Inhibition of the Antibacterial Lactoperoxidase-Thiocyanate-Hydrogen Peroxide System by Heat-Treated Milk

1985 ◽  
Vol 48 (6) ◽  
pp. 494-498 ◽  
Author(s):  
B. EKSTRAND ◽  
W. M. A. MULLAN ◽  
A. WATERHOUSE
Keyword(s):  
Heat Treatment ◽  
Hydrogen Peroxide ◽  
Skim Milk ◽  
Inhibitory Effect ◽  
Sulfhydryl Groups ◽  
Inhibitory Factor ◽  
Casein Micelle ◽  
Heated Milk ◽  
Heat Treated

The antibacterial system, lactoperoxidase-H2O2-SCN− was affected by the presence of heated milk or skim milk reconstituted from powders having received severe heat treatment. This inhibitory effect was related to the increase in exposed sulfhydryl groups and to the redistribution of protein between micellar and whey phases. Chromatographic analyses of heat-treated milk showed that the inhibitory factor was associated with the casein micelle fraction. The inhibition, however, was overcome by addition of unheated skim milk.

scholarly journals pH-Dependent behaviour of soluble protein aggregates formed during heat-treatment of milk at pH 6·5 or 7·2

2006 ◽  
Vol 73 (1) ◽  
pp. 79-86 ◽  
Author(s):  
Marie Renan ◽  
Omar Mekmene ◽  
Marie-Hélène Famelart ◽  
Fanny Guyomarc'h ◽  
Véronique Arnoult-Delest ◽  
...  
Keyword(s):  
Soluble Protein ◽  
Ph Value ◽  
Skim Milk ◽  
Protein Aggregates ◽  
Heated Milk ◽  
Heat Treated ◽  
Exclusion Chromatography ◽  
Soluble Aggregates ◽  
Ph Dependent ◽  
Dependent Behaviour

The pH-dependent behaviour of soluble protein aggregates produced by the pre-heating of reconstituted skim milk at 90 °C for 10 min was studied, in order to understand the role of these aggregates in acid gelation of heated milk. The following milk samples were prepared: (1) control (unheated reconstituted milk, pH 6·5); (2) milk heat-treated at pH 6·5 (mHtd6·5) and (3) milk heat-treated at pH 7·2 (mHtd7·2). They were centrifuged and the supernatants (SPNT 1) pH-adjusted to yield a series of pH values ranging from 6·5 or 7·2 to 4·6 using HCl at 20 °C or GDL at 20 and 38 °C. pH-Adjusted SPNTs 1 were re-centrifuged. The resulting supernatants (SPNTs 2) were analysed by OD (at 600 and 280 nm) and SDS-PAGE in order to characterise proteins still soluble as a function of pH. Particle size in SPNTs 1 was analysed by Steric Exclusion Chromatography. The OD600 nm revealed that during acidification soluble casein in both control and heat-treated samples exhibits variations in its optical properties or size as previously shown with micellar casein. In heat-treated samples, soluble casein and heat-induced covalent soluble aggregates precipitate at the same pH value. A progressive acidification of the soluble phase did not separate them. Increasing the temperature of acidification from 20 to 38 °C resulted in an increase in the precipitation pH of the proteins. However choice of acidifier did not have a significant effect on OD profiles. The soluble covalent aggregates from mHtd7·2 were smaller, more numerous, and had a higher content of κ-casein than mHtd6·5. Both types of aggregates began to precipitate at the same pH value but precipitation occurred over a narrower pH-range for soluble aggregates prepared from mHtd7·2. This may explain the higher gelation pH of mHtd7·2 compared with mHtd6·5.

scholarly journals Effects of Heat Treating Silane and Different Etching Techniques on Glass Fiber Post Push-out Bond Strength

