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Lipolysis in Milk. II. Effect of Milking Systems
Lipolysis in Milk. I I. Effect of Milking Systems V. T. P I L L A Y , 1 A. N. M Y H R , J. I. G R A Y , 2 and D. A. BIGGS Department of Food Science University of Guelph Guelph, Ontario, Canada N1G 2W1
transferring milk to the farm bulk tanks cause increased agitation and foaming of milk. Any condition in a raw milk system that causes excess formation of foam will increase lipolysis and susceptibility to development of rancidity (11, 13) with the greatest effects at temperatures at which milk fat is in the liquid state (4, 7, 13), such as when freshly drawn from the
ABSTRACT
The relative effect on lipolysis of four milking systems was investigated. Pipeline milkers induced the greatest amount of lipolysis in milk followed in descending order of extent of lipolysis by bucket milkers with sputnick conveyors (140-1iter containers on wheels for transferring milk from cows to bulk cooling tanks), bucket milkers with dumping stations, and bucket milkers with conventional carrying pails. Of the pipeline systems, parlor systems employing weigh jars induced more lipolysis in milk than around-thebarn installations and parlors without weigh jars. The latter system produced the least lipolysis. Weigh jars in parlor systems apparently have a greater effect on lipolysis than the longer lines and greater number of elbows and other fittings generally encountered in aroundthe-barn installations. To minimize lipolysis caused by weigh jars, these devices should be disconnected during routine milking operations and only used on days when weights are recorded.
COW.
Since the introduction of bulk milk cooling, the number of pipeline systems in Ontario has been growing steadily. In 1977 there were 12,856 dairy producers with bulk coolers of which 4,417 (34%) had installed pipeline milking system (1). Many producers over the years have opted for less expensive conveyor systems that can be used in conjunction with conventional bucket milking. The purpose of this investigation was to determine the relative effects on lipoiysis of various milking systems in Ontario with emphasis on factors affecting lipolysis in pipeline milkers. MATERIALS AND METHODS Milking Systems
INTRODUCTION
Following introduction of the farm bulk milk cooling tank, a number of mechanical means were developed for efficient transfer of milk from cows to bulk tank. The more sophisticated of these systems was the pipeline milker in which the milker unit was made an integral part of the transfer system. Other less expensive units have been developed for conveying milk to bulk tanks from conventional bucket milking operations. All of these mechanical means for
Received November 27, 1978. a Connors Bros., Blacks Harbor, New Brunswick, Canada. 2Department of Food Science and Human Nutrition, Michigan State University, East Lansing, MI. 1980 J Dairy Sci 63:1219-1223
Milk samples were collected from 35 dairy farms, 9 of which used bucket milkers and carrying pails, 5 had bucket milkers and transferred milk to the bulk tanks by means of "sputnicks" (140-liter containers on wheels), and 5 were equipped with dumping stations which consisted of a vessel into which milk is dumped and conveyed under vacuum through the milk line (plastic, glass, or stainless steel) to the bulk tank. The remaining 16 farms had pipeline milkers of which 10 were around-thebarn installations (all high milk lines), 4 were milking parlor systems with weigh jars (3 low line and 1 high line), and 2 had milking parlors without weigh jars (both with high lines). All of the pipeline milkers were equipped with probe-activated centrifugal milk pumps for automatic transfer of milk from receiver jars to the bulk tanks.
1219
1220
PILLAY ET AL.
Sampling
Sampling was during the fall of 1974 and w i n t e r and summer of 1976. Samples were o b t a i n e d from bulk tanks at the end of the fourth milking at the time of pick-up by the
milk transporter. The milk was agitated for 5 rain prior to removal of the sample by means of a sanitized stainless steel dipper. The sample containers were 177 ml whirl-pak plastic bags (Arnold-Nasco Ltd., Guelph, Ontario). Bags were filled as completely as possible to minimize agitation during transport and were carried in an insulated case containing an ice water mixture. Upon arrival at the laboratory, sample bags were inverted gently 20 times, an aliquot was removed for fat analysis, and the remainder of the milk in each sample was subdivided into four 60-ml screw-capped glass bottles. These samples were analyzed for free fatty acids initially and after 24, 48, and 72 h storage at 4.4°C. To assess the effect of weigh jars on lipolysis an apparatus was designed to obtain drip samples from the milk hose leading from the milker claw to the weigh jar. The sampling device consisted of a 227-ml glass Mojonnier sample bottle with hooded rubber stopper. A B-D Cornwall cannula (No. 1789 (1250 NR) 14 G, sawed off 28 mm from the point where the barrel entered the hub, was inserted through the underside o f the rubber stopper. The end of the cannula protruding through the top of the stopper was inserted just through the wall of a short piece of tygon milk hose. This constituted
..........
