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The Effect of Various Homogenization Pressures on the Leucocyte Count of Milk*
T H E E F F E C T OF V A R I O U S H O M O G E N I Z A T I O N P R E S S U R E S ON T H E L E U C O C Y T E COUNT OF M I L K ~ I. I. P E T E R S AnD G. ~I. TROUT
Michigan Agricultural l~xperiment Station
Adequate homogenization of milk sufficiently reduces the size of the f a t globules so as to inhibit f a t rising in the processed product. While the f a t is the chief component of milk affected b y the process, m a n y physical and chemical changes occur in the homogenized milk which are not n o r m a l in non-homogenized milk. One of these is the settling of leucocytes and other suspended material to f o r m a sediment. The every-other-day system of milk delivery has resulted in an increased consumer consciousness of the sediment in nonclarified homogenized milk. U n d e r this system some of the milk not only is held longer t h a n normally, but often some of the bottles are stored horizontally. Thus, any deposited sediment a p p e a r s as a yellowish grey streak the entire length of the vertical bottle. Since leucocytes are regarded as an i m p o r t a n t constituent of the sediment often noticed in homogenized milk, it seemed expedient to ascertain the influence of various homogenizing pressures on them, p a r t i c u l a r l y to determine whether they could be disintegrated sufficiently by the process to inhibit their settling out. INFLUENCE OF NORMAL FIOIVIOGENIZATION PRESSURE
Leucocyte counts were made on milk before and a f t e r homogenization, using 'an improved Neubauer counting chamber and Toisson's fluid as a stain. The milk was' pasteurized at 142 ° to 144 ° F. for 30 minutes and homogenized at pressures r a n g i n g f r o m 2,000 to 2,500 pounds per square inch. The intensity of sediment was determined by microscopic examination. The d a t a secured f r o m 30 trials are presented in table 1. The data show t h a t in all but four cases the n m n b e r of leucocytes f o u n d in the nonhomogenized milk exceeded the count in the homogenized milk. The inconsistency of these f o u r trials m i g h t be explained by the fact t h a t the counts were within the range of experimental error and occurred on relatively low count milk to which no leucocytes had been added. The reduction, based on the logarithmic average, was f o u n d to be 41.24 per cent. The decrease in the n u m b e r of leucocytes in the homogenized milk m u s t be attributed to the destructive action of the homogenization process. No other explanation can be given, since in making the counts the leucocytes were much more easily observed in the microscopic field of the homogenized milk t h a n of the non-homogenized milk. Received for publication October 307 1944. Journal Article No. 727 (n.s.), :M[ichigan Agricultural Experiment Station.
251
252
I. I. PETERS AND O. 1Vf. TROUT II~FLUENCE OF REPEATED HIGH PRESSURE HOMOGENIZATION
Since the results of previous trials had shown that normal homogenization pressures reduced the leucocyte count in the homogenized milk, trials were made to ascertain the influence of repeated high-pressure homogenization o n the leucocyte count. I t was believed t h a t high-pressure homogenization would demonstrate more f u l l y the destructive action of homogenization. TABLE 1 The influence o f normal hoqnogenization pressure on the destruction of leucocytes Leucocytes per ml. in milk when Trial number
5 6 '7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 3O Log. average
Non-homogenized
Homogenized
3,900,000 1,620,000 1,440,000 1,140,000 1,800,000 1,000,000 1,060,000 880,000 940,000 2,240,000 640,000 260,000
2,320,000 480,000 760,000 1,040,000 640,000 700,000 460,000 700,000 760,000 960,000 440,000 340,000 120,000 100,000 100,000 160,000 100,000 140,000 180,000 320,000 120,000 580,000 1,140,000 2,160,000 700,000 560,000 460,000 480,000 500,000 480,000 426,000
I00,000 80,000 180,000 440,000 160,000 200,000 120,000 320,000 140,000 2,260,000
3,000,000 4,060,000 1,460,000
1,900,000 1,580,000 960,000 1,060,000 800,000 725,000
The trials were made on raw, clarified milk to which was added fresh separ a t o r slime at the rate of 1.5 gin. p e r q u a r t of milk. The milk was pasteurized at 142 ° to 144 ° F. for 30 minutes and homogenized, first at 2,500 pounds pressure, then at 5,000 pounds pressure for five times. Q u a r t samples were collected, cooled and held for 48 hours at 40 ° F., a f t e r which examinations were made. The leucocyte count was decreased over 83 per cent b y subjecting the milk to 2,500 pounds pressure followed by homogenizing twice at 5,000
EFFECT OF HOMOGENIZATION ON LEUCOCYTE COUNT
253
TABLE 2 The influence of repeated high pressure homogenization on the leucocyte count and the intensity of sediment in quart bottles of homogenized milIc
(Average of three trials) Number of times homogenized
ttomogenization pressure
Leucocytes
Leucocyte reduction
no./ml.
