LIPOLYSIS IN RAW MILK


Voi. I, p. 2%. New Yoik. Chornical Cstnloi: Go.. 1926. (5) Harkins. W. D., and Brown, f. E., J. Am. C h m ~. Soc., 41, 502. (1919). (6) Intcmational C...
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INDUSTRIAL AND ENGINEERING CHEMISTRY

876

13

A

3. An increase in the butyl alcohol and butyl acetate content of solvent mixture A as used in solvent mixture A. was not factor. 4. Apparently the relative viscosity of solutions of mixture A was not a controlling factor. 5. The pulling-away effcct in a film seems to occur a t the point of discontinuity of tlie plane snrface-e. g., ridges, edges of film, specks of solid matter in the film. 6. The pulling-avay effect is undoubtedly influenced by other factors such as interfacial tension and the adsorbed surface layer, but the reduct.ion of surface tension by t.he addition of suitable substasicov results in uniformity of coating. Therefore, it appears that surface tension is tbe predominant factor in the systems studied.

TABLE VII.

VOL. 32, NO. 6

DILUENTSFOR NITROCELLULOSE SOLUTIONS

-

Mixture A

Butyl soelate Butsnol Toluene

Be"Zene

Tr"l"0il

30

30

10

10

,. ..

eo

60

Mixture B

.. .

..

..

P"lli.z-aw.yeBeat

Ye.

Yea

No

Anhydiolra ethyl alaohol

..

30

.. .. 35

..

.. .. .. 35

.. .. .. ..

N"

Nos

33

Petrobensolb

.,

33

a3 12 20 .. 33

.. ..

Apcothinnerr

Mixture X

Poilr by volume

12

20

12 20

10 30

30

NO

( 4 ) Harkins. W. D.. in Jerome .Iloxander's "Colloid Chemistry", Voi. I, p. 2%. New Yoik. Chornical Cstnloi: Go.. 1926.

(5) Harkins. W. D., and Brown, f. E., J . Am. C h m Soc., ~ 41, 502 (1919). (6) Intcmational Critioal Tables, Vol. IV, PP. 446, 454. New York, MoGraw-Hill Rook Co.. 1928; Central Soientifio Ca., Ball. 101, 7 (1939). (71 International Critical Tables, Val. IV. D. 451. Nsw York. MeGraw-Iiill Book Co., 1928. ( 8 ) Mardles, E. W. J., Trm8. Faiadny Snc.. 29, 476-85 (1938). (9) Moll, W. L. H., and Fuller, G. W.. Kolloid-Z.. 79, ZO9-1a ,1,,11\ ,LOO,>.

Acknowledgment The authors gratefully ackuowledge the suggestions and criticisins of several lacyuer chemists who have given unselfishly of their time.

Lilerature Cited (1) Doolittlc, W. K., IND.EXU.C a ~ r .30. . 1x9 (1938). ( 2 ) Dorsch, J. B.. and Stewart, J. K . , Ibid., 30, 325 (1938). (3) I'reundlich. H.. in "Wetting and Ikteri(eney". P. 3 , New York. Chemical Pub. Co., 1937,

(10) Murray, C. A., and Bnrtcil, li. E., page 152, Natl. Paint. Vainiah Laoqucr Aasoo., Sei. Seot., papers prevented before meeting Fed. Paint Varnish Production Clubs, Chicago, 1939. (11) Naksshirna. T., and Nexishi. M.. J . Soc. Chem. Ind. Jalawn. . . 37. Suppl. binding 327--31 (1934). (12) Stewart, J. X., Dorsch, J. B., and Eopper, C . B., IND. ENG. CHEM.,29, 899 (1937). (13) Waterman. H. I.. and Leendertse. J. J.. J . Inst. Pe2rolezm Tech.. 24, No. 171,25 (1938). (14) Womom, W. E., in "Wetting and Detergenoy". p. 97, New York, Cherniaal Pub. Co.. 1937. PASBSNTED beiore the Division of Paint and Vsrnisli Cbemiatry st the 98th kleeiing of tho Amciioan Chemioal Society, Boaton. Mass.

LIPOLYSIS IN RAW MILK Influence of Homogenization Temperature I. A. GOULD Michigan

State College, East Lansing, Mich.

IIE fact that homogenization of raw milk rapidly and greatly increases the lipolysis of the milk fat is now gcnerally accepted. Thisincrease in free fatty acids due to lipolytic action has been determined by titration of the milk, by titrat.ion of sugar substrates to which the homogenized milk is added, and b y titration of the milk f a t itself. Studies by Gould and Trout (3) showed that the latter procedure was more sensitive than those involving the milk. The titration of tlie free fatty acids in the fat bas since been used with excellent results by Herrington and Krukovsky (4, 6, 6) in determining certain of the factors influencing the fat splitting in normal raw milk. Various workers have studied the heat inactivation or inhibition of milk lipase, the most recent being Sharp and de Tomasi (9),Doan (Z), Krukovsky and Sharp (7), Krukovsky and Herrington (6), and Pfeffer, Jackson, and Weckel (8).