II
Automatic Take-off Control Panel
~_
Take-off device
/f
Mak
u0 ~ Claw and Teat Cup Cluster Milker
~Outlet
~.~p~rlmen~a) Fo,Au,om..c tI~
Take-off
\~ Milk HOSe MilkLine
Figure 1. Schematic illustration of the automatictake-off and weigh jar system showing the location of the apparatus for sampling ahead of the weigh jar, Journal of Dairy Science Vol. 63, No. 8, 1980
the sampling apparatus and was coupled to the milk hose leading to the weigh jar by stainless steel inserts (77 mm long × 13 mm id) as in Figure 1. This apparatus provided a drip sample collected throughout the entire milkings of from 5 to 7 cows and represented the beforeweigh-jar sample. The weigh jar samples consisted of a composite of milk samples taken from the weigh jar after each of the 5 to 7 cows was milked out. The weigh jars were De Laval Milk Receiver jars (No. 8301064). These jars were operated in conjunction with the Boumatic automatic-take-off system for removing milker units. Representative samples of milk were obtained from such weigh jars after mixing by admitting air (under the influence of vacuum in the jar) via the sample outlet vaIve. Chemical Analysis
The fat content was determined by the infra-red milk analyzer, Mark II (2). The extent of lipolysis was measured by determining the acid degree value (ADV) by a modified Frankel and Tarassuk method (ether extraction of the fat) as in (12). RESULTS AND DISCUSSION
The effect of type of milk transfer system on extent of lipolysis is shown in Table 1. Milk from farms using bucket milkers and carrying pails to convey milk to buIk tanks had the lowest ADV's, followed in order of increasing iipolysis by dumping stations, spumicks, and pipeline milkers. Differences between ADV means for the various systems were significant at 1%. All of the systems used to convey milk mechanically from cows to bulk tank significantly increased lipolysis, the highest ADV's being produced by pipeline milking systems. If the ADV's reflect differences in degree of agitation and foaming during transfer of milk to the bulk tank, it appears that milk is exposed to the severest treatment in pipeline systems, which render a comparatively higher proportion of the milk fat susceptible to lipolysis. One might expect Spumick-conveyed milk to have similar lipolytic activity to that of the bucket milker-carrying pail operations since the Spurnick (used in conjunction with bucket milking) is merely a larger carrying container on wheels. However, there are other differences. First, the milk in the Spumick (up to 140 liters) is
LIPOLYSIS IN MILK FROM MILKING SYSTEMS
1221
TABLE 1. Mean acid degree valuesa for milk from different milking systems.
System
No. of farms
No. of samples
Buckets Dumping stations Spumicks Pipelines
9 5 5 16
180 97
100 320
Mean ADV's Initial
24 h
48 h
72 h
1.80 2.27 2.50 2.99
1.92 2.40 2.60 3.14
1.97 2.46 2.65 3.21
2.04 2.52 2.70 3.26
aAs determined by a slightly modified version of the Frankel and Tarassuk method (12).
