Chemical changes produced in cows' milk by pasteurization

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Title:
Chemical changes produced in cows' milk by pasteurization
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Bulletin / United States. Dept. of Agriculture. Bureau of Animal Industry ;
Physical Description:
15 p. : 1 ill. ; 24 cm.
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English
Creator:
Rupp, Philip, 1862-1939
United States -- Bureau of Animal Industry
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U.S. Dept. of Agriculture, Bureau of Animal Industry
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Washington, D.C
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Milk -- Pasteurization   ( lcsh )
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bibliography   ( marcgt )
non-fiction   ( marcgt )

Notes

Bibliography:
Includes bibliographical references.
Statement of Responsibility:
by Philip Rupp.

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University of Florida
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Full Text


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Imued April 22, 1918.
U. S. DEPARTMENT OF AGRICULTURE,
BUREAU OF ANIMAL INDUSTRY.-BULLETIN 166.
A. D. MELVIN, CHIEF OF BUREAU.





CHEMICAL CHANGES PRODUCED IN COWS'

MILK BY PASTEURIZATION.






BY


PHILIP RUPP, M. D., PH. D.,
Chemist, Dairy Division.


WASHINGTON:
GOVERNMENT PRINTING OFFICE.
1913.




-Sm


BUREAU OF ANIMAL INDUSTRY.


Chief. A. D. MELVIN.
Assistant Chief: A. M. FARRINGTON.
Chief Clerk: CHARLES C. CARROLL.
Animal Husbandry Division: GEORGE M. ROMMEL, chief.
Biochemic Division: M. DORSET, chief.
Dairy Division: B. H. RAWL, chief.
Field Inspection Division: R. A. RAMSAY, chief.
Meat Inspection Division: R. P. 8TEDDOM, chief.
Pathological Division: JOHN R. MOnLER, chief.
Quarantine Division: RICHARD W. HICKMAN, chief.
Zoological Division: B. H. RANSOM, chief..
Experiment Station: E. C. SCHROEDER, superintendent.
Editor. JAMES M. PICKENS.

DAIRY DIVISION.
B. H. RAWL, Chief.
HELMER RABILD, in charge of Dairy Farmning Investigations.
S. C. THOMPSON, in charge of Dairy Manufacturing Investigations.
L. A. ROGERS, in charge of Research Laboratories.
ERNEST KELLY, in charge of Market Milk Investigations.
ROBERT MCADAM, in charge of Renovated Butter Inspection.
2:IIJ

















LETTER OF TRANSMITTAL.


U. S. DEPARTMENT OF AGRICULTURE,
BUREAU OF ANIMAL INDUSTRY,
Washington, D. C., January 30, 1913.
Smr: I have the honor to transmit for publication as a bulletin
of this bureau the accompanying manuscript, entitled "Chemical
Changes Produced in Cows' Milk by Pasteurization," by Dr. Philip
Rupp, chemist in the Dairy Division of this bureau. The paper de-
scribes a series of experiments made with the object of determining
the effect of pasteurization at various temperatures on the chemical
composition of cows' milk. The work was undertaken because of
certain objections which are made against pasteurization, it having
been asserted that the process injures the milk from a digestive and
nutritive standpoint, particularly as a food for infants. It is satis-
factory to note from the results of the work that, so far as the ordi-
nary temperatures used in commercial pasteurization are concerned,
these objections are not well founded.
The method of filtering the milk necessary for the carrying on of
the tests consists of a new application by Dr. Rupp of the clay-cell
filtration used by other scientists. This method is fully described
and illustrated by a diagram.
Respectfully, A. D. MELVIN,
Chief of Bureau.
Hon. JAMES WILSON,
Secretary of Agriculture.
800020-Bull. 166-13 .3

























CONTENTS. P I


Introduction.............................................................5 "
Method of pasteurization employed......................................... a '
Chemical changes in the phosphates ..................................... I
Method of filtration.................................................... 0
Methods of analysis-................................................... J
Changes in the composition of the serum during filtration................. ,,,
Chemical changes in the proteins........................................... U
Lactalbumin........................................................... 11
Methods of analysis................................................ U i
Casein-................................................................. .... II
Method of coagulation.............................................. 14 i
Changes in the acidity...................................................... 1 a
Sm ayadconclusions------------------15
Summary and conclusions .................................................. 16 |
":: ||




ILLUSTRATION.


