Effect of urea on the heat coagulation of the caseinate complex in skim-milk

1977 ◽  
Vol 44 (2) ◽  
pp. 249-257 ◽  
Author(s):  
D. D. Muir ◽  
A. W. M. Sweetsur
Keyword(s):  
Activation Energy ◽  
Skim Milk ◽  
Heat Stability ◽  
Coagulation Time ◽  
Temperature Range ◽  
The Stability

SummaryAdditions of urea progressively increased the heat stability of milk outside of its coagulation time (CT)–pH minimum. In the region of the CT–pH minimum larger amounts of urea were required before an increase in heat stability occurred. The effect of urea was observed over the temperature range 125–140 °Cfornaturalmilk, milk which had been dialysed against synthetic sera, and milk to which a sulphydrylblocking agent had been added. Urea additions did not affect the activation energy of the heat coagulation reaction or the stability of milk to rennet or ethanol.

Stability of buffalo casein micelles

1979 ◽  
Vol 46 (2) ◽  
pp. 401-405 ◽  
Author(s):  
Nripendra C. Ganguli
Keyword(s):  
Sialic Acid ◽  
Gel Filtration ◽  
Skim Milk ◽  
Heat Stability ◽  
Casein Micelles ◽  
Heat Stable ◽  
Micellar Casein ◽  
Acid Release ◽  
The Stability ◽  
Better Than

SUMMARYBuffalo skim-milk is less heat stable than cow skim-milk. Interchanging ultracentrifugal whey (UCW) and milk diffusate with micellar casein caused significant changes in the heat stability of buffalo casein micelles (BCM) and cow casein micelles (CCM). Buffalo UCW dramatically destabilized COM, whereas buffalo diffu-sate with CCM exhibited the highest heat stability.Cow κ-casein stabilizes αs-casein against precipitation by Ca better than buffalo º-casein. About 90% of αs-casein could be stabilized by κ: αs ratios of 0·20 and 0·231 for cow and buffalo, respectively.Sialic acid release from micellar κ-casein by rennet was higher than from acid κ-casein in both buffalo and cow caseins, the release being slower in buffalo. The released macropeptide from buffalo κ-casein was smaller than that from cow κ-casein as revealed by Sephadex gel filtration.Sub-units of BCM have less sialic acid (1·57mg/g) than whole micelles (2·70mg/g). On rennet action, 47% of bound sialic acid was released from sub-units as against 85% from whole micelles. The sub-micelles are less heat stable than whole micelles. Among ions tested, added Ca reduced heat stability more dramatically in whole micelles, whereas added phosphate improved the stability of micelles and, more strikingly, of sub-micelles. Citrate also improved the heat stability of sub-micelles but not of whole micelles.

Heat stability of milk

1980 ◽  
Vol 47 (2) ◽  
pp. 199-210 ◽  
Author(s):  
Donald F. Darling
Keyword(s):  
Temperature Dependence ◽  
Elevated Temperatures ◽  
Skim Milk ◽  
Heat Stability ◽  
Coagulation Time ◽  
Ph Values ◽  
Protein Polymerization ◽  
Casein Protein ◽  
Apparent Activation Energies ◽  
Β Lactoglobulin

SummaryThe heat stability of a standard reconstituted skim-milk preparation has been investigated as a function of pH, temperature of coagulation, and forewarming treatment. Apparent activation energies have been calculated from the temperature dependence of coagulation time, and a constant value of 144 kJ/mole has been found for milks between pH 6·6 and 6·9. The effect of forewarming resulted in a decrease in stability at the most acid pH values, a slight increase at higher pH but below the pH maximum, and a decrease in the region of the pH minimum. A working hypothesis is proposed for the mechanisms leading to the coagulation of milk at elevated temperatures, based upon Ca induced precipitation of casein, protein polymerization, β-lactoglobulin: κ-casein interaction, and precipitation of insoluble Ca phosphates.