transferred rapidly to the bulk tank by air pressure. This blasting of milk into the bulk tank causes considerable agitation and foaming. Second, there is a possibility of temperature activation of lipolysis during low production periods when the Spumick may hold an entire first milking before being transferred to the bulk tank. The second milking also would be added all at once to the cold milk in the tank, and this may result in a blend temperature high enough to increase the rate of lipolysis (9). Milk from dumping stations had ADV's which were intermediate between sputnick operations and bucket milkers. Unlike most pipeline milkers, where the pipeline is moving both air and milk, the plastic or rigid (stainless steel or glass) line conducting milk from the dumping station to the vacuum releaser is flooded fully. Thus, there is no admixing of air and milk in the line until it reaches the releaser where agitation occurs as the releaser alternately fills and empties milk into the bulk tank. However, as shown by the ADV's in Table 1, there is less
severe physical treatment of milk conveyed from dumping stations than that carried by Sputnicks and pipelines milking systems. The use of bucket milkers and carrying pails produced milk with least lipolysis. This has been the observation of others in comparative studies of lipolysis in milk from pipeline and bucket milking operations (3, 6, 8, 14, 15). This study showed the relative effects on lipolysis of two other milk conveying systems. Data from pipeline milking systems was rearranged (Table 2) to reveal the effect of type of pipeline installation on lipolysis. Parlor pipeline milkers with weigh jars produced the highest ADV's, followed in order of decreasing values by around-the-barn installations and parlor systems without weigh jars. In (12) the threshold for lipolyzed flavor detection was in the ADV range of 4.1 to 4.5 (with the ether extraction method) which means there was little overall margin of safety in milk produced with parlor systems using weigh jars. In today's market such high ADV's are diluted by pooling
TABLE 2. Mean acid degree valuesa of milk obtained from parlor and around-the-barn pipeline milkers. (No. of samples per farm = 20). Type of pipeline
No. of farms
No. of samples
Mean ADV's Initial
24 h
48 h
72 h
Parlor with weigh jar
4
80
3.76
3.92
3.89
4.03
Parlor without weigh jar
2
40
2.52
2.60
2.70
2.75
10
200
2.78
2.93
3.00
3.05
Around-the-barn
aAs determined by a slightly modified version of the Frankel and Tarassuk method (12). Journal of Dairy Science Vol. 63, No. 8, 1980
1222
P1LLAY ET AL.
with lower ADV milk from other types of milking systems in Tables 1 and 2. In this way a wider margin of safety against lipolyzed flavor is gained in milk at the dairy plant. However, pipeline milking systems are going to continue to increase in popularity and sophistication, and to maintain the current margin of safety, every system should be examined for possible ways to reduce agitation and foaming of milk. Since there were substantial differences in lipolysis between parlor systems with and without weigh jars, a separate experiment was designed to isolate the effect of weigh jars from other variables in the milking system. The results are presented graphically in Figure 2. After 24-h storage, samples taken from the weigh jar had significantly higher ADV's than samples taken from the milkline ahead of the jar. This is due to the additional agitation and foaming because of forceful impingement of milk against the walls of the weigh jar during milking and because of air agitation after milking to mix the milk for sampling purposes. The rate of lipolysis in milk taken from the weigh jar was rapid during the first 24 h, after which it was approximately the same as that of milk removed ahead of the weigh jar. In explanation, it seems logical to suggest that not all
fat globules were modified physically by agitation in the weigh jar. The portion of the fat rendered susceptible to rapid lipolysis probably was depleted during the first 24 h of enzymatic action, after which lipolysis proceeded at about the same rate as in milk collected before the weigh jar. The net effect with the weigh jars was an average increase of almost a whole ADV after storage at 4,4°C for 24 to 48 h. There are numerous designs and principles of operation of weigh jars (10) with possible variable effects on lipolysis, Another type of milk-metering device used in milklines, the "milk-o-meter", also substantially increased lipolysis (5). Most often when weigh jars are installed in milking parlors, they have been made an integral part of the milking system and as such are a cause for increased agitation and foaming at every milking. Results of this study indicate that as a control measure for lipolysis, weigh jars should be used only for weighing and sampling or when it is necessary to segregate abnormal milk from infected cows. The jars can be removed from the system by simply moving the milk hose from the inlet o f the weigh jar to the inlet of the milkline. Before accepting innovations in the form of accessories or design changes in milking systems, one should consider the effect of such modifications on the lipolytic activity in milk. ACKNOWLEDGMENTS
uJ
~3
__..._-----------2
..J
:> UJ
'IE" 2 O
j
,,
~
The financial support provided by the Ontario Ministry of Agriculture and Food, and the Ontario Milk Marketing Board for this research is acknowledged gratefully.
--1 REFERENCES
IJJ
1-BEFORE WEIGH JAR O
2-AFTER WEIGH JAR
,,
0
I
24 STORAGE
I
-,,
48
I
72
TIME (h)
Figure 2. Effect of weigh jar in a pipeline milking system on acid degree values (modified Frankel and Tarassuk method) in milk held at 4.4°C. Each point on the graph represents the mean of 10 samples. Journal of Dairy Science Vol. 63, No. 8, 1980
1 Anonymous. 1977. Cross-Canada bulk milk survey. Modern Dairy 56(4): 16. 2 Association of Official Analytical Chemists. 1975. Official methods of analysis. 12th ed. Assoc. Offic. Anal. Chem., Washington, DC. 3 Giesen, T.J.J. 1977. Private communication. Gelders-Overijselse Zuivelbond, Postbus 162, Zutphen-Nieuwstad 69, Netherlands. 4 Herrington, B. L. 1956. The control of rancidity in milk. J. Dairy Sci. 39:1613. 5 Jaazen, J. J. 1963. Milk flavor as affected by a milk-metering device. J. Dairy Sci. 46: 567. 6 Jensen, R. G., A. C. Smith, P. McLeod, and L. R. Dowd. 1957. The acid degree of milk obtained with pipeline and bucket milkers. J. Milk Food Technol. 20:352.
