Milk compositions having low fouling rates selected by reference to .beta.- l

This invention is based on the discovery that there is a relationship between the fouling rate of milk during processing into milk powder products and the .beta.-lactoglobulin phenotype of the cow whose milk is being processed. Milk from .beta.-lactoglobulin BB phenotype cows has a much lower fouling rate than that from .beta.-lactoglobulin AA phenotype cows. The invention consists in a method comprising testing milk from identified cows for the presence of non-fouling .beta.-lactoglobulin variants and recovering and maintaining that milk separate from the fouling variant containing milk. The non-fouling variant or blends of at least 30% by weight of the non-fouling variant are further processed into milk powder products. The invention also consists in a method of selecting a diary herd having only .beta.-lactoglobulin non-fouling variant phenotype cows.

TECHNICAL 
This invention relates to a method for the manufacture of skim milk powders 
and whole milk powders with improved properties. More particularly, the 
method relates to the selection of milk from cows producing milk which 
contains only the B variant of .beta.-lactoglobulin. 
BACKGROUND ART 
Plant Fouling 
The deposition of milk constituents on milk processing plant surfaces 
(fouling), particularly on heat exchanger surfaces, is an undesirable 
consequence of milk processing. Fouling can reduce the rate of heat 
transfer into the milk and increase the pressure drop across the heating 
equipment used. In addition, foulant material can act as a medium for the 
growth of bacteria, potentially compromising milk product sterility and 
safety. At some point during the heat processing of milk the level of 
fouling reaches a point at which processing must be interrupted to allow 
for plant cleaning. Cleaning of plant involves the use of expensive 
chemicals and this in combination with the reduced process run times, 
means that high rates of fouling can have a significant economic impact 
for the milk processor. 
Milk Composition 
It is known that there is a relationship between .beta.-lactoglobulin 
phenotypes and milk compositions in dairy cattle. Bulk milk collected from 
.beta.-lactoglobulin AA phenotype cows had a composition which was 
markedly different from that of .beta.-lactoglobulin BB phenotype cows 
(Hill, 1993). The .beta.-lactoglobulin AA phenotype bulk milk had 28% 
higher whey protein concentrations, 7% lower casein protein 
concentrations, 11% lower fat concentrations and 6% lower solids 
concentrations than .beta.-lactoglobulin BB phenotype bulk milk. The 
higher whey protein concentrations in .beta.-lactoglobulin AA phenotype 
bulk milk resulted from large increases in .beta.-lactoglobulin 
concentrations in this type of milk. However, concentrations of 
.alpha.-lactoglobulin were lower in .beta.-lactoglobulin AA phenotype bulk 
milk. It is believed that the high concentrations of .beta.-lactoglobulin 
or the presence of .beta.-lactoglobulin A variant gene suppresses the 
synthesis of other milk proteins (Hill, 1993). 
It has not previously been reported that differing milk compositions due to 
.beta.-lactoglobulin phenotypes give rise to different fouling rates. It 
would be desirable to be able to choose compositions with the lowest 
fouling rate and to select dairy cattle phenotypes to produce such 
compositions. 
It is an object of this invention to go some way towards achieving this 
desideratum or at least to offer the public a useful choice. 
DISCLOSURE OF THE INVENTION 
Accordingly, the invention may be said broadly to consist in a method of 
selecting milk for milk powder manufacturing properties which comprises 
testing milk from identified cows for the presence of variants of 
.beta.-lactoglobulin and selecting those cows whose milk contains any 
non-fouling variant and does not contain any fouling variant, and milking 
separately the non-fouling variant milk producing cows and recovering and 
maintaining their milk separately from milk from any other source. 
Preferably said non-fouling variant is the B variant of 
.beta.-lactoglobulin. 
Preferably said fouling variant is the A variant of .beta.-lactoglobulin. 
Preferably said resultant milk is tested for the presence of any fouling 
variant and discarded if any is found. 
