Showing papers in "Journal of Dairy Research in 1972"

Influence of temperature and composition on some physical properties of milk and milk concentrates. I. Heat capacity

Abstract: An isothermal jacket calorimeter was set up and apparent heat capacities of skim-milk, half-and-half milk, whole milk, and their concentrates up to about 30 % total solids were measured throughout the 5–70°C temperature range. Above the butterfat melting interval, the heat capacity of every sample was linearly related to temperature and a linear regression equation was found to relate heat capacity and total solids content for each one of the 3 milk sets. By means of an overall approximation, a single expression relating heat capacity, temperature and total solids content was also derived. To facilitate calculations of relative heat content for practical purposes, an average apparent heat capacity was computed for the whole temperature range and a nomogram was constructed for its determination from fat and solids-not-fat contents in any sample.

Cheese-making with a vegetable rennet from Cardo ( Cynara cardunculus )

Abstract: The milk-clotting enzyme found in the flowers of Cardo (Cynara cardunculus) was investigated as to its suitability as a substitute for traditional animal rennet used in cheese-making. The influence of milk pH, temperature and quantity on the clotting activity of this enzyme was studied. Rheological behaviour of cow's-milk and sheep-milk curds, from renneting to cutting, was determined with the Plint cheese curd torsiometer for various Ca contents and pH values. Edam, Serra and Roquefort cheeses were made and the protein breakdown which occurred in the cheese during the ripening period was determined. Animal rennet was used as a control in all the experiments. The enzyme from Cardo was a satisfactory substitute for animal rennet with cow's milk and was even more suitable for sheep's milk. It was found to be a very good clotting enzyme for soft-bodied cheese like Serra, but because of its high proteolytic activity it presented some problems in Edam cheese-making. In Roquefort cheese it gave satisfactory results, but with some loss in yield.

Volatile compounds in butter oil: II. Flavour and flavour thresholds of lactones, fatty acids, phenols, indole and skatole in deodorized synthetic butter

Abstract: The flavours of the following compounds were determined in synthetic butter prepared from 84% steam-deodorized butter oil and 16% water: C6, 8, 10, 12, 14 δ-lactones, C12 γ-lactone, C2, 4, 6, 8, 10, 12, 14n-alkanoic acids, phenol, m- and p-cresols, o-methoxyphenol, indole and skatole. C6, 8, 10 δ-lactones, C2, 4, 6, 8, 10, 12, 14n-alkanoic acids, phenol, m- and p-cresols, o-methoxyphenol and volatile fractions from butter oil were also evaluated in bland butter. None of the compounds listed constitute basic butter flavour on their own, but C8, 10 δ-lactones, C10 acid, phenol, p-cresol, indole and skatole contribute to butter flavour.

Formaldehyde-treated casein–safflower oil supplement for dairy cows: I. Effect on milk composition

Abstract: The effects of feeding lactating cows a daily supplement of 1 kg formaldehyde-treated casein–safflower oil (1:1, w/w) on the milk composition are reported. Three breeds, Jersey, Sahiwal and Sahiwal × Jersey crossbred were used. The formaldehyde treatment not only eliminated the suppressing effect on the milk, fat and protein yields and on the fat and protein contents usually encountered when such a level of unsaturated oil is fed to lactating cows, but also resulted, on the average, in 15 and 6% increases in the fat and protein contents respectively. The formaldehyde-treated dietary supplement also caused a decline of 5% in the solids-not-fat content, presumably due to a decrease in the lactose content. It is suggested that the formaldehyde treatment protects the casein from the ruminal proteolysis and this in turn prevents the encapsulated unsaturated oil from biohydrogenation and eliminates the diverse effects on rumen microflora and environment.

Formaldehyde-treated casein-safflower oil supplement for dairy cows. II. Effect on the fatty-acid composition of plasma and milk lipids.

