REPORT
Alkaline Phosphatase Levels
in Pasteurised Cows Milk
and Cream Produced in
On-Farm Dairies
A Watson, Rochdale Metropolitan Borough Council
A Walker, Preston City Council
G Allen, Preston Microbiology Services
K Williamson, Preston Microbiology Services
Survey Number: 304007 March 2005
CO-ORDINATED SURVEY
Greater Manchester Food Liaison Group
Lancashire Food Officer Group
FEMS-NW Preston
Introduction
Pasteurisation is an essential process in the production of milk which is safe and free from
pathogens. The Dairy Products (Hygiene) Regulations 1995 specify the temperature to
which cows milk must be heated and the length of time it must be held, to ensure that it is
adequately pasteurised.
Alkaline Phosphatase (ALP) is an enzyme which is naturally present in milk, but which is
destroyed by heat treatment. As such, the Alkaline Phosphatase test is used to measure
the level of residual ALP present in milk and indicate whether milk has been adequately
pasteurised or whether it has been contaminated raw milk after pasteurisation. The
maximum level of ALP permitted in pasteurised milk and cream is detailed in the
Regulations. A fluorimetric assay (Fluorophos) is a method used to measure ALP levels.
The maximum level using this test, which is equivalent to that specified in the Regulations
is 500mU/L. Because of the increased sensitivity of this test over other methods, some
local authorities and testing laboratories consider levels above 100mU/L to be of concern
and recommend further investigation.
Skimmed milk and cream are produced by the separation (skimming) of whole milk. In
large industrial dairies, these products may be pasteurised separately, however in many
on farm dairies, pasteurised whole milk is separated to produce pasteurised skimmed milk
and pasteurised cream.
It has been noted that on occasions, pasteurised skimmed milk and cream which have
originated from an on-farm dairy on the same date have given different ALP results, with
the ALP level in the cream significantly higher than that in the skimmed milk (Ref. 1). This
has resulted in situations where the skimmed milk has passed the ALP test, while the
cream has a result above 500mU/l. This is despite the fact that both products have
originated from the same batch of pasteurised whole milk.
ALP is readily absorbed on fat globules within the milk, hence cream which has a higher
butterfat content will contain more ALP than skimmed milk (Ref. 2). This may be one
explanation for the pattern of results described above.
Definitions
Pasteurised milk: Milk which has been heated to a temperature of 71.7C for a period of
15 seconds (or an equivalent method).
Phosphatase test: The test specified in the Dairy Products (Hygiene) Regulations 1995
which is used to determine whether milk has been adequately pasteurised or whether it
has been contaminated with raw milk after pasteurisation.
Residual Phosphatase: ALP enzyme remaining in a product due to incomplete
pasteurisation or contamination with raw milk.
Reactivated phosphatase: ALP enzyme which has been inactivated by correct
pasteurisation, but has recovered its activity due to storage conditions.
Equivocal: Results are considered equivocal when it is not possible to distinguish between
residual and reactivated ALP.
2
Objectives
1. To compare the levels of phosphatase in farm pasteurised skimmed milk and cream
with that of the whole milk from which it originated.
2. To investigate the hypothesis that phosphatase present in milk is attached to the
butterfat within the milk and that when pasteurised milk is separated to produce
skimmed milk and cream, the phosphatase is concentrated within the cream.
3. To investigate whether when pasteurised milk is separated to produce skimmed milk
and cream, any bacteria present are equally distributed between the skimmed milk and
the cream, or whether they are concentrated within either product.
4. To determine whether the current legal limit for phosphatase which applies equally to
all types of milk and cream is appropriate and provides adequate protection in relation
to the safety of each of these products.
Method
An initial pilot survey was carried out by officers from Preston City Council and Rochdale
Metropolitan Borough Council during May and June 2003.
Thirteen sets of milk and cream samples were obtained from eleven on-farm dairies
pasteurising and separating whole milk to produce skimmed milk and cream. All samples
were taken from the same batch, during the same production run. Wherever possible this
consisted of a sample of each of the following; whole pasteurised milk, skimmed
pasteurised milk and pasteurised cream. In some premises it was not possible to obtain a
sample of whole pasteurised milk, as the pipework leading from the pasteuriser and the
intake to the separator formed a sealed unit. In these cases samples of only skimmed milk
and pasteurised cream were obtained.
Following the pilot survey, the results of the examinations were assessed and a further
thirteen sets of samples from twelve on-farm dairies across five Greater Manchester and
Lancashire local authorities were obtained between October and December 2003.
The results for 7 of the 13 of the cream samples obtained during the pilot survey were not
included in the data analysis as they contained reactivated ALP or had ALP levels which
were equivocal. These problems may have been related to the temperature at which the
sample was stored between collection and receipt at the laboratory (Ref. 3). Accordingly, the
protocol for the second batch of samples was modified to request that the samples should
be packed in ice immediately after collection to improve cooling. It is considered that this
change to the sampling procedure should not preclude the use of all of the results
obtained, as it should not have had any effect on the levels of residual ALP present in the
samples.