Fia. 1. Apparatus for filtering milk.......................................... 7 :
4
i o woom o o o oIool emlo ll B O:@
....:














CHEMICAL CHANGES PRODUCED IN COWS' MILK BY PASTEURIZATION.

INTRODUCTION.
One of the objections frequently raised against pasteurized milk
is that the heating produces changes in the chemical composition
which make it unsuitable for infant nourishment. It is claimed that
a portion of the soluble phosphate of lime becomes insoluble and that
this change produces defective nutrition, while the changes in the
lactalbumin and in the casein render the pasteurized milk more
indigestible than raw milk, and therefore inferior as a food. These
objections were brought forward at a time when high temperatures
were employed in the sterilization of infants' milk, and they are made
use of at the present day by the opponents of pasteurization, even
though the temperatures used in pasteurizing are considerably lower.
The objects of the work herein described were to study the chemical
changes produced by the heating of milk at the different temperatures
used in commercial pasteurization and to determine whether a tem-
perature that destroys all pathogenic germs can be used in pasteuri-
zation without having any appreciable effect on the chemical compo-
sition of the milk. Three points are considered: First, the changes
in the phosphates are discussed in order to show to what extent the
soluble phosphate of lime becomes insoluble. Second, the proteins
are examined to determine to what extent the albumin is precipi-
tated and the casein changed in its characteristic property of coagu-
lating with rennin. Finally, the acidity of the milk is considered.

METHOD OF PASTEURIZATION EMPLOYED.
The milk was pasteurized in a constant-temperature bath. The
water having reached the required temperature, the cool milk, in an
Erlenmeyer flask closed with a valve to prevent evaporation, was
.placed in the water and occasionally moved about until it had ac-
quired the temperature of the water. This usually required from
15 to 20 minutes, according to the height of the temperature. It
was then allowed to remain for 30 minutes, after which it was rapidly
cooled to about 12 C. (53 F.). The milk used was of very good
quality and had a very low bacterial count. The variation in tem-
perature during pasteurization was less than 0.5 C. (0.9 F.).






CHEMICAL CHANGES PRODUCED BY PASTEURIZATION.


CHEMICAL CHANGES IN THE PHOSPHATES.o|
The vast majority of the experiments which show a diminution ln"i
thle quantity of soluble calcium salts in heated milk as compared with."..
raw milk refer to milk which has been heated to the boiling point.::f
But few definite results can be found showing a diminution of the.
soluble calcium phosphate in pasteurized milk. i
DiflothI found a decrease in the soluble phosphates, amounting to 3
a loss of 25.9 per cent, on heating milk to 60 C. (140 F.) for :
minutes, while Babcock2 believes that a change in the solubility of tihno-I
lime salts is brought about when the milk is pasteurized, and basm:i
his conclusion on the less ready coagulability of the milk by rennet,
In order to determine the effect of pasteurization on the solubility 1
of the phosphates in the milk, the serum of both raw and pasteurized "I
milk was examined. 3
METHOD OF FILTRATION. i
A new application of the clay-cell filtration as used by SoXhlfiW
was employed. The clay cell of a galvanic element is thoroughly
cleansed by boiling in dilute caustic soda and then washed by filqel.
ing hot water through the cell by suction. The cell is next boiled in
dilute hydrochloric acid and again washed by suction with hot disU
tilled water until the filtrate no longer gives a reaction for chloria.
The method of filtration is easily understood by a description of f
the accompanying diagram (figure 1). |
An inverted bell jar (a) (9 inches high and 4 inches in diameer) is
covered with a perforated glass plate (b) holding a tube contain g
a plug of cotton to admit air. Inside the jar is a porous clay cell (4)
of a galvanic element (51 inches high, 2t inches in diameter, and th I
cell wall one-eighth of an inch thick) the opening of which is covered
with a piece of rubber dam (d) of medium thickness and supported o#
a heavy glass plate (e). Both the rubber dam and the glass platq. qq M
perforated for the passage of a rubber stopper containing a glass t Ni
with a Geissler stopcock (f). The upper end of the tube is flush with
the glass plate e, while the lower end passes into a filtering flask (g)
of 750 c. c. capacity. A glass tube with a two-way stopcock (At) is .
attached to the outlet of the flask, and this in turn is connected vith *
the suction apparatus by means of a heavy rubber tube. In order t W
obtain airtight joints a little stopcock grease is placed on the glam
plate, and the edge of the clay cell is also coated with a thin layer,'
The cover (b) of the bell jar is held down in the same manner.
'Diffloth,PauL Du rOle de quelquesagentsphysiquesetchimiques dans l'insolubilisation desP "h
du lait. Bulletin des Sciences Pharmacologiques, vol. 10, p. 273-279. Paris, 1904. Abstract: Zet"uift
fuir Untersuchung der Nahnrmgs- und Genussmlttel, vol. 11, no. 7, p. 455-456. Berlin, Apr. 15, iS."". '
SBabcock, 8. The centrifugal separation of casein and insoluble phosphates from milk. Wi.Jm..*
Agricultural Experiment Station, Twelfth Annual Report (1895), p. 93-09. Madison, 186.
I Soxhlet, Franz. Beitrilge zur physiologischen Chemie der Milch. Journal far PzuktlSmhe C |
new series, vol. 6, no. 1/2, p. 1-52. Leipsie, Aug. 24,1873.






