l-f&b person charging to th, , Hbr belov,. JAN 1 5 1991 L 1 61 __0-1096 Certain Biological Factors Related to Tallowiness in Milk and Cream By P. H. TRACY, R. J. RAMSEY, and H. A. RUEHE UNIVERSITY OF ILLINOIS AGRICULTURAL EXPERIMENT STATION BULLETIN 389 CONTENTS PAGE Definition of Tallowiness 579 Relation of Incubation of Milk After Contamination With Metal to the Development of Tallowiness 581 Relation of Incubation of Milk Previous to Contamination With Metal to the Development of Tallowiness 582 Variation in Tendency of Milk to Become Tallowy 583 Yeast Cells as a Retarder of Tallowiness 583 The Homogenizer as a Retarder of Tallowiness 584 Incubation of Cream as a Retarder of Tallowiness in Butter 585 Relation of Oxidation-Reduction Potential to the Develop- ment of Tallowiness 587 Method of Measuring Oxidation-Reduction Potential 588 Oxidation-Reduction Potential of Milk 588 Oxidation-Reduction Potential of Cream 592 Summary 593 Conclusions 594 Literature Cited.. . 595 Urbana, Illinois April, 1933 Publications in the Bulletin series report the results of investigations made by or sponsored by the Experiment Station Certain Biological Factors Related to Tallowiness in Milk and Cream By P. H. TRACY, R. J. RAMSEY, and H. A. RUEHE' B OTH producers and distributors have spent considerable effort in improving the bacterial quality of city milk supplies. Thru the adoption of milk grading systems and the establishment of sanitary inspection services the bacterial quality of raw milk has been greatly improved. Coincident with this improvement, however, there has been an increasing tendency for bottled milk to have a tallowy flavor. Tho in most of the instances of this flavor defect brought to the attention of the authors, metal contamination has been found to be an important cause of the difficulty, the present greater occurrence of tallowiness cannot logically be attributed entirely to this cause. There probably is but little more opportunity for metal contamination to occur now than formerly, and as a matter of fact, some of the most troublesome cases of tallowiness have been found to occur in those plants where special efforts were made to reduce the amount of cop- per and iron contamination to a minimum. This suggests that there is some factor other than those already studied that is related to the development of this off-flavor. In an earlier study Tracy and Ruehe 11 * found that tallowiness in market milk was more common in winter than in summer. They also noted that the tallowy flavor developed to a greater extent when the milk containing metallic salts was stored at 40 F. than when stored at 68 F. These observations led to a further study of the problem, the results of which are set forth in this publication. Definition of Tallowiness The confusion in the literature in the matter of flavor nomencla- ture has made it difficult to correlate the work done on tallowiness in dairy products by the different investigators, both in this country and in Europe. Tallowiness has been described in various ways, possibly because of the different degrees of development that may occur. Such terms as oily, cappy, papery, astringent, and metallic have been used. Tallowiness is recognized as a defect due to the oxidation of the butter fat. Not only is the oxidized fat flavor modified by the intermediate 'P. H. TRACY, Associate Chief in Dairy Manufactures, R. J. RAMSEY, As- sistant in Dairy Manufactures, and H. A. RUEHE, Chief in Dairy Manufactures. 580 BULLETIN No. 389 [April, and end products formed, but it is also influenced by the presence of certain metallic salts which may be detected by taste before the true tallowy flavor is evident. This fact undoubtedly has led to the use of different terms in the description of this defect. Flavors caused by fat oxidation should not be confused with those flavors, commonly called rancid, that are brought about thru fat hy- drolysis. It is evident from studies conducted by the authors that the reaction responsible for hydrolysis is progressive, intermediate products being formed that give different taste reactions. Samples of raw milk having a normal flavor when freshly drawn from the udder may sometimes acquire a "cowy" taste upon storage. This defect later develops into the characteristic rancid flavor and finally reaches a degree of development in which a soapy flavor predominates. Oxi- dation-reduction potential measurements indicate that oxidation plays no part in the formation of these flavors. That the reaction is hydroly- sis is suggested by the increase in titratable acidity that occurs simul- taneously with the development of the flavor. Milk evidently contains an enzyme or other substance responsible for the reaction, since heat- ing the milk to 142 F. renders the agent inactive. Homogenizing the raw milk at low temperatures (90-100 F.) hastens the reaction and intensifies the defect, possibly because in the homogenized milk a greater fat surface is exposed to the agent responsible for the hydroly- sis. Furthermore, an antagonistic reaction between the agents of tal- lowiness and rancidity in raw milk containing copper salts has been shown to exist. This antagonistic reaction makes it necessary in flavor studies to pasteurize samples of milk and cream so as to destroy the cause for rancidity in order to produce a tallowy flavor. Another flavor defect that may be confused with tallowiness is the flavor caused by the action of sunlight upon milk proteins. Tracy and Ruehe 11 * have shown that a short-time exposure of milk in uncolored glass bottles to sunlight will result in the characteristic tallowy flavor. As the time of exposure of the milk to sunlight is increased, however, a point is eventually reached where the tallowy flavor is overshadowed by a burnt flavor. Metallic salts are not a factor in this reaction. Skim milk and low- fat milks develop more pronounced burnt flavors than whole milks or cream. Tracy and Ramsey 10 * have studied a similar flavor defect in cottage cheese. A disagreeable burnt flavor was shown to result from the exposure of cottage cheese in uncolored glass con- tainers to either direct or indirect sunlight, the flavor being more pro- nounced in the curd exposed to direct sunlight. The defect was not so highly developed in the creamed curd as in the plain curd. The 1933] TALLOWINESS IN MILK AND CREAM 581 occurrence of a more pronounced flavor in the plain curd is contrary to