Abstract: This study reports the effect of feeding formaldehyde-treated or untreated spray-dried casein–safflower oil (1:1, w/w) particles on the fatty-acid composition of milk and plasma lipids of cows.When the formaldehyde-treated particles were given to Jersey, Sahiwal and Jersey × Sahiwal crossbred cows (1 kg per cow per day) the linoleic acid (18:2) present in the safflower oil was not hydrogenated by the rumen micro-organisms and was incorporated into milk fat.When the untreated supplement was fed, however, the 18:2 fatty acid was hydrogenated in the rumen and there was an increased proportion of octadecenoic acid (18:1) in the milk fat.The increased proportions of 18:2 (treated supplement) and 18:1 (untreated supplement) were associated with decreased proportions of palmitic (16:0) and myristic (14:0) acids in the milk fat. All 3 breeds showed similar responses.The fatty-acid composition of plasma triglycerides, which are an important source of long-chain fatty acids for mammary-gland lipogenesis, was similarly affected. Furthermore, there were significant changes in the fatty-acid composition of other plasma lipids (e.g. phospholipids and cholesteryl esters). The interrelationships between dietary, plasma and milk fatty-acid compositions are discussed.

Metabolism of cod-liver oil in relation to milk fat secretion.

Abstract: The effects of daily supplements of 300 g native and 2 hydrogenated cod-liver oils (CLO) to the diets of lactating cows have been examined. Native CLO supplements increased the proportion of propionate and decreased the proportion of acetate in the rumen and also decreased the yields in milk of fatty acids synthesized within the mammary gland and those derived from plasma triglycerides. These effects were reduced or eliminated when the hydrogenated oils were given instead of the native CLO. With all 3 supplements about 15% of the dietary C 20 and C 22 acids was secreted in milk. Both native and hydrogenated CLO supplements increased the concentrations of the cholesteryl ester and phospholipid components of the α-lipoproteins in the blood plasma. These components contained most of the C 20 and C 22 acids of the CLO supplements that were incorporated into the blood plasma lipids. With the native CLO supplement about half of the C 20 and C 22 acids present in the blood plasma were polyunsaturated. There were no differences in the effectiveness of high-density plasma lipoproteins as activators of triglyceride emulsions for lipoprotein lipase hydrolysis whether the lipoproteins were from cows receiving the native or the hydrogenated CLO supplements or the control diets. Significant rates of hydrolysis by lipoprotein lipase could not be demonstrated using as substrates low- or high-density plasma lipoproteins or activated emulsions of their extracted lipids. Additional in vitro experiments using activated triglyceride emulsions as substrates for mammary lipoprotein lipase showed that replacement of a soybean oil emulsion by an emulsion of native CLO reduced the rate of hydrolysis considerably, whereas an emulsion of hydrogenated CLO was without effect unless it was present at levels in excess of 50%. It is concluded that the change in rumen fermentation induced by the polyunsaturated fatty acids of CLO is implicated in the decreased intramammary synthesis of fatty acids, but that additional information is required before the reason for the reduced mammary uptake of plasma fatty acids can be established.

Factors affecting the action of rennin in heated milk

Abstract: The effect of temperature and time of heating whole milk on the renninclotting time, the primary phase of rennin action and the protein (mainly β-lactoglobulin) soluble in 2% trichloroacetic acid (TCA), have been studied. Considerable changes in these parameters occurred above 60°C. The primary phase was inhibited (the degree of inhibition being both temperature and time-dependent), the clotting time was increased, and the protein soluble in 2% TCA decreased considerably.It is suggested that the inhibition of the primary phase was due to complex formation between κ-casein and β-lactoglobulin, the increase in clotting time to a combination of complex formation and a change in the distribution of Ca, and the decrease in β-lactoglobulin to both its interaction with κ-casein and its heat denaturation. The relevance of such changes to the heat stability of milk is discussed.

The composition of milk of British Alpine and Anglo-Nubian goats imported into Trinidad.

Abstract: The variations in the composition of milk over an 18-week period from lactating British Alpine and Anglo–Nubian goats imported into Trinidad are reported. The animals were fed Napier grass (Pennisetum purpureum) ad lib. and 2 lb of a proprietary concentrate mixture daily.The mean percentage contents of the milks of British Alpine and Anglo–Nubian goats were: total solids 11·49±0·22, 12·17±0·28; butterfat 3·42±0·18, 4·06±0·22; total N 0·462±0·04, 0·530±0·07; ash 0·78±0·02, 0·79±0·03 and ‘lactose’ 4·38±0·28, 4·05±0·55. Anglo–Nubian goats had a higher content of percentage total solids, fat, total N and ash. For all constituents the coefficient of variation between weeks was higher for Anglo–Nubian goats. No significant trends were found between weeks for each of the components analysed for both breeds. Statistically significant correlations (P < 0·01) were found between percentage fat and percentage total N for both breeds.The mean mineral contents (mg/100ml) for the milks of British Alpine and Anglo–Nubian goats were: Na 52·6±4·6, 55·5±1·9; K164·0±8·4, 133·4±11·4; Ca 85·5±11·6, 89·9±9·8; Mg 13·2±3·8, 10·2±1·6 and P 74·7±3·9, 82·1±3·9. British Alpine goat's milk had a higher content of K and that of Anglo–Nubian goats had a higher content of P; both differences were statistically significant (P < 0·01).The milk composition figures in this study together with those from a similar study in Guadeloupe suggest that the values are low and considerably lower in comparison with the same breeds of goats in a temperate environment. This could be a feature of dairy goats imported into the tropics due perhaps to inadequate nutrition. Much more information is needed to verify this possibility.