Preferably said process includes the additional step of processing said 
milk into a milk powder product. 
Preferably said additional step comprises UHT processing. 
Preferably said method of testing is a phenotyping method. 
In one alternative said phenotyping method is capillary electrophoresis. 
In another alternative said phenotyping method comprises polyacrylamide gel 
electrophoresis. 
The invention may be said broadly to consist in milk selected according to 
any one of the processes herein above defined. 
The invention may also be said broadly to consist in a milk powder product 
prepared by any one of the processes described herein above. 
In another embodiment the invention may be said broadly to consist in a 
method for selecting breeding cows which produce daughters whose milk is 
non-fouling which comprises determining the genotype of said cows and 
selecting those whose daughters produce milk which does not contain the A 
variant of .beta.-lactoglobulin. 
Alternatively, the invention may be said broadly to consist in a process 
for selectively breeding bulls which produce daughters whose milk does not 
contain the A variant of .beta.-lactoglobulin which comprises determining 
the genotype of said bulls and selecting those which daughters which 
produce milk which does not contain the A variant of .beta.-lactoglobulin. 
Preferably, the phenotyping of daughters to determine the genotype of said 
bull is done by testing the milk of said daughters for absence of fouling 
variants of .beta.-lactoglobulin and the presence of non-fouling variants 
of .beta.-lactoglobulin. 
Alternatively, said cows or bulls are genotyped directly by using 
appropriate probes and polymerase chain reaction technology. 
In another embodiment the invention may be said broadly to consist in cows 
selected in accordance with the immediately preceding method. 
In a still further embodiment the invention may be said broadly to consist 
in bulls selected in accordance with the above defined method. 
In a still further embodiment the invention may be said broadly to consist 
in semen of bulls selected in accordance with the above defined method. 
In an alternative to any of the above processes or products the milk or 
milk product is goat's milk or milk product, sheep's milk or milk product, 
buffalo's milk or milk product, or milk or milk product from any other 
mammal which is fit for human consumption. 
In a further embodiment the invention consists in a method of selecting 
milk as defined above including the additional step of blending up to 70% 
by weight of the combination of fouling milk with no less than about 30% 
by weight of the non-fouling milk. 
The invention also consists in a blend of up to 70% by weight of the 
combination of fouling milk with no less than 30% by weight of the 
non-fouling milk. 
This invention may also be said broadly to consist in the parts, elements 
and features referred to or indicated in the specification of the 
application, individually or collectively, and any or all combinations of 
any two or more of said parts, elements or features, and where specific 
integers are mentioned herein which have known equivalents in the art to 
which this invention relates, such known equivalents are deemed to be 
incorporated herein as if individually set forth. 
The invention consists in the foregoing and also envisages constructions of 
which the following gives examples.

MODES OF CARRYING OUT THE INVENTION 
Milk Protein Genetic Variants 
Most of the major milk proteins exist in a number of variant forms 
(Ng-Kwai-Hang and Grosclaude, 1992). The major whey protein in milk, 
.beta.-lactoglobulin (.beta.-LG) is found in two common forms (the A and B 
variants). Cows can produce only one variant of .beta.-LG in milk (AA or 
BB phenotype cows) or a mixture of A and B variants of .beta.-LG in milk 
(AB phenotype cows). The milk supplied to dairy factories is composed of a 
mixture of all three phenotype milks. The relative frequencies of 
.beta.-LG phenotypes in the New Zealand cow population is shown in Table 
1. 
TABLE 1 
______________________________________ 
Relative frequency of .beta.-LG Phenotypes in New Zealand Cows*. 
AA AB BB 
______________________________________ 
19 50 31 
______________________________________ 
*10261 cows were phenotyped for LG A and B variants. 
EXAMPLE 1 
Milk Protein Phenotyping 
Milk samples from individual cows were phenotyped for .beta.-LG A and B 
variants using polyacrylamide gel electrophoresis (PAGE) run under non 
reducing conditions as described by Singh and Creamer (1991). 