CHEMICAL CHANGES IN THE PHOSPHATES.


To begin filtration remove the cover, evacuate the apparatus, and
while the suction is still on fill the bell-jar with milk. Then cut off
the suction at h, replace the cover, and remove the suction tube. The
apparatus is now ready to be placed in the refrigerator.
The advantage of this method over those previously employedis
S that the filtration can be continued indefinitely and the serum
|* removed at any time without interfering with the filtration. Further-
( more, no concentration of the serum can take place, as evaporation is
excluded. The serum can be removed at any time by closing the
stopcock f, admitting air by opening h,
and removing the filtering flask. Then = ,
replace the flask, evacuate, close the stop-
cock h, and open, and the apparatus is al
ready for further filtration.

METHODS OF ANALYSIS.
Weigh about 40 grams of milk (equiva-
lent to about 0.1 gram of phosphoric
acid), evaporate to dryness, and ignite
at a low red heat until the ash is free from
carbon. Dissolve the ash in hot water e
containing a little hydrochloric acid and
dilute to about 100 c. c.
Basic acetate precipitation.-Almost -f
neutralize the solution of the ash with
ammonia, add 2 c. c. of dilute acetic acid h,
and a slight excess of ferric chlorid solu-
tion of known strength (7.5 c. c. of a 10
per cent solution). Now add 13 to 14
c. c. of a 10 per cent ammonium acetate
solution, dilute to 350 to 400 c. c. and
boil for about one-half to one minute, /
stirring occasionally to prevent bumping.
If the quantity of ferric chlorid added was FG. .-Apparatus for filtering ml.
sufficient the precipitate will be brownish-
red, and the precipitation will be complete as the boiling point is
reached if the acetate was added in sufficient quantity. Filter boil-
ing hot through two 12.5 cm. filters and wash immediately with a hot
dilute ammonium acetate solution (one-half to one per cent), using a
fine jet which is played around the edge of the precipitate, thus cut-
ting it free from the paper in order to produce rapid filtration. Do
not allow to drain dry. Wash the precipitate in this manner three
to four times until free from chlorids, return to the original beaker
with hot water, and dissolve by the addition of nitric acid. When


a a.. .






CHEMICAL CHANGES PRODUCED BY PASTEURIZATION
CHEMICAL CHANGES PRODUCED BY PA.BTEURIZATION.


the basic acetate precipitation is carried out as described above tSI
filtration is always rapid and the precipitate never runs through th
filter. In washing the precipitate with hot water, some flakes '
orally appear on concentrating the filtrate and washings. T
however, is not the case if a hot dilute solution of ammonium acetate:'
is used. :
The phosphoric acid in the basic acetate precipitate was dtermiiw&
by the molybdate method and weighed as magnesium pyrophosphbs.
The filtrate and washings from the basic acetate precipitation wisri
concentrated and the calcium precipitated with ammonium oxalate..:!
The oxalate was redissolved, reprecipitated, and weighed as calcin I'
oxid. The filtrate and washings from calcium precipitation wore 3
evaporated, ammonium salts removed, and the magnesium deterw:.....
mined as pyrophosphate. i
For serum analysis evaporate about 70 grams and ignite at a dull .:
red heat until the ash is free from carbon. In the basic acetate pre- !
cipitation use 6 c. c. of ferric chlorid solution and 9 to 10 c. c. of IJ
ammonium acetate solution.
The casein phosphorus was determined by Neumann's method, i
using, however, only 10 c. c. of concentrated sulphuric acid. The i
total phosphorus in the milk was also determined by Neumann's ..
method. .
The specific gravity was taken by means of a picnometer.

