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 stability of milk protein to heat: III. Objective measurement of heat stability of milk

1966 ◽  
Vol 33 (1) ◽  
pp. 93-102 ◽  
Author(s):  
J. C. D. White ◽  
D. T. Davies
Keyword(s):  
Induction Period ◽  
Milk Protein ◽  
Heat Stability ◽  
Objective Measurement ◽  
Objective Test ◽  
Subjective Test ◽  
Coagulation Time ◽  
Rapid Coagulation ◽  
The Stability

SummaryAn objective test has been developed to help in assessing the value, as a method for determining the heat stability of milk, of the subjective test described by Davies & White (1966a). The objective test showed that coagulation time, as determined by the subjective test, is a reasonably accurate measure of the induction period that precedes the onset of initial rapid coagulation, but that coagulation proceeds in 2 different ways depending primarily on whether the coagulation of the milk is good (initial clots large) or poor (initial clots small). The latter finding confirms the view that in studying heat stability these 2 categories of milk should be examined separately.

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.

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.

Studies on the heat stability of milk protein: I. Interconversion of type A and type B milk heat-stability curves

1974 ◽  
Vol 41 (3) ◽  
pp. 349-358 ◽  
Author(s):  
A. W. M. Sweetsur ◽  
J. C. D. White
Keyword(s):  
Calcium Phosphate ◽  
Milk Protein ◽  
Heating Temperature ◽  
Type A ◽  
Heat Stability ◽  
Type B ◽  
Coagulation Time ◽  
Higher Temperature ◽  
Ph Curve ◽  
Β Lactoglobulin

SummaryCoagulation time–pH curves with a coagulation-time minimum around pH 6·8 (type A curve) could progressively become type B (no minimum) as the heating temperature was decreased from 150 to 130°C. The short coagulation time that most milks have when pH is around 6·8 was found to be the result of a ‘premature’ coagulation, probably caused by calcium phosphate deposition on the larger caseinate micelles. This is followed by a second coagulation, not visually detected, that coincides with the coagulation time that would be expected if no coagulation-time minimum existed on the coagulation time-pH curve. The coagulation time of milks giving type A and type B curves may therefore not be comparable.Forewarming milk for 30 min at 80°C can introduce or accentuate a coagulationtime minimum when the milk is subsequently heated at a higher temperature. The effects of adding β-lactoglobulin, copper and N-ethylmaleimide on the heat stability of milk were examined and explanations proposed for these effects.

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.

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.

Studies on the heat stability of milk protein: III. Effect of heat-induced acidity in milk

1975 ◽  
Vol 42 (1) ◽  
pp. 73-88 ◽  
Author(s):  
A. W. M. Sweetsur ◽  
J. C. D. White
Keyword(s):  
Special Reference ◽  
Milk Protein ◽  
Heat Stability ◽  
Total Serum ◽  
Ion Content ◽  
Coagulation Time ◽  
Initial Ph ◽  
Ph Decrease ◽  
The Relationship

SummaryAn examination was made of the effect of varying the protein, lactose and total serum ion content of milk on the rate of production of heat-induced acidity (as measured by pH decrease), on heat stability (as measured by coagulation time), on the relationship between coagulation time and initial pH of milk (as measured by coagulation time-pH curves) and on the interrelationship of these parameters. In addition, the effect on these parameters and their interrelationship of varying the composition and volume of the headspace atmosphere in contact with the milk was investigated. Explanations are proposed for the observed effects on heat stability of varying the composition of milk and the heating conditions, with special reference to the influence of heat-induced acidity.