Capillary Electrophoresis .beta.-LG C Phenotyping Method 
Whey was made from the milk samples supplied from individual cows by 
removal of casein by acid precipitation at pH 4.6 using hydrochloric acid. 
These whey samples were then subjected to free zone capillary 
electrophoresis (uncoated capillary--72 cm total length, 50 cm effective 
length and 50 .mu.m internal diameter) on an Applied Biosystems 270-HT CE 
system (Foster City, Calif., USA). Samples were injected at the anode 
using vacuum (17 kPa) for 4 seconds. The individual proteins in the whey 
samples were separated using a 2-(N-morpholino) ethane sulphonic acid 
buffer at pH 8.0 and a voltage of 20 kV followed by detection by 
absorbance at 215 nm. The whey proteins were eluted from the capillary in 
the order .alpha.-lactalbumin, .beta.-LG C variant, .beta.-LG B variant, 
.beta.-LG A variant, bovine serum albumin. In this way the milk samples 
from individual cows were phenotyped for .beta.-LG variants. The C variant 
is less common than the .beta.-LG A and B variants and is only present at 
low frequencies in the milks from the Jersey cattle breed. 
Other Methods 
Other methods which may be used for .beta.-LG phenotype identification are 
summarized by Ng-Kwai-Hang and Grosclaude (1992) and include a variety of 
alternate electrophoresis techniques: paper electrophoresis, reduced and 
non reduced PAGE and starch gel electrophoresis, agar gel electrophoresis 
and a variety of isoelectric focusing techniques. Other phenotyping 
methods include HPLC on reverse phase or anion exchange columns. 
Alternatively it is possible to identify the .beta.-LG genotype of bull 
sires using the polymerase chain reaction and restriction fragment length 
polymorphism (Medrano and Aguilar-Cordova, 1990). 
EXAMPLE 2 
Milk Segregation, Collection and Processing 
Trials 1 and 2 
The selection and segregation of the milks used in Trials 1 and 2 is 
described by Hill (1993). Milk was collected from 41 .beta.-LG AA 
phenotype Friesian cows and 56 .beta.-LG BB phenotype Friesian cows. These 
milks together with a control of bulk milk from a local dairy factory were 
processed into a range of whole milk powders in a spring trial (Trial 1) 
and an autumn trial (Trial 2) in a pilot-plant facility. The recombined 
milk powders were then subjected to a number of functional tests of UHT 
fouling properties as described below 
Trial 3 
To confirm the findings of Trials 1 and 2, Trial 3 was performed in early 
to mid spring. Milk for this trial was collected from approximately 200 
.beta.-LG AA phenotype cows and 200 .beta.-LG BB phenotype cows (Friesian, 
Jersey and cross-breeds). The selection, segregation and collection of 
these milks is described by Hill and Paterson (1994). 
EXAMPLE 3 
Effect of .beta.-LG Variant on Milk Powder Manufacture 
To examine the effect of .beta.-LG variant on the manufacture of milk 
powder, a further trial was performed using the milk supply described in 
Trial 3. This trial was primarily designed to examine the effect of 
.beta.-LG variant on the fouling of a milk powder manufacturing plant. The 
three milk types were pasteurized at 73.degree. C. for 15 seconds, cooled 
to less than 18.degree. C. and stored in refrigerated silos at 4.degree. 
C. Milk was pumped to an evaporator feed balance tank to maintain the 
balance tank level between 10-20 kg. The milk was pumped out of the 
balance tank at 100 kg/h and heated in a plate heat exchanger (PHE) from 
15-20.degree. C. to 85.degree. C. The heated milk was then cooled (in a 
second PHE) and collected in a refrigerated vat prior to disposal. 