Assessment of swine, bovine and chicken pepsins as rennet substitutes for Cheddar cheese-making

Abstract: Three enzymes were assessed as rennet substitutes for cheese-making. The bovine and chicken pepsins used were relatively crude extracts of bovine stomach mucosa and chicken proventriculae respectively; the swine pepsin was a partially purified commercial product. The ratios of milk-clotting activity to general proteolytic activity were high for rennet and bovine pepsin and low for swine and chicken pepsins. Both bovine mucosa and chicken stomach gave low milk-clotting activities compared with calf stomach. For all the enzymes the chemical reactions causing milk clotting appeared to be the same. The milk-clotting activity showed a decrease with increase in substrate pH for all the enzymes, although they were all still active at pH 6·81.Duplicate cheeses were made from each of the swine, bovine and chicken pepsins, with rennet as a standard in each trial. The cheese-making process was similar with each enzyme, but differences appeared during ripening. The chicken-pepsin cheeses had poor body and weak Cheddar-cheese flavour, with many and intense off-flavours. The cheeses made with bovine and swine pepsins were only slightly inferior in quality and intensity of Cheddar-cheese flavour to the rennet cheeses. From a simulated cheese-making experiment it was concluded that 30–40 % of the added rennet, bovine pepsin and chicken pepsin was probably inactivated during the cheese-making process and that most or all of the swine pepsin was lost. These results provide an explanation for the variations observed in cheese ripening.It was concluded that chicken pepsin would not prove a suitable rennet substitute for making Cheddar cheese because of the quality of the cheese produced, and that bovine pepsin would not prove suitable because of the cost of preparing a suitable extract. Swine pepsin would appear to be suitable if the ripening time were to be lengthened or if another enzyme were to be added to assist ripening; it is cheaper than rennet and other rennet substitutes.

Effect of varying enzyme concentration on the action of rennin on whole milk

Abstract: The kinetics of the release of glycopeptides by the action of rennin on bovine whole milk have been studied. The initial rate of release of glycopeptides was proportional to the concentration of rennin. Using the integrated form of the Michaelis–Menten equation, values have been obtained for Km and V. These values varied between milk samples from individual cows, and for a single milk sample the value for Km increased with increasing rennin concentration. It is suggested that the Km value is partly dependent on the carbohydrate composition of individual κ-casein molecules.

Properties of aseptically packed ultra-high-temperature milk: II. Molecular weight changes of the casein components during storage

Abstract: Storage of aseptically packed ultra-high-temperature (UHT) milk has been shown to be accompanied by pronounced changes in the molecular weight distribution of the pH 4·6 insoluble casein. These changes were both time-dependent and temperature-dependent, proceeding much more rapidly at 37 °C than at 30 °C, but even at 4 °C the changes were considerable. The proportions of high molecular weight material present before and after storage have been studied by gel filtration in dissociating solvents using Sephadex G-200. Measurements have also been made on casein material isolated from in-bottle sterilized milks and canned evaporated milk for comparison. The results of gel filtration have been compared with sedimentation coefficients recorded by ultracentrifugation and with changes in the content of amino groups titratable with trinitrobenzene-sulphonic acid. The results are compatible with the suggestion that the Maillard reaction occurred at ambient temperatures, and over a period of several months led to browning and sediment formation due to covalent cross-linking of polypeptide chains. The implications of this are discussed with reference to spoilage of UHT milk on storage and the phenomenon of gelation.

Metabolism of (U- 14 C)-L-threonine and (U- 14 C)-L-phenylalanine by the isolated perfused udder.