the result expected if the flavor were due to the oxidation of butter- fat. In the production of tallowiness oleic acid is thought to be the main constituent concerned. This unsaturated fatty acid has the ability to combine with oxygen to produce aldehydes and acids, some of which have the characteristic tallowy flavor and odor. The butterfat does not become oxidized immediately but passes thru an induction period during which there is practically no absorption of oxygen. The dura- tion of this period depends upon such factors as the amount of oxygen present, heat, light, acidity, and the presence of certain metals such as copper and iron. It thus becomes apparent that the problem of tal- lowiness in dairy products is related to those procedures which may affect the length of the induction period that precedes the rapid ab- sorption of oxygen by the fat. The term tallowiness will be used in this bulletin to refer only to those flavors that result from such reactions. Relation of Incubation of Milk After Contamination With Metal to the Development of Tallowiness When tallowiness occurs in market milk, the first milk thru the system usually has the most noticeable off-flavor, which is undoubtedly due to the fact that the soluble metal oxids which form on the plant TABLE 1. INCUBATION OF PASTEURIZED MILK AS A RETARDER OF TALLOWINESS Milk held at Degree of tallowiness Bacterial count per cc. 40 F. for 12 hre + + + + + 200 80 F. for 2 hre., 40 F. (or 10 hre. 4. 600 80 F. for 4 hre., 40 F. for 8 hre 15 000 80 F. for 6 hrs., 40 F. for 6 hre 32 000 Methylene blue reduction 40 F. for 24 hn + + + + + 10 hre. 68 F. for 2 hre., 40 F. for 22 hre + + + 9 hra. 68 F. for 4 hre., 40 F. for 20 hre 4- 6 hre. 68 F. for 6 hre., 40 F. for 18 hre 5'-j tin. equipment between runs are to a great extent removed by the first milk coming into contact with the metal surfaces. It has been demon- strated many times that during the winter months a sample of the first milk bottled each day at the University of Illinois creamery, when 582 BULLETIN No. 389 [April, held at 40 F. for 24 hours, will become tallowy, whereas a companion sample held at room temperature two or three hours and then placed at 40 F. will have little or no tallowiness 24 hours later. Representa- tive data are given in Table 1. The milk used was the first of a day's run (200 gallons) bottled at the University creamery. Raw milk to which a copper salt had been added was found to respond to incubation in the same way as pasteurized milk. Relation of Incubation of Milk Previous to Contamination With Metal to the Development of Tallowiness As previously mentioned, a tallowy flavor in pasteurized University milk was not noticeable in the summer but was usually pronounced during the winter. This was particularly true of the first milk run thru Benedict nickel internal tubular coolers. This condition was par- tially corrected by eliminating the Benedict nickel coolers and passing the hot milk over a new tinned copper surface cooler. However, even in this case, enough metal was apparently added by passage of the milk thru sanitary pipe lines and thru a bronze piston pump to cause the first milk bottled during cool weather to acquire a distinct tallowy flavor after being held at 40 F. for 24 hours. The defect was much worse during extremely cold weather. With the return of milder outdoor temperatures, the tallowy flavor would be less noticeable and with the arrival of warm weather would disappear entirely. In the fall, how- ever, the trouble would recur. The apparent correlation between climatic conditions and the oc- currence of tallowiness suggested a relation between the extent of biological activity in the raw milk and the tendency of the bottled product to become tallowy. Davies, 2 * working independently in Eng- land, has also come to the conclusion that bacteria are a factor in pre- venting tallowiness, for he states "conditions favoring the develop- ment of taint are low temperature of storage and low bacterial count." Kende 7 * believes "oiliness" of whole milk is caused by an oxidizing enzyme in the milk. He also has found that microorganisms will counteract the oxidation reaction, and he advances the theory that a "factor" is formed in the milk which has the power to counteract the action of the enzyme. The theory that bacteria when present reduce the tendency of the milk to become tallowy is further substantiated by the fact that tallowiness seems to be most prevalent in the milk sold by those distributors who are able to control the bacterial quality of their milk from the time of its production until bottled. In order to determine whether incubation of the milk previous to metal contamination might be a factor in the retardation of tallowiness, 1933] TALLOWINESS IN MILK AND CREAM 583 a series of experiments was performed by the authors, representative results from which are given in Table 2. The incubation of raw milk previous to contamination with metal proved to be a very important factor in retarding tallowiness. In some cases of incubation the in- crease in numbers of bacteria, as determined by the plate count, was very slight, yet the retarding effect upon fat oxidation was marked. TABLE 2. RELATION OF INCUBATION OF MILK PREVIOUS TO METAL CONTAMINA- TION TO DEVELOPMENT OF TALLOWY FLAVOR Treatment of millc* Degree of tallowiness Bacterial count per cc. Aseptically drawn held at 40 F. for 18 hrs ++++++ 15 Aseptically drawn held at 80 F. for 3 hrs., 40 F. for 15 hrs + + 100 Drawn from udder into unsterilized utensils held at 40 F. for 18 hrs 6 600 Drawn from udder into unsterilized utensils held at 80 F. for 3 hrs.. 40 F. for 15 hrs + 34 000 'All samples were exposed to Ambrac metal for 3 minutes at 142 F. three hours after storage at the indicated temperatures. Variation in Tendency of Milk to Become Tallowy The addition of equal amounts of copper salt to different milks does not always result in the development of tallowy flavors of the same degree. In such experiments some milks may become distinctly tallowy in 24 hours, whereas others may not taste tallowy even after 48 hours' storage at 40 F. This was found to be true of milks drawn aseptic- ally from the cow's udder as well as of milks selected from the ship- ments of different patrons delivering milk to the University creamery. The variation in degree of flavor could not be correlated with the per- centage of fat present in the milk. This lack of correlation suggests that milks may contain reducing bodies other than bacteria, such as leucocytes, 1 that are a factor in retarding oxidation of the butterfat. The addition of udder tissue was not found to change the intensity of the defect. Davies 2 * suggests that some of the minor constituents of milk, such as lecithin," cholesterol, and the soluble nonprotein materials, react with some of the chemical oxygen, thus causing variations in the degree of fat oxidation. Yeast Cells as a Retarder of Tallowiness Bacteria having been found to have the power to retard the de- velopment of tallowy flavor in milk, the authors decided to determine to what extent the same effect might be secured by using yeast cells. 