Vol. 3, No. 4
ANALYTICAL EDITION
376
separated curd-serum mixture by either the Clark shaking electrode or the Hildebrand electrode, the Leeds and Northrup type K potentiometer equipment being used as the voltagerecording apparatus. To facilitate accurate control of temperature, the beaker containing the electrodes is immersed in a thermostatically controlled water bath and the whole apparatus mounted in a cabinet whose temperature is also under control. The quinhydrone procedure using a saturated calomel cell and the gold spiral electrode gave results comparing very well with those obtained by the hydrogen electrode and was accordingly adopted for the hydrogen-ion work on butter on account of its greater rapidity, equilibrium being established in usually less than Yj minutes.
of individual values. I n Table IV an attempt has been made to average the values in the graph, all of the acidities corresponding to an interval of 0.1 pH being grouped together. Two sets of averages are shown, those in the third column being an average of all the acidities in any particular group. These show several rather wide variations, however, and may not form as correct a picture as the values in the last column which were obtained from a median on the graph. These latter figures form a beautiful scale, but unfortunately are not always possible of realization experimentally. There must be many as yet unknown factors operating in this relationship between the hydrogen-ion concentration of butter and its titratable acidity which can only be clarified by a great deal of additional experimentation. Nevertheless, from a practical value it appears that the hydrogen-ion concentration forms a truer index of the real reaction involved in the churning operation and of the products formed. of pH t o Titratable Acidity of Butter (Averages of values) BUTTER ACIIXTY Av. of all Av. value PH RANGE values found taken from graph 4.80-5.09 0.120 0.104 5.10-5.19 0.098 0.091 5.20-5.29 0.073 0.086 5.30-5.39 0.077 0.081 5.40-5.49 0.064 0.076 5.50-5.59 0.061 0,072 5.60-5.69 0.059 0,068 5.70-5.79 0.063 0.063 5.80-5.89 0 055 0.059 5.90-5.99 0 056 0.055 6.00-6.09 0.n53 n ,052 6.10-6.19 0.047 0.049 6.20-6.29 0.054 0.046 6.30-6.39 0.051 0.043 6.40-6.49 0.047 0 040 0.051 0.036 6.60-6.59 0.051 0.033 6.60-8.69 6.70-6.79 0.047 0.030 0 040 0.028 6.80-6.89 0.025 6.90-6.99 0.041 0.036 0.022 7,OO-7.09 0.020 7.10-7.I9 0.036 0.017 7.20-7.29 0.030 0.015 7.30-7.39 0.01s n 020 0.013 7.40-7.49 0.010 7.50-7.69 0 017
Table IV-Relation No.
OF
SAMPLES
Figure 1-The
pH of Butter as Related t o Titratable Acidity
Whether or not hydrogen-ion determinations thus made on the curd-serum mixture of butter actually represent the true reaction of whole butter is as yet a matter for further study. Certain preliminary experiments, however, made in the author’s own laboratory seem to justify the opinion that the fat has absolutely no effect on the pH of butter and acts merely as a diluent of the active substances present. Sharp and McInerney ( 6 ) hold a similar opinion in regard to cream. In perfecting the above method for the pH of butter several factors which, because of the complex nature of the product involved, might justifiably be considered as possible sources of error have been carefully investigated by Hunziker, Cordes, and Nissen (4). Relationship of pH and Titratable Acidity
Various investigators have reported comparisons between the hydrogen-ion concentration and the titratable acidity of fresh milk where the amount of free acid present is relatively small. One of these investigators (9)states that no exact relationship exists. Sharp and McInerney ( 7 ) , on the other hand, show a relatively good agreement between titratable acidity and pH of sweet milk and an even better relationship for milk which has been allowed to sour. A similar comparison of such values for butter-i. e., the titratable acidity and the hydrogen-ion concentration as determined by the modified procedures outlined above-are presented here. No attempt has been made to classify the butter as to source, treatment during manufacture, or composition of the main constituents. Such factors may all have a marked effect on the relationship to be expected and at times may cause one value to vary more than the other. Figure 1, representing 325 samples of butter selected at random, shows merely a tendency towards such a relationship. I n general, the majority of the titratable acidities for any particular hydrogen-ion concentration vary within less than *0.015 per cent from a line drawn midway through the mass
6 5 2 3 8 12 28 41 31 23 21 19 23 12 14 8 8 12 13 10 5 3 6 4 6 3
The methods presented for the titratable acidity and the hydrogen-ion concentration of butter, as well as the rather general relationship observed in the graph and Table IV, are presented with due consideration of the complex nature of the product involved. It is hoped, however, that these methods and dat,a may encourage further investigation along similar phases of this rather important process, the manufacture of butter. Literature Cited (1) Haglund, E., and Waller, E.,1923 to 1929. Medd. Centralanstalt. flirsdksvUsendet jordbruks., Nos. 232, 261, 290, 321, 347 (1923-29). (2) Hortvet, J., J . Assocn. O 8 c i a l Agv. Chem., 9,, 231 (1926). (3) Hunziker, 0.F.,“The Butter Industry,” 2nd ed., 1927. (4) Hunziker, 0.F.,Cordes, W. A,, and Nissen, B. H., J . Dairy Sci., 14, 4 (1931). (5) Hunziker, 0.F., Spitzer, G . , Mills, F. C., and Switzer, H. B . , Purdue Agr. Coll., Bull. 208, 45 (1917). (6) Sharp, P. F., and McInerney, T . J., J . B i d . Chem., 70,749 (1926). (7) Sharp, P.F.,and McInerney, T. J., Ibid., 75, 177 (1927). (8) Sherman, H. C., “Methods of Organic Analysis,” p. 147 (1917). (9) Vandevalde, J. J., Lait, 1, 140 (1927). (10) Watson, F.D.,J . Dairy Sci., 12, 289 (1929).
New Protein Conversion Factors-Investigations of proteins during recent years by the U. S.Department of Agriculture have resulted in the formulation of a new set of factors for converting the percentages of nitrogen in foods and feeds into protein equivalents. Comparisons for several foods show that the new conversion factors vary considerably from the single factor now in general use. Data on the subject are presented in Department of Agriculture Circular 1 8 3 4 , copies of which may be obtained free from the Office of Information, U. S. Department of Agriculture, Washington, D. C.
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