Composition of Ultrafiltrates from Milk Heated at 80 to 230° F. in Relation to Heat Stability

Summary Analyses of ultrafiltrates collected from milk at temperatures up to 230° F. indicated that temperature changes affect the inorganic composition of milk much more drastically than has previously been demonstrated from the analyses of cooled milks. At 200° F., the amount of calcium passing into the ultrafiltrate was approximately 50%, and the phosphate about 82%, of that found at 80° F. On the other hand, the hydrogen ion concentration of ultrafiltrate collected at 200° F. was at least double that of ultrafiltrate Collected at 80° F. Similar tests made with solutions of calcium and phosphate indicated that these changes in the inorganic composition of milk can be explained entirely on the basis of changing solubility and composition of the insoluble calcium phosphate salts. No change in the dissociation of calcium citrate with temperature could be detected. No correlation was observed between the changes induced by heat and the heat stability of various samples of milk

Heat Stability of Casein in the Presence of Calcium and Other Salts

Summary The extent of calcium binding and the heat stability of colloidal suspensions of freeze-dried casein in calcium hydroxide solution, with added phosphates, citrates, and chlorides in some tests, was studied. The calcium-binding power of freshly prepared freeze-dried casein was greater (pK 4.5) than that reported for other casein preparations. However, the pK value decreased during storage of the casein at room temperature and within 1 or 2 mo. attained a value (pK = 3.0 ± 0.3) in agreement with published values. The heat stability of simple casein caseinate suspensions was inversely related to the extent to which the casein was saturated with calcium, and this relation appeared to be linear at calcium levels sufficient to give over 80% saturation. The heat stability of more complex suspensions was inversely related to the ratio of soluble or ionic calcium to soluble phosphate in the suspension. Chlorides and phosphates of sodium, potassium, and ammonium displaced calcium from caseinate to about the same extent, but ammonium ion appeared to have a specific depressant effect on heat stability

Influence of κ-casein and β-lactoglobulin on the Heat Stability of Skimmilk

Abstract Milks from individual cows were classified according to their heat stability-pH relation as Type A (maximum and minimum heat stability) and Type B (no minimum heat stability). The heat stability responses of these milks could be changed from Type A to B and from B to A by adding κ -casein and β -lactoglobulin, respectively. Addition of either α s - or β -casein did not affect the heat stability of milk. The heat stability-pH relation of milk heated at 90C for 10min was no longer affected by the addition of κ -casein

Effect of Various Salts on the Coagulation of Casein

Summary Addition of potassium or sodium chloride (80 or 130m M ) to skimmilk increased the time the milk could be held in frozen storage without development of 4% precipitate by volume. Addition of phosphate or calcium (10m M ) had the opposite effect. Addition of large amounts of sodium chloride (up to 1.0 M ) offset the destabilizing effect of phosphate or calcium at 0, 10, and 20° F., but addition of similar amounts of potassium chloride stabilized the samples only at 10 and 20° F. Addition of potassium chloride (1.0 M or more) and of phosphate (100m M or more) induced gelation of milk at room temperature. Addition of sodium chloride and phosphate did not induce gelation. Addition of either potassium or sodium chloride (2.3 M ) shifted approximately 20% of the insoluble calcium and 7.5% of the insoluble phosphate to the soluble forms, displaced calcium from casein, and increased the dissociation of calcium citrate. A possible explanation of these effects, based on the interlinking of potassium-calcium-caseinate micelles by precipitating calcium phosphate, is presented