'Milk may contain several million leucocytes per cubic centimeter. 584 BULLETIN No. 389 [April, A heavy suspension of yeast cells was prepared by using Fleishman's yeast cake and distilled water. The suspension was then added to milk in the manner indicated in Table 3. TABLE 3. EFFECT OF YEAST CELLS ON DEVELOPMENT OF TALLOWY FLAVOR IN MILK Method of preparing sample" Degree of tallowiness Control + + + + Milk with yeast suspension held at 40 F. for 24 hrs. 1 cc. suspension to J^ pint of milk _ (slight Milk held at 40 F. after yeast suspension heated to 170 F. had been added 1 cc. suspension to % pint of milk yeast flavor) + + + + + + + + 10 cc. suspension to J^ pint of milk + + + + 'All of the milk contained 2.6 parts of copper per million. In this and all subsequent experi- ments the copper used was in the form of copper sulfate. The live yeast cells were found to be very effective retarders of fat oxidation. Heating the yeast suspension to 170 F., however, destroyed the ability of the yeast cells to act in this way. It was not necessary to incubate milk containing live yeast cells in order to pre- vent the formation of tallowiness; the inoculated samples held at 40 F. did not acquire a tallowy flavor. The filtrate from a yeast suspen- sion was also tested and was found to have no effect in retarding tal- lowiness. These data indicate that unless there is an agent formed which is either nonfiltrable or destroyed by heat, it is the metabolism process itself, rather than the end products of metabolism of the cells, that is responsible for the retardation of tallowiness. The Homogenizer as a Retarder of Tallowiness According to Davies, 2 * homogenized milk, because of the increased fat surface, is more susceptible to oxidation than unhomogenized milk. In the Illinois studies, however, it was found that milk to which copper had been added was when homogenized less likely to become tallowy than milk to which copper had been added but which had not been homogenized. In passing the milk thru the homogenizer without pres- sure, the milk apparently became sufficiently contaminated with copper from the machine to cause a tallowy flavor to develop in 24 hours, but with the application of pressure to the milk, tallowiness did not de- velop in any noticeable degree. When a copper salt was added to the milk at the rate of 2.6 parts per million, the homogenized milk still 1933] TALLOWINESS IN MILK AND CREAM 585 remained free from tallowiness after 24 hours of incubation altho both the control milk and that to which the copper was added and which was passed thru the machine without pressure were strongly tallowy. This effect of the homogenizer is thought to be apparent rather than actual. Homogenization changes the physical consistency of the milk, which may affect the taste. When varying amounts of gelatin were added to milk that was contaminated with copper, the degree of tal- TABLE 4. EFFECT OF HOMOGENIZATION ON DEVELOPMENT OF TALLOWY FLAVOR IN MILK Treatment Degree of tallowiness after 24 hre. at 40 F. No copper added Copper added at rate of 2.6 p. p.m. Control + + + Pumped thru 1 Homogenized . valve and lomogenizer without pressure it 142 F. with 2,000 Ibs. pressure on the first 1,000 Ibs. pressure on the second valve lowiness resulting was found to be in inverse proportion to the amount of gelatin added. Such milk, however, when agitated to reduce its vis- cosity, became more noticeably tallowy. The addition of gelatin to milk that had already acquired a tallowy flavor caused the flavor defect to become much less apparent. It would seem, therefore, that the effect of homogenization in reducing tallowiness may be due to a difference in the taste reaction rather than to any reduction in the intensity of the oxidation of the butterfat. As shown in the discus- sion on page 591 the homogenization process has no apparent effect on the oxidation-reduction potential of the milk. Incubation of Cream as a Retarder of Tallowiness in Butter Altho the cream used for buttermaking at the University creamery in the winter is more nearly a sweet cream than that used in the sum- mer months, the authors have observed that the summer cream invari- ably produces a butter freer from metallic and tallowy flavors than butter from the winter cream. It is the usual practice at the University creamery to churn twice each week, using cream delivered by farmers as well as any sweet cream that is left after the needs of the market milk and ice-cream departments have been met. This mixture produces a churning cream of low acidity free from bacterial defects, yet it has a tendency during the winter season to produce a butter with a metal- lic or tallowy flavor. The cream delivered by farmers, as soon as 586 BULLETIN No. 389 [April, weighed and sampled, is usually stored at 40 F. in 10-gallon milk cans for one to three days before being prepared for churning. On several occasions churnings composed almost entirely of sweet cream have been found to produce a butter having the characteristic fat- oxidized flavor. To determine whether incubation of the cream might be a factor in preventing the flavor defect, the writers arranged to have the cream as it was received from the farmers and the surplus pasteurized cream dumped daily into a glass-lined forewarming vat. The cream was kept at room temperature until enough had been received to make a churn- ing. This usually meant storage of the cream for one to three days. With this change of procedure a marked improvement in the quality of butter was noted. For a period of several weeks during the winter this practice of mixing the creams and holding them at room tem- perature for one to three days was continued, with a