ORGANIC
BIOLCXICAL.
TABLE117.- (Continued).
Description o f s a m p l e
C
Xo. 303-Same as No. 302. No. 153-Chicken of known history, two years in storage. Aqueous extract of No. 253. No. zjq-Chicken of known history, two years in storage. Slightly gnawed by mice. No. z56-Same as 254. No. 298-Sarne as 254. KO. 258-Same as 254. No. 299-Chicken of known history, two years in storage. Excellent condition. Aqueous extract 299. No. 304-Chicken of unknown history in storage six years.
Percentage o f arnmoxiiacal nitrogen obtained Time by distillcon.-rrtricri ing 1 hour f i n hours). wit11 hlgO
Pr;cetitayc ininioniacn! nitrogen evolved.
Cu. i t . cfa i r used.
0.01g
6,700
(i
0,OjO
0.027
5,175
3.66
...
0.025
5,175
3.66
0.032 0.031
4,820 11,130 7,350 5,988
3.66 4.5 5 4.25
..,. . .....
11,610 11,610
8
0.036
0.022
8
.....
0.058
12,978
6
0.109
0.030
0.029
0.023
,
.
..... .., ..
FOODRESE.4RCH LhBORATORY, B L J R E AOF ~ CHEXISTRY, UKITED STAT& DSPARTUENTO F AGRICLLTURE.]
[CONTRIBCTION FROM THE
THE DETERMINATION OF THE ACID VALUE OF CRUDE FAT AND ITS APPLICATION IN THE DETECTION OF AGED FOODS. B Y h.1 E PENNINGTON A N D J. S HEPBUAN.
Received March 3 , 1910
During the study of the handling of poultry intended for food, a t present under way in this laboratory, i t has been found necessary to devise methods for a more accurate estimation of changes in the composition of flesh than have been in common use and which would be sufficiently prompt to permit of the testing of a larger number of samples each day than is ordinarily accomplished with a moderate laboratory force. The acidity of the f a t of the chicken has been found to be a sensitive index of the state of preservation of the whole bird. I t increases from a very low value in the freshly killed specimen to forty or fifty times the original number, according to the method of preservation and the length of the keeping period. However, the usual procedure for the estimation of the amount of free acid in the fat, that is, extraction with a suitable solvent, drying, etc., was so time-consuming that its use a a s greatly restricted. It seemed desirable, therefore, to SO modify the iriethod that accurate results could be obtained without such an expenditure of time.
DETERMINATION
On THE ACID VALUE OF CRUDE PAT.
569
It is a common practice in packing-house work to render by a low heat beef or mutton fat and store for commercial purposes. The acid value of such a rendered t a t is determined directly in hot alcoholic solution. The rendering of crude fat as a preparation for analysis is mentioned by Dieterich' and Pastrovich* studying the autohydrolysis of raw tallow rendered it on the water bath with the addition of a few drops of sulphuric acid to decompose the ammonium soaps which had formed in the decomposition. Several washings with hot water freed the fat from excess of mineral acid and i t was then dried, weighed, and its acidity determined. Rendering a fat to free i t from enclosing membranes must be carefully done else the heat will cause a splitting, and oxidation must also be considered. A determination of the amount of water present in the gizzard fat or subcutaneous fat of chickens shows but 5 per cent., or less. This quantity of water, when samples of IO grams are taken for the determination of the acidity, can be disregarded. The supporting membranes are also a negligible quantity. Accordingly, the fat, both that from the gizzard and from beneath the skin, separated mechanically is ground in a meat chopper and weighed directly into a 250 cc. Erlenmeyer flask. To this is added 50 cc. of alcohol which is neutral to phenolphthalein. This dye is then added as an indicator and the whole brought to brisk boiling, preferably on an electric stove which gives an even heat. The hot alcohol dissolves the fat. It is titrated immediately with 0.1 N sodium hydroxide, shaking vigorously, until a pink color appears. The color is not permanent. Indeed it fades very rapidly; hence, a color persisting for one-fourth of a minute can be taken as the end reaction. From the amount of sodium hydroxide used the acid value can be calculated or, if the result is to be expressed as free oleic acid, the latter is found by multiplying the acid value by the factor 0.503. A simultaneous determination of the acidity of the fat by this method and by extraction with petroleum ether according to the official method of the Association of the Official Agricultural Chemists,s as modified by this laboratory, namely, using heat with the solvent to ensure thorough e ~ t r a c t i o n has , ~ been made on fat from chickens kept for varying lengths of time after slaughter and from which the animal heat had been removed both by cold air and by water and ice. The acid value has been determined, also, for both gizzard and subcutaneous fat. The results are collected in Table I. Helfenberger Anmlen, I1 Bd., I1 Dezennuims, 138 (1897). Monatshejte fur Chem., 25, 335 (1904). U. S . Department of Agriculture, Bureau of Chemistry, Bull. 107,revised 1908. Ibid., Bull. 1x5, 66.
5 70
ORGANIC AKD BIOLOGICAI,.
TABLEI.
