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.

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.

Heat stability of milk: influence of modifying sulphydryl-disulphide interactions on the heat coagulation time–pH profile

1987 ◽  
Vol 54 (3) ◽  
pp. 347-359 ◽  
Author(s):  
Harjinder Singh ◽  
Patrick F. Fox
Keyword(s):  
Heat Stability ◽  
Casein Micelle ◽  
Coagulation Time ◽  
Casein Micelles ◽  
Ph Profile ◽  
Ph Values ◽  
Stabilizing Effect ◽  
Ph Range ◽  
Β Lactoglobulin ◽  
Minimum Ratio

SummaryAddition of reducing agents such as 2-mercaptoethanol (2-ME), dithio-threitol and Na sulphite to milk markedly reduced its heat stability at pH values below 7·1. 2-ME reversibly destabilized milk or serum protein-free casein micelle dispersions and promoted the release of κ-casein-rich protein from the micelles. Reduction of either casein micelles or β-lactoglobulin (β-lg) with 2-ME and subsequent blocking of the newly formed –SH groups with N-ethylmaleimide irreversibly reduced the maximum to minimum ratio in the heat stability profile. 2-ME disrupted κ-casein/β-lg complexes and stripped κ-casein from the micelles on heating. The milk or caseinate systems were thus destabilized. Addition of KBrO4 or iodosobenzoate to milk at 5 HIM eliminated the minimum but destabilized milk in the region of the maximum. However, KIO3 at 5 mm had a strong stabilizing effect throughout the pH range 6·5–7·3.

Heat stability of milk: pH-dependent dissociation of micellar κ-casein on heating milk at ultra high temperatures

1985 ◽  
Vol 52 (4) ◽  
pp. 529-538 ◽  
Author(s):  
Harjinder Singh ◽  
Partick F. Fox
Keyword(s):  
Whey Protein ◽  
Whey Proteins ◽  
Heat Stability ◽  
Casein Micelle ◽  
Casein Micelles ◽  
Ph Profile ◽  
Ph Values ◽  
Maximum Stability ◽  
Β Lactoglobulin ◽  
Maximum Minimum

SUMMARYPreheating milk at 140 °C for 1 min at pH 6·6, 6·8, 7·0 or 7·2 shifted the heat coagulation time (HCT)/pH profile to acidic values without significantly affecting the maximum stability. Whey proteins (both β-lactoglobulin and α-lactalbumin) co-sedimented with the casein micelles after heating milk at pH < 6·9 and the whey protein-coated micelles, dispersed in milk ultrafiltrate, showed characteristic maxima–minima in their HCT/pH profile. Heating milk at higher pH values (> 6·9) resulted in the dissociation of whey proteins and κ-casein-rich protein from the micelles and the residual micelles were unstable, without a maximum–minimum in the HCT/pH profile. Preformed whey protein–casein micelle complexes formed by preheating (140 °C for 1 min) milk at pH 6·7 dissociated from the micelles on reheating (140 °C for 1 min) at pH > 6·9. The dissociation of micellar-κ-casein, perhaps complexed with whey proteins, may reduce the micellar zeta potential at pH ≃ 6·9 sufficiently to cause a minimum in the HCT/pH profile of milk.

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.

Heat stability of milk: influence of colloidal calcium phosphate and β-lactoglobulin

1975 ◽  
Vol 42 (3) ◽  
pp. 427-435 ◽  
Author(s):  
P. F. Fox ◽  
M. C. T. Hoynes
Keyword(s):  
Calcium Phosphate ◽  
Fold Increase ◽  
Heat Stability ◽  
Protein Charge ◽  
Ph Values ◽  
Colloidal Calcium Phosphate ◽  
Maximum Stability ◽  
Ph Range ◽  
Ph Curve ◽  
Β Lactoglobulin

SummaryReduction of the level of colloidal calcium phosphate (CCP) progressively increased the heat stability of milk at pH values <~7·0 and increased the pH of maximum stability. Removal of 40% CCP also stabilized the system at the pH of minimum stability, but removal of ≥60% CCP rendered milk very unstable at pH values >7·2, an effect not offset by a 4-fold increase in κ-casein concentration. Doubling CCP had a slight destabilizing effect in the pH range 6·5–7·5.Addition of β-lactoglobulin to serum protein-free casein micelles had a marked destabilizing effect at pH values > ~6·8, but increased stability in the pH range 6·4–6·8. β-Lactoglobulin had a similar and more apparent effect on the heat stability of Na caseinate dissolved in milk diffusate.It is suggested that rather than being a stabilizing factor responsible for the maximum in the heat stability-pH curve, the true effect of β-lactoglobulin is to shift the curve to more acid pH values (reason unknown) and to sensitize the caseinate system to heat-induced Ca phosphate precipitation at pH values > ~7·0. Low stability at ~pH 7·0 introduces an apparent maximum in the heat stability-pH curve at ~pH 6·8, but this has no independent existence. At pH values >7·2, increased protein charge more than off-sets the influence of heat-precipitated CCP and stability again increases in micellar but not in soluble casein systems.