resulting improve- ment in the butter score from the usual 89-90 to as high as 92. As a result of this practical demonstration of the beneficial effect (from the standpoint of avoiding metallic and tallowy flavors in the butter) of incubating cream to be churned, a series of experiments was conducted under controlled conditions to determine to what extent biological activity in the cream may aid in preventing tallowiness in butter. In these experiments 40-percent cream direct from the separator was cooled to 70 F. and 2.6 parts per million of soluble copper was added. The cream was placed in five glass milk bottles. One bottle was stored at 40 F. and the remaining four bottles were placed at 68 F. At the end of the first day and each succeeding day one bottle was removed from the 68 F. incubator to the 40 F. refrigerator. At the end of five days all the incubated samples were standardized to .3 percent acidity and all lots were pasteurized in the bottles by heating to 142 F. for 30 minutes. After cooling, the samples were stored over night and churned. With the above differences in treatment there was a marked differ- ence in the flavor of the creams and a similar difference in the flavor of the butters. The data in Table 5 are representative of the results obtained. The butter made from cream stored continuously at 40 F. was by far the poorest in flavor, being very tallowy. It was evident that excess incubation would also cause a tallowy flavor to occur in the butter. Sometimes one-day incubation was insufficient, whereas hold- ing the cream at about 70 F. for two days prevented the tallowy flavor from occurring in the fresh butter. It should not be construed from the above findings that proper 1933] TALLOWINESS IN MILK AND CREAM 587 cooling and storing of cream to be made into butter is of no value. As a matter of fact, the incubation of cream when the cream was not contaminated with metal was of no benefit. The data, however, do offer a possible explanation for the fact that practical buttermakers often have difficulty, particularly in the winter or during cool weather, TABLE 5. EFFECT OF INCUBATION OF CREAM ON DEVELOPMENT OF TALLOWY FLAVOR IN BUTTER Cream held at Addity in cream before neutralizing Score of butter 1 day old 40 F. for 5 days perct. .13 87 (very tallowy) 68 F. for 1 day, 40 F. for 4 days .40 90.5 (good) 68 F. for 2 days. 40 F. for 3 days .50 90.5 68 F. for 3 days, 40 F. for 2 days .55 89 68 F. for 4 days, 40 F. for 1 day .60 88.5 (slight tallowiness) in making a good grade of butter from surplus sweet cream obtained from milk and ice-cream plants. Such cream is probably sufficiently contaminated with metal from vats, sanitary pipe lines, coolers, storage cans, and the like, to become tallowy upon storage at 40 F., yet this same cream, if held for a short time at a temperature high enough to encourage the growth of lactic acid bacteria, would probably produce butter with a higher score, or at least with less metallic or tallowy flavor, than if not so treated. Relation of Oxidation-Reduction Potential to the Development of Tallowiness From the data already presented it is to be concluded that organ- isms growing in milk or cream have the power, in some way or other, to prevent or retard the development of tallowiness. This biological action may be explained in various ways. On the basis of phagocytosis the bacterial or yeast cells might be assumed to have the power to sur- round the small metal ions, thus removing them from the field of action and preventing them from exerting their catalytic activity. Such a course, however, does not seem likely because of the physical state in which the metal exists in the milk. That the action is not due to an antioxidizing substance formed thru metabolism was shown by the failure of a filtered or heated yeast cell suspension to prevent the for- mation of tallowiness. It is more logical to believe that the bacteria and yeast function thru their removal of oxygen from the milk. Davis 3 * explains the action of bacteria as one by which the oxy- gen is removed not only by respiratory processes but by the production of systems that are capable of inducing a high-reducing intensity. 588 BULLETIN No. 389 [April, Thornton and Hastings 9 * have reported that milk has reducing proper- ties as it comes from the udder, and Skar 8 * has suggested that the leucocytes may play an important role in causing a reducing potential. The part that these cells play in the reducing of milk in the reductase test is well known. Coulter 1 * has observed the reducing properties of sterile bouillon and ascribes this to a removal of molecular oxygen. Bacteria differ widely in their ability to induce low reducing po- tentials. Hewitt 6 * believes that this ability depends upon the ease with which the organisms form peroxid and catalase. Peroxid-forming or- ganisms such as pneumococci and haemolytic streptococci are not able to induce extremely low potentials. The formation of catalase, accord- ing to Hewitt, prevents the complete dying off of organisms which results from the formation of peroxids, thus maintaining a reducing potential. Frazier and Whittier 4 * have studied the effect of various pure cultures on the oxidation-reduction potential of milk. They found that each organism produced potentials characteristic of that particu- lar species. In another study 5 * they found that Escherichia coli, Es- cherichia communior, and Aerobacter arogenes when grown with streptococcus lactis, all exerted a restraining influence upon the rapid drop in Eh values usually caused by pure cultures of streptococcus lactis. Method of Measuring Oxidation-Reduction Potential To determine to what extent the oxidation-potential reading of milk might be correlated with certain flavor changes, a series of ex- periments was performed to study the significance of those factors already found to be related to the development of tallowiness. The potentials were determined by observing the E.M.F. exerted on bright platinum electrodes, using a saturated KC1 calomel cell as the reference electrode. The burnished platinum foil electrodes were one centimeter square and .003 inch thick. Connections were made from the reference electrode to the samples under measurement by means of a saturated KC1 liquid junction and saturated KC1 agar bridges. Potential readings were reduced to the conventional hydro- gen scale. A Leeds and Northrup Type K