LIPOLYSIS IN MILK FROM MILKING SYSTEMS
7 Jezeski, J. J. 1958. Pages 8 to 18 in The use o f the acid degree value test in the solution o f rancid flavor problems. Milk Ind. Found., Cony. Proc. Lab. Sect. 8 Kankare, V., and V. Antila. 1978. Influence of pipeline milking machines on lipolysis in farm milk. XX Int. Dairy Congr., Paris, Brief Communications Vol. E: 132. 9 Krukovsky, N. V., and B. L. Herrington. 1939. Studies o f lipase action. II. The activation o f milk lipase by temperature changes. J. Dairy Sci. 22:137. 10 Noorlander, D. O. 1973. Mechanics and production o f quality milk. 2nd ed. Webcrafters, Inc., Madison, WI. 11 Olson, J. C., Jr., E. L. Thomas, and A. J. Nielsen. 1956. The rancid flavor in raw milk supplies. Am.
1223
Milk Rev. 18(10):98. 12 Pillay, V.T.T., A. N. Myhr, and J. I. Gray. 1980. Lipolysis in milk. I. Determination o f free fatty acids and threshold value for lipolyzed flavor detection. J. Dairy Sci. 63:1213. 13 Tarassuk, N. P., and E. N. Frankel. 1955. On the mechanism o f activation of lipolysis and the stability o f lipase systems o f normal milk. J. Dairy Sci. 38:438. 14 Thomas, E. L., A. J. Nielsen, and J. C. Olson, Jr. 1955. Observations on the extent o f lipolysis in raw milk supplies as related to various milk handling procedures. J. Dairy Sci. 38: 596. 15 Whittlestone, W. G. 1965. Milk lipolysis and the milking machine. Milk Board J., New South Wales 16(5):19.
Journal of Dairy Science Vol. 63, No. 8, 1980
transferring milk to the farm bulk tanks cause increased agitation and foaming of milk. Any condition in a raw milk system that causes excess formation of foam will increase lipolysis and susceptibility to development of rancidity (11, 13) with the greatest effects at temperatures at which milk fat is in the liquid state (4, 7, 13), such as when freshly drawn from the
ABSTRACT
The relative effect on lipolysis of four milking systems was investigated. Pipeline milkers induced the greatest amount of lipolysis in milk followed in descending order of extent of lipolysis by bucket milkers with sputnick conveyors (140-1iter containers on wheels for transferring milk from cows to bulk cooling tanks), bucket milkers with dumping stations, and bucket milkers with conventional carrying pails. Of the pipeline systems, parlor systems employing weigh jars induced more lipolysis in milk than around-thebarn installations and parlors without weigh jars. The latter system produced the least lipolysis. Weigh jars in parlor systems apparently have a greater effect on lipolysis than the longer lines and greater number of elbows and other fittings generally encountered in aroundthe-barn installations. To minimize lipolysis caused by weigh jars, these devices should be disconnected during routine milking operations and only used on days when weights are recorded.
COW.
