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 milk: influence of dilution and dialysis against water

1978 ◽  
Vol 45 (2) ◽  
pp. 149-157 ◽  
Author(s):  
Patrick F. Fox ◽  
Catherine M. Hearn
Keyword(s):  
High Temperatures ◽  
Type A ◽  
Heat Stability ◽  
Type B ◽  
Normal Type ◽  
Coagulation Time ◽  
Micelle Structure ◽  
Ph Curve

SummaryThe marked precipitation of Ca phosphate found to occur at ~ pH 6·8 when milk is heated to high temperatures may account for the minimum in the heat coagulation time (HCT)–pH curve at ~ pH 6·8. Dialysis of milk against water for about 3 h converted a normal type A milk to one with type B heat stability characteristics by reducing stability in the region of the HCT maximum while increasing stability in the region of the minimum. Reduction of the concentration of urea, lactose, Na or chloride did not cause these changes and gross micelle structure appeared to be intact following short dialysis as indicated by turbidity and sedimentability. Dilution of milk with water increased stability at the minimum without significantly affecting stability at the maximum. Pre-heating at 80°C for 10 min precluded the effect of dilution but not of dialysis.

Heat stability of milk: influence of κ-casein hydrolysis

1978 ◽  
Vol 45 (2) ◽  
pp. 173-181 ◽  
Author(s):  
Patrick F. Fox ◽  
Catherine M. Hearn
Keyword(s):  
Heat Stability ◽  
Principal Factor ◽  
Coagulation Time ◽  
Casein Micelles ◽  
Ph Profile ◽  
Acetylneuraminic Acid ◽  
Ph Values ◽  
Colloidal Calcium Phosphate ◽  
Maximum Stability ◽  
Ph Range

SummaryThe release of 12% (w/v) TCA-soluble N-acetylneuraminic acid from casein at 5 temperatures between 110 and 150°C was determined and showed a Q10 °C about 3; coagulation occurred when about 20% of the κ-casein was hydrolysed. Renneting of milk or colloidal calcium phosphate-free milk rendered the caseinate very heat-labile at its normal pH when more than about 20% of the κ-casein had been hydrolysed. Heat stability at the pH of maximum stability was not significantly decreased until after very prolonged renneting, but stability at pH values alkaline to the minimum was very sensitive to such hydrolysis suggesting that κ-casein is the principal factor responsible for heat stability in that region. Systems which do not have a maximum or minimum in the heat coagulation time–pH profile, i.e. serum protein-free casein micelles in milk diffusate, or milk which had been dialysed against water, were destabilized by renneting throughout the pH range 6·4–7·4.

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.

Heat stability of milk: interrelationship between assay temperature, pH and agitation

1981 ◽  
Vol 48 (1) ◽  
pp. 123-129 ◽  
Author(s):  
Douglas B. Hyslop ◽  
Patrick F. Fox
Keyword(s):  
Heat Stability ◽  
Kcal Mole ◽  
Temperature Dependent ◽  
Total Solids ◽  
Ph Values ◽  
Assay Procedure ◽  
Concentrated Milk ◽  
The Stability ◽  
Ph Curve ◽  
Maximum Minimum

SummaryAs determined by the standard subjective assay procedure, the minimum in the heat stability–pH curve of milk persisted down to at least 116 °C. However when samples were not agitated during heating the minimum became progressively less pronounced as the assay temperature was lowered and it disappeared at approximately 116 °C. Activation energies (Ea) for unagitated samples were approximately 30 Kcal/mole at pH 6·87 (maximum) and at pH 7·18, throughout the temperature range 116–145 °C and for the pH 6·95 (minimum) sample at 116–125 °C; however Eα for the pH 6.95 sample increased to approximately 100 Kcal/mole in the range 127–135 °C suggesting that some highly temperature-dependent reaction had occurred and caused premature coagulation at certain pH values, i.e. to a heat stability minimum. The stability of concentrated milk (20% total solids) was very low at pH values above 6·9, regardless of whether the samples were agitated or not during heating and the maximum/minimum in the heat stability–pH curve persisted down to at least 90 °C in both agitated and quiescent samples.

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.

