Application of a Sodium Carbonate-Bicarbonate Buffer in the Phosphatase Test for Cheese

In the past a number of different buffers have been used in the buffer substrate when conducting the phosphatase test.Kay and Graham (6) have successfully used sodium barbitol in their test for milk, Aschaffenburg and Neave (1) have suggested the use of sodium carbonate, whereas Scharer (10) has used a borate buffer.As far as cheese was concerned, Caulfield and Martin (2), Lambert (8) and Sanders and Sager (9) all have stressed the importance of a proper buffer as the cheese, because of its different buffering capacity, exerts a decided effect on the pH of the buffer substrate.If a buffer were unable to maintain the proper pH for optimum phenol production low values would be obtained.Although Sanders and Sager (9) appear to use a very good modified borate buffer, it still is necessary in their test to make adjustments for different aged cheeses or cheeses of different varieties.During a recent study (7) on the elimination of interfering substances in the phosphatase test, it was noted that the sodium barbitol buffer used was affected greatly by cheeses of different age or variety and that additions of cheese invariably would carry the pH of the cheese-buffer substrate solution much lower than that recommended by earlier investigators for optimum phenol production by the alkaline phosphatases.As a result, it was decided to abandon the sodium barbitol buffer and substitute one which would maintain the pH near its optimum for phenol production.A study of several buffers pointed to a sodium carbonate-sodium bicarbonate combination as showing the most promise.This buffer had been studied earlier on the alkaline phosphatase systems by Fischer (4), Schwarz and Fischer (11), Horwitz (5) and Delory and King (3).The latter investigators stated that the carbonate-bicarbonate buffer can be held for as long as 6 months over a pH range of from 8.8 to 10.6 at 37 ° C. in well-stoppered wax bottles without any demonstrable change in pH.As this buffer covered a region of higher pH than did the sodium barbitol buffer, a study was made to determine the optimum pH for phenol production with this buffer and also its effectiveness in maintaining the optimum pH in the presence of cheese.The concentration of carbonate in the buffer used for this experimental work was much greater than that used in the carbonate buffer of Delory and Kling (3) and others (4,11). METHODSTo study phenol production at varying pH vahm% the trichloracetic acid technic for the Kay-Graham test recently presented by Kosikowsky and Dahlberg (7) was used with the exception that the sodium carbonate-bicarbonate buffer was