2014 ◽  
Vol 39 (5) ◽  
pp. E217-E224 ◽  
Author(s):  
P Samimi ◽  
V Mortazavi ◽  
F Salamat
Keyword(s):  
Heat Treatment ◽  
Hydrogen Peroxide ◽  
Bond Strength ◽  
Glass Fiber ◽  
Control Group ◽  
Fiber Post ◽  
Fiber Posts ◽  
Heat Treated ◽  
Significant Difference ◽  
Push Out

SUMMARY The aims of this study were to compare two pretreatment methods of a fiber post and to evaluate the effect of heat treatment to applied silane on the push-out bond strength for different levels of root. In this in vitro study, 40 glass fiber posts were divided into five groups (n=8) according to the kind of surface treatment applied. They were then inserted into extracted and endodontically treated human canines using a self-etch resin cement (Panavia F2.0, Kuraray, Japan). Group HF+S = hydrofluoric acid (HF) etching and silane (S) application; group HF+S+WP = HF etching and heat-treated silane application and warmed posts (WP); group H2O2+S = hydrogen peroxide etching and silane application; group H2O2+S+WP = hydrogen peroxide and heat-treated-silane application and warmed post; and group C, the control group, received no pretreatment. After completion of thermal cycling (1000 cycles, 5-55°C), all specimens were cut horizontally to obtain three sections. Each section was subjected to a push-out test, and the test results were analyzed using two-way analysis of variance, post-hoc Tukey honestly significant difference test, and a paired sample t-test (α=0.05). It was found that bond strength was not statistically influenced by the kind of etching material used (p=0.224), but was significantly affected by heat treatment of applied silane (p<0.001). The interaction between these two factors was not statistically significant (p=0.142). Group HF+S+WP showed the highest bond strength (12.56±1.73 MPa) (p<0.05). Scanning electron microscopy revealed the effect of the different treatments on the surface characteristics of posts. In the four pretreated groups, the bond strength decreased significantly from the coronal to the apical root canal sections (p≤0.05). The results of this study show that the use of heat-treated silane significantly enhances the push-out bond strength of the fiber posts to root. HF acid etching with heat-treated silane application led to the highest bond strength.

Potassium iodate-induced proteolysis in ultra heat treated milk during storage: the role of β-lactoglobulin and plasmin

1986 ◽  
Vol 53 (4) ◽  
pp. 601-613 ◽  
Author(s):  
Mary B. Grufferty ◽  
Patrick F. Fox
Keyword(s):  
Whey Proteins ◽  
Inhibitory Effect ◽  
Casein Micelle ◽  
Ph Optimum ◽  
Heat Treated ◽  
Sh Group ◽  
90 C 30 ◽  
C 30 ◽  
Subsequent Storage ◽  
Β Lactoglobulin

SummaryThe report that addition of KI03 (0·1 mm) to milk before ultra high temperature (UHT) treatment induces extensive proteolysis during subsequent storage at 37 °C was confirmed. None was produced by addition of H202 KMn04 or K2Cr207. The pH optimum for KI03-induced proteolysis was between 7·0 and 8·0 and the temperature optimum 37—45 °C. β-Casein was particularly susceptible and the proteolysis pattern was similar to that caused by indigenous alkaline milk proteinase (MPA, plasmin). Addition of plasmin to milk before UHT treatment (140 °C/10 s) caused slight proteolysis during subsequent storage but addition of 0·1 mm-KI03 and plasmin caused extensive proteolysis which was prevented by addition of soyabean trypsin inhibitor, indicating the probable involvement of plasmin in KI03-induced proteolysis in UHT-treated milk. Equally extensive proteolysis occurred in serum protein-free casein micelle systems (SPFCM), with or without KI03, during storage at 37 °C following UHT treatment, indicating a role for whey proteins in KI03-induced proteolysis. Addition of β-lactoglobulin (β-lg) to a SPFCM system inhibited proteolysis, but extensive proteolysis occurred in a SPFCM system containing both β-lg and KI03. MPA-free Na caseinate (prepared by heating at 140 °C for 7 min) underwent extensive proteolysis when treated with plasmin before UHT treatment; proteolysis was inhibited by addition of °-lg to this system and KI03 reversed the inhibitory effect of β-lg. Plasmin proteolysis of isolated αs1-casein was inhibited by denatured β-lg (90 °C/30 min) at a level of 4 mg/ml but not by native β-lg. When denatured in the presence of KI03, β-lg had a lower free SH content than the control and was less inhibitory for plasmin in proteolysis of isolated αsl-casein. The results show that denatured β-lg inhibits plasmin proteolysis of caseins in UHT milk and that inhibition is prevented by KI03. This inhibition may occur via thiol–disulphide interchange, which is prevented if the SH group of ²-lg is oxidized by KI03, thus permitting the stimulatory effect of KI03 on proteolysis in UHT-treated milk.