The PHE was heated using hot water at a flow rate of approximately 200 
kg/h. The hot water temperature was controlled by varying the flow of 
steam to a steam/cold water mixer (DSI unit). The hot water set point was 
set automatically based on the desired outlet milk temperature and a five 
minute average of the difference between the hot water temperature and the 
outlet milk temperature (approach temperature). The inlet milk temperature 
and outlet water temperatures were also monitored. 
The PHE used for heating was a Pasilac-Therm Type T4RV from Pasilac Therm 
A/S, Kolding, Denmark. It is designed to heat 400 l milk/h from 4.degree. 
C. to 70.degree. C. using 800 l/h water supplied at 71.degree. C. It has 
30 plates and seven passes. Milk was passed through the PHE until the 
approach temperature reached 15.degree. C. The PHE was stripped and the 
plates cleaned and reassembled before CIP treatment with caustic and acid 
between each run. 
EXAMPLE 4 
Manufacture of Milk Powders Used for UHT 
Prior to processing the .beta.-LG AA, .beta.-LG BB and control milk 
(.beta.-LG AB type milk) were stored separately at 4.degree. C. in 
refrigerated vats. Each milk type was separated, pasteurized and 
standardized prior to processing. All milk types were subjected to a range 
of preheat treatments from low heat (72.degree. C./15s) to high heat 
(120.degree. C./180s) prior to evaporation and spray-drying. On entering 
the evaporator the milk was first heated to 72.degree. C. in heat recovery 
coils before passing through a direct steam injection (DSI) unit to raise 
it to the required preheat temperature. The conditions used are set out in 
Table 2. 
TABLE 2 
______________________________________ 
.degree.C. Seconds 
______________________________________ 
Trial 1 Preheat Treatments (WMP) 
72 15 
80 22 
95 20 
100 46 
120 180 
Trial 2 Preheat Treatments (WMP) 
72 15 
20 180 
Trial 3 Preheat Treatments (WMP) 
72 15 
95 20 
120 180 
Trial 3 Preheat Treatments (SMP) 
120 180 
______________________________________ 
From the DSI unit the milk flowed through holding tubes of known volume, to 
give the required holding time and was then cooled to 70.degree. C. in a 
flash vessel and fed into a pilot scale (evaporative capacity 1800 kg 
h.sup.-1) triple effect falling-film evaporator (Wiegand GmbH, Karlsruhe, 
Germany). The concentrate was fed to a pilot scale (125 kg h.sup.-1) De 
Laval tall-form spray drier (De Laval Separator Company, Spray Division, 
River Falls, Wis., USA) via a balance tank. 
In between batches or when the preheat tubes were being changed, the spray 
drier used concentrate from the balance tank and the evaporator was run on 
water. For Trials 1 and 3, the WMP made using a preheat treatment of 
95.degree. C./22s was agglomerated by returning the fines to the spray 
drier nozzle. For each preheat temperature-time combination and for each 
milk type, a 50 kg powder sample was collected. The powder produced whilst 
the evaporator and preheat conditions were reaching steady state was 
discarded. 
EXAMPLE 5 
UHT Processing 
The WMPs were reconstituted to 12.65% total solids (w/w) and the SMP 
recombined to 12.65% total solids (w/w). The reconstituted and recombined 
milks were then stored at 4.degree. C. with agitation, for 1-2 h prior to 
UHT processing. 
UHT processing was performed using an Alfa Laval UHT (Type D) pilot scale 
plant (Alfa Laval, Lund, Sweden) operated in an indirect heating mode. The 
UHT section of the plant was a plate heat exchanger which used pressurized 
hot water as the heating medium. The UHT plant operating conditions are 
shown below: 
Preheat temperature 75.degree. C. 
UHT temperature 140.degree. C. 