Details of the sampling protocol, transportation method and sample submission form are
attached at Appendix 2 & 3.
3
Sample Examination
All samples were examined on the day of receipt for the presence of ALP using UKAS
accredited methods.
All samples with an ALP level of above 500mU/L were further tested to determine if the
phosphatase present was residual or reactivated. Where it was not possible to
differentiate between the two, the results were considered equivocal. This test was not
carried out on samples with an ALP level of 100 - 500mU/L. It is thus not possible to be
certain that these samples did not contain reactivated phosphatase, however for the
purpose of this survey these samples have been considered to be “of concern”.
Samples were also examined for Aerobic Colony Count (ACC).
Results
In total, 26 sets of samples comprising 65 individual samples from 19 on-farm dairies were
submitted for examination.
The full results of the survey are contained in Appendix 1.
ALP results for 17/65 samples (25%) were either reactivated or equivocal. These results
have been excluded from the following discussion as it is considered that they are
unreliable for the reasons detailed above. The results of the remaining valid samples are
summarised in Table 1.
Table 1 Analysis of valid ALP test results (Fluorophos method)
Product
Total number of
samples
Satisfactory
(<100 mU/L)
Of concern
(100–500 mU/L)
Unsatisfactory
(>500 mU/L)
Whole milk
Skimmed milk
Cream
10
23
15
4 (40.0%)
20 (87.0%)
1 (6.6%)
4 (40.0%)
3 (13.0%)
9 (60.0%)
2 (20.0%)
0
5 (33.3%)
Discussion
ALP Results
The results show that the level of residual ALP in all of the 15 cream samples was higher
than that contained in the corresponding samples of liquid milk.
For seven of the nine sets of samples where valid results were obtained for both a whole
milk and skimmed milk sample, the level of ALP was higher in the whole milk than in the
skimmed milk. In the remaining two cases, the results were within the range of uncertainty
of measurement provided by the testing laboratory.
In the five cases shown in Table 2, where the result of the residual ALP level in the cream
sample was above the legal limit (500mU/L) the corresponding sample of skimmed milk
was satisfactory (below 100mU/L). This was despite the fact that the two products had
4
been separated from the same whole milk and subject to the same pasteurisation
process.
Table 2 Sets of samples where the cream ALP level was above 500mU/L
Date of sample
08.05.03
08.05.03
16.06.03
01.10.03
26.04.04
Premises
Farm D
Farm E
Farm J
Farm E
Farm S
Whole Milk
587.5
33.6
Skimmed Milk
47.3
73.1
27.6
25.7
28.0
Cream
573.8
3515.8
1742.2
2408.0
505.2
The results of further analysis of the ALP levels in relation to the number of sets of
skimmed milk and cream samples which were satisfactory, of concern or unsatisfactory is
given in Table 3.
Table 3 Analysis of Skimmed milk and cream ALP levels
Skimmed Milk
Cream
Satisfactory
Satisfactory
Satisfactory
Of concern
Satisfactory
Of concern
Unsatisfactory
Of concern
No of sets of
samples
1
8
5
1
Table 3 clearly demonstrates that a higher proportion of cream samples were
unsatisfactory or of concern than corresponding skimmed milk samples.
These patterns of results can lead to difficulties in enforcement of the Regulations by local
authorities where the results of samples of skimmed milk, whole milk and cream which
have been subject to the same pasteurisation process must be interpreted against the
single standard detailed in the Regulations.
In particular, this could lead to samples of skimmed milk which have been inadequately
pasteurised meeting the legal standard and potentially putting the safety of consumers at
risk. Similarly, samples of cream which have been adequately pasteurised may fail the
legal standard, resulting in wasted time and resources for producers, local authorities and
the food examiner.
The interpretation of the results of individual samples (e.g. samples obtained during a
routine sampling programme) can be even more problematical as these must be viewed in
isolation.
Additionally, even where a number of retail samples of different products are obtained
from a premises at the same time, it is often difficult to determine whether they have
originated from the same production run or been produced under identical conditions,
making comparison of results difficult.
5
Microbiological results
The results of the Aerobic Colony Counts from the samples examined were inconclusive
and it has not been possible to draw any meaningful conclusions from this data.
Conclusions
1.
The results of this survey show significant differences between the levels of ALP
found in related samples of whole milk, skimmed milk and cream.
2.
The results support the hypothesis that the ALP enzyme is “attached” to the butterfat
within these products and that when whole milk is separated to produce skimmed milk
and cream, the ALP is concentrated within the cream.
3.
