94. A Study of the Titratable Acidity of Milk. I. The Influence of the Various Milk Buffers on the Titration Curves of Fresh and Sour Milk

Wiley, W. J.

doi:10.1017/s0022029900001205

Cited by 11 publications

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“…Typical values for β of bovine milk range from 0.018 to 0.040 (mol/L)/pH unit (Wiley, 1935;Lucey et al, 1993), similar to that found in the study reported here (Figure 1). The buffer value of the BACG-ORT solution in cow's milk was, in general, greater than that of cow's milk over the acid titration of pH range 2.0 to 6.5.…”

Section: Discussionsupporting

confidence: 88%

Comparative effects of two oral rehydration solutions on milk clotting, abomasal luminal pH, and abomasal emptying rate in suckling calves

Constable

Grünberg

Carstensen

2009

Journal of Dairy Science

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The effect of adding an oral rehydration therapy (ORT) solution containing bicarbonate, citrate, and acetate to cow's milk on milk clotting, abomasal luminal pH, and abomasal emptying rate was determined in suckling calves. Six male Holstein-Friesian calves with abomasal cannulae, 5 to 13 d of age, were used in a crossover design. Calves were fed 2 L of cow's milk alone, milk with an ORT solution containing a low bicarbonate concentration (25 mmol/L), acetate (12 mmol/L), citrate (12 mmol/L), and glycine (7 mmol/L; group BACG), or milk with an ORT solution containing formate (58 mmol/L) and acetate (15 mmol/L) in randomized order. Clotting of milk was assessed in vivo and in vitro. Abomasal luminal pH was monitored continuously. Abomasal emptying rates were determined by using the change in abomasal luminal pH, acetaminophen absorption, and glucose absorption. The addition of a BACG-ORT solution to cow's milk increased in vitro clotting time by approximately 6 min. All 3 test solutions clotted in vivo by 15 min after the beginning of suckling. The addition of a BACG-ORT solution to cow's milk increased the pH of cow's milk and abomasal fluid by approximately 0.3 pH units. The addition of a BACG-ORT or a formate and acetate-ORT solution to cow's milk increased solution osmolality and slowed the rate of abomasal emptying. We concluded that the addition of BACG-ORT solution to cow's milk did not affect milk clotting in vivo. Recommendations based on the results of in vitro studies that bicarbonate- or citrate-containing ORT solutions should not be fed concurrently with cow's milk do not appear to be relevant to in vivo conditions when 2 L of a low-bicarbonate (25 mmol/L), low-citrate (12 mmol/L) ORT solution is fed.

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Section: Discussionsupporting

confidence: 88%

Comparative effects of two oral rehydration solutions on milk clotting, abomasal luminal pH, and abomasal emptying rate in suckling calves

Constable

Grünberg

Carstensen

2009

Journal of Dairy Science

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“…In the backtitration, the experimental results show a pH buffering peak between pH 5 and 8 (peak maximum at pH 6). Similar peaks were observed by Wiley (1935a), who attributed this buffering maximum to calcium phosphate precipitation. Similar conclusions were drawn by , who attributed the strong pH buffering effect in the pH range from 6 to 7 to the formation of Ca 3 (PO 4 ) 2 .…”

Section: Backtitration: Ph Buffering Between Ph 5 and 8 (Region 4)supporting

confidence: 85%

Influence of Calcium and Phosphorus, Lactose, and Salt-to-Moisture Ratio on Cheddar Cheese Quality: pH Buffering Properties of Cheese