Feed flow rate 115-120 L h.sup.-1 
EXAMPLE 6 
UHT Fouling Rates 
Fouling Rate Determination 
The rate of deposit formation on the heat exchanger surfaces (fouling rate) 
was determined by monitoring the rise in the temperature difference 
(.DELTA.T) between the milk and the hot water (.degree.C. h.sup.-1). This 
was calculated by measuring the difference between the inlet hot water 
temperature and the outlet milk temperature from the UHT section. 
Measurements were made every 10 s by use of a datalogger. The fouling rate 
(.degree.C. h.sup.-1) for each UHT run was calculated from a linear 
regression of a plot of .DELTA.T versus time. 
Milk Composition 
The detailed compositions of the .beta.-LG AA and BB type milks used in 
these trials was determined as described by Hill (1993), Hill et al. 
(1993, 1995) and Hill and Paterson (1994). 
The UHT fouling rates for the recombined variant milk powders are shown in 
FIGS. 1-4. In all cases the line across the figures at a fouling rate of 
0.5.degree. C./h corresponds to a UHT run time of approximately 8 hrs, 
which is the minimum run time which is normally required by UHT milk 
processors. The results from Trial 1 (FIG. 1) clearly show that .beta.-LG 
AA type whole milk powder was not suitable for the UHT application, with 
the .beta.-LG BB type whole milk powder giving significantly lower fouling 
rates than the whole milk powder made from the control milk (.beta.-LG 
AB). Although the same trend was again observed in Trial 2 (FIG. 2), all 
three variant type powders generally gave lower UHT fouling rates than the 
corresponding mid season powders. 
To further examine the findings from Trials 1 and 2, in Trial 3 (FIGS. 3 
and 4) WMP manufactured from .beta.-LG AA type milk fouled UHT plant 
rapidly and was not suitable for this application. Although not shown in 
FIG. 3 (because of the scale), the fouling rate of the low heat powder 
manufactured from .beta.-LG AA type milk in a first run was 6.3.degree. 
C./h and in a second run was 5.6.degree. C./h. Apart from one run the 
.beta.-LG BB type WMP of powder gave fouling rates below 0.5.degree. C. 
and also significantly lower than those observed for the control milk. 
Generally the fouling rates were higher in the low heat WMPs than in the 
high heat WMPs for all three milk types. A medium preheat treatment 
.beta.-LG AA type WMP gave the lowest fouling rate observed with this type 
of powder. No seasonal trend in the UHT fouling rate was apparent. 
FIG. 4 shows the UHT fouling rates of the variant SMPs manufactured during 
Trial 3. Although the trend AA&gt;AB&gt;BB was again observed, all powder types 
manufactured during the first and second runs had fouling rates above 
0.5.degree. C./h. Remarkably the .beta.-LG AA type high heat SMP 
manufactured in a third run gave a UHT fouling rate of 13.7.degree. C./h, 
compared with 1.5.degree. C./h (.beta.-LG AB) and 0.3.degree. C./h 
(.beta.-LG BB) type SMP fouling rates. 
EXAMPLE 7 
Milk Powder Manufacture 
.beta.-LG variant had a marked effect on milk powder manufacture. With both 
.beta.-LG BB type milk and the control milk (.beta.-LG AB), a marked lag 
phase (FIG. 5) was observed before the onset of preheater fouling, but 
with .beta.-LG AA type milk no lag was observed prior to preheater 
fouling. FIG. 6 shows the effect of .beta.-LG variant on preheater 
fouling, the time taken to reach a temperature drop across the preheater 
of 14.degree. C. and the length of the lag phase prior to the onset of 
preheater fouling. Clearly preheater fouling is higher with .beta.-LG AA 
type milk (AA&gt;AB&gt;BB), the run time is shorter with .beta.-LG AA type milk 
(AA&lt;AB&lt;BB) and time before the onset of fouling less with .beta.-LG AA 
type milk (AA&lt;AB&lt;BB). 