Since the introduction of bulk milk cooling, the number of pipeline systems in Ontario has been growing steadily. In 1977 there were 12,856 dairy producers with bulk coolers of which 4,417 (34%) had installed pipeline milking system (1). Many producers over the years have opted for less expensive conveyor systems that can be used in conjunction with conventional bucket milking. The purpose of this investigation was to determine the relative effects on lipoiysis of various milking systems in Ontario with emphasis on factors affecting lipolysis in pipeline milkers. MATERIALS AND METHODS Milking Systems
INTRODUCTION
Following introduction of the farm bulk milk cooling tank, a number of mechanical means were developed for efficient transfer of milk from cows to bulk tank. The more sophisticated of these systems was the pipeline milker in which the milker unit was made an integral part of the transfer system. Other less expensive units have been developed for conveying milk to bulk tanks from conventional bucket milking operations. All of these mechanical means for
Received November 27, 1978. a Connors Bros., Blacks Harbor, New Brunswick, Canada. 2Department of Food Science and Human Nutrition, Michigan State University, East Lansing, MI. 1980 J Dairy Sci 63:1219-1223
Milk samples were collected from 35 dairy farms, 9 of which used bucket milkers and carrying pails, 5 had bucket milkers and transferred milk to the bulk tanks by means of "sputnicks" (140-liter containers on wheels), and 5 were equipped with dumping stations which consisted of a vessel into which milk is dumped and conveyed under vacuum through the milk line (plastic, glass, or stainless steel) to the bulk tank. The remaining 16 farms had pipeline milkers of which 10 were around-thebarn installations (all high milk lines), 4 were milking parlor systems with weigh jars (3 low line and 1 high line), and 2 had milking parlors without weigh jars (both with high lines). All of the pipeline milkers were equipped with probe-activated centrifugal milk pumps for automatic transfer of milk from receiver jars to the bulk tanks.
1219
1220
PILLAY ET AL.
Sampling
Sampling was during the fall of 1974 and w i n t e r and summer of 1976. Samples were o b t a i n e d from bulk tanks at the end of the fourth milking at the time of pick-up by the
milk transporter. The milk was agitated for 5 rain prior to removal of the sample by means of a sanitized stainless steel dipper. The sample containers were 177 ml whirl-pak plastic bags (Arnold-Nasco Ltd., Guelph, Ontario). Bags were filled as completely as possible to minimize agitation during transport and were carried in an insulated case containing an ice water mixture. Upon arrival at the laboratory, sample bags were inverted gently 20 times, an aliquot was removed for fat analysis, and the remainder of the milk in each sample was subdivided into four 60-ml screw-capped glass bottles. These samples were analyzed for free fatty acids initially and after 24, 48, and 72 h storage at 4.4°C. To assess the effect of weigh jars on lipolysis an apparatus was designed to obtain drip samples from the milk hose leading from the milker claw to the weigh jar. The sampling device consisted of a 227-ml glass Mojonnier sample bottle with hooded rubber stopper. A B-D Cornwall cannula (No. 1789 (1250 NR) 14 G, sawed off 28 mm from the point where the barrel entered the hub, was inserted through the underside o f the rubber stopper. The end of the cannula protruding through the top of the stopper was inserted just through the wall of a short piece of tygon milk hose. This constituted
..........
II
Automatic Take-off Control Panel
~_
Take-off device
/f
Mak
u0 ~ Claw and Teat Cup Cluster Milker
~Outlet
~.~p~rlmen~a) Fo,Au,om..c tI~
Take-off
\~ Milk HOSe MilkLine
Figure 1. Schematic illustration of the automatictake-off and weigh jar system showing the location of the apparatus for sampling ahead of the weigh jar, Journal of Dairy Science Vol. 63, No. 8, 1980
the sampling apparatus and was coupled to the milk hose leading to the weigh jar by stainless steel inserts (77 mm long × 13 mm id) as in Figure 1. This apparatus provided a drip sample collected throughout the entire milkings of from 5 to 7 cows and represented the beforeweigh-jar sample. The weigh jar samples consisted of a composite of milk samples taken from the weigh jar after each of the 5 to 7 cows was milked out. The weigh jars were De Laval Milk Receiver jars (No. 8301064). These jars were operated in conjunction with the Boumatic automatic-take-off system for removing milker units. Representative samples of milk were obtained from such weigh jars after mixing by admitting air (under the influence of vacuum in the jar) via the sample outlet vaIve. Chemical Analysis
The fat content was determined by the infra-red milk analyzer, Mark II (2). The extent of lipolysis was measured by determining the acid degree value (ADV) by a modified Frankel and Tarassuk method (ether extraction of the fat) as in (12). RESULTS AND DISCUSSION
The effect of type of milk transfer system on extent of lipolysis is shown in Table 1. Milk from farms using bucket milkers and carrying pails to convey milk to buIk tanks had the lowest ADV's, followed in order of increasing iipolysis by dumping stations, spumicks, and pipeline milkers. Differences between ADV means for the various systems were significant at 1%. All of the systems used to convey milk mechanically from cows to bulk tank significantly increased lipolysis, the highest ADV's being produced by pipeline milking systems. If the ADV's reflect differences in degree of agitation and foaming during transfer of milk to the bulk tank, it appears that milk is exposed to the severest treatment in pipeline systems, which render a comparatively higher proportion of the milk fat susceptible to lipolysis. One might expect Spumick-conveyed milk to have similar lipolytic activity to that of the bucket milker-carrying pail operations since the Spurnick (used in conjunction with bucket milking) is merely a larger carrying container on wheels. However, there are other differences. First, the milk in the Spumick (up to 140 liters) is
LIPOLYSIS IN MILK FROM MILKING SYSTEMS
1221
TABLE 1. Mean acid degree valuesa for milk from different milking systems.