% o f total
957,000 625,400 357,200 159,100 106,300 84,300 72,700
34.6 62.7 83.4 88.9 91.2 92.4
lbs./sq, in. 0
2,500 5,000 5,000 5,000 5,000 5,000
Intensity of sediment*
0.0 3.0 3.0 3.0 3.0 3.0 3.0
* Key : 0.0 = no sediment. 1.0 = slight sediment. 2.0 = distinct sediment. 3.0 = pronounced sediment. p o u n d s ( t a b l e 2, f i g u r e 1). C o n t i n u e d - h i g h - p r e s s u r e h o m o g e n i z a t i o n u n t i l t h e m i l k h a d b e e n h o m o g e n i z e d five t i m e s a t 5,000 p o u n d s r e s u l t e d i n a m a x i m u m r e d u c t i o n i n l e u c o c y t e s of 92.4 p e r cent. Although the leucocyte count decreased with repeated high pressure h o m o g e n i z a t i o n , no r e d u c t i o n in t h e i n t e n s i t y of s e d i m e n t was observed. A l l m i l k s h o w e d s e d i m e n t of a g r e y i s h color a n d was g i v e n a n i n t e n s i t y r a t i n g of 3.0. Some difference was n o t i c e d in the g e n e r a l a p p e a r a n c e of t h e s e d i m e n t . T h e s e d i m e n t d e p o s i t s of t h e m i l k h o m o g e n i z e d a t 5,000 p o u n d s s o m e t i m e s r e s e m b l e d fine s a n d in a p p e a r a n c e ; b u t , w i t h r e p e a t e d h i g h p r e s sure, h o m o g e n i z a t i o n a p p e a r e d s m o o t h a n d even t h r o u g h o u t . M i c r o s c o p i c /,~
"~ o,~
I
I
I
I
/
I
\--LEUCOCW TES
/
$
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',
l~
/,,,',
1
/
'
o.o I
TIMES
~'
a
4
; 7° 5
6
HOMO6ENIZED
FIG. 1. The influence of repeated high pressure homogenization on the leucocyte count and on the intensity of sediment.
254
I. I. PETERS AND O. ~. TROUT
examinations of the sediment showed it to be composed, in large part, of fragments of leucocytes. The conclusion was reached that the broken leucocytes tended to settle down and form sediment, similarly to the nonbroken leucocytes f o u n d in milk. INFLUENCE OF CONTINUOUS, HIGH-PRESSUREHOMOGENIZATION
The previous experiment had shown the destructive action of high pressure homogenization upon leucocytes. A trial was conducted with the purpose of attempting to accomplish their complete destruction. Fresh separator slime was added to 5 gallons of pasteurized milk at the rate of 1.5 gin. per quart. The milk was heated to 140 ° F. and homogenized at 5,000 pounds pressure for ten minutes continuously. Quart samples of milk were collected before and after homogenization as well as' at two-minute intervals during the continuous process. All samples were cooled and held at 4() ° F. for 48 hours, after which examinations for sediment and leucocytes were made. TABLE 3 The influence of continuo~m high pressure homogenization on the leucocyte count and on the intensity of sediment
Time homogenized minutes
Control 0 2 4 6 8 10
Homogenizetion pressure lbs./sq, in. 0
2,500 5,000 5,000 5,000 5,000 5,000
Leucocytes per ml. 2,240,000 960,000 320,000 180,000 100,000 40,000 20,000
Leucocyte reduction % o f total 0.0
57.1 85.8 92.0 95.5 98.2 99.1
Intensity of sediment ~ 0.0 3.0 3.0 3.0 3.0 3.0 3.0
Key : 0.0 = no sediment. 1.0 = slight sediment. 2.0 = distinct sediment. 3.0 = pronounced sediment. Virtually complete destruction of leucocytes was accomplished (table 3, figure 2). The leucocyte count was reduced from 2,240,000 per ml. to 20,000 per ml. as a result of homogenizing at 5,000 pounds for 10 minutes. Microscopic examination of the homogenized milk showed the last samples to contain leucocytes of small size only. The leucocyte fragments, although not readily stained, could be seen as small particles in the microscopic field. The intensity of sediment was f o u n d to be the same in all samples of homogenized milk. This would indicate that the broken leucocytes settled and formed sediment, similarly to the nonbroken leucocytes. Microscopic examination of the sediment in milk which had been homogenized continually for ten minutes at 5,000 pounds pressure showed the sediment to consist largely of f r a g m e n t a r y materials.