potentiometer and a sensi- tive galvanometer were used to measure the E.M.F. Oxidation-Reduction Potential of Milk The variation in the oxidation-reduction potential of milk sub- jected to certain conditions previously found to affect the development of tallowiness is shown in the data in Tables 6, 7, and 8. In Table 6 are the measurements taken on mixed cows' milk of 1933] TALLOWINESS IN* MILK AND CREAM 589 the University herd. In comparing the Eh value of the milk held at 70 F. for 5 hours, and then stored at 40 F., with the measurements made of some of the same milk held at 40 F. continuously, it will be noted that the reading on milk held at 40 F. continuously changed TABLE 6. OXIDATION-REDUCTION POTENTIAL OF MIXED Cows' MILK Time elapsing after setting sample Samples stored at 70 F. for 5 hrs., 40 F. for 14 hrs. Samples stored at 40 F. for 19 hra. Control Copper added 2.6 p.p. in. Control Copper added 2.6 p. p.m. hrs. H Eh .29402 .28795 .27878 .25630 .25980 . 26390 .15837 Eh .32291 .33864 .37288 .34756 .37105 .37016 . 28208 Eh .30730 .31315 .31262 .31226 .30420 .30337 .30242 Eh .30987 .30721 .30342 .30150 .29877 .39891 .43803 1H... 2H 5. . . 6 19 Degree of tallowiness after 24 hrs . . very little while the reading on the milk held at 70 F. made almost a continual drop from the first hour on. The presence of copper changed the potential toward the oxidation side very noticeably in the case of the milk stored at 40 F., while the effect was less pronounced in the milk stored at 70 F., in which sample there seemed to be two forces working, one in the direction of oxidation and the other in the direc- tion of reduction. A more detailed study of potential changes in milk, as brought about by metal contamination and storage temperature variations, is shown by the data in Table 7. Here again it is seen that the milk, upon storage, gradually changed in potential toward the reduction side, the drop being lower in the milk stored at the higher temperature. The introduction of a copper salt, however, caused the potential to swing toward the oxidation side, the milk held at the lower temperature giving the higher reading. As might be expected, there was a greater drop in the milk held at 90 F. for 5 hours than in the milk held at 80 F. for 3 hours, while milk held at 90 F. for 5 hours and then at 80 F. for 3 hours had the greatest drop of all. The incubation of the milk at 90 F. before storage at 40 F. caused a greater decrease in potential than when the milk was stored at 40 F. without incubation. This rapid decline in potential was only slightly checked by the addition of the copper; which fact indicates that incubation starts a reduction action that con- tinues for some time after the temperature is lowered to a point that is 590 BULLETIN No. 389 [April. expected to stop bacterial reproduction. This offers a possible expla- nation for the great difference between the tendency of summer milk and winter milk to become tallowy. The data in Table 7 show rather conclusively that the rapid de- velopment of a tallowy flavor in milk may be brought about by the TABLE 7. OXIDATION-REDUCTION POTENTIAL OF MILK FROM AN INDIVIDUAL Cow Milk held at 40 F. for 5 hrs.. Milk held at 90 F. for 5 hra., then treated as below then treated as below Time of Control Copper added 2.6 p.p.m. Control Copper added 2.6 p.p.m. Held at Held at Held at Held at Held at 80 F. for Held at 80 F. for Held at 80 F. for Held at 80 F. for 40 F. for 3 hrs.. 40 F. for 3 hrs.. 40 F. for 3 hrs.. 40 F. for 3 hrs.. 24 hrs. 40 F. for 24 hrs. 40 F. for 19 hrs. 40 F. for 19 hrs. 40 F. for 21 hrs. 21 hrs. 16 hrs. 16 hrs. hrs. Eh Eh Eh Eh Eh Eh Eh Eb 5 . 28346 .28372 .28755 .27630 .26526 . 23607 .27168 .25125 .28206 . 26996 . 28059 .30075 .24530 . 1 7984 .23820 .20262 JQ1X .27560 .26787 .28262 .29846 23095 17278 .22617 .18109 JJI/ .27297 .26630 .28745 . 29663 .22751 .19677 .20630 . 16325 24 .27166 .26416 . 33246 .31180 .15408 .09127 .19728 . 12429 Degree of tal- lowiness after 24 hrs.... ~++ + + + + presence of a catalyst such as copper, and that incubating the milk at 80 to 90 F. may result in a retardation of the oxidation. In these tests the potential of milk containing added copper held at room tem- perature would sometimes change rapidly at first towards the oxidation side and later swing back towards the reduction side sufficiently to pre- vent the tallowy flavor. This condition is possibly due to the ability of the copper salts to catalyze oxidation reactions more rapidly at first than the metabolism of the bacteria can cause the reverse reaction to occur. The data in Table 8 show how the presence of yeast cells affect the potential, bringing it well below .3000 Eh, which seems to be the approximate point above which tallowy flavors are likely to occur. The drop in the potential to .26830 Eh of the milk containing the cop- per and held at 80 F. for 3^ hours, followed by a rise to .33483 Eh 4 hours later, probably accounts for the fact that this sample was slightly tallowy after 24 hours. 1933] TALLOWINESS IN MILK AND CREAM 591 TABLE 8. EFFECT OF YEAST ON THE OXIDATION-REDUCTION POTENTIAL OF RAW MILK Time elapsing after setting sample Samples held at 80 F. for 3M hrs.. 40 F. for 8 hrs. Samples held at 40 F. for 11 )$ hrs. Control Copper added 2.6 p. p.m. Control Copper added 2.6 p. p.m. Copper 2.6 p. p.m. plus yeast hrs. Eh .31397 . 29303 .27867 .27287 .25703 .25161 Eh .32108 .33132 .30793 .29960 .26830 .33483 + Eh .33460 .31846 .31345 .30960 .30755 .29494 Eh .33471 .33573 .33080 .33595 .36394 .35970 + + + Eh .33353 .32186 .31462 .31600 .31987 .27096 l\t 314 5 V yix 11>$ Degree of tallowiness after 24 hrs A comparison of the Eh value of homogenized milk with that of unhomogenized milk is shown in Table 9. The milk pumped thru the homogenizer had practically the same increase in Eh regardless of whether or not it was subjected to pressure. This was true of the milk to which the copper was added as well as of the control samples. Ap- parently enough metal contamination occurred in passing thru the homogenizer to catalyze the oxidation process, resulting in an increase of Eh toward the oxidation side. The close relationship between the Eh value of the homogenized and unhomogenized milk indicates that the lessened intensity of the tallowy flavor developing in homogenized milk needs to be explained in some other way than on an oxidation- reduction basis. TABLE 9. EFFECT OF HOMOGENIZATION ON THE OXIDATION-REDUCTION POTENTIAL OF FRESHLY DRAWN MILK PASTEURIZED AT 142 F. FOR 30 MINUTES Time elapsing after setting sample Control (no copper) (40 F.) Copper added 2.6 p.p.m. (40 F.) Control Passed thru homogenizer no pressure Homogenized 2 500 Ibs. 1st valve, 1 000 Ibs. 2d valve (135 F.) Control Passed thru homogenizer no pressure Homogenized 2 500 Ibs. 1st valve, 1 000 Ibs. 2d valve (135 F.) hrs. V.. . 