with guinea-pigs were also done to confirm the extraordinary richness of sow’s colostrum in ascorbic acid reported in our earlier paper (Braude et al. 1945-6).

A comparison of biological methods with rats for determining the nutritive value of proteins

The old-established growth method of Osborne, Mendel & Ferry (1919) for determining the protein efficiency ratio (PER) of protein sources has recently been suggested both in Canada (Chapman, Castillo & Campbell, 1959) and the USA (Derse, 1960) as a routine method for assessing the nutritive value of proteins. Njaa (1963) in a detailed study of the nitrogen balance sheet method for measurement of biological value (BV) (Mitchell, 1923-4a) considers that it and the growth method (PER) are preferable to other biological methods of protein assessment and that the former is more satisfactory than the latter in short-term experiments as it gives both more detailed information and more consistent results. Bigwood (1964) has also recommended BV as the most satisfactory estimate of protein quality. We have already reported (Henry & Toothill, 1962) a good correlation between the N balance sheet and the body-water (Miller & Bender, 1955) methods in assessing the nutritive value of a series of thirty-five protein sources. Sufficient quantities of twenty-four of them were available for the determination of their PER and the results are now reported for values obtained at an 8% level of protein intake. Several methods of protein assessment are compared and the definitions of the terms used are: Retained N x I O O Absorbed N (Mitchell, I 923-4 a) ; Biological value (Bv) =

The relationship between calcium retention and body stores of calcium in the rat: effect of age and of vitamin D.

Serum chemistry in kwashiorkor I47 Trowell, H. C., Davies, J. N. P. & Dean, R. F. A. (1952). Brit. med. -7. ii, 798. Van der Sar, A. (1951). Docum. need. indones. Morb. trop. 3 , 25. Vbghelyi, P. V. (1949). Pediatrics, 3, 749. Viollier, G. (1951). Liver Diseuse. A Ciba Foundation Symposium. London: J. and A. Churchill. Walt, F., Wills, L. & Nightingale, R. P. (1950). S. Afr. med. J . 24, 920. Waterlow, J. C. (1948). Spec. Rep. Ser. med. Res. Coun., Land., no. 263. Waterlow, J. (1950). Lancet, 258, 908. Waterlow, J. C. (1951). W. Indies med. J . I, 15.

Effect of level of protein intake and of age of rat on the biological value of proteins.

Mitchell & Beadles (1950) have reported a very low biological value of 51 for casein, determined with adult rats at 2 and 4% levels of protein intake. They compared this value with one of 69, obtained with young rats, quoted by Block & Mitchell (1946-7) and considered that their low value reflects an increased requirement by the adult rat for the sulphur amino-acids. No support for this view was found in this laboratory, where biological values of 83 and 91 were obtained for dried skim milk with young and adult rats respectively, at a 4% level of protein intake (Henry & Kon, 1952). Milk and casein are equally deficient in methionine, but the cystine deficiency is more marked in the latter (Block & Mitchell, 1946-7); this difference seemed a possible explanation for the conflicting results in the two laboratories. We, therefore, made tests on young rats with casein, alone or supplemented with methionine, at 4 and 8% levels of protein intake, and repeated the experiment on the same rats when adult. Another aspect of changes, with age, in the amino-acid requirements of the rat was studied in similar experiments with a sample of stored, deteriorated dried skim milk in which the lysine had been partly inactivated by the Maillard reaction (cf. Henry, Kon, Lea & White, 1947-8). It has long been established, both in growth (Osborne, Mendel & Ferry, 1919) and nitrogen-balance studies (Mitchell, 1923-4b) that the utilization of protein is affected by its dietary level. T o obtain further information on this subject, and provide a background to our studies in this laboratory, the biological value of two high-quality proteins, egg and casein, was determined at several levels of intake on young rats. The results of some other experiments with young rats, primarily planned in connexion with a different problem, where the biological values of casein and of soya-bean meal were determined at 8 and 16% levels of protein intake, are also reported.

Autoradiographic study of growth and calcium metabolism in the long bones of the rat.