System
No. of farms
No. of samples
Buckets Dumping stations Spumicks Pipelines
9 5 5 16
180 97
100 320
Mean ADV's Initial
24 h
48 h
72 h
1.80 2.27 2.50 2.99
1.92 2.40 2.60 3.14
1.97 2.46 2.65 3.21
2.04 2.52 2.70 3.26
aAs determined by a slightly modified version of the Frankel and Tarassuk method (12).
transferred rapidly to the bulk tank by air pressure. This blasting of milk into the bulk tank causes considerable agitation and foaming. Second, there is a possibility of temperature activation of lipolysis during low production periods when the Spumick may hold an entire first milking before being transferred to the bulk tank. The second milking also would be added all at once to the cold milk in the tank, and this may result in a blend temperature high enough to increase the rate of lipolysis (9). Milk from dumping stations had ADV's which were intermediate between sputnick operations and bucket milkers. Unlike most pipeline milkers, where the pipeline is moving both air and milk, the plastic or rigid (stainless steel or glass) line conducting milk from the dumping station to the vacuum releaser is flooded fully. Thus, there is no admixing of air and milk in the line until it reaches the releaser where agitation occurs as the releaser alternately fills and empties milk into the bulk tank. However, as shown by the ADV's in Table 1, there is less
severe physical treatment of milk conveyed from dumping stations than that carried by Sputnicks and pipelines milking systems. The use of bucket milkers and carrying pails produced milk with least lipolysis. This has been the observation of others in comparative studies of lipolysis in milk from pipeline and bucket milking operations (3, 6, 8, 14, 15). This study showed the relative effects on lipolysis of two other milk conveying systems. Data from pipeline milking systems was rearranged (Table 2) to reveal the effect of type of pipeline installation on lipolysis. Parlor pipeline milkers with weigh jars produced the highest ADV's, followed in order of decreasing values by around-the-barn installations and parlor systems without weigh jars. In (12) the threshold for lipolyzed flavor detection was in the ADV range of 4.1 to 4.5 (with the ether extraction method) which means there was little overall margin of safety in milk produced with parlor systems using weigh jars. In today's market such high ADV's are diluted by pooling
TABLE 2. Mean acid degree valuesa of milk obtained from parlor and around-the-barn pipeline milkers. (No. of samples per farm = 20). Type of pipeline
No. of farms
No. of samples
Mean ADV's Initial
24 h
48 h
72 h
Parlor with weigh jar
4
80
3.76
3.92
3.89
4.03
Parlor without weigh jar
2
40
2.52
2.60
2.70
2.75
10
200
2.78
2.93
3.00
3.05
Around-the-barn
aAs determined by a slightly modified version of the Frankel and Tarassuk method (12). Journal of Dairy Science Vol. 63, No. 8, 1980
1222
P1LLAY ET AL.