Abstract: A lactating mammary gland of a goat was perfused for 9 h in the presence of [U-14C]-l-threonine and received adequate quantities of glucose, acetate and amino acids. Two lactating sheep udders were likewise perfused in the presence of [U-14C]-l-phenylalanine: the plasma levels of phenylalanine in the first of these experiments were 4 times higher than in the second.In the [14C]threonine experiment, 4 % of the casein and 0·4 % of the expired CO2 were derived from threonine; 85 % of the threonine and 1·6 % of the glycine residues in casein originated from plasma threonine. Small 14C levels were found in glutamic acid, aspartic acid and serine of casein. The relative specific activities amongst the casein amino acids and the appearance of appreciable labelling in plasma glycine are consistent with the view that threonine is split by threonine aldolase.In the [14C]phenylalanine experiments virtually no radioactivity was detected in CO2, lactose or citric acid, indicating that this substrate is not broken down by mammary tissue. In the second experiment, 96 % of the phenylalanine and 0·3 % of the tyrosine of casein originated from plasma phenylalanine. In the first experiment, a 30-fold higher 14C incorporation into casein tyrosine relative to phenylalanine was observed. The possible significance of the phenylalanine concentration in the plasma on the degree of conversion of phenylalanine into tyrosine within the mammary gland is discussed.

The alkali-induced elimination of phosphate from β-casein

Abstract: The dephosphorylation of β-casein, type A 1 , by dilute aqueous solutions of sodium hydroxide has been studied. It has been found that the mechanism whereby inorganic phosphate is liberated by the action of alkali is one of β-elimination from O -phosphoserine residues which are themselves converted initially to dehydroalanyl residues.

The susceptibility of milked and unmilked udder quarters to intra-mammary infection

Abstract: The teats of quarters which were milked, and those in which milking had ceased, of 16 cows were exposed to bacteria twice daily for 2 weeks by dipping them in a suspension of streptococci and staphylococci. Of 32 quarters in which milking had ceased 22 became infected in this period. Eighteen infections were with Streptococcus dysgalactiae , 2 with Streptococcus uberis , 1 with Staphylococcus aureus and 2 with organisms not used in the culture. Only 3 of 32 milked quarters became infected in the experimental period: 2 infections were with Str. aureus and 1 with an organism not used in the culture. Animals differed in their susceptibility to infection. Quarters which had been unmilked for 2 weeks were as susceptible to new infectionas those in which milking had just ceased. In this experiment, factors such as intramammary pressure, leakage of milk, concentration of bacterial inhibitors, composition of secretion and cell counts of the secretion did not appear to influence the rate of infection. Yield at drying-off, milking rates and teat patency were not related to the differences in susceptibility between animals. It is suggested that the main reason for the lower new infection rate in the milked quarters is that pathogens entering the streak canal or teat sinus are usually flushed out with the secretion during milking and do not cause infection.

Variations in the concentrations of free amino acids in the plasma of the dairy cow at parturition.

Abstract: The plasma levels of individual amino acids were studied in 6 dairy cows from 4 days before to 3 days after calving. During this sampling period, the concentrations of 13 amino acids showed significant changes. The levels of several amino acids were depressed markedly in the sample collected immediately before calving. Following parturition, the concentration of most amino acids gradually returned to values obtained 3 days before calving. The glutamine and alanine contents of the plasma rose to a peak value 1 day after calving and subsequently decreased. The mean concentrations of glycine and α-aminobutyric acid did not change before parturition but rose significantly thereafter. These observations are discussed in terms of amino-acid utilization for milk protein synthesis and gluconeogenesis at the onset of lactation. The changes in plasma amino acid levels appear to be synchronized with those reported for prolactin and progesterone in the 24 h before parturition. This may indicate an important influence of both hormones on the lactogenic process in the cow. The highly significant correlations obtained between the concentrations of 14 individual amino acids are discussed.

Nature of ceramide in bovine milk.

Abstract: Ceramide, an N-acyl derivative of sphingosine bases, has been isolated for the first time from bovine milk in the free form and its constitution studied. Sixteen component fatty acids were found, among which C23:0 (38·1%), C24:0 (29·5%), C22:0 (17·9%) and C16:0 (7·2%) were predominant. Seven component long-chain bases were detected. The principal bases were C18-sphingosine (35·0%) and C16-sphingosine (31·6%).

Seasonal variations in the total nitrogen, non-protein nitrogen and urea nitrogen contents of Friesian and Jersey milk.