Effect of interactions between denatured whey proteins and casein micelles on the formation and rheological properties of acid skim milk gels

1998 ◽  
Vol 65 (4) ◽  
pp. 555-567 ◽  
Author(s):  
JOHN A. LUCEY ◽  
MICHELLE TAMEHANA ◽  
HARJINDER SINGH ◽  
PETER A. MUNRO
Keyword(s):  
Heat Treatment ◽  
Rheological Properties ◽  
Loss Tangent ◽  
Whey Proteins ◽  
Skim Milk ◽  
Casein Micelles ◽  
Heated Milk ◽  
Tan Δ ◽  
Reconstituted Milk ◽  
Acid Milk Gels

The effect of interactions of denatured whey proteins with casein micelles on the rheological properties of acid milk gels was investigated. Gels were made by acidification of skim milk with glucono-δ-lactone at 30°C using reconstituted skim milk powders (SMP; both low- and ultra-low-heat) and fresh skim milk (FSM). The final pH of the gels was ∼4·6. Milks containing associated or ‘bound’ denatured whey proteins (BDWP) with casein micelles were made by resuspending the ultracentrifugal pellet of heated milk in ultrafiltration permeate. Milks containing ‘soluble’ denatured whey protein (SDWP) aggregates were formed by heat treatment of an ultracentrifugal supernatant which was then resuspended with the pellet. Acid gels made from unheated milks had low storage moduli, G′, of <20 Pa. Heating milks at 80°C for 30 min resulted in acid gels with G′ in the range 390–430 Pa. The loss tangent (tan δ) of gels made from heated milk increased after gelation to attain a maximum at pH ∼5·1, but no maximum was observed in gels made from unheated milk. Acid gels made from milks containing BDWP that were made from low-heat SMP, ultra-low-heat SMP and FSM had G′ of about 250, 270 and 310 Pa respectively. Acid gels made from milks containing SDWP that were made from ultra-low-heat SMP or FSM had G′ values in the range 17–30 Pa, but gels made from low-heat SMP had G′ of ∼140 Pa. It was concluded that BDWP were important for the increased G′ of acid gels made from heated milk. Addition of N-ethylmaleimide (NEM) to low-heat reconstituted milk, to block the —SH groups, resulted in a reduction of the G′ of gels formed from heated milk but did not reduce G′ to the value of unheated milk. Addition of 20 mm-NEM to FSM, prior to heat treatment, resulted in gels with a lower G′ value than gels made from reconstituted low-heat SMP. It was suggested that small amounts of denatured whey proteins associated with casein micelles during low-heat SMP manufacture were probably responsible for the higher G′ of gels made from milk containing SDWP and from milk heated in the presence of 20 mm-NEM, compared with gels made from FSM.