T

Doan determined lipase action by titrating raw homogenized milk, supplementing the titration with pH and surface tcnsioii measurements. However, Sharp and de Tomasi (9) and Pfeffer et al. (8) titrated sugar substrates t o determine lipolytic changes; and Krukovsky and Herrington made their titrations directly on the fat. Doan studied heat inactivation of lipase and found that increases in acidity due to lipolysis were prevented by heating the milk t o 147' F. momentarily, t o 134"for 15 minutes, and t o 132' for 30 minutes. Krtikovsky and Sharp (7) found that milk separated at 45-50' C. (113-122" F.) gave eream showing less lipolysis than did cream from the same milk separated a t 10-15" C . (50-59O F.). They attributed the difference t o the fact that the fat in one instance was in a liquid state when separated. Tbesc results are in accord with the earlier suggestions of

JUNE, 1940

IhDUSTRIAL AXD ENGINEERING CHEMISTRY

877

Sharp and de Tomasi. Pfeffer et nl. (8) attributed the decrease in lipase activity secured when milk was separated a t 120" F. to inhibition of the enzyme by heat. Krukovsky and Herrington ( 6 ) determined the influence of preheating temperatures on the acid degree of the milk fat. They found that warming of cold raw milk followed by cooling greatly accelerated the lipolysis which occurred during storage. The lipase action was increased a t temperatures u p to approximately 35" C. (95" F.), whereas higher temperatures of 40" C. (104" F.) or above gave results practically identical with those secured for 15" C. (59' F.). The maximum acceleration was secured by warming the milk to 30" C. (86" F.). Consideration is giren in this study to the influence of different temperatures of homogenization on the rate and extent to which lipolysis occurs.

ture was 105" although 115" F. gave results practically as great. The same trend existed both in the 0-hour and T2hour samples. Homogenizing at 125" F. also gave a high degree of fat splitting, whereas a marked decrease in lipolysis occurred a t 135" F. However, even this temperature gave an appreciable increase of fat acidity during the 72-hour storage period; appreciable lipase activity was indicated as well as the fact that this temperature is not sufficient to inactivate, although it does inhibit, the enzyme. Indeed, the milk which was homogenized a t 145" F. underwent a certain amount of lipolysis, as shown by the fact that the acid degree increased on a n arerage from approximately 0.5 to approximately 2 during the '72-hour period.

Procedure A large quantity of mixed raw milk was obtained and divided into lots. Each lot was quickly heated t o the temperature desired, in a ivater hath maintained at 180-190" F. Immediately upon reaching the proper temperature, the milk was homogenized (vixolized) at 1500 pounds per square inch pressure and promptly cooled to beloxT 40" F. Each lot was then divided into two portions. One portion was immediately pasteurized at 145-150' F. for 30 minutes to prevent further lipolytic changes; the other portion was stored at 35-40' F. for 72 hours and then pasteurized

Raw milk heated momentarily and hoinogenized at 70°, 105O, 115O, 125', 135', and 145' F. underwent lipolysis i n every case. The maximum fat splitting occurred within the temperature range 105-125O F. Temperatures of 135-145' F. inhibited but did not entirely prevent lipolysis accelerated by homogenization.

The samples homogenized a t 70" F. showed slight fat splitting. The average titration Talues for these samples was slightly above those secured foi the 133" F. samples a t 0 hour but Bere considerably lower than the values secui ed after the storage period. The lon degree of l i p o l p s in the 70" F. sample might be attributed to the fact that the fat globules were in the Tolid state nlien homogenized and nere not broken donn as efficiently as were the globule.. in the othei samples.

il

i

/ I

-

0 HOUR

\ '0 I------O

FIGURE1.

ISFLUENCEOF TEMPERATURE OF HOMOACID D E G R E E OF FATAFTER 0 AND 72 HOURSOF STORAGE The acid degree is defined as the milliliters of 1.0 N sodium hydroxide required to neutralize the free fatty acids in 100 grams of fat. GESIZATION U P O N

Following pasteurization, the milk was separated and the cream cooled. The cream was churned in a small glass churn; the fat was melted, centrifuged, and filtered free of water and solidsnot-fat. The purified fat was then titrated for free fatty acids by the A. 0. A. C. method ( 1 ) . This method involves the use of 20 grams of fat and 50 ml. of neutral alcohol. In these trials the titration m-m conducted using 0.1 N sodium hydroxide and titrating t o the phenolphthalein end point. The following temperatures of homogenization were used: 7 0 ° , 105", llj', 125", 135", and 145' F. Three trials were conducted with practically identical results in each case. As Figure 1 shows, the maximum amount of fat splitting occurred when the homogenization tempera-

Literature Cited (1) Assoc. Official Agr. Chem., Official and Tentative Methods o f Analysis, 3rd ed, 1530. (2) Doan, F. J., M i l k Dealer, 23 (Z), 40 (1933). (3) Gould, I. A , , and Trout, G. M.,J . A g r . Research. 52, 49 (1936). (4) Herrington, B. L., and Krukovsky, V. N., J . Dairy Sci.. 22, 127 (1939). (5) Ibid., 22, 145 (1939). (6) Krukovsky, V. N., and Herrington, B. L., Ibid.. 22, 137 (1939). (7) Krukovsky, V. N.. and Sharp, P. F., Ibid.. 19, 279 (1936). ( 8 ) Pfeffer, J. C., Jackson, H. C., and Weckel, K. G., Ibid., 21, 143 (1938). (5) Sharp, P. F.. and Tomasi, J. A. de Proc. 25th Alan. Cona. Intern. Assoc. M i l k Dealers, Lab. S c c f . , 1932, 3. AUTHORIZED as Journal .irticle S o . 400, S. S., from the Uichigan Agricultural Experiment Station.

Ignition in Beds of Solid Fuel-Correction An error has been discovered in Figure 1 of the paper by M. A . Mayers and H. G. Landau, n-hich appeared in the -4pri1, 1940, issue of IXDUSTHIAL .ISD ESGISEERIXG CHEMISTRY, pages 563 to 568. In this nomograph the w scale is in the wrong position: to be correct, it should he shifted horizontally to the left, to the line which is now the margin of the drawing. In the correct position the zero of the u: scale is at the intersection of this scale with the T I scale extended. h1. 4 .

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