CHANGES IN THE COMPOSITION OF THE SERUM DURING FILTRATION.

De Vries and Boekhout,2 using a Chamberland filter and pressure,
found that the quantity of calcium in the serum did not vary in differ-
ent fractions during the filtration, the first 20 c. c. of serum containing .:
the same quantity of calcium as the second and third. In order to
-0
determine whether the serum remains of constant composition during
filtration and for what length of time milk can be filtered at a tern- |
perature of 5 to 8 C. (41 to 46. 40 F.) without changing its composi-
tion, skim milk was filtered and the serum analyzed during a period I
of two weeks. Skim milk was used for this experiment because it
filters more rapidly than whole milk. The results are shown In "
Table 1.
4Nelumann, Albert. Einlache Veraschungsmethode (Sluregenusoh-Verahung). Zeitmobrift t
Phyalologische Chemie, vol. 37, no. 2, p. 115-142. Strasburg, Dec. 20, 1902. ,
" Ott de Vries, J. J., and Boekhout, F. W. J. Beitrag zur Kenntnis der Labgerinnung. Die Laid..
wlrtachaftlichen Versuchs-Statlonen, voL 56, no. 3, p. 221-239. Berlin, Feb. 12, 1901.
.. : i

"ii
.r






CHEMICAL CHANGES IN THE PHOSPHATES. 9

TABLE 1.-Quantityof solublephosphorus in the serum on different days during the
., ~filtratRon of raw skim milk, separated at 300 C. (863 F.).

Quantity. Specific Acidity.' PO6. CaO. MgO.
gravity.

Grams. Per cent. Per cent. Per cent.
aa.................... ..........................00638....................
Rawskimmilk...................................... 1.034 17.8 .2352 0.1671 0.0185
First day-3 hours.................... 34.3 1.023 .......... .0753 .0450 .0133
First day-next 18 hours............... 81.5 1.025 8.8 .1029 .0554 .0133
Second day-........................... 109.8 1.025 9.0 .1054 .0581 .0134
Do........................ ............................... 1055 .0588 .0133
Thirdday.......................... 109.3 1.025 9.0 .1055 .0578 .0127
Fourthday........................... 112.0 1.025 9.0 .1048 .0585 .0127
Fifthday..................... .... 105.7 1.025 9.0 .1054 .0589 .0130
Bizth and seventh days................ 205.0 1.025 9.0 .1057 .0579 .0129
Do.................................................................. .1053 .0582 .0131
Tenth and eleventh days............... 155.0 1.025 10.0 .1074 .0609 .0131
t.irteenth and fourteenth days....... I 158.5 1.025 12.0 .1082 .0633 .0139
); Bfl eth and part of sixteenth day.... 105.0 .......... 14.6 .1110 .0683 .0145


iNumber of cubic centimeters of N alkali required to neutralize 100 c. c. of serum.
10
As will be seen from the above table there is an absorption of both
phosphoric acid and calcium at the beginning of filtration, while the
magnesium passes completely through the cell wall. For this reason
the first portion of the serum must be rejected as worthless for making
comparisons. The quantity to be rejected varies with the ize of the
cell used and may amount to from 60 to 90 c. c.
The specific gravity of the serum collected during the first 3 hours
was 1.023, and it increased to 1.025 during the next 18 hours, after
which time it remained constant during the remainder of the experi-
ment.
The acidity was 8.8 on the first day and 9 on the second day. After
S the ninth day the acidity began to increase gradually, being 10 on the
tenth and eleventh days, while on the fifteenth day it was 14.6, showing
that the lactic acid had considerably increased.
The phosphoric acid during the first 3 hours amounted to only
0.0753 per cent, and it increased to 0.1029 per cent during the next
18 hours. On the second day it was, 0.1054 per cent, and then re-
mained constant until the tenth and eleventh days, when it began
gradually to increase, amounting to 0.1110 per cent on the fifteenth day.
The calcium content was also low during the first 3 hours of filtra-
S tion, arhounting to 0.045 per cent, and it increased to 0.0554 per cent
during the next 18 hours. On the second day it was 0.0581 per cent,
and began to increase gradually as the acidity increased, amounting
to 0.0683 per cent on the fifteenth day.
The magnesium remained constant during the first 11 days and
then increased very slowly up to the fifteenth day.
The experiment shows, furthermore, that the filtration of a clean
milk with low bacterial count can be continued for about one week
without any appreciable chemical changes taking place in the serum,
provided the temperature be kept at 6 to 8 C. (42.8 to 46.4 F.).