Studies on the heat stability of milk protein: II. Effect of exposing milk to light

1975 ◽  
Vol 42 (1) ◽  
pp. 57-71 ◽  
Author(s):  
A. W. M. Sweetsur ◽  
J. C. D. White
Keyword(s):  
Milk Protein ◽  
Necessary Conditions ◽  
Type A ◽  
Heat Stability ◽  
Coagulation Time ◽  
Stability Curve ◽  
Photo Oxidation ◽  
Rennet Coagulation

SummaryIt was found that the increase in heat stability (coagulation time) that occurs when some milks are stored in light was not caused by changes in pH. These labile milks invariably gave a type A heat-stability curve, had a pH in the range corresponding to the coagulation-time minimum of the curve, and showed the expected abnormal 2-stage type of coagulation. The increase in coagulation time following exposure to light resulted from a delay in the occurrence of the first coagulation, the second coagulation time remaining unaltered. The presence of riboflavin in milk and of O2 in the headspace atmosphere during storage were necessary conditions for milk to be labile. Since light, headspace O2 and riboflavin had similar influences on rennet coagulation time it is suggested that in both instances the causative reaction, as proposed by others to account for the increase in rennet coagulation time of H2O2-treated milk, is stabilization of the heat- and rennin-sensitive methionine-phenylalaninebond in κ-casein by photo-oxidation of the methionine to methionine sulphoxide.

scholarly journals Entrapment of the Fastest Known Carbonic Anhydrase with Biomimetic Silica and Its Application for CO2 Sequestration

Polymers ◽  
2021 ◽  
Vol 13 (15) ◽  
pp. 2452
Author(s):  
Chia-Jung Hsieh ◽  
Ju-Chuan Cheng ◽  
Chia-Jung Hu ◽  
Chi-Yang Yu
Keyword(s):  
Carbonic Anhydrase ◽  
High Activity ◽  
Co2 Sequestration ◽  
Residual Activity ◽  
Entrapment Efficiency ◽  
Free Form ◽  
Uncatalyzed Reaction ◽  
The Stability ◽  
Time Required

Capturing and storing CO2 is of prime importance. The rate of CO2 sequestration is often limited by the hydration of CO2, which can be greatly accelerated by using carbonic anhydrase (CA, EC 4.2.1.1) as a catalyst. In order to improve the stability and reusability of CA, a silica-condensing peptide (R5) was fused with the fastest known CA from Sulfurihydrogenibium azorense (SazCA) to form R5-SazCA; the fusion protein successfully performed in vitro silicification. The entrapment efficiency reached 100% and the silicified form (R5-SazCA-SP) showed a high activity recovery of 91%. The residual activity of R5-SazCA-SP was two-fold higher than that of the free form when stored at 25 °C for 35 days; R5-SazCA-SP still retained 86% of its activity after 10 cycles of reuse. Comparing with an uncatalyzed reaction, the time required for the onset of CaCO3 formation was shortened by 43% and 33% with the addition of R5-SazCA and R5-SazCA-SP, respectively. R5-SazCA-SP shows great potential as a robust and efficient biocatalyst for CO2 sequestration because of its high activity, high stability, and reusability.

scholarly journals The Application of an Impedance-Passivity Controller in Haptic Stability Analysis

2021 ◽  
Vol 11 (4) ◽  
pp. 1618
Author(s):  
Ping-Nan Chen ◽  
Yung-Te Chen ◽  
Hsin Hsiu ◽  
Ruei-Jia Chen
Keyword(s):  
Control Systems ◽  
Force Feedback ◽  
Training System ◽  
Considerable Time ◽  
Virtual Training ◽  
Control Gain ◽  
Negative Damping ◽  
The Stability ◽  
Time Required ◽  
Stable Control

This paper proposes a passivity theorem on the basis of energy concepts to study the stability of force feedback in a virtual haptic system. An impedance-passivity controller (IPC) was designed from the two-port network perspective to improve the chief drawback of haptic systems, namely the considerable time required to reach stability if the equipment consumes energy slowly. The proposed IPC can be used to achieve stability through model parameter selection and to obtain control gain. In particular, haptic performance can be improved for extreme cases of high stiffness and negative damping. Furthermore, a virtual training system for one-degree-of-freedom sticking was developed to validate the experimental platform of our IPC. To ensure consistency in the experiment, we designed a specialized mechanical robot to replace human operation. Finally, compared with basic passivity control systems, our IPC could achieve stable control rapidly.

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