Robert Jenness

Calculation of the ion equilibria in milk diffusate and comparison with experiment

Abstract A model is described for the ion equilibria between the main salt constituents of bovine milk diffusate. A mass balance equation is constructed for each of the strongly interacting components, consisting of the sum of the concentrations of free and complexed forms of that substance, and an efficient algorithm is given for solving the set of mass balance equations. The model gives calculated free calcium ion concentrations which lie between experimental values determined by ion-selective electrode and murexide methods. Calculated free calcium and magnesium ion concentrations are in general agreement with values determined by a resin equilibrium procedure. The calculated concentrations of ions and complexes in a typical milk diffusate are tabulated.

Composition of milk.

Milk is secreted by all species of mammals to supply nutrition and immunological protection to the young. It performs these functions with a large array of distinctive compounds. Interspecies differences in the quantitative composition of milk (Jenness and Sloan 1970) probably reflect differences in the metabolic processes of the lactating mother and in the nutritive requirements of the suckling young.

Comparative biochemical studies of milks—IV. Constituent fatty acids of milk fats

Abstract 1. 1. Fatty acid analyses of milk fats of fifty-seven species representing eleven orders of mammals are presented. 2. 2. Palmitic and oleic acids are prominent constituents of the milk fats of all species studied. 3. 3. Saturated acids of shorter chain length than C 14 are present in considerable concentrations in the milk fat of ruminants and several other taxa but butyric was found only in ruminant milk fat. 4. 4. Milk fat from the three orders of marine mammals that were studied contained high concentrations of C 16:1 and poly-unsaturated acids with twenty or more carbons.

Comparative Aspects of Milk Proteins

The current status of knowledge of the major proteins of milks of various species is evaluated. Most of the non-bovine milk proteins are homologous with the recognized families of those of Bos taurus, alpha S1-caseins, alpha S2-caseins, beta-caseins, kappa-caseins, beta-lactoglobulins, and alpha-lactalbumins, each family representing a separate genetic locus specific to the mammary gland. No prominent milk protein not homologous to one of these families has yet been discovered in milk of any species. Genetic polymorphism resulting from substitutions in the polypeptide chains and various degrees of post-translational phosphorylation, glycosylation, and proteolysis have been identified in milk proteins of several species. Total protein production ranges among species from about 0.5 to 10 g/d per kg0.75 maternal weight. Proportions of the several proteins vary greatly among species, but few accurate analytical data are available except for total casein and total whey protein contents.

Fundamentals of dairy chemistry.

Fundamentals of dairy chemistry , Fundamentals of dairy chemistry , کتابخانه دیجیتال جندی شاپور اهواز

Comparative biochemical studies of milks— II. Dialyzable carbohydrates☆

Abstract 1. 1. Dialyzable non-ionized milk sugars from forty-nine placental and three marsupial species have been investigated chromatographically. Conspicuous taxonomic differences in proportions of sugars occur. 2. 2. The most characteristic placental sugar with some exceptions in lactose followed in amount by a component that appears to be a trisaccharide and in turn by glucose, galactose and various oligosaccharides. 3. 3. In the marsupial milks, lactose, although present, is not the predominant milk sugar. Free glucose, galactose and oligosaccharides are present in the milk of each marsupial species. With one minor exception, the oligosaccharides of the marsupial milks yielded both glucose and galactose on hydrolysis. None of them appeared to be pentoses or yielded fucose or pentoses upon hydrolysis. 4. 4. The marsupial milks were tested for bifidus activity using Lactobacillus bifidus var. pennsylvanicus and found active. Some 40–70 per cent of the bifidus activitiy occurred in small molecular weight (i.e. dialyzable) milk constituents. Bifidus activity decreased markedly with the stage of lactation.

Interrelationships of constituents and partition of salts in milk samples from eight species

Skim-milk samples from rat, rabbit, pig, sheep, goat, horse and man were analysed for lactose, casein and the total and ultrafilterable concentrations of the main salts. Results are compared with data for the cow. The ultrafiltrate concentrations of Ca and Mg were positively correlated with that of citrate and the colloidal concentrations of Ca, Mg and citrate were positively correlated with that of Pi, suggesting that common, general, principles determine the partition of salts in milks. Casein concentration in the skim-milks was inversely related to that of lactose in accordance with a recent theoretical treatment of the principal mechanism of milk secretion. It is postulated that much of the interspecific diversity in milk composition can be explained by adaptations in a single secretory mechanism.

Effect of chymosin action on the hydrodynamic diameter of casein micelles

Quasi-elastic light scattering shows an initial decrease of about 5 nm in the hydrodynamic radius of casein micelles after adding chymosin, assuming the decrease to be equal for all micelles. This is consistent with the hypothesis that casein micelles have a hairy outer layer that is partly made up of the caseino-macropeptide part of kappa casein.

Some Comparative Aspects of Milk from Four Species of Bears

Milk specimens obtained from 26 individual bears representing Ursus americanas, U. maritimus , three subspecies of U. arctos , and Helarctos malayanus were analyzed for gross composition and were characterized for carbohydrates, fats, and proteins. Bear milks contain high concentrations of fat, proteins, and minerals, but are low in carbohydrates. The lactose content of milk from bears maintained in zoos was much higher than that from wild bears. Myo -inositol was identified as a prominent constituent. The principal fatty acids are palmitic (C16:0) and oleic (C18:1). Polar bear milk fat, however, has significant concentrations of palmitoleic (C16:1) and long chain fatty acids, probably derived from food fat. The caseins of bear milk consist of two principal groups of proteins readily separable by gel electrophoresis. The whey proteins contain five groups of proteins not found in blood. These exhibit evidence of great species specificity and, in some cases, of genetic polymorphism within species.

Effect of ascorbic acid deficiency on the in vivo synthesis of carnitine

The effects of ascorbate deficiency on carnitine biosynthesis was investigated in young male guinea pigs. Liver and kidney carnitine levels were not affected by the deficiency, but scorbutic animals had 50% less carnitine in heart and skeletal muscle than control animals. Labeled carnitine precursors, 6-N-tri-methyl-L-lysine and 4-N-trimethylaminobutyrate, both of which require ascorbate for their enzymatic hydroxylation, were injected into the vena cava of control, pair-fed and scorbutic animals. The distribution of isotope in compounds present in the liver and kidney after 1 h was determined. The uptake of trimethyllysine by the liver was less than 2% in 1 h, while the kidney took up approx. 20% of the 14C. Control and pair-fed animals converted trimethyllysine to kidney trimethylaminobutyrate 8--10 times as well as did scorbutic animals. Trimethylaminobutyrate hydroxylase, present in the liver but almost absent from the kidney, converted nearly all of substrate taken up by the liver to carnitine in both the scorbutic and control animals.