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Because of low energy reserves at birth, piglets are dependent on the sow’s milk for survival. Breed differences can influence milk composition. The objective of this study was to examine litter characteristics, milk composition including calcium and the water holding capacity of casein, solvation, between the highly prolific Meishan breed and lean crossbred pigs. Samples were collected by hand-milking at early (days 3–5) and late (days 20–21) lactation. Milk fat percentage for Meishans was higher than for the crossbred, especially during early lactation (10.72±0.5>8.91±0.4 (crossbred); P 6.49±0.39 (crossbred); P>0.05. No differences were observed between breeds for lactose or protein at either sampling time. Calcium concentration (mg/dl) was higher in Meishan milk than in crossbred milk at early lactation (0.204±0.01>0.178±0.01; P 11.1±0.7; P

The strong calcium-binding site of alpha-lactalbumin comprises the carboxylate side chains of aspartic acid 82, 87, and 88 and the carbonyl oxygens of residues 79 and 84. A single methionine residue was selectively modified by controlled CNBr cleavage to yield homoserine at position 90. The CNBr-cleaved alpha-lactalbumin lost the ability to bind calcium strongly as monitored by intrinsic fluorescence, electrophoretic mobility, atomic absorption, and x-ray fluorescence. Remarkably, the modified protein was still competent in lactose biosynthesis, although activity was reduced to 1/40th that of the native form of the protein. Although the strong calcium-binding site was destroyed as a result of the cleavage of the calcium-binding loop, a secondary calcium site was retained that directly affects a rate enhancement of lactose biosynthesis when saturated, resulting in approximately a two- to threefold increase in rate at 1 mM CaCl2 with an activation equilibrium constant of 350 +/- 40 microM.

Potato acid phosphatase was immobilized on succinamidopropyl-derivatized glass beads for use in removing phosphate groups from bovine whole casein. Controlled pore glass beads (with and without glyceryl coating) were silanized and succinylated. The enzyme was covalently bound to derivatized glass beads through carbodiimide coupling. The pH optima for the immobilized enzyme remained at pH 5.5 for p -nitrophenyl phosphate and pH 6.0 to 6.5 for casein substrates. Activities of acid phosphatase (pH 5.5, p -nitrophenyl phosphate substrate) immobilized on the plain and glyceryl-coated controlled pore glass beads were 14 and 4%, respectively, of the free enzyme. When whole casein was used as substrate, the 15 to 20min enzyme activity of free enzyme was 16% of its activity on p -nitrophenyl phosphate and after 4h, 14% of its original rate on casein. After 18h of incubation, the activity of the immobilized enzyme was 36 to 40% of its rate at 4h. A 70% dephosphorylation of whole casein was attained using a concentration of 2.6mg enzyme controlled pore glass beads complex per milligram of whole casein at pH 6.5, 37°C, for 18h.

Textural differences between Cheddar and Cheshire cheeses were examined rheologically to provide a means of distinguishing these two English cheeses. Body breakdown of a 60-wk Cheshire sample occurred at a lower strain than did a 20-wk sample, whereas a 60-wk Cheddar sample did not break down under the same conditions. All cheeses followed the Arrhenius equation, and the energy of activation obtained varied with age and type of cheese. Other analytical techniques showed differences between the samples but were not suitable for distinguishing one type of cheese from the other.

