I B RARY OF THE U N IVER.SITY OF ILLINOIS 630-7 TM> 445-4-57 25 * and his coworkers have devised means for measuring the length of the induction period and the susceptibility of butterfat to oxidation and have correlated these with the keeping quality of the butter. Triebold, 60 * Coe, 8 * Coe and LeClerc, 9 * Royce, 51 ' 52 * Henderson and Roadhouse, 23 * and Lea 31 * have studied photochemical action as it in- fluences the oxidation of fats. Wright and Overman 66 * observed that heat, copper, and lactic acid reduced the induction period, and that moisture did not retard the oxidation reaction. Others 26 * have found that copper alloys, as well as copper, and Fe 2 O 3 are catalytic oxidizing agents ; that the presence of lactose favors oxidation ; and that over- neutralization of cream accelerates oxidation. Garrett and Overman 14 * found that as the volume of oxygen absorbed by butterfat increased, the permanganate requirement of the fat decreased. In their investigations Mattill and his coworkers, 10 ' 13> 37> 42 * Gret- tie, 20 * Greenbank and Holm, 17 * Shrewsbury and Kraybill, 55 * Caldwell and Bibbins, 6 * Olcott, 41 * and Lea 32 ' 33 * found that among the substances which were found to inhibit oxidation of butterfat are napthols, quinones, cephalin, glycin, asparagin, sodium citrate, sodium malonate, and certain unsaturated polybasic acids such as maleic. OUTLINE OF INVESTIGATION General Procedure Thirty-six butters were studied from differently treated creams. They were taken directly from the churn and were packed in 3-pound paraffined, parchment-lined, Sealright cartons. Eleven to twelve car- tons were filled from each churning except for Butter 28, which had only ten. The first sample of every lot was taken to the laboratory for immediate examination. This was the only sample subjected to the regular routine analysis to determine the percentages of water, fat, casein, ash, and salt.* The remainder of the butter sample was melted over a steam- heated water bath and allowed to stand until the liquid fat had sep- 'Official and tentative methods of analysis of the Association of Official Agricultural Chemists, 1925. 1938] KEEPING QUALITY OF BUTTER IN COLD STORAGE 51 arated in a clear layer. The fat was carefully decanted thru a folded filter paper into a liter bottle with a ground-glass stopper. The other cartons of butter were placed in storage immediately after being packed and were kept at a temperature usually between o and -10 F. One carton of each butter was taken from storage at approximately regular intervals and the fat separated as described above. The usual time intervals between the removal of consecutive samples from storage were 6 weeks for the first six lots of butter, and 10 weeks for the remaining thirty lots. Most of the butters were scored frequently by a competent judge. Examination of Fat The butterfat in every sample of each butter was examined in the laboratory as follows: The index of refraction was determined with a Zeiss Butyro-refrac- tometer. The readings were taken at about 45 C., reduced to corre- spond to 25 C. by formula (Leach, 34 * p. 93) and converted into indices of refraction by referring to the table giving such conversions (Leach, 34 * p. 91). The official Hanus method was used for the iodin absorption number. The saponification (Koettstorfer) number, the soluble acids, the insoluble acids (Hehner number), the free fatty acids, and the acetyl value were determined by the official methods. The method given in Leach 34 * (pp. 499-501) was used for the Reichert- Meissl, Polenske, and Jensen-Kirschner numbers, except that glass beads instead of pumice stone were used in the flasks from which the volatile acids were distilled. Hydrogen-ion concentration of the serum was determined using the quinhydrone method. The mean molecular weights of the fats were computed by the formula: W X 6.000 Mean molecular weight = 3y in which W = weight of fat used and y = ml. of N/2 KOH used in the saponification (Bolton, 2 * p. 36). The induction time and the volume of oxygen absorbed were measured, for the first six butters, by the method used by Wright and Overman. 66 * The apparatus used is shown in the photograph (Fig. 1) and in the detailed diagram (Fig. 2). Before Butter 7 was started, the apparatus was modified by the substitution of a gasometer con- structed of sheet metal for the gas burette and a recording machine" 'Gasometer and record ; ng machine built by J. 73. Hayes, Urbana, 111. [September, FlG. 1. AUTOXIDATION APPARATUS which automatically recorded elapsed time in minutes and the volume of oxygen absorbed at 110 ml. intervals. A DeKhotinsky constant temperature bath, in which transformer oil was the medium for trans- fer of heat, was used thruout the investigation. The oil was heated with Cenco knife-type units thermostatically controlled so that the tem- perature of the fat in the oxidation flask was maintained at 105-107 C. The