EXAMPLE 8 
Milk Composition 
The effect of .beta.-LG variant on milk composition for Trials 1 and 2 is 
shown in Tables 3, 4, 5 and 
TABLE 3 
______________________________________ 
The relationship between milk type and milk composition 
TRIAL 2 TRIAL 1 
Comp % w/w 
AA BB AB AA BB AB 
______________________________________ 
Total protein 
3.36 3.38 3.49 3.13 3.16 3.27 
Casein 2.48 2.61 2.75 2.49 2.66 2.54 
Whey protein 
0.88 0.77 0.74 0.64 0.50 0.73 
Fat 4.92 5.41 5.05 4.12 4.62 4.58 
Lactose 4.60 4.65 4.82 4.73 4.68 5.02 
Ash 0.71 0.71 0.73 0.70 0.70 0.72 
Total solids 
13.54 14.10 13.93 
12.46 13.23 13.59 
______________________________________ 
TABLE 4 
______________________________________ 
The relationship between milk type and mineral content 
Mineral TRIAL 2 TRIAL 1 
mM/kg AA BB AB AA BB AB 
______________________________________ 
Ca.sup.2+ 
31.87 32.26 33.40 
31.33 31.08 
31.80 
PO.sub.4.sup.- 
21.04 21.80 21.60 
22.53 23.05 
23.80 
Na.sup.- 17.85 17.59 17.28 
15.70 15.83 
14.90 
K.sup.- 37.81 37.26 38.32 
38.73 38.20 
39.80 
Cl-- 30.35 29.35 30.24 
30.73 30.76 
31.60 
Mg.sup.2- 
4.74 4.64 4.64 4.13 4.13 4.10 
______________________________________ 
TABLE 5 
______________________________________ 
The relationship between milk type and the content of 
.beta.-lactoglobulin and .alpha.-lactalbumin 
TRIAL 2 TRIAL 1 
Protein AA BB AB AA BB AB 
______________________________________ 
.beta.-LG g/L 
5.50 4.37 4.79 4.48 3.28 4.67 
.alpha.-LA g/L 
0.92 0.97 1.12 1.02 1.31 1.31 
______________________________________ 
TABLE 6 
______________________________________ 
The relationship between milk type and protein distribution 
TRIAL 2 TRIAL 1 
Protein % 
AA BB AB AA BB AB 
______________________________________ 
Casein 73.81 77.22 78.80 
79.55 84.18 
77.67 
Whey 26.19 22.78 21.20 
20.45 15.82 
22.32 
______________________________________ 
The relative differences in the compositions of the .beta.-LG AA and BB 
type milks and control milk during different annual seasons (Hill et al., 
1995) were very similar to those shown in Tables 2-5. 
A detailed description of how the composition of milk produced under New 
Zealand farming conditions is affected by .beta.-LG phenotype is discussed 
in detail in a number of papers (Hill, 1993, Hill et al., 1993, 1995, Hill 
and Paterson, 1994). The milk produced by .beta.-LG BB phenotype cows 
contains more casein, fat and total solids than the milk produced by 
.beta.-LG AA phenotype cows which contains more whey protein and 
.beta.-LG. The content of milk minerals was very similar in both types of 
milk. 
SUMMARY 
All .beta.-LG AA type milk powders fouled UHT plant at rates that would be 
considered commercially unacceptable, except those manufactured during 
late season. Even in Trial 2 the UHT fouling rates of recombined .beta.-LG 
AA type powders were higher than either those given by the control powders 
or .beta.-LG BB type powders (AA&gt;AB&gt;BB). 
FIG. 7 shows the relationship between UHT fouling, whey protein 
concentration and .beta.-LG concentration for the three high heat powder 
types in Trial 1 and Trial 2. There is no clear relationship between whey 
protein concentration or .beta.-LG concentration and UHT fouling rate. In 
Trial 1 although the .beta.-AA type milk contained more whey protein and 
.beta.-LG than the .beta.-LG BB type milk, it had a lower concentration of 
these milk components than the control (AB type) milk, yet still gave the 
highest fouling rate of the three milk powder types. In Trial 2, the 
concentrations of whey protein and .beta.-LG were higher in all three milk 
types than the concentration of these milk components found in Trial 1, 
but the UHT fouling rates were lower than those observed in Trial 1. The 
.beta.-LG concentration in the March .beta.-LG BB type milk is almost the 
same as the .beta.-LG concentration in the Trial 1 .beta.-LG AA type milk. 