EFFECT
OF
HOMOGENIZATION
2'4
I
~ 2.0
[
ON I
LEUCOCYTE
COUNT
25~}
1
-LEUCOCYTES
k
3~ ",4 "~ 1.5
=It/tl /-'-,~EDIMEHT
K.
to
l I
k.
t i
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\ \ \ i
0.4
O.C 0
,4
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2
4
~
7-[0 N
TIME
HOMOGENIZA
-'~'~ ....
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8 I0 ('M/IV.)
FIG. 2. The influence of continuous high-pressure homogenization on the leucocyte ,count and the i n t e n s i t y of sediment in quart bottles of homogenized milk. Homogenized once at 2~500 pounds pressure.
EPFECT ON SEDIMENTATION OF ADDING INCREASING PORTIONS OF CONTINUOUS HIGH-PRESSURE-HOMOGENIZED MILK TO NORMAL HOMOGENIZED ~ I L K Since it appeared
that leucocytes could be fragmented,
ble to a s c e r t a i n if m i x t u r e s
of high-pressure
it seemed desira-
and low-pressure homogenized
milk would result in variations in the intensity of sediment. TABLE ¢
The influence of adding increasing portions of continuo~s high pressure treated ~i.l~ to normal homogenized mill: on the intensity of sediment produced S~mple number
Per cent of normal homogenized milk per bottle
Per cent of continuous h i g h pressure treated milk per bottle
] 2 3 4 5 6 7 8 9 10 11
100 90 80 70 60 50 40 30 20 10 0
0 10 20 3O 4O 5O 6O 7O 8O 9O 100
* Key : 0 -- no sediment. 1 -- slight sediment. 2 = distinct sediment. 3 = pronounced sediment. 4 -=very pronounced sediment.
I n t e n s i t y of sediment ~
256
Z.I.
PETERS AND G. M. TROUT
To a series of eleven quart bottles containing decreasing amounts of normal homogenized milk were added increasing amounts of the continuous, high-pressure homogenized milk prepared earlier in this experiment. All samples were mixed well and allowed to remain undisturbed for 48 hours at 40 ° F, Sediment studies were made at the end of the storage period. The intensity of sediment increased with the addition of increasing portions of continuous, high-pressure homogenized milk. This is shown ia the data of table 4 and figure 3. Apparently the sediment was not due primarily to whole leucocytes, since none of the samples contained a leucocyte count above 80,000 per ml. A high correlation seemed to exist between the intensity of the sediment and the proportion of high-pressure homogenized milk (figure 3). Undoubtedly, therefore, the settling of the broken leucocytes in normal homogenized milk occurs readily. ~-- /00
j
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J
[
I
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$ 4t.,,"
40
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:1:
Ioo
i
=
80 NORMAL
K
i
i
60. 40 HOMO. M / L K
~
L
i
0
~o o ?'PERCENT)
FIG. 3. T h e influence of a d d i n g i n c r e a s i n g p o r t i o n s of c o n t i n u o u s h i g h - p r e s s u r e t r e a t e d milk to n o r m a l h o m o g e n i z e d milk on t h e i n t e n s i t y of s e d i m e n t produced. SUMMARY
Results of 30 trials showed that homogenizing milk at 2,500 pounds pressure at 142 ° to 144 ° F. reduced the leucocyte count on an average of 41.28 per cent. Rehomogen!zing milk five times at 5,000 pounds pressure reduced the leucocyte count 92.4 per cent with little effect on the intensity of the sediment. Milk homogenized at 5,000 pounds pressure for 10 minutes showed a reduction of leucocyte count of 99.1 per cent. The intensity of the sediment was the same in all homogenized samples. The addition of increasing portions of high-pressure homogenized milk to normal clarified homogenized milk resulted in a corresponding increase in the intensity of the sediment in the milk mixture.