The Role of β-lactoglobulin in the primary phase of rennin action on heated casein micelles and heated milk

1974 ◽  
Vol 41 (3) ◽  
pp. 367-372 ◽  
Author(s):  
J. V. Wheelock ◽  
A. Kirk
Keyword(s):  
Heat Treatment ◽  
Complex Formation ◽  
Skim Milk ◽  
Primary Phase ◽  
Casein Micelles ◽  
Heated Milk ◽  
Β Lactoglobulin

SummaryIt has been shown that the inhibition caused by heat treatment, of the primary phase of rennin action on casein micelles, is dependent on the presence of β-lactoglobulin. The degree of inhibition increased with increasing amounts of added β-lactoglobulin for both heated casein micelles and heated skim-milk to a constant value. The results are fully consistent with the hypothesis that the inhibition is caused by complex formation between β-lactoglobulin and κ-casein when milk is heated.

Rheological properties of milk gels formed by a combination of rennet and glucono-δ-lactone

2000 ◽  
Vol 67 (3) ◽  
pp. 415-427 ◽  
Author(s):  
JOHN A. LUCEY ◽  
MICHELLE TAMEHANA ◽  
HARJINDER SINGH ◽  
PETER A. MUNRO
Keyword(s):  
Heat Treatment ◽  
Rheological Properties ◽  
Large Scale ◽  
Whey Proteins ◽  
Skim Milk ◽  
Rheological Behaviour ◽  
Intermolecular Forces ◽  
Heated Milk ◽  
Rennet Coagulation ◽  
Tan Δ

The effects of heat treatment of milk, and a range of rennet and glucono-δ-lactone (GDL) concentrations on the rheological properties, at small and large deformation, of milk gels were investigated. Gels were made from reconstituted skim milk at 30 °C, with two levels each of rennet and GDL. Together with controls this gave a total of sixteen gelation conditions, eight for unheated and eight for heated milk. Acid gels made from unheated milks had low storage moduli (G′) of < 20 Pa. Heating milks at 80 °C for 30 min resulted in a large increase in the G′ value of acid gels. Rennet-induced gels made from unheated milk had G′ values in the range ∼ 80–190 Pa. However, heat treatment severely impaired rennet coagulation: no gel was formed at low rennet levels and only a very weak gel was formed at high levels. In gels made with a combination of rennet and GDL unusual rheological behaviour was observed. After gelation, G′ initially increased rapidly but then remained steady or even decreased, and at long ageing times G′ values increased moderately or remained low. The loss tangent (tan δ) of acid gels made from heated milk increased after gelation to attain a maximum at pH ∼ 5·1 but no maximum was observed in gels made from unheated milk. Gels made by a combination of rennet and GDL also exhibited a maximum in tan δ, indicating increased relaxation behaviour of the protein–protein bonds. We suggest that this maximum in tan δ was caused by a loosening of the intermolecular forces in casein particles caused by solubilization of colloidal calcium phosphate. We also suggest that in combination gels made from unheated milk a low value for the fracture stress and a high tan δ during gelation indicated an increased susceptibility of the network to excessive large scale rearrangements. In contrast, combination gels made from heated milk formed firmer gels crosslinked by denatured whey proteins and underwent fewer large scale rearrangements.

Rennet coagulation of heated milk: influence of pH adjustment before or after heating

1988 ◽  
Vol 55 (2) ◽  
pp. 205-215 ◽  
Author(s):  
Harjinder Singh ◽  
Samweul I. Shalabi ◽  
Patrick F. Fox ◽  
Albert Flynn ◽  
Anne Barry
Keyword(s):  
Heat Treatment ◽  
Adverse Effect ◽  
Adverse Effects ◽  
Skim Milk ◽  
Ph Adjustment ◽  
Milk Samples ◽  
Heated Milk ◽  
Rennet Coagulation ◽  
Low Concentrations ◽  
Influence Of Ph

SummaryThe rennet coagulation times of infant milk formulae or fresh skim milk (milk) samples heated at temperatures in the range 70–140 °C for 1–10 min decreased on acidification, usually to pH < 6·0. Heated milk samples acidified to pH 5·5 and reneutralized to pH 6·6 retained good rennet coagulability. Acidification of such milk samples before heating also reduced the adverse effect of severe heat treatment (95 °C for 1 min) on rennet coagulation. Addition of low concentrations of CaCl2 to heated milks offset the adverse effects of heating. Acidification of heated milks increased the [Ca2+], and reneutralization of acidified milk only partly restored the [Ca2+], i.e. acidified/reneutralized milk had a higher [Ca2+] than normal milk, suggesting this as the mechanism via which acidification/neutralization improves the rennet coagulability of heated milk. Approximately 50% of the whey protein can be incorporated into rennet gels in heated milks while retaining good coagulability and curd tension; this may be a useful technique for increasing cheese yield.