In order to study the effect of .beta.-LG variant on milk powder 
manufacturing properties the plate heat exchanger was used under 
conditions which were designed to give a high fouling rate. The flow rate 
used in the experiment (100 kg/h) was less than that which would generally 
be used in a commercial plant and thus fouling rates in the experiment are 
most likely to be higher than those which would be observed under truly 
commercial milk powder manufacturing conditions. However a commercial 
plant could not accept a three fold increase in approach temperature 
(5.degree. to 15.degree. C.) during a run. The experimental design did 
enable the marked differences in the behaviour of the variant milk types 
to be determined and showed that .beta.-LG AA type milk is probably less 
suitable for the milk powder manufacturing process than .beta.-LG BB type 
milk or the control (AB) milk. 
EXAMPLE 8 
Comparison of fouling rates between different blend ratios of high heat 
whole milk powders manufactured from .beta.-lactoglobulin AA and BB 
phenotype cows 
High heat whole milk powders manufactured from the milk supplied by 
.beta.-LG AA and BB phenotype cows were combined to produce large enough 
quantities of milk for UHT treatment The composite powders were blended at 
different ratios (see Table 7) to determine the effect of different levels 
of the powders manufactured from the milk supplied by .beta.-LG AA and BB 
phenotype cows on the fouling rate of UHT plant. The fouling rates 
obtained from the blended powders are shown in FIG. 8. 
TABLE 7 
______________________________________ 
Blend ratios of .beta.-lactoglobulin AA and BB composite powders 
Level of .beta.-lactoglobulin AA 
Level of .beta.-lactoglobulin BB 
Blend (w % in blend) (w % in blend) 
______________________________________ 
1 100 0 
2 70 30 
3 30 70 
4 0 100 
______________________________________ 
It will be seen from FIG. 8 that the highest fouling rate is achieved when 
the powder is made entirely from milk from .beta.-LC AA phenotype cows. 
However, at blends containing even as little as 30 weight per cent of BB 
type there is a marked reduction in the fouling rate which may be 
acceptable for some applications. 
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phenotypes and milk composition in New Zealand dairy cattle. Journal of 
Dairy Science, 76, 281-286. 
Hill, J. P., Boland, M. J. & Creamer, L. K. (1993). The alteration of bulk 
milk composition through the selection of .beta.-lactoglobulin phenotypes. 
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Hill, J. P. & Paterson, G. R. (1994). The variation of milk composition 
from individual .beta.-lactoglobulin AA and BB phenotype cows. Proceedings 
of the New Zealand Society of Animal Production 54, 293-295. 
Hill, J. P., Paterson, G. R., Lowe, R. and Wakelin, M. (1995). The effect 
of season and .beta.-lactoglobulin phenotype on milk composition. 
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amplification of bovine .beta.-lactoglobulin genomic sequences and 
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New Zealand Dairy Board (1992) NZDB Laboratory Services Heat Stability 
Manual. New Zealand Dairy Board Laboratory, 114 Dominion Road, Auckland, 
New Zealand. 
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Proteins (Ed. Fox P F) Elsevier Science Publishers Ltd, London, pp. 
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Paterson, G. R., Hill, J. P. and Otter, D. E. (1995). Separation of 
.beta.-lactoglobulin A, B and C variants of bovine whey using capillary 
zone electrophoresis. Journal of Chromatography A, 700, 105-110. 
Singh, H. and Creamer, L. K. (1991). Denaturation, aggregation and heat 
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