Michigan Agricultural l~xperiment Station
Adequate homogenization of milk sufficiently reduces the size of the f a t globules so as to inhibit f a t rising in the processed product. While the f a t is the chief component of milk affected b y the process, m a n y physical and chemical changes occur in the homogenized milk which are not n o r m a l in non-homogenized milk. One of these is the settling of leucocytes and other suspended material to f o r m a sediment. The every-other-day system of milk delivery has resulted in an increased consumer consciousness of the sediment in nonclarified homogenized milk. U n d e r this system some of the milk not only is held longer t h a n normally, but often some of the bottles are stored horizontally. Thus, any deposited sediment a p p e a r s as a yellowish grey streak the entire length of the vertical bottle. Since leucocytes are regarded as an i m p o r t a n t constituent of the sediment often noticed in homogenized milk, it seemed expedient to ascertain the influence of various homogenizing pressures on them, p a r t i c u l a r l y to determine whether they could be disintegrated sufficiently by the process to inhibit their settling out. INFLUENCE OF NORMAL FIOIVIOGENIZATION PRESSURE
Leucocyte counts were made on milk before and a f t e r homogenization, using 'an improved Neubauer counting chamber and Toisson's fluid as a stain. The milk was' pasteurized at 142 ° to 144 ° F. for 30 minutes and homogenized at pressures r a n g i n g f r o m 2,000 to 2,500 pounds per square inch. The intensity of sediment was determined by microscopic examination. The d a t a secured f r o m 30 trials are presented in table 1. The data show t h a t in all but four cases the n m n b e r of leucocytes f o u n d in the nonhomogenized milk exceeded the count in the homogenized milk. The inconsistency of these f o u r trials m i g h t be explained by the fact t h a t the counts were within the range of experimental error and occurred on relatively low count milk to which no leucocytes had been added. The reduction, based on the logarithmic average, was f o u n d to be 41.24 per cent. The decrease in the n u m b e r of leucocytes in the homogenized milk m u s t be attributed to the destructive action of the homogenization process. No other explanation can be given, since in making the counts the leucocytes were much more easily observed in the microscopic field of the homogenized milk t h a n of the non-homogenized milk. Received for publication October 307 1944. Journal Article No. 727 (n.s.), :M[ichigan Agricultural Experiment Station.
251
252
I. I. PETERS AND O. 1Vf. TROUT II~FLUENCE OF REPEATED HIGH PRESSURE HOMOGENIZATION
Since the results of previous trials had shown that normal homogenization pressures reduced the leucocyte count in the homogenized milk, trials were made to ascertain the influence of repeated high-pressure homogenization o n the leucocyte count. I t was believed t h a t high-pressure homogenization would demonstrate more f u l l y the destructive action of homogenization. TABLE 1 The influence o f normal hoqnogenization pressure on the destruction of leucocytes Leucocytes per ml. in milk when Trial number
5 6 '7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 3O Log. average
Non-homogenized
Homogenized
3,900,000 1,620,000 1,440,000 1,140,000 1,800,000 1,000,000 1,060,000 880,000 940,000 2,240,000 640,000 260,000
2,320,000 480,000 760,000 1,040,000 640,000 700,000 460,000 700,000 760,000 960,000 440,000 340,000 120,000 100,000 100,000 160,000 100,000 140,000 180,000 320,000 120,000 580,000 1,140,000 2,160,000 700,000 560,000 460,000 480,000 500,000 480,000 426,000
I00,000 80,000 180,000 440,000 160,000 200,000 120,000 320,000 140,000 2,260,000
3,000,000 4,060,000 1,460,000
1,900,000 1,580,000 960,000 1,060,000 800,000 725,000
The trials were made on raw, clarified milk to which was added fresh separ a t o r slime at the rate of 1.5 gin. p e r q u a r t of milk. The milk was pasteurized at 142 ° to 144 ° F. for 30 minutes and homogenized, first at 2,500 pounds pressure, then at 5,000 pounds pressure for five times. Q u a r t samples were collected, cooled and held for 48 hours at 40 ° F., a f t e r which examinations were made. The leucocyte count was decreased over 83 per cent b y subjecting the milk to 2,500 pounds pressure followed by homogenizing twice at 5,000
EFFECT OF HOMOGENIZATION ON LEUCOCYTE COUNT
253
TABLE 2 The influence of repeated high pressure homogenization on the leucocyte count and the intensity of sediment in quart bottles of homogenized milIc
(Average of three trials) Number of times homogenized
ttomogenization pressure
Leucocytes
Leucocyte reduction
no./ml.