I'






10 CHEMICAL CHANGES PRODUCED BY PASTEURIZATION.

Before proceeding to the filtration of raw milk in the refrigB .4.
several experiments were made in which formaldehyde had be
added to the milk as a preservative. This was done in order SJt
carry on the filtration at room temperature. The results obtai.B
showed that the serum, after the first day's filtration, remained 4i
constant composition, and led up to carrying out the filtration-Q
pure milk in the refrigerator. I;r
Having thus shown that the serum remains of constant co=mo
tion after the first day of filtration, the next step was to deo% HA
whether there were any demonstrable changes produced in
soluble phosphates by pasteurization. In order to produce a
mum precipitation the highest temperature, 68.3 C. (155,.
employed in the holder process was chosen. The results obtain:e::d.
are shown in Table 2. **|
TABLE 2.-Quantity of soluble phosphates irt the serum of raw whole milk and in te 'ie
milk pasteurized at 68.3 (.55 F.) for 30 minutes. |

Specific Acidity. P.O. Cgo.
gravity.

Per cent. Per cmn. PiFaL 4
Casein.................. ...................... 0595 .......... ..........Pe ...rIII...
Raw whole milk........................................ 1.029 i .2219 0.1749 -
Raw serum: ..
Second and third days............................ 1.026 9.8 .1074 .0A S =
Do........................ .... ... ............ .......... 1078 .0A 4
Fifthandsixthdays............................. 1 .026 9.6 .1082 .0631
Pasteurized serum:
Second and third days.......................... .026 9.6 .1078 .0611 .0 4
Do..................................... ................. 1063 .061n :
Fifthandsixthdays............................. .. .026 9.4 .1089 .027 OW

It will be seen from the table that the changes produced g -
pasteurization at 68.3 C. (155 F.) for 30 minutes are trifling, Tb :
phosphoric acid content remains the same in both the raw awd t 'r
pasteurized serum. The quantity of lime salts, while a trifle 1o q1m
in the pasteurized than in the raw serum, is still within the limi4
error, and the magnesia remains the same in both serums.
Other experiments made with skim milk showed results agrqij .
in every particular with this one made with whole milk. All prli
inary experiments were made with skim milk because, as previowly 0
stated, it filters more readily and thus gives a larger quantity 4.
serum for analysis. :
Comparing Table 1 with Table 2 we find that the variation in fg
quantity of soluble lime salts between the two samples of milk i
far greater than that found between the raw and pasteurized serum"
For this reason the objection frequently raised against pasteurij
milk as an infant food, on the ground that the soluble lime salts ar o
diminished by the process of pasteurization, is without foundation




g:






CHEMICAL CHANGES IN THE PROTEINS.


CHEMICAL CHANGES IN THE PROTEINS.

LACTALBUMIN.

Different investigators do not agree as to the exact temperature
at which the coagulation of the albumin begins. Steiner found no
change on heating milk for 25 minutes at 60 C. (140 F.), while
Solomin2 says that the change seems to begin at this temperature,
and Jensen and Plattner3 also found some coagulation in milk
heated for five hours at 60 C. (140 F.). Babcock 4 could find no
change on heating milk for 20 minutes at 65 C. (149 F.), while
Woll 5 states that coagulation begins at this temperature. According
to Willoughby 6 the change begins at 70 C. (158 F.), while de Freud-
enreich' found 15 to 20 per cent coagulated on heating milk for
30 minutes at 68 to 69.5 C. (154.4 to 157 F.). A series of experi-
ments were therefore undertaken to determine at what temperature
the change in the albumin begins, and to what extent it is coagulated
at the different temperatures commonly employed in the pasteuriza-
tion of milk.
METHODS OF ANALYSIS.