Reduction of Cheddar cheese making time was investigated by regulating the amount of lactic starter culture initially added to the milk and preparing the cheese at 37.8°C. Laboratory trials showed that in conventional cheese making at 31.1°C, an initial cell count of 10 7 cfu/ml was necessary to achieve a 10 9 cfu/g population density and desirable acidity (pH 5.3 to 5.4) at the milling stage. In the modified process, cheese curd was prepared by prewarming milk to 37.8°C and adding starter culture at 10 8 cfu/ml and milk coagulant (veal rennet) simultaneously. This method shortened preparation time by as much as 90min, depending on the acid production of the starter culture. Cheeses made in six trials were stored at 4.4°C for 1 yr. Ratings by an expert panel showed no significant differences in flavor, body, and texture characteristics that could be attributed to the method of preparation. On a 5-point intensity scale, increase in sharpness correlated significantly (P⩽.05) with storage time with slightly greater increase observed in the experimental cheese. No difference in sharpness was significant between samples made by conventional and experimental methods. Decline in curdiness with storage time showed similar correlations. The results suggested that reduction of make time by increasing starter culture inoculum to 10 8 cfu/ml and renneting at the time of setting at a higher temperature (37.8°C) improved aging characteristics of the finished cheese over the storage time studied.

β -Lactoglobulin and α -Lactalbumin were isolated and crystallized by the classical method of Aschaffenburg and Drewry, and the purity of the crystals was assessed by native PAGE and SDS-PAGE. Although β -lactoglobulin was free of contaminants, α -lactalbumin was still contaminated after five recrystallization steps. Yields of crystals in this study were lower than reported by Aschaffenburg and Drewry. Further, it was observed that α -lactalbumin undergoes a Ca 2+ /Ca 2+ -free, dependent electrophoretic shift characteristic of many calcium-binding proteins.

Bovine mammary gland calmodulin, purified by conventional fractionation procedures, was compared with similarly purified bovine brain calmodulin. Affinity chromatography on W-7 agarose of the crude fractions from mammary gland and brain yielded pure proteins containing one trimethyllysine residue per 16,800 daltons with essentially identical amino acid compositions. Kinetic parameters of these two proteins with respect to their ability to activate phosphodiesterase were determined. The constants for half maximum activation were .39 and .44 nM for bovine brain and bovine mammary gland calmodulins, respectively; both proteins gave similar maximum velocities. Based on the amino acid composition and kinetic data, it is concluded that the two proteins are essentially identical.

With a simple, sensitive, and rapid SDS-PAGE procedure, developed during the course of this study, calmodulin was not found in cows' milk. The absence of calmodulin at the level of detection provided by this procedure (.4 μ g) was unexpected. Because milk is a repository for many protein and enzyme systems, and because the mammary gland is known to contain calmodulin, it was conjectured that at least some "leakage" of the protein into milk would occur, especially into colostrum.

α s1 -Casein has been observed to differ from α s1 -B by its solubility in CaCl 2 solutions at 1 and 37C, and by its stabilization profile in the presence of κ-casein and calcium ions. The different characteristics of the protein α s1 -A have been attributed to the deletion of a segment of nonpolar amino acids resulting in decreased hydrophobic interactions among α s1 -A molecules. The deletion also has impaired the formation of α s1 -κ-casein micelles under conditions of normal formation.

Milk protein polymorphism has been studied in depth since Aschaffenburg's discovery of genetically distinct forms of β-lactoglobulin in 1955. The significance of these various protein polymorphisms, as related to the synthesis and secretion of milk, is yet to be elaborated fully. However, certain areas in milk protein polymorphism warrant particular attention. These include: assignment of mRNA triplet codons to known amino acid substitutions; biosynthesis and primary structure of polymorphs; observations of micelle formation in vivo through electron microscopy; mode of inheritance, breed specificity, and linkage of these genes; and, finally, biological function of the milk protein variants.

The three known genetic variants of β -casein (A, B, and C) have been purified by column chromatography in 3.3m urea, and their purity verified by polyacrylamide-gel electrophoresis. Qualitative determination of the amino terminal amino acid by two independent chemical methods revealed arginine for each of the three variants. During reaction with carboxypeptidase A, valine was released most rapidly and was closely followed by isoleucine. The data indicate either an ileu-ileu-val or an ileu-val-ileu C-terminal sequence in each variant. Molecular weights of about 25,000 for β -caseins A, B, and C were calculated from the amount of valine released.