% o f total
957,000 625,400 357,200 159,100 106,300 84,300 72,700
34.6 62.7 83.4 88.9 91.2 92.4
lbs./sq, in. 0
2,500 5,000 5,000 5,000 5,000 5,000
Intensity of sediment*
0.0 3.0 3.0 3.0 3.0 3.0 3.0
* Key : 0.0 = no sediment. 1.0 = slight sediment. 2.0 = distinct sediment. 3.0 = pronounced sediment. p o u n d s ( t a b l e 2, f i g u r e 1). C o n t i n u e d - h i g h - p r e s s u r e h o m o g e n i z a t i o n u n t i l t h e m i l k h a d b e e n h o m o g e n i z e d five t i m e s a t 5,000 p o u n d s r e s u l t e d i n a m a x i m u m r e d u c t i o n i n l e u c o c y t e s of 92.4 p e r cent. Although the leucocyte count decreased with repeated high pressure h o m o g e n i z a t i o n , no r e d u c t i o n in t h e i n t e n s i t y of s e d i m e n t was observed. A l l m i l k s h o w e d s e d i m e n t of a g r e y i s h color a n d was g i v e n a n i n t e n s i t y r a t i n g of 3.0. Some difference was n o t i c e d in the g e n e r a l a p p e a r a n c e of t h e s e d i m e n t . T h e s e d i m e n t d e p o s i t s of t h e m i l k h o m o g e n i z e d a t 5,000 p o u n d s s o m e t i m e s r e s e m b l e d fine s a n d in a p p e a r a n c e ; b u t , w i t h r e p e a t e d h i g h p r e s sure, h o m o g e n i z a t i o n a p p e a r e d s m o o t h a n d even t h r o u g h o u t . M i c r o s c o p i c /,~
"~ o,~
I
I
I
I
/
I
\--LEUCOCW TES
/
$
4 I~
',
l~
/,,,',
1
/
'
o.o I
TIMES
~'
a
4
; 7° 5
6
HOMO6ENIZED
FIG. 1. The influence of repeated high pressure homogenization on the leucocyte count and on the intensity of sediment.
254
I. I. PETERS AND O. ~. TROUT
examinations of the sediment showed it to be composed, in large part, of fragments of leucocytes. The conclusion was reached that the broken leucocytes tended to settle down and form sediment, similarly to the nonbroken leucocytes f o u n d in milk. INFLUENCE OF CONTINUOUS, HIGH-PRESSUREHOMOGENIZATION
The previous experiment had shown the destructive action of high pressure homogenization upon leucocytes. A trial was conducted with the purpose of attempting to accomplish their complete destruction. Fresh separator slime was added to 5 gallons of pasteurized milk at the rate of 1.5 gin. per quart. The milk was heated to 140 ° F. and homogenized at 5,000 pounds pressure for ten minutes continuously. Quart samples of milk were collected before and after homogenization as well as' at two-minute intervals during the continuous process. All samples were cooled and held at 4() ° F. for 48 hours, after which examinations for sediment and leucocytes were made. TABLE 3 The influence of continuo~m high pressure homogenization on the leucocyte count and on the intensity of sediment
Time homogenized minutes
Control 0 2 4 6 8 10
Homogenizetion pressure lbs./sq, in. 0
2,500 5,000 5,000 5,000 5,000 5,000
Leucocytes per ml. 2,240,000 960,000 320,000 180,000 100,000 40,000 20,000
Leucocyte reduction % o f total 0.0
57.1 85.8 92.0 95.5 98.2 99.1
Intensity of sediment ~ 0.0 3.0 3.0 3.0 3.0 3.0 3.0
Key : 0.0 = no sediment. 1.0 = slight sediment. 2.0 = distinct sediment. 3.0 = pronounced sediment. Virtually complete destruction of leucocytes was accomplished (table 3, figure 2). The leucocyte count was reduced from 2,240,000 per ml. to 20,000 per ml. as a result of homogenizing at 5,000 pounds for 10 minutes. Microscopic examination of the homogenized milk showed the last samples to contain leucocytes of small size only. The leucocyte fragments, although not readily stained, could be seen as small particles in the microscopic field. The intensity of sediment was f o u n d to be the same in all samples of homogenized milk. This would indicate that the broken leucocytes settled and formed sediment, similarly to the nonbroken leucocytes. Microscopic examination of the sediment in milk which had been homogenized continually for ten minutes at 5,000 pounds pressure showed the sediment to consist largely of f r a g m e n t a r y materials.