26448 .26167 .25973 .26500 .26610 .28237 + + + + .26495 .26485 .28445 + .26650 .26497 .28526 + + + + .27026 .28136, .32329 + + + + + .27003 .28079 .32558 + s\i . I6\i Degree of tallowiness 24 hrs. after setting 592 BULLETIN No. 389 [April, Oxidation-Reduction Potential of Cream As previously noted, incubation of cream contaminated with metal at temperatures high enough to permit bacterial growth was found to improve the flavor of butter made from the cream as compared with the flavor of butter made from some of the same cream stored at 40 F. Eh measurements of such cream revealed much the same situa- tion as exists in the case of milk (Table 10). With incubated cream, TABLE 10. OXIDATION- REDUCTION POTENTIAL OF RAW CREAMS CONTAINING 35 PERCENT BUTTERFAT Time elapsing after setting sample Eh measurements of cream (copper added 2.6 p.p.m.) Held at 40 F. Held at 90 F. hrs. U .28555 .31124 .33191 .34824 .37662 .36708 .34951 .31786 .28040 .27443 .23264 -.02429 -.11039 -.08961 -.10553 - . 10585 - . 10555 - . 10693 3W 5j| 24. . 48 96 120 144 Butter scores (one day after manufacture) Butter made from cream held at 40 F. for 5 days 86.5 at 90 F. for 1 day. 40 F. for 4 days 90.5 at 90 F. for 2 days, 40 F. for 3 days 90.0 at 90 F. for 3 days. 40 F. for 2 days 89 5 at 90 F. for 4 days, 40 F. for 1 day 89.0 (slightly metallic) at 90 F. for 5 days 89.0 (slightly metallic) however, the Eh values dropped well below the positive side. After the second day there was practically no change in Eh reading, a fact which suggests a change in the nature of the biological activity in the cream at that time. The quality of the butter also became less desirable at this point. In studying the Eh values of the cream held constantly at 40 F., a maximum oxidation about the end of the first day was noted, after which the potential moved toward the reduction side. This phase of the study deserves further investigation, for it suggests the possible application of Eh measurements in the laboratory control of commercial butter manufacturing processes. 1933] TALLOWINESS IN MILK AND CREAM 593 Summary Data presented in this study show that milk contaminated with a copper salt is more likely to become tallowy if stored immediately at 40 F. than if held at higher temperatures (68 -90 F.) for 1 to 6 hours before being placed at 40 F. It was also found that milk incu- bated previous to contamination with metal is less likely to become tal- lowy than milk cooled immediately to 40 F. after being drawn from the udder of the cow. Milks from individual cows differed in their tendency to become tallowy. This difference is thought to have been due to cells or other antioxidizing substances contained in the milk. Living yeast cells retarded the development of tallowiness in milk stored at 40 F. Dead cells or the filtrate of a yeast suspension had no such effect. Homogenization was found to retard the development of a tallowy flavor in milk. This retardation is thought to have been due to certain physical change in the milk which made it less possible for the judge to detect the development of tallowiness organoleptically. Incubation of cream to which copper had been added raised the score of the butter 3.5 points. Holding the cream at room temperature for one to two days resulted in a butter free from tallowiness, while the butter made from cream stored at 40 F. was very tallowy. Oxidation-reduction studies showed a normal tendency toward re- duction in freshly drawn milk. Upon the introduction of copper the potential was found to move toward the side of oxidation. Incubation of the milk usually caused a rapid drop in potential. Yeast cells like- wise caused a reduction in potential. Eh values of cream showed much the same effect of metal and temperature variables as Eh values of milk. It is evident that oxidation-reduction potentials are related to fat oxidation in dairy products. Bacteria and yeast result in a change of potential towards the reduction phase, which suggests that a removal of oxygen occurs thru the metabolism process of the organisms. This undoubtedly explains why milk of very good quality, from a bacterial standpoint, is more likely to become tallowy than is milk more highly contaminated. Winter milk, especially that from certified dairies and other careful producers, may be expected to become tallowy readily when contaminated with copper salts. 594 BULLETIN No. 389 [April, Conclusions 1. Incubation of milk contaminated with copper at 68-90 F. retards the development of tallowiness which normally occurs in such milk stored at 40 F. 2. Incubation of milk at 68-90 F. previous to contamination with copper retards the development of tallowiness. 3. Growth of bacteria in milk will retard the development of tallowiness. 4. Yeast cells will retard the development of tallowiness in milk stored at 40 F. 5. Milks differ in their tendency to become tallowy. 6. Homogenization of milk contaminated with copper causes the tallowy flavor to be less apparent. 7. Incubation of cream contaminated with copper greatly re- duces the degree of tallowiness in the butter. As much as 3.5 points difference in the score of butter may be effected by ripening metal- contaminated cream one or two days before churning. 8. Oxidation-reduction measurements on milk show that: a . Aseptically drawn milk will develop a lower Eh reading upon storage at either 40 F. or room temperature. b. The addition of a copper salt will cause the potential to rise rapidly toward the oxidation phase. c. Bacteria or yeast cells cause a rapid reduction to take place in the milk. 9. Oxidation-reduction measurements on cream show the same general effects of metal contamination and incubation as in the case of milk. 10. The metabolism of bacteria and yeast cells in dairy products plays an important part in the control of tallowy flavors. The effect is probably that of oxygen removal. 11. Bacterial metabolism in the raw milk probably accounts for the general absence of tallowy flavors in pasteurized milk produced during the summer months. 