The stability of milk protein to heat: II. Effect on heat stability of ageing milk at different temperatures

1966 ◽  
Vol 33 (1) ◽  
pp. 83-91 ◽  
Author(s):  
D. T. Davies ◽  
J. C. D. White
Keyword(s):  
Milk Protein ◽  
Heat Stability ◽  
Subclinical Mastitis ◽  
Progressive Increase ◽  
Common Occurrence ◽  
Coagulation Time ◽  
Rate Of Increase ◽  
Different Temperatures ◽  
Significant Change ◽  
The Stability

SummaryThe effect on heat stability as measured by coagulation time, of storing separated milk at 20, 4 and −20 °C has been examined. Milk with a good coagulation (initial clots large) could be stored for at least 30 h at 20 °C, 1 week at 4 °C and 1 month at −20 °C with no significant change in coagulation time. With milks giving a poor coagulation (initial clots small), a common occurrence during storage at 20 °C was a marked progressive increase in coagulation time; the rate of increase was reduced by storage at 4 °C. The increase in coagulation time of these labile milks, which are usually obtained from cows with subclinical mastitis, may occur to the same extent in darkness as in light, may be enhanced by exposure to light or may occur only when the milk is exposed to light. From these results, together with others reported by Davies & White (1966) and White & Davies (1966) it is concluded that, in studying heat stability, milks giving a good coagulation should be regarded as in a different class from milks giving a poor coagulation.

Heat stability of recombined milk: influence of lecithins on the heat coagulation time-pH profile

1992 ◽  
Vol 59 (2) ◽  
pp. 177-185 ◽  
Author(s):  
Catharina H. McCrae ◽  
D. Donald Muir
Keyword(s):  
Milk Powder ◽  
Skim Milk ◽  
Heat Stability ◽  
Skim Milk Powder ◽  
Coagulation Time ◽  
Ph Profile ◽  
Mineral Equilibria ◽  
Soya Lecithin ◽  
Before And After ◽  
Wide Ph Range

SummaryTwo types of lecithin, namely egg and soya lecithin, were investigated as potential stabilizers of recombined milk. They were incorporated into recombined milk both before and after homogenization (20·7 MPa; 60 °C). Their presence at homogenization changed neither mineral equilibria nor homogenization efficiency. However, heat stability varied significantly irrespective of batch of low-heat skim milk powder used in recombined milk. The variation in heat stability depended on type of lecithin. Soya lecithin proved to be a very effective stabilizer. It improved heat stability over a wide pH range (6·3–7·1) and the effect occurred even when the lecithin was added after homogenization. In contrast, egg lecithin destabilized the system to heat at pH < 6·7 by converting a Type A into a Type B heat coagulation time-pH profile if it was incorporated before homogenization; after homogenization it had no effect. The effects of both egg and soya lecithin on the heat stability of recombined milk strongly suggest that interactions occur between phospholipids and milk protein.

715. The relation between the chemical composition of milk and the stability of the caseinate complex: IV. Coagulation by heat

1958 ◽  
Vol 25 (2) ◽  
pp. 281-296 ◽  
Author(s):  
J. C. D. White ◽  
D. T. Davies
Keyword(s):  
Calcium Phosphate ◽  
Milk Protein ◽  
Heat Stability ◽  
Milk Composition ◽  
Ionized Calcium ◽  
Coagulation Time ◽  
Complex Iv ◽  
Stage Of Lactation ◽  
The Stability ◽  
The Relationship

1. The variation in the stability of milk protein to heat and the relationship between milk composition and heat stability were examined.2. The coagulation times of the majority of the milk samples decreased by a factor of about 3 with an increase in temperature of 10°C. over the range 130–150°C. Because of the general proportionality of the coagulation times at 130, 140 and 150°C., the coagulation time at 130°C. only were used as a measure of the stability of the samples to heat.3. The coagulation times of herd bulk milks ranged from 17·2 to 59·0 min. at 130°C., whereas the range for samples from individual cows was 0·6–86·2 min.4. Samples of colostrum were very unstable to heat, and milk from cows in late lactation tended to have the longest coagulation times, but otherwise there was little relation between the heat stability of milk and the stage of lactation of the cow.5. Although colostrum samples were comparatively rich in ionized calcium, their marked instability to heat appeared to be caused solely by their high content of lactalbumin plus lactoglobulin.6. The stability to heat of the calcium caseinate-calcium phosphate complex in all samples, other than colostrum, could not be closely related either to the concentration and composition of the complex or to the composition and salt-balance of the aqueous phase.7. When the calcium phosphate content of the caseinate complex was relatively low, the heat stability of the complex tended to be inversely related to the concentration of ionized calcium in the milk, but in general coagulation time was not related to the concentration of ionized calcium.