Abstract: A large number of samples (433) from the milk of Friesian herds was taken during the period November 1968 – September 1969, and a smaller number (159) from Jersey herds during the dairy ‘season’ September 1969 – April 1970, and analysed for total nitrogen (TN) and for non-protein nitrogen (NPN). The Friesian milk sample varied in TN from 0·456 to 0·624% (average 0·531 ± 0·021%) and in NPN from 0·024 to 0·054% (average 0·035 ± 0·004%). The Jersey samples varied in TN from 0·467 to 0·718% (average 0·584 ± 0·036%) and in NPN from 0·022 to 0·051% (average 0·033 ± 0·006%).The average NPN value for all the milks was 0·034 ± 0·005%.There was a seasonal trend in NPN and TN for the Jersey and in TN but not in NPN for the Friesian milks. The proportion of NPN as a percentage of TN varied widely – for the Friesian samples from 4·9 to 10·2% (average 6·46%) and for the Jersey samples from 3·7 to 8·7% (average 5·74%).Urea N also was estimated in 125 of the Friesian and in all the Jersey milk samples. It varied from 0·012 to 0·029% (average 0·020 ± 0·004%) in the Friesian and from 0·009 to 0·031% (average 0·020 ± 0·004%) in the Jersey samples. For all the milks the urea N as a percentage of NPN varied from 33 to 79 (average 56·5%).It is suggested that values for ‘protein content’ of milk should refer only to ‘true’ protein ((TN – NPN) × 6·38) and that in the absence of an analytical result for NPN the use of an average value such as that above would be justified.

On the mechanism of milk clotting by rennin

Abstract: Two possible hypotheses for the mechanism of milk clotting were tested. The results obtained constituted strong evidence against one and suggested that the second is improbable. Milk was separated into a 5-fold-concentrated casein micelle suspension and milk serum. Pre-renneting of the serum did not reduce the rate of clotting on subsequent addition to the micelle suspension whether or not the conditions were such that the para-κ-casein became extensively aggregated. Washing of casein micelles up to 3 times with milk dialysate at 23°C extracted very little casein from the micelles and did not increase the clotting time of micelles resuspended to about the same concentration as in milk. The results appear to constitute decisive evidence against the hypothesis of milk clotting proposed by Parry & Carroll (1969). S-carboxymethyl-κ-casein, S-carboxymethyl-κ-casein containing 2·5 dimethylaminonaphthalene sulphonyl residues per mole, and rennin-treated dimethylaminonaphthalene sulphonated-S-carboxymethyl-κ-casein all bound Ca to the same extent at 30°C and pH 6·5, over the range 0·5–15·3 mM-CaCl 2 . This adds support to existing evidence that milk clotting does not involve formation of Ca bridges between casein micelles.

Changes in proteins of Domiati cheese during pickling

Abstract: Domiati cheese from homogenized and unhomogenized pasteurized milk was pickled for 4 months at room temperature. During pickling, the soluble tyrosine and tryptophan contents of the cheese gradually increased, indicating progressive proteolysis.Gel filtration of cheese extract on Sephadex G-25 revealed the presence of nitrogenous substances of various molecular weights. The maximum formation of amino acids and related substances was observed after 15 days storage.The changes in the electrophoretic patterns of proteins in the cheese during pickling indicated that both αs - and β-caseins were attacked. β-Casein, however, was much less affected.Homogenization was found to affect the formation of soluble nitrogenous substances, but was without effect on the electrophoretic pattern of the protein in the cheese.

Flavour defects in edible casein and skim-milk powder: I. The role of Maillard browning

Abstract: Two chemical tests were used to measure the extent of lactose degradation by Maillard browning in casein and skim-milk powder during storage. At the same time these products were evaluated organoleptically. Highly significant correlations between age, flavour score and level of browning in skim-milk powder were in contrast to the lack of any relationship between the flavour score or age of casein and its level of browning. Maillard browning occurring during storage of skim-milk powder was accompanied by increasing levels of cereal and malty flavours. A stale flavour, which closely resembled the musty flavour common to casein, was not observed in skim-milk powder until after storage for 9 months. A distinct difference in the flavour stability of rennet casein and acid casein could not be accounted for in terms of the relative extent of lactose degradation. Evaluation of casein samples with different lactose contents suggested that Maillard browning does not contribute to flavour defects during storage unless the curd is so insufficiently washed during manufacture as to produce an abnormally high level of lactose in the dried product.