oxidation flask was a 6-liter, tubulated, round-bottom pyrex flask. The. larger opening was closed with a paraffined cork, thru which passed a motor-driven stirrer and a glass tube with a ground- glass stopcock to act as a vent. The cork in the smaller opening car- ried a thermometer which extended into the fat, an oxygen inlet tube, 1938] KEEPING QUALITY OF BUTTER IN COLD STORAGE 53 FIG. 2. AUTOXIDATION APPARATUS and a separatory funnel thru which the fat was introduced into the flask. The stirrer was constructed of glass and wood and was made gas- tight by means of a mercury seal. The upper portion of the stirrer shaft extending thru the stopper was turned from a piece of straight- grained, well-seasoned birch. After turning, the wood was impreg- nated with hot paraffin. Into the lower end of the wood shaft was fitted a glass rod which extended almost to the bottom of the flask and carried two glass vanes at its lower end. The operation of the oxidation experiments was started by bringing the bath to the desired temperature and replacing the air in the con- necting tubes and the flask with oxygen from the gasometer which had been filled previously from a cylinder of compressed oxygen. Three hundred grams of the melted fat were introduced into the flask, the vent was closed and the stirrer run at such speed that the fat was 54 BULLETIN No. 446 [September, continuously splashed upon the sides of the flask. For the first six butters the induction period was taken as the time which elapsed from exposure of the fat to oxygen until the first visible evidence of oxygen absorption appeared upon observation of the gas burette. The ex- periments were continued until a considerable volume absorption had occurred, in many cases until the rate of absorption had become ex- tremely slow. The volumes of oxygen absorbed and the elapsed time were read and recorded frequently during these experiments. The induction periods for Butters 7 to 36 could not be determined because the electrically operated recording device did not mark volume of oxygen absorbed until the first 110 ml. had been used. For that reason the initial period for these butters includes the induction time and the time necessary for the absorption of the first 110 ml. of oxygen. History and Treatment of Creams The treatment and churning data for the butters are given in Table 1. Butters 1, 2, 3, and 6 were taken from four different churn- ings at the University of Illinois creamery. The history of these creams and the churning data were not obtained. Butters 4 and 5 were obtained as follows: Raw cream testing 50.5 percent fat was separated from the mixed milk delivered by several patrons to the University creamery. The milk was from an evening milking and the following morning milking. The cream was standardized to 40 percent fat with some of the raw skimmed milk and was divided into two batches. The first batch (Butter 4) was pasteurized at 142 F. for 30 minutes, cooled, and standardized to 30 percent fat by adding pasteurized, cooled, skimmed milk obtained from the same skimming in which the cream was obtained. The acidity of the cream after pasteurizing, cooling, and standardizing was .11 percent. The cream was held overnight in a refrigerator at 40 F. or lower, and churned sweet. The second batch of raw 40-percent cream (Butter 5) was stand- ardized to 30 percent by adding raw skimmed milk obtained in the same skimming, and was cooled to 40 F. in ice water. The acidity after standardizing was .11 percent. The cream was held at tem- peratures ranging from 40 to 85 F. until it had become sour and had developed a disagreeable odor. At that time the acidity, having reached .68 percent, was reduced with magnesium lime suspension at 90 to 100 F. The cream was pasteurized at 142 to 145 F. for 30 minutes, cooled to 47 F., held overnight at 40 F. or lower, and churned in a 100-pound churn. 1938} KEEPING QUALITY OF BUTTER IN COLD STORAGE 55 '^ =lll ts IO ID to tO OT -3 '-> iii zz gtO C CD 1 1 -1= 222222 & X&'Z'K COOOOOOOOO OO O O3 OO O O mill zzzzzz CO 00 00 00 00 00 III zzz O5OCO PO O H >. Q Z <|i s 1 H Is "3 i ^;; ssssss O if5 iO tO io iO COC^KMfMO^ CO 00 t~ 00 CO OO 0000000 CO to CO to CO CM * O CO CO CO OCM'W i CHURNING DATA FOR BUTTERS 4 AND 5 j 1 < I o 11 1 "3 Z M erct. Qt. gal. "F. minutes 12 None None 27 10 None Magnesium lime . . ... 22 J ^^^JJJ TP U5 -^ -^ CO C^J I-H i i O OO lO O a> v JJ C C C CTS-O OOOOOO ZZZZJJ G c es c s o o o o co o ^zzz Z ooo^^ OOOOlO t~O .1 ..1 c-a G a-o-a OOOOOO ZJZZJJ o o o oco o ZZZZ Z CM CM CM CM CM oooooo JJ J G fi G C G OCO 0000 Z ZZZZ CO CM CM G G e o o o zzz III zzz 5 given 22 revolutions, jther creams were pasteurized the same day they were separa a Z - oooooo sis 31 revolutions in w pasteurized 5 days "3 3 || OJCM 111111 2222J2 SISSSS CO CO CO CO CO CO I 1 1 fc !*! s n o COCO i-N ^H ^H 1| ig ss d.d> 222222 22iii2 CO CO CO CO CO CO COCOCOMCOCO CO CO CO .1 '3 22 NCMCMNCNKM 777777 C-J