Sialic Acid as an Index of the κ-Casein Content of Bovine Skimmilk

Summary The sialic acid content of skimmilk proteins has been examined, using a modification of Warren's thiobarbituric acid method. Lactose interferes with this method and was removed by thorough washing of the proteins. κ -casein and proteose-peptone appear to be the only two skimmilk proteins containing significant amounts of sialic acid. Treatments with DEAE cellulose almost completely removed the low concentrations of sialic acid present in α s - and β -caseins, and examination of these caseins by starch gel electrophoresis indicates that such removal involved traces of κ -casein. Since the stability of α s - κ -casein mixtures in the presence of calcium appeared to be directly related to the sialic acid content of the mixture at all levels below the 0.37% (uncorrected for moisture) needed to give complete stability, it is concluded that sialic acid measurements can be used as an index of the intact κ -casein content of such mixtures. Proteose-peptone is precipitated by 12% TCA, but remains in solution at pH 4.5, so analysis of sialic acid can also be used as an index of the κ -casein concentration of whole acid casein. Values of 0.26–0.59% sialic acid were obtained in washed whole acid caseins prepared from individual lots of milk, indicating that the proportion of κ -casein is variable. The sialic acid content of κ -casein appears to be close to 2.3%; on this basis, the proportion of κ -casein in whole acid casein varies between 11–26%

Decomposition of Time-Series by Level and Change

This article examines whether decomposing time series data into two parts – level and change – produces forecasts that are more accurate than those from forecasting the aggregate directly. Prior research found that, in general, decomposition reduced forecasting errors by 35%. An earlier study on decomposition into level and change found a forecast error reduction of 23%. The current study found that nowcasts consisting of a simple average of estimates from preliminary surveys and econometric models of the U.S. lodging market, improved the accuracy of final estimates of levels. Forecasts of change from an econometric model and the improved nowcasts reduced forecast errors by 29% when compared to direct forecasts of the aggregate. Forecasts of change from an extrapolation model and the improved nowcasts reduced forecast errors by 45%. On average then, the error reduction for this study was 37%

Starch Gel Electrophoresis of Various Fractions of Casein

Summary Preparations of α-, β -, γ-, λ-, and κ-caseins were compared by electrophoresis in starch gel and in free solution. Acid casein separated into at least 17 zones. All fractions of casein contained numerous proteins, but the preparatory procedures brought about considerable enrichment of certain zones while weakening or eliminating others, and a tentative identification of specific zones with each casein fraction was, therefore, possible. α s -Casein appeared to be contaminated with traces of β -, κ-, and γ-casein, but the main contaminants were unidentified fractions travelling between α s - and β -casein. β -Casein was contaminated with traces of γ- and κ-casein, and with the unidentified fractions observed in α s -casein. Our preparations of γ-casein were heavily contaminated with κ- and β -casein, and contained lesser amounts of α s -casein and of unidentified fractions. Identification of the κ-casein zone was confirmed by zone electrophoresis from urea solution into urea-free gel, whereupon the κ-casein formed a characteristic precipitation zone, and by electrophoresis in gels containing calcium. Comparison of three κ-casein preparations indicated differences among them, both in stabilizing power and in electrophoretic properties. The preparation of κ-casein with the least contamination from other casein components appeared to be partially denatured

Zonal Ultracentrifugation of β-Lactoglobulin and κ-Casein Complexes Induced by Heat

Abstract A zonal ultracentrifuge was used to isolate the heat-induced complexes of β -lactoglobulin and κ -casein. The complexes formed at 80C in sodium cacodylate buffer, pH 6.65, ionic strength 0.08, varied in size and composition, but moved as a single band in starch-gel electrophoresis. The maximum ratio in the complex was estimated to be 3 β -lactoglobulin:1 κ -casein. When a 1:1 mixture was heated at 110C the major component banded in 6.9% sucrose, had a sedimentation coefficient of 2.35, and moved as a single band in starch gel. At 140C, κ -casein was degraded extensively, and no complex could be detected. The complex formed at 90C from a 1:1 mixture in a synthetic serum containing calcium had a sedimentation coefficient of 39. For other mixtures in the presence of calcium the unreacted proteins could not be quantitatively separated from the complex. Zonal ultracentrifugation of heated skimmilk and colloidal calcium phosphate free milk failed to show a discrete complex peak

Thiol-disulfide Interchange in Formation of β-Lactoglobulin-κ-Casein Complex

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