Upreti

Bühlmann

Metzger

2006

Journal of Dairy Science

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The pH buffering capacity of cheese is an important determinant of cheese pH. However, the effects of different constituents of cheese on its pH buffering capacity have not been fully clarified. The objective of this study was to characterize the chemical species and chemical equilibria that are responsible for the pH buffering properties of cheese. Eight cheeses with 2 levels of Ca and P (0.67 and 0.47% vs. 0.53 and 0.39%, respectively), residual lactose (2.4 vs. 0.78%), and salt-to-moisture ratio (6.4 vs. 4.8%) were manufactured. The pH-titration curves for these cheeses were obtained by titrating cheese:water (1:39 wt/wt) dispersions with 1 N HCl, and backtitrating with 1 N NaOH. To understand the role of different chemical equilibria and the respective chemical species in controlling the pH of cheese, pH buffering was modeled mathematically. The 36 chemical species that were found to be relevant for modeling can be classified as cations (Na+, Ca2+, Mg2+), anions (phosphate, citrate, lactate), protein-bound amino acids with a side-chain pKa in the range of 3 to 9 (glutamate, histidine, serine phosphate, aspartate), metal ion complexes (phosphate, citrate, and lactate complexes of Na+, Ca2+, and Mg2+), and calcium phosphate precipitates. A set of 36 corresponding equations was solved to give the concentrations of all chemical species as a function of pH, allowing the prediction of buffering curves. Changes in the calculated species concentrations allowed the identification of the chemical species and chemical equilibria that dominate the pH buffering properties of cheese in different pH ranges. The model indicates that pH buffering in the pH range from 4.5 to 5.5 is predominantly due to a precipitate of Ca and phosphate, and the protonation equilibrium involving the side chains of protein-bound glutamate. In the literature, the precipitate is often referred to as amorphous colloidal calcium phosphate. A comparison of experimental data and model predictions shows that the buffering properties of the precipitate can be explained, assuming that it consists of hydroxyapatite [Ca5(OH)(PO4)3] or Ca3(PO4)2. The pH buffering in the region from pH 3.5 to 4.5 is due to protonation of side-chain carboxylates of protein-bound glutamate, aspartate, and lactate, in order of decreasing significance. In addition, pH buffering between pH 5 to 8 in the backtitration results from the reprecipitation of calcium and phosphate either as CaHPO4 or Ca4H(PO4)3.

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“…6-6 to 8-0 there is not a great difference. The whey curve can be interpreted from the results obtained in the first part of this work (4). The minimum at pS.…”

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confidence: 80%

95. A Study of the Titratable Acidity of Milk. II. The “Buffer Curves” of Milk

Wiley

1935

Journal of Dairy Research

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THE previous section of this study in which the titration curves of various milk constituents were discussed approximately denned their influence on the titration. Some of the conclusions arrived at are amplified and more clearly defined when the buffer index of the curves is considered.In this discussion Van Slyke's(i) buffer index will be used, i.e. dBjdpK, the ratio of the change in normality of acid or base to the corresponding change in pE. when the change of pH. is infinitely small. The values recorded in this paper were obtained by measuring the slopes of the corresponding titration curves.Buchanan and Peterson (2) used this method of expressing the buffer capacity of milk. They found a maximum value of 0-0326 in the region 5-0-5-5 falling to a minimum of 0-00635 between pTL 8-0 and 8-5. While the general shape of their buffer curve has been confirmed by the following work they draw some rather surprising conclusions from it. They state that there is a great similarity between the titration curves of milk and sodium phosphate and that therefore "phosphates are at least among the most important buffers of milk." While the conclusion is undoubtedly correct, sufficient work has been described in the previous section of this study to show that there is little similarity between the two curves. They also claim that, as the value of the buffer index is not affected greatly near the isoelectric point of the casein, the casein can have little effect on the buffering in this region, pK 4-5-5-0. On the other hand, Whittier (3) comes to the opposite conclusion, i.e. that the buffer action of the casein is exerted principally between pH 4-50 and 5-70 with a maximum at approximately pB. 5-20. This follows from a consideration of the buffer curves of milk and of the acid whey prepared from it. Whittier considers that the difference between these two curves shows the effect of casein.Whittier was concerned particularly with the region between pH. 4 and 7 and did not consider the more alkaline portion of the curves. Moreover, he reached a condition of approximate equilibrium in making the titrations, so that his results are not applicable to the rapid titration of milk to the phenolphthalein end-point. Unless otherwise noted the curves in the following work were obtained from titrations made in the manner described in the previous

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94. A Study of the Titratable Acidity of Milk. I. The Influence of the Various Milk Buffers on the Titration Curves of Fresh and Sour Milk

Cited by 11 publications

References 14 publications

Comparative effects of two oral rehydration solutions on milk clotting, abomasal luminal pH, and abomasal emptying rate in suckling calves

Comparative effects of two oral rehydration solutions on milk clotting, abomasal luminal pH, and abomasal emptying rate in suckling calves

Influence of Calcium and Phosphorus, Lactose, and Salt-to-Moisture Ratio on Cheddar Cheese Quality: pH Buffering Properties of Cheese

95. A Study of the Titratable Acidity of Milk. II. The “Buffer Curves” of Milk

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