Casein.-To 10 grams of milk were added 50 c. c. of distilled water
at 40 C. (104 F.), then 1.5 to 2 c. c. of a saturated alum solution
were added gradually. The precipitate was allowed to settle, was
then filtered and washed. The precipitate and filter paper were
treated by the Gunning method, adding about 0.2 gram of copper
sulphate.
Albumin and globulin.-The albumin and globulin in the filtrate
and washings were precipitated with 10 c. c. of Alm6n's tannin solu-
tion; this was allowed to settle, was then filtered and washed. The
precipitate was treated the same as under casein.
Tables 3 to 6 show the results of the experiments to determine the
lactalbumin precipitated in whole milk pasteurized for 30 minutes at
temperatures ranging from 62.8 C. (145 F.) to 71.1 C. (160 F.).
1 Steiner, R. Beitriige zur Kenntnis des Einflusses der Pasteurisierung auf die Beschaffenheit der Milch
und auf den Butterungs Prozesz. Milch-Zeitung, vol. 30, no. 26, p. 401-403, June 29; no. 28, p. 435, July 13.
Lipsic, 1901.
Solomin, P. Ueber die beim Erhitzen der Milch ausfallenden Eiweissmengen. Archiv fUr Hygiene,
vol. 28, no. 1, p. 43-48. Munich and Leipsic, 1896.
Jensen, Orla, and Plattner, Ernest. De l'action du chauffage sur le lait de vache. Revue Genrale du
Lait, vol. 4, no. 16, p. 361-368, May 30; no. 17, p. 388-397, June 15; no. 18, p. 419-424. Lierre, 1905.
4 Babcock, S. M. The centrifugal separation of casein and insoluble phosphates from milk. Wisconsin
Agricultural Experiment Station, Twelfth Annual Report (1895), p. 93-99. Madison, 1896.
.6 Woll, F. W. The effect of pasteurization and sterilization on the viscosity and fat globules of milk
S and cream. Wisconsin Agricultural Experiment Station, Twelfth Annual Report (1895), p. 164-173.
Madison, 1896.
4 Willoughby, Edward F. Milk, its production and uses. London, 1903. See p. 125-126.
De Freudenreich, Ed. Sur la pasteurisation du lait dans l'alimentation de 1'enfance. Revue Generale
du Lait, vol. 4, no. 19, p. 433-437. Lierre, July 15,1905.


11







CHEMICAL CHANGES PRODUCED BY PASTEURIZATION.


TABLS 3.--Quantity of albumin precidpitated in raw whole mil
at 62.80 C. (1456 F.)for 30 minutia.


and in milk patms


Caein nitrogen ..........................
Albumin+globulin nitrogen ..............


Raw milk.


L.


PaMtau d m .. : 1 7:,


- .3, -


Avmse.


I I F t


Percent.
M 4003
.009a


Per cent.
0. 4027
.0008M


Per cent.
0.4015
.0997


Per tet.
0.4016
.0-m


Percent.
0.4010
.0m0


A..spi


- -a.


PROTEIN- NITROGEN X&. 38.


No albumin precipitated.


TABLE 4.-Quantity of albumin precipitated in raw whole milk
at 65.6 C. (150 F.) for 30SO minutes.


and min m jilk 4
*


Raw milk. Pasteurized milk.

I. II. Average. I. EL Avmqt

Pere. Percecet Per cece. Per cent. Peraces.L PPreW
Caaein nitrogen............................ 0.4260 0.4218 0.4239 0.43M 0.438 MOL4M
Albumin+globulin nitrogen ............... 0983 .0978 .0081 .0- 0 .OM .0

PROTEIN- NITROGEN X6. 38.

Casein.................................... 2.717 2.691 2.704 2.756 2.7M i &
Albumin+globulin....................... .627 .624 .626 .587 ...

Albumin precipitated- 5.75 per cent.

TABLE 5.-Quantity of albumin precipitated in raw whole milk and in min p eurd
at 6S.30 C. (155 F.) for 30 minutes.


Raw milk. Pasteuried iM1k.

I. II. Average. I. U. AVifq .

Per cent. Per cent. Per cent. Per cent. Percent.P Pt It
Caseinnitrogen .......................... 0.3739 0.3812 0.3776 0.3910 0.3878 L3
Albumin+globulin nitrogen .............. 0963 .0981 .0972 .0863 .0633


PROTEIN-NITROGEN X&6.38.


Albumin precipitated- 12.75 per cent.