The heat stability of milk as affected by variations in pH and milk salts

1969 ◽  
Vol 36 (3) ◽  
pp. 343-351 ◽  
Author(s):  
P. A. Morrissey
Keyword(s):  
Calcium Phosphate ◽  
Calcium Ion ◽  
Narrow Range ◽  
Heat Stability ◽  
Salt Composition ◽  
Ion Concentrations ◽  
Ph Values ◽  
Soluble Calcium ◽  
Β Lactoglobulin ◽  
Minimum Heat

SummaryThe maximum and minimum heat stability exhibited by most milks over a relatively narrow range of pH values is shown also by synthetic colloidal calcium caseinate-calcium phosphate systems and even by simple caseinate systems, provided all possess adequate contents of β-lactoglobulin, soluble calcium and phosphate. The phenomenon is not, however, dependent on the presence of the characteristic micellar structure of the casein of milk. The minimum stability observed, usually around pH 6·9, is the most characteristic feature of the phenomenon and arises from heat induced deposition of calcium phosphate on a caseinate/β-lactoglobulin complex. This reaction, which tends to occur to a marked degree at relatively high pH values and calcium ion concentrations, sensitizes the complex to precipitation by calcium ions. The precise pH values at which the maximum and minimum stabilities occur can vary depending on the salt composition of the serum, since the latter can influence the solubility of calcium phosphate.

Heat stability of milk: the mechanism of stabilization by formaldehyde

1985 ◽  
Vol 52 (1) ◽  
pp. 65-76 ◽  
Author(s):  
Harjinder Singh ◽  
Patrick F. Fox
Keyword(s):  
High Temperatures ◽  
Crosslinking Agent ◽  
Heat Stability ◽  
Cross Linking ◽  
Amino Groups ◽  
Coagulation Time ◽  
Ph Profile ◽  
Ph Values ◽  
Dimethyl Suberimidate ◽  
Ph Curve

SUMMARYThe increase produced by formaldehyde (HCHO) in the heat stability of milk did not occur when milk was treated with HCHO at temperatures up to 60°C followed by dialysis at 5°C. However, the minimum in the heat coagulation time (HCT)–pH curve was irreversibly removed if the milk was preheated at 80–C for 10 min in the presence of 5 mM-HCHO. Although this treatment blocked the ε-amino groups of lysyl residues, the stabilizing mechanism is considered to be due to the cross linking action of HCHO which reduced the level of non-sedimentable, κ-casein-rich protein dissociated from the micelles on heating. The specific crosslinking agent, dimethyl suberimidate, modified the HCT-pH profile of milk in a manner similar to preheating at 80°C for 10 min with 5 mM-HCHO, supporting the crosslinking hypothesis. The results of this study appear to lend some support to the proposal of Kudo (1980) that the minimum in the HCT-pH curve of milk is due to the dissociation of κ-casein from the micelles on heating at high temperatures at pH values greater than 6η7.

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.

scholarly journals Improved heat stability of recombined filled evaporated milk emulsions by wet heat pre-treatment of skim milk powder dispersions at different pH values

LWT ◽  
2021 ◽  
pp. 112739
Author(s):  
Jianfeng Wu ◽  
Simin Chen ◽  
Lydivine Nyiransabimana ◽  
Els J.M. Van Damme ◽  
Bruno De Meulenaer ◽  
...  
Keyword(s):  
Milk Powder ◽  
Skim Milk ◽  
Heat Stability ◽  
Skim Milk Powder ◽  
Ph Values ◽  
Wet Heat ◽  
Pre Treatment

The effect of concentration on the heat stability of skim-milk

1978 ◽  
Vol 45 (1) ◽  
pp. 37-45 ◽  
Author(s):  
D. D. Muir ◽  
A. W. M. Sweetsur
Keyword(s):  
Opposite Effect ◽  
Skim Milk ◽  
Heat Stability ◽  
Progressive Change ◽  
Ph Profile ◽  
Total N ◽  
Heated Milk ◽  
Depletion Curve ◽  
Concentrated Milk ◽  
Β Lactoglobulin

SummaryA progressive change takes place in the heat stability of skim-milk during concentration. At the maximum in the coagulation time (CT)–pH profile of milk concentrated to over 20% of total solids (TS) the total N depletion curve changed from single- to 2-stage and CT became insensitive to the addition of urea. Furthermore, addition of β-lactoglobulin to skim-milk concentrates destabilized the heated milk whilst the opposite effect was observed in the presence of sulphydryl-group blocking agents. As a result of these observations, it has been suggested that the mechanism of coagulation in concentrated milk is similar to that which occurs within the minimum of the CT–pH profile of skim-milk at normal levels of TS.

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