with lower ADV milk from other types of milking systems in Tables 1 and 2. In this way a wider margin of safety against lipolyzed flavor is gained in milk at the dairy plant. However, pipeline milking systems are going to continue to increase in popularity and sophistication, and to maintain the current margin of safety, every system should be examined for possible ways to reduce agitation and foaming of milk. Since there were substantial differences in lipolysis between parlor systems with and without weigh jars, a separate experiment was designed to isolate the effect of weigh jars from other variables in the milking system. The results are presented graphically in Figure 2. After 24-h storage, samples taken from the weigh jar had significantly higher ADV's than samples taken from the milkline ahead of the jar. This is due to the additional agitation and foaming because of forceful impingement of milk against the walls of the weigh jar during milking and because of air agitation after milking to mix the milk for sampling purposes. The rate of lipolysis in milk taken from the weigh jar was rapid during the first 24 h, after which it was approximately the same as that of milk removed ahead of the weigh jar. In explanation, it seems logical to suggest that not all
fat globules were modified physically by agitation in the weigh jar. The portion of the fat rendered susceptible to rapid lipolysis probably was depleted during the first 24 h of enzymatic action, after which lipolysis proceeded at about the same rate as in milk collected before the weigh jar. The net effect with the weigh jars was an average increase of almost a whole ADV after storage at 4,4°C for 24 to 48 h. There are numerous designs and principles of operation of weigh jars (10) with possible variable effects on lipolysis, Another type of milk-metering device used in milklines, the "milk-o-meter", also substantially increased lipolysis (5). Most often when weigh jars are installed in milking parlors, they have been made an integral part of the milking system and as such are a cause for increased agitation and foaming at every milking. Results of this study indicate that as a control measure for lipolysis, weigh jars should be used only for weighing and sampling or when it is necessary to segregate abnormal milk from infected cows. The jars can be removed from the system by simply moving the milk hose from the inlet o f the weigh jar to the inlet of the milkline. Before accepting innovations in the form of accessories or design changes in milking systems, one should consider the effect of such modifications on the lipolytic activity in milk. ACKNOWLEDGMENTS
uJ
~3
__..._-----------2
..J
:> UJ
'IE" 2 O
j
,,
~
The financial support provided by the Ontario Ministry of Agriculture and Food, and the Ontario Milk Marketing Board for this research is acknowledged gratefully.
--1 REFERENCES
IJJ
1-BEFORE WEIGH JAR O
2-AFTER WEIGH JAR
,,
0
I
24 STORAGE
I
-,,
48
I
72
TIME (h)
Figure 2. Effect of weigh jar in a pipeline milking system on acid degree values (modified Frankel and Tarassuk method) in milk held at 4.4°C. Each point on the graph represents the mean of 10 samples. Journal of Dairy Science Vol. 63, No. 8, 1980
1 Anonymous. 1977. Cross-Canada bulk milk survey. Modern Dairy 56(4): 16. 2 Association of Official Analytical Chemists. 1975. Official methods of analysis. 12th ed. Assoc. Offic. Anal. Chem., Washington, DC. 3 Giesen, T.J.J. 1977. Private communication. Gelders-Overijselse Zuivelbond, Postbus 162, Zutphen-Nieuwstad 69, Netherlands. 4 Herrington, B. L. 1956. The control of rancidity in milk. J. Dairy Sci. 39:1613. 5 Jaazen, J. J. 1963. Milk flavor as affected by a milk-metering device. J. Dairy Sci. 46: 567. 6 Jensen, R. G., A. C. Smith, P. McLeod, and L. R. Dowd. 1957. The acid degree of milk obtained with pipeline and bucket milkers. J. Milk Food Technol. 20:352.
LIPOLYSIS IN MILK FROM MILKING SYSTEMS
7 Jezeski, J. J. 1958. Pages 8 to 18 in The use o f the acid degree value test in the solution o f rancid flavor problems. Milk Ind. Found., Cony. Proc. Lab. Sect. 8 Kankare, V., and V. Antila. 1978. Influence of pipeline milking machines on lipolysis in farm milk. XX Int. Dairy Congr., Paris, Brief Communications Vol. E: 132. 9 Krukovsky, N. V., and B. L. Herrington. 1939. Studies o f lipase action. II. The activation o f milk lipase by temperature changes. J. Dairy Sci. 22:137. 10 Noorlander, D. O. 1973. Mechanics and production o f quality milk. 2nd ed. Webcrafters, Inc., Madison, WI. 11 Olson, J. C., Jr., E. L. Thomas, and A. J. Nielsen. 1956. The rancid flavor in raw milk supplies. Am.
1223
Milk Rev. 18(10):98. 12 Pillay, V.T.T., A. N. Myhr, and J. I. Gray. 1980. Lipolysis in milk. I. Determination o f free fatty acids and threshold value for lipolyzed flavor detection. J. Dairy Sci. 63:1213. 13 Tarassuk, N. P., and E. N. Frankel. 1955. On the mechanism o f activation of lipolysis and the stability o f lipase systems o f normal milk. J. Dairy Sci. 38:438. 14 Thomas, E. L., A. J. Nielsen, and J. C. Olson, Jr. 1955. Observations on the extent o f lipolysis in raw milk supplies as related to various milk handling procedures. J. Dairy Sci. 38: 596. 15 Whittlestone, W. G. 1965. Milk lipolysis and the milking machine. Milk Board J., New South Wales 16(5):19.
Journal of Dairy Science Vol. 63, No. 8, 1980