12


11 11






CHEMICAL CHANGES IN THE PROTEINS. 13

TABLE 6.-Quantity of albumin precipitated in raw whole milk and in milk pasteurized
at 71.10 C. (160 F.) for 80 minutes.

*. Raw milk. Pasteurized milk.

I I. I. Average. I. II. Average.

ij Per cent. Per cent. Per cent. Per cent. Per cent. Per cent.
Casein nitrogen ........................... 0.3860 0.3851 0.3856 0.4200 0.4169 0.4185
tA1bumin+g lobulin nitrogen.............. .0961 .0989 .0975 .0681 .0667 .0674

qIJ PROTEIN- NITROGENX6.38.

CaJ n .................................... 2.462 2.457 2.460 2.679 2.660 2.670
S Albumin+globulin ....................... .613 .631 .622 .434 .426 .430
7| Albumin precipitated= 30.87 per cent.
I From an analysis of the above tables it is apparent that no albumin
is coagulated on heating milk for 30 minutes at 62.8 C. (145 F.),
iil the temperature most commonly used in the holder process in com-
S mercial pasteurization. At 65.6 C. (150 F.) the separation of the
.. albumin has begun, 5.71 per cent having become insoluble. At 68.3
S C. (155 F.) the quantity has increased to 12.76 per cent, wnile at
| 71.1 C. (160 F.) 30.87 per cent of the albumin has been coagulated

I,: CASEIN.
i. The condition in which casein exists in milk has not as yet been
f* fully explained. The effect of heat shows itself in two ways. In the
i. first place, the rennin coagulation may be accelerated, retarded, or
even inhibited; and in the second place, the coagulum may assume
S a different character from that obtained from raw milk.
The great majority of authors agree that no change in rennin
S coagulation takes place below 65 C. (149 F.). Steiner found a
retardation in milk heated to 60 C. (140 F.), while Fleischmann and
Morgen2 found the milk less sensitive to rennin when heated for two
hours from 60 to 70 C. (140 to 158 F.). According to Van Slyke
and Publow 3 milk heated above 65.6 C. (150 F.) for a considerable
length of time coagulates less rapidly and the coagulum is highly
flocculent. De Freudenreich 1 finds the coagulum unchanged at 68
S to 69.5 C. (154.4 to 157.1 F.). Jensen and Plattner 1 state that
retardation begins on heating milk for five hours at 70 C. (158 F.),
while Mayer4 places the beginning at 75 C. (167 F.). Stassano and
*4: Loc. eft.
i Fleischmann, W., and Morgen, A. Einiges fiber die nach Scherff's Verfahren conservirte Flasehen
S milch. Die Landwirthschaftlichen Versuch Stationen, vol. 28, p. 321-332. Berlin, 1883.
'8 Van Slyke, Lucius L., and Publow, Charles A. The science and practice of cheese-making, p. 310.
S New York, 1909.
,;i. 4 Mayer, Adolf. Bestimmungen der Wirksamkeit des Labfermentes unter verschiedenen luszeren Um-
istinden. Milch-Zeitung, vol. 10, no. 2, p. 17-19, Jan. 12; no. 3, p. 33-38, Jan. 19; no. 4, p. 49-52, Jan. 26; no.
63 p. 81-84, Feb. 9. Bremen, 1881.
..a



L.







14 CHEMICAL CHANGES PRODUCED BY PASTEURIZATION. II
Talarico 1 differ from all the preceding in that they observed an ad
oration of rennin coagulation in milk heated from 55 to 65 C. (1$11:6,
t) 149 F.), while at 70 C. (158 F.) the heated milk behaved
same as raw milk, and above 70 C. (158 F.) the retardation begaim
Thie following experiments were made with raw milk and mWi-t
pasteurized at various temperatures: :, :i
METHOD OF COAGULATION. .::Hl