Isolated α s5 -casein (zone 0.86) is converted by treatment with 2-mercaptoethanol into two components with electrophoretic mobilities identical to those of α s3 -casein (zone 1.04) and of α s4 -casein (zone 1.00). The molar ratios of amino acids of α s3 -, α s4 -, and α s5 -caseins are similar. The data suggest that α s5 -casein is a molecule of α s3 -casein united to a molecule of α s4 -casein by at least one intermolecular disulfide bond. Moreover, a close relationship between α s3 -casein and α s4 -casein is revealed by the similarity of their amino acid molar ratios.

κ -Casein, after reduction of the disulfide bond(s) by 2-inercaptoethanol, can be separated from α s1 - and β -casein variants, as well as from whole casein, by DEAE-cellulose-urea chromatography. When κ -easein is in the reduced form it elutes from DEAE-cellulose at 0.05m NaCl. Use of a reduction step simplifies purification of the major casein components ( α s1 -, β ) by chromatography.

The Nomenclature Committee has given particular attention to genetic polymorphism in the proteins of cow's milk, and has adopted a nomenclature scheme which embraces genetic designations. The β-lactoglobulins are to be referred to as β-lactoglobulins A, B, and C. Three genetic forms of β-casein have been reported to occur either singly or in pairs in the milk of individual cows, and are appropriately referred to as β-caseins A, B, and C. The term αs1-casein has been recommended and refers to those components of the α-casein complex that are precipitated by calcium and stabilized by κ-casein against precipitation by calcium. They constitute the major proportion of the αs-caseins, and have been reported to exist in three genetic forms, A, B, and C. The genetic forms of αs1- and β-caseins can be conveniently identified by their relative mobilities by zonal electrophoresis.

A linear relationship (r=.89) was found between casein-pellet-solvation and heat stability at 135C for individual cow milks. Casein-pellet-solvation was determined by centrifugation of whole milk at 68,000 g for 35min at 37C.

α-Lactalbumin undergoes a calcium-dependent electrophoretic shift at pH 8.3. When Ca 2+ is removed by a chelator, the mobility of the protein increases, reflecting the exposure of negative electrical charges. The shift, however, is not observed by electrophoresis in the presence of SDS, which demonstrates that α-lactalbumin does not undergo a measurable conformational change upon debinding of Ca 2+ . Relative electrophoretic mobilities vary from 1.0 (no shift) to 1.4 among α-lactalbumins of different orders of mammals. The differences suggest a variable number of gram atoms of Ca 2+ bound to α-lactalbumin or substitution of amino acid Ca 2+ ligands in the calcium-binding loop.

A variety of methods for phenotyping whey proteins and the caseins is summarized. The writer suggests what he believes are the best methods for phenotyping genetic variants of the milk protein system depending upon the availability of apparatus. No single method has yet been devised to simultaneously type the variants of α s1 - and β -caseins

α s1 -Casein A, a rare genetic polymorph of the α s1 -casein fraction of cow's milk, probably arose through the sequential deletion of eight amino acid residues. The α s1 -A allele was thought to occur only in American Holstein cattle; however, it has been reported to occur in low frequency in Red Danish cattle. No ancestral relationship can be found between Red Danish cattle and the Holstein breed, hence further confirmation of the identity of these two polymorphs was sought. The proteins were isolated by DEAE-cellulose chromatography and the fingerprints of their chynotryptic digests compared. The α s1 -A variant from the Red Danish breed proved to be identical with that of the Holstein breed where α s1 -A was first observed. Therefore, it is proposed that this mutant form of α s1 -casein is of more ancient ancestry, since no relationship between the Red Danish and the American Holstein breeds can be documented.

The amino acid composition of highly purified preparations of the genetically controlled variants of α s1 -casein, A, B, and C has been determined. B and C are virtually identical in composition, the only significant difference being that C contains one more glycine residue per mole than B. The data suggest that in B the missing glycine might be replaced by glutamic acid. The differences between A and the other variants are numerous and more substantial and, at present, cannot be accounted for in terms of single amino acid substitutions.