EFFECT
OF
HOMOGENIZATION
2'4
I
~ 2.0
[
ON I
LEUCOCYTE
COUNT
25~}
1
-LEUCOCYTES
k
3~ ",4 "~ 1.5
=It/tl /-'-,~EDIMEHT
K.
to
l I
k.
t i
1.2
\
h. k.
\ \ \ i
0.4
O.C 0
,4
I
I
I
I
I ¢-
2
4
~
7-[0 N
TIME
HOMOGENIZA
-'~'~ ....
o
8 I0 ('M/IV.)
FIG. 2. The influence of continuous high-pressure homogenization on the leucocyte ,count and the i n t e n s i t y of sediment in quart bottles of homogenized milk. Homogenized once at 2~500 pounds pressure.
EPFECT ON SEDIMENTATION OF ADDING INCREASING PORTIONS OF CONTINUOUS HIGH-PRESSURE-HOMOGENIZED MILK TO NORMAL HOMOGENIZED ~ I L K Since it appeared
that leucocytes could be fragmented,
ble to a s c e r t a i n if m i x t u r e s
of high-pressure
it seemed desira-
and low-pressure homogenized
milk would result in variations in the intensity of sediment. TABLE ¢
The influence of adding increasing portions of continuo~s high pressure treated ~i.l~ to normal homogenized mill: on the intensity of sediment produced S~mple number
Per cent of normal homogenized milk per bottle
Per cent of continuous h i g h pressure treated milk per bottle
] 2 3 4 5 6 7 8 9 10 11
100 90 80 70 60 50 40 30 20 10 0
0 10 20 3O 4O 5O 6O 7O 8O 9O 100
* Key : 0 -- no sediment. 1 -- slight sediment. 2 = distinct sediment. 3 = pronounced sediment. 4 -=very pronounced sediment.
I n t e n s i t y of sediment ~
256
Z.I.
PETERS AND G. M. TROUT
To a series of eleven quart bottles containing decreasing amounts of normal homogenized milk were added increasing amounts of the continuous, high-pressure homogenized milk prepared earlier in this experiment. All samples were mixed well and allowed to remain undisturbed for 48 hours at 40 ° F, Sediment studies were made at the end of the storage period. The intensity of sediment increased with the addition of increasing portions of continuous, high-pressure homogenized milk. This is shown ia the data of table 4 and figure 3. Apparently the sediment was not due primarily to whole leucocytes, since none of the samples contained a leucocyte count above 80,000 per ml. A high correlation seemed to exist between the intensity of the sediment and the proportion of high-pressure homogenized milk (figure 3). Undoubtedly, therefore, the settling of the broken leucocytes in normal homogenized milk occurs readily. ~-- /00
j
f
J
[
I
I
~oo
J
i
i
~, - ..............
$ 4t.,,"
40
z~
I
:1:
Ioo
i
=
80 NORMAL
K
i
i
60. 40 HOMO. M / L K
~
L
i
0
~o o ?'PERCENT)
FIG. 3. T h e influence of a d d i n g i n c r e a s i n g p o r t i o n s of c o n t i n u o u s h i g h - p r e s s u r e t r e a t e d milk to n o r m a l h o m o g e n i z e d milk on t h e i n t e n s i t y of s e d i m e n t produced. SUMMARY
Results of 30 trials showed that homogenizing milk at 2,500 pounds pressure at 142 ° to 144 ° F. reduced the leucocyte count on an average of 41.28 per cent. Rehomogen!zing milk five times at 5,000 pounds pressure reduced the leucocyte count 92.4 per cent with little effect on the intensity of the sediment. Milk homogenized at 5,000 pounds pressure for 10 minutes showed a reduction of leucocyte count of 99.1 per cent. The intensity of the sediment was the same in all homogenized samples. The addition of increasing portions of high-pressure homogenized milk to normal clarified homogenized milk resulted in a corresponding increase in the intensity of the sediment in the milk mixture.