12. Lack of bacterial metabolism in raw milk probably accounts for the tendency for some pasteurized milk to become tallowy during the winter, especially in the case of those dairies that are able to control the quality of their milk from the time of production until it is placed in the bottle. 1933] TALLOWINESS IN MILK AND CREAM 595 13. Lack of bacterial metabolism in the surplus sweet cream of milk plants and ice-cream plants during the winter months is probably the reason this cream, when churned, often produces a butter with a metallic, tallowy flavor. Literature Cited 1. COULTER, C. B. Oxidation-reduction equilibria in biological systems. I. Re- duction potentials of sterile culture bouillon. Jour. Gen. Physiol. 12, 139-146. 1928. 2. DAVIES, W. L. The action of strong sunlight on milk. Certified Milk 6, No. 61, 4-5. 1931. 3. DAVIS, J. G. The oxidation-reduction potentials of ripening cheddar cheese. Jour. Dairy Res. 3, 241-253. 1932. 4. FRAZIER, W. C., and WHITTIER, E. O. Studies on the influence of bacteria on the oxidation-reduction potential of milk. I. Influence of pure cul- tures of milk organisms. Jour. Bact. 21, 239-251. 1931. 5. - Studies on the influence of bacteria on the oxida- tion-reduction potential of milk. II. Influence of associated cultures of milk organisms. Jour. Bact. 21, 253-262. 1931. 6. HEWITT, L. F. XXIII. Oxidation-reduction potentials of pneumococcus cul- tures. II. Effect of catalase. Biochem. Jour. 25, 169-176. 1931. 7. KEXDE, SIGMUND. Reasons for and combating of "oily" milk defects ("Olei- nase," a new enzyme in the milk). Internat. Dairy Cong. Paper No. 137 (Summary), Section 3, Supplement, p. 55. 1931. 8. SKAR, OLAV. Verhalten der Leukozyten der Milch bei der Methylenblau- Reduktaseprobe. Ztschr. Fleisch u. Milchhyg. 23, 442-447. 1913. 9. THORNTON, H. R., and HASTINGS, E. G. Studies on oxidation-reduction in milk. I. Oxidation-reduction potentials and the mechanism of reduction. Jour. Bact. 18, 293-318. 1929. 10. TRACY, P. H., and RAMSEY, R. J. Sunlight develops off-flavors in cottage cheese. Milk Dealer 21, No. 8, 48. 1932. 11. - and RUEHE, H. A. The relation of certain plant processes to flavor development in market milk. Jour. Dairy Sci. 14, 250-267. 1931. AUTHOR INDEX 597 AUTHOR INDEX 1. ANDERSON, H. \V., and KADOW, K. J. Anthracnose and Gray Bark of Red Raspberries. .281-292 2. ASHBY, R. C. Shrinkage of Hogs From Farm to Market by Truck and by Rail 557-576 3. ASHBY, R. C. See NORTON 16 4. BAUER, F. C. Crop Yields From Illinois Soil Experiment Fields in 1931 225-280 5. BURLISON, \V. L. See STEWART 21 6. DORSEY, M. J. and POTTER, J. S. A Study of the Structure of the Skin and Pubescence of the Peach in Relation to Brushing 405-424 7. JONES, FRED REUEL See KOEHLER 9 8. KADOW, K. J. See ANDERSON 1 9. KOEHLER, BENJAMIN, and JONES, FRED REUEL Alfalfa Wilt as Influenced by Soil Tempera- ture and Soil Moisture 37-80 10. LEWIS, E. P. See LLOYD 1 1 11. LLOYD, J. W., and LEWIS, E. P. Fertilizer Experiments With Ten Market-Garden Crops in Cook County, Illinois 1-36 12. LLOYD, J. W., and NEWELL, H. M. Causes of Damage to Fruits and Vegetables During Shipment 81-120 13. LLOYD, J. W. See NEWELL 14 14. NEWELL, H. M., and LLOYD, J. W. Air Circulation and Tem- perature Conditions in Refrig- erated Carloads of Fruit . . 157-224 15. NEWELL, H. M. See LLOYD 12 16. NORTON, L. J., and ASHBY, R. C. Price Differences Between Four Hog Markets Used by Illinois Stockmen 121-156 17. NORTON, L. J. See STEWART 21 18. POTTER, J. S. See DORSEY 6 19. RAMSEY, R. J. See TRACY 23 20. RUEHE, H. A. See TRACY 23 21. STEWART, C. L.; BURLISON, W. L.; NORTON, L. J.; and WHALIN, O. L. Supply and Marketing of Soybeans and Soybean Pro- ducts 425-544 22. TRACY, P. H. How to Make Honey-Cream, a Mixture of High-Test Sweet Cream and Extracted Honey 545-556 23. TRACY, P. H.; RAMSEY, R. J.; and RUEHE, H. A. Certain Biological Factors Related to Tallowiness in Milk and Cream 577-596 24. WHALIN, O. L. See STEWART 21 25. WOODWORTH, C. M. Genetics and Breeding in the Improve- ment of the Soybean 293-404 598 INDEX INDEX Air circulation in refrigerated fruit cars, experiments on 157-224 See Contents 158 Aledo experiment field yields. . .246-247 Alfalfa, growth of, influence of soil moisture 59-61 of soil temperature 48-53 roots, chemical composition of. . 72-74 development of wilt bacteria in 68-71 modifications in structure of. .62-68 Alfalfa wilt, characteristics of 39-40 influence of soil temperature and soil moisture on development of 37-79 Anthracnose of red raspberries. .281-292 See also Gray bark Antioch experiment field yields. . . . 247 Apples, tests with refrigerated trans- portation 170-197 Beans, fertilizer experiments with . . 17-21,33-36 Beets, fertilizer experiments with. . . 13-15,33-36 Bloomington experiment field yields 247 Butter, tallowy flavor in, effect of incubation of cream on . . . .585-587 Carlinville experiment field yields. . 248-249 Carthage experiment field yields. 249-251 Carrots, fertilizer experiments with .28-29,33-36 Cauliflower, fertilizer experiments with 31-36 Chicago hog market, prices compared with East St. Louis, Indianap- olis, and Cincinnati 127-147, 153-154 Cincinnati hog market, prices com- pared with Chicago, East St. Louis, and Indianapolis 128-134, 147-150, 153-154 Clayton experiment field yields. .251-252 Cream, high-test, use in making honey -cream 547-552 Cream, tallowy flavor in 578-595 Crop increases from soil treatments, net value of 240-241 Crop quality, influence of soil treat- ment on 242-244 Crop residues, value of in soil treat- ment 233-234 See also Index. . . 245 Crop rotations ending in 1931, sum- mary of results of on experiment fields 230-245 Crop yields on experiment fields in 1931 227-229,246-278 Dixon experiment field yields. . .252-253 East St. Louis hog market, prices compared with Chicago, Indian- apolis, and Cincinnati 127-150, 153-154 Elizabethtown experiment field .... yields 253 Enfield experiment field yields 254 Ewing experiment field yields. . . 255-257 Farm scales, accuracy of 561, 564 Fertilizers, organic manures, index to tables showing results from .... 245 mineral, index to tables showing results from 244-245 Fruit, air circulation and tempera- ture conditions in refrigerated carloads of 158-224 causes of damage to during ship- ment 81-119 Fertilizers, experiments with on market-garden crops in Cook county 1-36 Gray bark, disease of red raspberries 281-292 control 291-292 history 283 symptoms 284-291 Hartsburg experiment field yields. . 