Reactions of β-Sulphato-ethylsulphone Crosslinking Agent with Wool

1992 ◽  
Vol 62 (6) ◽  
pp. 309-316 ◽  
Author(s):  
B. M. Smith ◽  
P. L. Spedding ◽  
M. S. Otterburn ◽  
D. M. Lewis
Keyword(s):  
Hplc Analysis ◽  
Crosslinking Agent ◽  
Cross Linking ◽  
Chemical Crosslinking ◽  
The Novel ◽  
Burst Strength ◽  
Ph Values ◽  
Wool Fibers ◽  
Ph Range ◽  
Original Strength

In Part I of our study of the application to wool of the novel chemical crosslinking agent, 2-chloro-4,6-di(-aminobenzene-4-β-sulphato-ethylsulphone)-1,3,5-triazine (XLC), HPLC analysis showed the compound to have good substantivity for wool fibers when applied from boiling aqueous dyebaths in the pH range 3 to 6. In Part II, various solubility and swelling tests have been used to determine whether XLC introduces additional crosslinks into the fiber. The extent of crosslinking depends on the application pH: there is little crosslinking at pH values up to 4, but extensive cross-linking occurs when the compound is applied at pH 5 and 6. Studies on the wet burst strength of XLC treated fabrics indicate that the compound can limit the damage caused to wool by boiling aqueous treatments. For fabrics treated with XLC at pH 6, the compound preserves the original strength of the fabric. Although these results indicate that XLC treatment of wool introduces crosslinks into wool fibers, the mechanism and morphological sites of reaction with wool require further study.

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.

Influence of 2-mercaptoethanol on heat stability of concentrated whey-protein-free milk and formation of soluble casein

1984 ◽  
Vol 51 (3) ◽  
pp. 439-445 ◽  
Author(s):  
Takayoshi Aoki ◽  
Yoshitaka Kako
Keyword(s):  
Whey Protein ◽  
Heat Stability ◽  
Coagulation Time ◽  
Casein Micelles ◽  
Ph Profile ◽  
Very High

SummaryThe heat coagulation time (HCT) of concentrated whey-protein-free (WPF) milk measured at 120 and 130 °C was reduced to by addition of 5–20 mM-2-mercaptoethanol (ME). However, although the amount of soluble casein formed on heating was doubled by addition of ME, the shape of the HCT–pH profile was affected only slightly. The proportion of κ-casein in the soluble casein from heated concentrated WPF milk containing ME was very high, though it was somewhat lower than that of the soluble casein from heated concentrated WPF milk containing no ME. No solubilization of colloidal Ca phosphate was observed in either unheated or heated concentrated WPF milk on addition of ME. These facts suggest that ME probably promotes the formation of soluble casein with release of κ-casein from micelles on heating, thus destabilizing the casein micelles.

Effects of added salts on the heat stability of recombined concentrated milk

1990 ◽  
Vol 57 (2) ◽  
pp. 213-226 ◽  
Author(s):  
Mary-Ann Augustin ◽  
Phillip T. Clarke
Keyword(s):  
Skim Milk ◽  
Heat Stability ◽  
Ph Control ◽  
Ph Profile ◽  
Heat Stable ◽  
Low Levels ◽  
Concentrated Milk ◽  
Milk Solids ◽  
Ph Curve

SummaryChanges in heat stability and Ca2+ activity of recombined concentrated milk (18% solids non-fat:8% fat) induced by the additions of 0·011–0·217 mol phosphate/kg skim milk solids (SMS), 0·022–0·217 mol citrate/kg SMS, 0·011–0·022 mol Ca/kg SMS and 0·016–0·067 mol EDTA/kg SMS were evaluated. Heat stability was assessed using an objective method which involved determination of viscosity after heating under controlled conditions. Low levels of added phosphate and citrate generally effected an acid shift of the viscosity–pH profile, while higher levels caused a broadening of the profile. Addition of CaCl2 at a level of 0·011 mol/kg SMS resulted in a narrowing of the viscosity–pH curve; additions of higher levels resulted in a non-heat stable recombined milk concentrate. EDTA also caused a narrowing of the viscosity–pH curve. The results highlight the importance of pH control for effective stabilization of recombined milk concentrates by additions of phosphate and citrate.

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