The survey shows that the differing ALP results obtained from related samples of
skimmed milk and cream can lead to one product passing the statutory test while the
other is above the legal limit. This is despite the fact that both have been through the
same pasteurisation process.
4.
The results of the survey suggest that further consideration should be given to
whether the single limit (500mU/L) imposed by the Regulations provides adequate
protection in relation to the safety of the foods examined.
Recommendations
1.
The sample size used in this survey was relatively small. It is recommended that a
larger survey should be carried out to confirm the reproducibility of the results. This
could be coordinated by the Food Standards Agency, Health Protection Agency or
Local Authorities Coordinators of Regulatory Services (LACORS).
2.
A review of the legal limits included in the Regulations should be carried out to
determine whether the current single limit is appropriate for skimmed milk, whole milk
and cream or whether separate limits would provide a greater level of food safety for
consumers.
3.
In the meantime, enforcement officers should take the findings of this survey into
consideration when interpreting ALP results for milk and cream produced in on-farm
dairies. Wherever possible, the results of samples of skimmed milk or cream should
not be considered in isolation, but should be compared with the results of samples of
whole milk produced during the same production run.
4.
In particular, it is suggested that cream samples should not be submitted for
examination on their own, but should be accompanied by a corresponding sample of
whole milk.
5.
Any future survey should also consider the microbiological results for these
pasteurised products and the degree of food safety provided by the current
Regulations.
6
References
1.
Assessment of pasteurisation of milk and cream produced by on-farm dairies using a
fluorimetric method for alkaline phosphatase activity. G Allen, FJ Bolton, DRA Wareing,
JK Williamson, PA Wright. Communicable Disease and Public Health, June 2004.
2. Alkaline Phosphatase Monitoring Revisited. R.L. Bradley, Dairy Pipeline, June 2002,
Volume 14 Number 2. Centre for Dairy Research, Wisconsin.
3. Milk Quality. Edited by F Harding. (Aspen Publications)
7
Appendix 1: Results of examination of samples
DATE
RECEIVED
LAB NO
PLACE OF
SAMPLING
SAMPLE POINT
ALKALINE
CATEGORY OF
PHOSPHATASE
ALKALINE
ACC
SAMPLE DETAILS
(MU/LITRE) PHOSPHATASE 30C/48H
Pasteuriser outlet (skimmed
milk)
Skimmed milk
Separator cream sprout
Double cream
01.05.03
01.05.03
4924 Farm A
4925 Farm A
01.05.03
4921 Farm B
01.05.03
4923 Farm B
Pasteuriser outlet pipe
leading to separator
Whole milk
Pasteuriser outlet (skimmed
milk)
Skimmed milk
01.05.03
4922 Farm B
Separator cream sprout
08.05.03
5105 Farm C
08.05.03
08.05.03
5107 Farm C
5106 Farm C
Pasteuriser outlet pipe
leading to separator
Separator outlet (skimmed
milk)
Separator cream sprout
08.05.03
5104 Farm D
Pasteuriser outlet (skimmed
milk)
Skimmed milk
08.05.03
5103 Farm D
Separator cream sprout
Double cream
573.8
08.05.03
08.05.03
5109 Farm E
5108 Farm E
Pasteuriser outlet (skimmed
milk)
Skimmed milk
Separator cream sprout
Double cream
73.1
3515.8
10.07.03
10.07.03
7654 Farm F
7655 Farm F
Separator outlet (skimmed
milk)
Separator cream sprout
Skimmed milk
Double cream
34.5
3178.4 Reactivated
15.05.03
15.05.03
5409 Farm G
5410 Farm G
Other - Balance tank
Other - outlet to tank
Skimmed milk
Single cream
Double cream
54.7
1821.4
Equivocal
<100 Alfa Laval 200 gal/hr
<100 Alfa Laval 200 gal/hr
1113.4
Equivocal
300 Mallinson 110gal/hr
552.6
Equivocal
<100 Mallinson 110gal/hr
2013.4 Reactivated
Whole milk
Skimmed milk