257-258 Hog markets, price differences be- tween 122-154 Hog prices, methods of reducing inter-market variations. . . . 151-153 Hogs, shrinkage of from farm to mar- ket, comparison of by truck and by rail 557-576 effect of feeding on 566-573 effect of method of handling on 565-570 Honey, use of in honey-cream 547,551-556 Honey-cream, description 547, 555 flavoring 553 keeping qualities 553-555 manufacture 546-555 packaging 552 use. . . 555 INDEX 599 Indianapolis hog market, prices com- pared with Chicago, East St. Louis, and Cincinnati 127-134, 143-150, 153-154 Joliet experiment field yields.. . .258-260 Kewanee experiment field yields. 259-261 LaMoille experiment field yields. 261-262 Lebanon experiment field yields. 262-264 Lettuce, fertilizer experiments with 10-13,33-36 Limestone, as vegetable fertilizer. . .6-36 importance of in soil treatment. . 234-237 See also Index 244 Livestock, shrinkage of during ship- ment 558-576 McNabb experiment field yields.. . . 265 Manchuria, production of soybeans in 429^30,537,544 Manure, as vegetable fertilizer 6-36 variable response to 231-233 See also Index 245 Marketing, fruit, investigations of refrigerated transportation. 159-224 fruits and vegetables, experiments with 83-119 hogs, by truck and by rail .... 558-576 Markets, hog, factors influencing choice of 124-127 price differences between. . . 122-154 Milk, effect of sunlight on flavor . 580-581 rancid flavor in 580-581 tallowy flavor in 578-595 Minonk experiment field yields. . . . 265 Morrow plots, yields on (1931) 278 Mt. Morris experiment field yields 266-267 Newton experiment field yields. .267-268 Nitrogen, as vegetable fertilizer. . . .8-36 See also Index 244 Oblong experiment field yields. .269-270 Odin experiment field yields. . . .269-271 Oquawka experiment field yields. . . 271 Paint, use ot soybean oil in 463-466 Palestine experiment field yields. 271-273 Peaches, brushing of 418-424 effect on keeping quality. . .422-424 effect on peach hairs 419-422 effect on skin 419 study of skin structure and pubes- cence in relation to brushing. . 405-124 tests with refrigerated transpor- tation of 197-213 Peas, fertilizer experiments with. . . ...15-17,33-36 Peppers, fertilizer experiments with 25-27, 33-36 Phosphates, as vegetable fertilizers. . 6-36 Phosphorus, need for by some soils 237-239 See also Index. . . 244 See also Phosphates Phytomonas insidiosum 40 See also Alfalfa wilt Plectodiscella veneta, causal fungus of anthracnose 286-290 See also Gray bark Potash, as vegetable fertilizer 6-36 importance in soil treatment 239 See also I ndex 245 Potatoes, fertilizer experiments with 29-31,33-36 Price differences between four hog markets used by Illinois stock- men 121-154 Prices, farm products, reasons for variability in 150-151 Prices, hog, methods of reducing intermarket variation 151-153 Pubescence of the peach, study of in relation to brushing 406-424 Rail, use of in hog marketing. . .558-576 Raleigh experiment field yields 272 Rancidity in honey-cream, preven- tion of 554-555 Raspberries, anthracnose and gray bark of 282-292 Separator, cream, use in manufac- ture of honey-cream 547-551 Shrinkage of hogs during shipment, comparison of by truck and by rail .558-576 Soil, systems of treatment on Illinois fields ....230-245 Soil experiment fields, crop yields from in 1931 246-278, 227-229 Soils, variation in natural produc- tivity 230-231 Soybean breeding, experiments with 295-404 improvement of oil and protein content 357-371 quality of oil. . 371-373 resistance to disease 373-377 yield of seed 377-399 inheritance in 305-335 genes, list of 333-334 plant characters 323-333 linked characters 334-336 seed characters 305-323 method of reproduction 300-304 methods of breeding, selection . . . 344-351 cross-fertilization or hybridiza- tion 352-357 variation in 336-344 Soybean cake, duties on 454-455 exports of 532-533 imports of 453, 532-533 Soybean oil, contracts for sale of .491-493 competition from other oils. . .469-473 duties on 454-455 exports of 533 600 INDEX imports of 453-454, 531-532 prices of 509-510, 519-524 supply of 455-458 utilization of in paint, soap, edible products 463-467 Soybean oil meal, contracts for sale of 491-193 duties on 454-455 exports of 532-533 imports of 453-454, 532-533 prices of 509-510, 524-528 effect on use 526-528 use- values of in feeding 507-509 utilization of 462-463 Soybean products, industrial, list of 460 feed, list of 460 food, list of 460 See also Soybean cake, Soybean oil , and Soybean oil meal Soybeans, consumption of 459-475 costs and returns in producing. 448-453 disposition of domestic crop. . .459 160 duties on 454-455 exports of 530-534 gathered, distribution by uses. 473-475 genetics and breeding in improve- ment of See Soybean breeding imports of.. 453-454, 531-534 increase in importance of .427, 537-541 marketing of, costs in 493-503 information on 477-482 practices of 475-493 price risks in 528-530 systems of, federal inspection. . 503-507 federal grade requirements. . 505-507 place of in Illinois farming. . .534-536 prices of, effect on use 526, 528 processing of, methods for. . . .467-469 production of in Illinois 443-446 in selected countries 432-433 in the United States 433-443 seed, industrial uses for 486-491 price of 510-519 sale of 482-486 supply of 432-458 use of as feed for livestock 536 use-values of in feeding 507-5 10 varieties of in Illinois 446-447 Sparta experiment field yields. . .273-274 Spinach, fertilizer experiments with 6-10,33-36 Springvalley experiment field yields ....274-275 Strawberries, tests with refrigerated transportation 213-222 Sunlight, effect on flavor of milk and cheese 580-581 Tallowiness, in milk and cream, bio- logical factors related to. . .577-595 in dairy products, definition of. . 579-581 in honey-cream 553-555 Temperature conditions in refriger- ated fruit cars, experiments on 159-224 See Contents 158 Toledo experiment field yields. .275-276 Tomatoes, fertilizer experiments with 21-25,33-36 Train schedules, influence on differ- ences in intermarket hog prices 150 Trucks, use of in hog marketing. 558-576 Unionville experiment field yields. . 277-278 Urbana experiment field yields 278 Vegetables, causes of damage to dur- ing shipment 81-119 West Salem experiment field yields. 278 UNIVERSITY OF ILLINOIS-URBANA Q 630 7IL6B C002 BULLETIN. URBANA 377-3891932-33 30112 019529228