Production, composition, and manufacturing properties of milk from grazing cows fed on a formaldehyde-treated sunflower seed supplement

1976 ◽  
Vol 27 (6) ◽  
pp. 917 ◽  
Author(s):  
BD Bartsch ◽  
NJS Ellis ◽  
DM McLean ◽  
JC Radcliffe
Keyword(s):  
Milk Fat ◽  
Sunflower Seed ◽  
Energy Content ◽  
Plasma Cholesterol ◽  
Milk Powder ◽  
Skim Milk ◽  
Heat Stability ◽  
Skim Milk Powder ◽  
Powder Manufacture ◽  
The Stability

Eight cows in each of four treatment groups grazed regulated areas of green oats and consumed either 0, 1.3, 2.5 or 3.1 kg of a formaldehyde-treated sunflower seed supplement (FSS) per head per day. The digestible energy content of the rations was balanced with hammer-milled barley. Milk fat percentages and milk fat yields were higher from cows fed on FSS, responses being in proportion to the amount of FSS eaten. Protein percentages were significantly lower in milk from cows fed on FSS. Milk and protein yields did not differ significantly between treatments. The linoleic acid (C18:2) content of milk fat was three to five times as high in cows fed on FSS as in those not fed on FSS. The stability to oxidation and the rennet curd firmness of the milk decreased as the percentage of C18:2 in milk fat increased. Changes in the heat stability of milk were associated with the introduction of FSS feeding. Plasma cholesterol levels increased with increasing intakes of FSS. Milk of high C18:2 content can be produced by dairy cows fed on FSS and grazed on green oats. The milk readily oxidizes and its properties for cheese and skim milk powder manufacture are altered.

Effects of milk protein genetic variants and composition on heat stability of milk

1987 ◽  
Vol 54 (2) ◽  
pp. 219-235 ◽  
Author(s):  
Douglas M. McLean ◽  
E. R. Bruce Graham ◽  
Raul W. Ponzoni ◽  
Hugh A. Mckenzie
Keyword(s):  
Genetic Variants ◽  
Skim Milk ◽  
Heat Stability ◽  
Coagulation Time ◽  
Maximum Heat ◽  
Milk Samples ◽  
Stage Of Lactation ◽  
Ph Curve ◽  
Jersey Cows ◽  
Β Lactoglobulin

SummarySkim milk samples from 126 Friesian and 147 Jersey cows in eight commercial herds were preheated at 85 °C for 30 min and concentrated to 200 g l−1 total solids. A heat coagulation time–pH curve was determined at 120 °C for each treated sample. Heat coagulation times ranged from 1 to 50 min at the non-adjusted pH and 1 to 60 min at the pH of maximum stability. The following statistically significant effects were found. Maximum heat stability was affected by genetic variants of κ-casein (B > AB > A; P < 0·001) and β-lactoglobulin (B, AB>A; P < 0·05) whereas natural heat stability was affected only by κ-casein genetic variants (B > AB > A; P < 0·001). Maximum and natural heat stability were corre-lated positively with β-casein and κ-casein concentrations and were negatively correlated with αs1-casein and β-lactoglobulin concentrations. Milk from Jersey cows had greater maximum and natural heat stability than milk from Friesian cows. Differences were found between herds within breed for natural heat stability, but not for maximum heat stability. Maximum heat stability declined with age of the cow. The heat stability of skim milk samples taken from 40 Jersey cows in one of the herds was determined at 140 °C. A considerable variation was found in the coagulation time–pH curves. There was a difference in natural heat stability between κ-casein variants (B > AB; P < 0°05). Natural and maximum heat stability were correlated positively with urea concentration. No relationship was found between the heat stability of preheated concentrated skim milk and the heat stability of the original skim milk. The pH of skim milk samples was associated with αs1-casein genetic variant, age of cow, stage of lactation and concentration of γ-casein.