Heat-induced and other chemical changes in commercial UHT milks

2005 ◽  
Vol 72 (4) ◽  
pp. 442-446 ◽  
Author(s):  
Anthony J Elliott ◽  
Nivedita Datta ◽  
Boka Amenu ◽  
Hilton C Deeth
Keyword(s):  
Heat Treatment ◽  
Bovine Serum Albumin ◽  
Bovine Serum ◽  
Room Temperature ◽  
Whey Proteins ◽  
Thermally Induced ◽  
Heated Milk ◽  
Heat Treated ◽  
Induced Changes ◽  
Β Lactoglobulin

The properties of commercial directly and indirectly heated UHT milks, both after heating and during storage at room temperature for 24 weeks, were studied. Thermally induced changes were examined by changes in lactulose, furosine and acid-soluble whey proteins. The results confirmed previous reports that directly heated UHT milks suffer less heat damage than indirectly heated milk. During storage, furosine increased and bovine serum albumin in directly heat-treated milks decreased significantly. The changes in lactulose, α-lactalbumin and β-lactoglobulin were not statistically significant. The data suggest that heat treatment indicators should be measured as soon as possible after processing to avoid any misinterpretations of the intensity of the heat treatment.

Association of denatured whey proteins with casein micelles in heated reconstituted skim milk and its effect on casein micelle size

2003 ◽  
Vol 70 (1) ◽  
pp. 73-83 ◽  
Author(s):  
Skelte G Anema ◽  
Yuming Li
Keyword(s):  
Heat Treatment ◽  
Particle Size ◽  
Whey Protein ◽  
Volume Fraction ◽  
Whey Proteins ◽  
Skim Milk ◽  
Casein Micelle ◽  
Casein Micelles ◽  
Prolonged Heating ◽  
Micelle Size

When skim milk at pH 6·55 was heated (75 to 100 °C for up to 60 min), the casein micelle size, as monitored by photon correlation spectroscopy, was found to increase during the initial stages of heating and tended to plateau on prolonged heating. At any particular temperature, the casein micelle size increased with longer holding times, and, at any particular holding time, the casein micelle size increased with increasing temperature. The maximum increase in casein micelle size was about 30–35 nm. The changes in casein micelle size were poorly correlated with the level of whey protein denaturation. However, the changes in casein micelle size were highly correlated with the levels of denatured whey proteins that were associated with the casein micelles. The rate of association of the denatured whey proteins with the casein micelles was considerably slower than the rate of denaturation of the whey proteins. Removal of the whey proteins from the skim milk resulted in only small changes in casein micelle size during heating. Re-addition of β-lactoglobulin to the whey-protein-depleted milk caused the casein micelle size to increase markedly on heat treatment. The changes in casein micelle size induced by the heat treatment of skim milk may be a consequence of the whey proteins associating with the casein micelles. However, these associated whey proteins would need to occlude a large amount of serum to account for the particle size changes. Separate experiments showed that the viscosity changes of heated milk and the estimated volume fraction changes were consistent with the particle size changes observed. Further studies are needed to determine whether the changes in size are due to the specific association of whey proteins with the micelles or whether a low level of aggregation of the casein micelles accompanies this association behaviour. Preliminary studies indicated lower levels of denatured whey proteins associated with the casein micelles and smaller changes in casein micelle size occurred as the pH of the milk was increased from pH 6·5 to pH 6·7.

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