Cobalt dejiciency and appetite in lambs 23 5 deficiency. Moreover, since a cobalt supplement did not enhance live-weight gains at the level of food intake of the cobalt-deficient lambs, the increase in live weight that occurred when lambs on an unrestricted cobalt-deficient diet received a cobalt supplement must have been due to an increased consumption of food, that is, to an increase in the appetite of the lambs. 4. The bearing of this finding on the physiological role of cobalt in ruminants is briefly discussed.

Effect of reaction with glucose on the nutritive value of casein

Abstract The nutritive value of casein for young rats was greatly reduced by storage in the presence of glucose at 70% relative humidity and 37°C for 30 days. The change was considerable even after storage for 5 days.

A comparison of the body-water and nitrogen balance-sheet methods for determining the nutritive value of proteins.

Biological methods available for determining the nutritive value of proteins have recently been reviewed by Allison (1955), Bender (1958) and Adrian & Rerat (1958), and several reports of comparisons between methods for the evaluation of selected proteins have appeared (Rutger’s University : Bureau of Biological Research, 1950; Forbes & Yohe, 1955 ; Chapman, Castillo & Campbell, 1959; Rippon, 1959; Tomarelli, Minnick, d’Amato & Bernhart, 1959). It is generally agreed (Forbes & Yohe, 1955; Bender, 1958 ; Rippon, 1959) that the balance-sheet method of Mitchell (Mitchell, 1923-4; Mitchell & Carman, 1926), measuring the biologicalvalue and true digestibility of proteins, gives more fundamental information and is more precise than other available methods. This method has been in use in this laboratory for many years and has been preferred to the growth method of Osborne, Mendel & Ferry (1919) because of its greater precision, particularly for relatively small differences (cf. Henry, Kon, Lea & White, 1947-8). It is, however, time-consuming, and the method, based on body-water determinations, described by Miller & Bender (1955) seemed to offer a more rapid way of assessing Mitchell’s (Mitchell & Villegas, 1923) net protein value (NPV), that is biological value x true digestibility -+ 100. We have applied the method of Miller & Bender (1955) to a series of thirty-five proteins or protein foods of different quality and compared the results with the NPV determined by the balance-sheet method. Before doing so it was necessary to establish, for our colony, the relationship between the age of the rat and the water and nitrogen content of its body. For this purpose two series of experiments were carried out, in the second of which the livers of the rats were analysed separately from the rest of the body, with a view to the possible application of the method to larger animals with which carcass analysis would be impracticable. In the second series some preliminary tests were also done to establish whether the ratio between body content of water and N was affected by dietary changes.

170. The effect of commercial sterilization on the nutritive value of milk

We have dealt in a previous communication (1) with the effects-of commercial pasteurization on the nutritive value of milk. We present here the results of an enquiry into the nutritional effects of the more drastic heat treatment to which milk is subjected during commercial sterilization. There is no legal definition of either sterilized milk or of the process of sterilization, but in commerce it is customary to apply the term to milk which has been heated to at least 212° F. for varying lengths of time.

The effect of heat on the vitamin B 6 of milk: II. A comparison of biological and microbiological tests of evaporated milk

1. For chicks and rats pyridoxine, pyridoxal and pyridoxamine were equally active in terms of the free bases when given separately from the diet. 2. Under our experimental conditions pyridoxine mixed with the chick diet was stable, but 20% of pyridoxamine, and a variable amount of pyridoxal was lost. 3. The vitamin B 6 activities measured with Saccharomyces carlsbergensis , chicks and rats respectively and expressed as μg. pyridoxine/g. freeze-dried milk were: raw milk 3·4, 3·2 and 4·9; evaporated milk 1·0, 2·1 and 2·7; stored evaporated milk 0·6, 1·4 and 2·0. For the chicks the milks were mixed with the diets; they were given separately to the rats. 4. The microbiological and biological results for raw milk agreed within the limits of experimental error. For the processed milks the differences between biological and microbiological tests were statistically significant. 5. All three methods of assay showed a 45–70% loss of vitamin B 6 activity on processing and a further loss of 30% of the remainder after storage for 6 months at room temperature. We are indebted to Mr J. Rothwell, Department of Dairying, University of Reading, for preparing the evaporated milk and to Dr B. Record, Ministry of Supply, Microbiological Research Establishment, Porton, for freeze-drying the milk. We should like to thank Dr S. K. Kon for his interest in this work.