TIhe apparatus consisted of a large galvanized-iron box having"
four cylindrical compartments surrounded by water. The uppaii
openings were of sufficient size to admit a cylindrical percola&L
(1 foot high and 21 inches in diameter), the lower openings be*ing::J
about one-fourth of an inch in diameter. A small glass tube drawa.
out into a capillary was inserted into the neck of the percolator by
means of a perforated rubber stopper.
In making the test, the water in the box was heated to the required l
temperature, the percolators were then placed in the compartment
and allowed to remain until they had acquired the temperature of
the bath, the upper openings being covered. Next 200 c. c. of milk
were heated, the rennin solution added, and, after mixing, poured
into the percolator. The upper opening was then closed with a cover
andi the time required for the milk to coagulate in the tube noted.
Thle flow through the tube was regulated by breaking off the capillary
to such an extent that all tubes dropped at the same rate.
For each experiment 200 c. c. of milk were heated in an Erlenmeym
flask to 35 C. (95 F.) and 5 c. c. of rennin solution (0.15: 100 c.'c.
of water) added. This was taken as the beginning of the coagular
tion time; the end point was when the milk stopped dropping frqm
the capillary tube. The rennin solution was made of such strength i
that tlhe raw milk coagulated in about 20 minutes. The results are
shown in the following table:
TABLE 7.-Time required for rennin coagulation of rauw whole milk and of whole Skm-
pasteurized at different temperatures. Milk 200 c. c., rennin solution (0.15 gr9 :
100 c. c. of water) 5 c. c.

Milk pasteurized at-
Raw
Experiment. _i
Experiment milk. 55, c. c. 65C. 70 C.
(131- F.). (140- F.). 149" F.). (158" F.). (167 4.
1. a. M.S. 9 S. H. a. M. M. .
" 18 30 17 28 17 10 17 12 ........... ....
18 08 16 56 16 53 17 12 .............
................................ 19 34 .......... ... .......... 20 38 36
S. ............... . .{ 19 .......... .... ............... 20 2S a

S-tassano, II., and Talarico, J. De l'influencede lacuisson sur la casicationdu Ia parto (ib .t l
Competes Rendus Hebdomadaires des Seances et Mdmolres de la Societe de Biologi, ro. 6 (
tome 2), no. 28, p. 254-255. Par Aug. 5, 1910.






SUMMARY AND CONCLUSIONS.


From the above table it will be seen that milk pasteurized at 55 C.
(131 F.), 60 C. (140 F.), and 65 C. (149 F.) all coagulate
more rapidly with rennin than does the raw milk. This result was
obtained in all cases in a large number of experiments. At 70 C.
(158 F.) the retardation of rennin coagulation has begun, while at
75- C. (167 F.) the time has about doubled and the coagulum is
highly flocculent.
CHANGES IN THE ACIDITY.
Woll I and de Freudenreich I find no appreciable change in the
acidity of milk pasteurized at 67 to 68 C. (153 to 154.4 F.) for
20 minutes. H6ft2 and Jensen and Plattner 1 on the other hind
find a diminution in the acidity on heating milk.
From a large number of experiments made during the coagulation
of milk by rennin, it was found that the acidity of the milk always
diminished during pasteurization. While the diminution was slight
it amounted to several tenths of a cubic centimeter, and was always
sufficient to be determined by titration with tenth-normal caustic-
soda solution. The diminution, however, is insignificant and is
probably due to a loss of carbonic acid during the heating. Further-
Smore, the diminution varies in different samples of milk.

SUMMARY AND CONCLUSIONS.
1. Milk pasteurized by the holder process at 62.8 C. (145 F.) for
30 minutes does not undergo any appreciable chemical change.
2. The soluble phosphates of lime and magnesia do not become
insoluble. At 68.3 C. (155 F.) the quantity of phosphoric acid,
lime, and magnesia in the serum of both raw and pasteurized milk
are practically the same.
3. The albumin does not coagulate at 62.8 C. (145 F.), but at
65.6 C. (150 F.) 5.75 per cent of the albumin is.rendered insoluble.
As the temperature increases the amount of coagulated albumin
increases. At 68.3 C. (155 F.) the quantity increases to 12.75 per
cent, and at 71.1 C. (160 F.) it amounts to 30.78 per cent.
4. The time required for coagulating the casein by rennin is slightly
less in milk pasteurized at temperatures up to 65 C. (149 F.) than it
is in raw milk. At 70 C. (158 F.) there is a slight retardation,
while at 75 C. (167 F.) the time has almost doubled.
5. The acidity as determined by titration is slightly diminished
in pasteurized milk.
SLoc. cit.
H5ft, 11. Ueber die VerAnderung der Aciditit der Milch beim Erhitzen. Mlilch-Zeitung, vol. 30, no.
7, p. 103. Leipzig, Feb. 16,1901.


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