The stability of milk protein to heat: I. Subjective measurement of heat stability of milk

1966 ◽  
Vol 33 (1) ◽  
pp. 67-81 ◽  
Author(s):  
D. T. Davies ◽  
J. C. D. White
Keyword(s):  
Milk Protein ◽  
Heating Temperature ◽  
Glass Tube ◽  
Heat Stability ◽  
Volume Effect ◽  
Sample Volume ◽  
Subjective Test ◽  
Coagulation Time ◽  
The Stability ◽  
Time Required

SummaryA subjective test for the determination of the stability of milk protein to heat is described. In the test, the time required for particles of coagulated protein to become visible throughout a 2·5-ml sample of separated milk maintained at 135°C in a glass tube rocking at 8 c/min is taken as a measure of stability. The precision of the test was such that single determinations were generally adequate.Coagulation time decreased by about 12% as rocking speed was increased over the range 4–12 c/min and increased by a factor of about 3 for a decrease in heating temperature of 10 degC over the range 140–105 °C; with some milks the Q10 °C value increased to 5–8 a temperature decreased. As sample volume was increased over the range 1–3 ml coagulation time increased, especially With milks whose coagulation was poor (initial clots small). This volume effect appeared to be a consequence of the accompanying decrease in the proportion of headspace oxygen to volume of milk.

The heat stability of milk and concentrated milk containing added aldehydes and sugars

1978 ◽  
Vol 45 (1) ◽  
pp. 47-52 ◽  
Author(s):  
C. Holt ◽  
D. D. Muir ◽  
A. W. M. Sweetsur
Keyword(s):  
Heat Treatment ◽  
Skim Milk ◽  
Type A ◽  
Heat Stability ◽  
Coagulation Time ◽  
Prolonged Heat ◽  
Concentrated Milk ◽  
Ph Range ◽  
Prolonged Heat Treatment

SummaryThe addition of simple aldehydes brought about large increases in the heat stability of both skim-milk and concentrated skim-milk over a comparatively wide milk–pH range. The coagulation time–pH minima of type A milks were completely removed by aldehyde treatment. Some sugars, which react readily as aldehydes on heating, were also shown to stabilize concentrated milk to prolonged heat treatment at 120 °C.

scholarly journals Milk protein-carbohudrate interactions in sterilised milk products

1990 ◽  
Author(s):  
Αθηνά Τζιμπουλά
Keyword(s):  
Milk Protein ◽  
Binding Capacity ◽  
Skim Milk ◽  
Milk Proteins ◽  
Heat Stability ◽  
Complete Recovery ◽  
Limited Information ◽  
Coagulation Time ◽  
Water Binding ◽  
Time Required

The present work deals with the nature of milk-protein carbohydrate interactions during the heat treatment of milk. Starches of different botanical origin were added (0.5-1.5% w/w) to milk (9% TS or 22% TS) and the mixtures were preheated at 70°C to ensure gelatinization of the starch granules. The heat stability of the milk-starch mixtures was defined as the time required for the coagulation of the milk proteins to occur on heating at 140°C (skim milk of 9% TS) or at 120°C (concentrated milk 22% TS), over the pH range, 6.5-7.1. On addition of native starches there was a reduction in the coagulation time of milk. The various starches hadsimilar effects on the coagulation time of milk, the destabilisation being proportional to the amount of starch added. The destabilisation of milk was not associated either with the amylose to amylopectin ratio of the starches sor to the granular structure of the starch. Further experiments probed the effects on heat stability of changing the molecular structure of starch in two ways: a) by the addition of acid modified starches and b) by the addition of cross-linked starches. Both types of treatment promoted a reduction in the water-binding capacity of the starch and both resulted in an improvement of the coagulation time of the milk-carbohydrate mixture. However,complete recovery of the heat stability was achieved only in the case of unconcentrated milk. Most of the research to date on milk proteincarbohydrate interactions has involved acidic polysaccharides, whereas there is limited information for non-ionic gums. Due to the importance of the heat stability of milk in the dairy industry it was useful to initiate this study by investigating the effect of various forms of carbohydrates on the stability of the milk proteins upon heating.

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