Double cream
100 Mallinson 110gal/hr
TYPE OF SEPARATOR
Nagema 200gal/hr
Nagema 200gal/hr
Alfa Laval 120-180
(restricted to 110gal/hr)
Alfa Laval 120-180
(restricted to 110gal/hr)
Alfa Laval 120-180
(restricted to 110gal/hr)
281.8
<100 Mallinson 110gal/hr
Elecrem 110g/hr
166.0
630.6 Reactivated
100 Mallinson 110gal/hr
<100 Mallinson 110gal/hr
Elecrem 110g/hr
Elecrem 110g/hr
Residual
5200 APV 500gal/hr
West Falia 3300l/hr
restricted to 2240l/hr
West Falia 3300l/hr
restricted to 2240l/hr
Residual
100 Alfa Laval 220g/hr
<100 Alfa Laval 220g/hr
Unknown make 220g/hr
Unknown make 220g/hr
47.3
38.2
282.2
8
TYPE OF PASTEURISER
1600 APV 500gal/hr
8800
11000
<100 APV 800 gal/hr
<100 APV 800 gal/hr
Septicil 800 gal/hr
Septicil 800 gal/hr
16.04.03
16.04.03
4476 Farm G
4475 Farm G
Pasteuriser outlet (skimmed
milk)
Skimmed milk
Single cream
20.2
144.4
<100 APV 800 gal/hr
<100 APV 800 gal/hr
Septicil 800 gal/hr
Septicil 800 gal/hr
16.04.03
16.04.03
4474 Farm H
4473 Farm H
Pasteuriser outlet (skimmed
milk)
Skimmed milk
Separator cream sprout
Single cream
16.5
744.8 Reactivated
<100 APV 480 gal/hr
<100 APV 480 gal/hr
West Falia 480 gal/hr
West Falia 480 gal/hr
16.06.03
6651 Farm I
16.06.03
16.06.03
6653 Farm I
6652 Farm I
16.06.03
6655 Farm J
16.06.03
6657 Farm J
Pasteuriser outlet pipe
leading to separator
Whole milk
Pasteuriser outlet (skimmed
milk)
Skimmed milk
16.06.03
6656 Farm J
Separator cream sprout
Double cream
1742.2
18.06.03
18.06.03
6721 Farm K
6720 Farm K
Separator cream sprout
Skimmed milk
Double cream
27.6
1031.1 Reactivated
19.06.03
6808 Farm B
Pasteuriser outlet pipe
leading to separator
Whole milk
19.06.03
6810 Farm B
19.06.03
6809 Farm B
P03.00145
23/10/2003 30.W
Farm L
P03.00145
23/10/2003 31.A
Farm L
Pasteuriser outlet pipe
leading to separator
Separator outlet (skimmed
milk)
Separator cream sprout
Separator cream sprout
Whole milk
62.1
33000 Mallinson MR500 150g/hr Elecrem 5 120g/hr
Skimmed milk
Double cream
29.0
161.8
33000 Mallinson MR500 150g/hr Elecrem 5 120g/hr
43000 Mallinson MR500 150g/hr Elecrem 5 120g/hr
587.5
Residual
27.6
Residual
Mallinson Read 200g/hr
1400 (mod to 300g/hr)
Mallinson Read 200g/hr
1600 (mod to 300g/hr)
Mallinson Read 200g/hr
5100 (mod to 300g/hr)
800 Mallinson Read 200g/hr
200 Mallinson Read 200g/hr
Westvalier Creamer 275g/hr
Westvalier Creamer 275g/hr
Westvalier Creamer 275g/hr
Nagema 200gal/hr
Nagema 200gal/hr
Skimmed milk
359.5 Reactivated
<100 Mallinson 110gal/hr
Double cream
1799.2 Reactivated
<100 Mallinson 110gal/hr
Alfa Laval 120-180
(restricted to 110gal/hr)
Alfa Laval 120-180
(restricted to 110gal/hr)
Alfa Laval 120-180
(restricted to 110gal/hr)
639.4
Equivocal
<100 Mallinson 110gal/hr
Separator outlet (skm) milk Skimmed milk
18.4
3600 Alfa Laval 110 Gallons
Elecrem (5)
Separator cream spout
29.4
200 Alfa Laval 110 Gallons
Elecrem (5)
Whipping cream
9
P03.00163
12/12/2003 72.F
Farm M
P03.00163
12/12/2003 71.P
Farm M
P03.00166
19/12/2003 25.S
Farm M
P03.00166
19/12/2003 26.Z
Farm M
P03.00137
01/10/2003 62.K
Farm C
P03.00137
01/10/2003 64.B
Farm C
P03.00137
01/10/2003 63.J
Farm C
P03.00155
25/11/2003 97.F
Farm B
P03.00156
25/11/2003 00.N
Farm B
P03.00155
25/11/2003 98.T
Farm B
P03.00139
08/10/2003 55.H
Farm N
P03.00139
08/10/2003 54.Q
Farm N
P03.00139
08/10/2003 53.Z
Farm N
P03.00164
15/12/2003 09.P
Farm O
P03.00164
15/12/2003 11.E
Farm O
P03.00164
15/12/2003 10.N
Farm O
Mallinson Read 200
<100 gals/hr
Mallinson Read 200
200 gals/hr
Past outlet (skim milk)
Skimmed milk
60.2
Separator cream spout
Double cream
231.6
separator outlet
Skimmed milk
<10.0
separator cream spout
Double cream
218.8
Mallinson Read 200
<100 gals/hr
Mallinson Read 200
<100 gals/hr
Past outlet pipe to sep
Whole milk
211.9
100 Mallinson 110gal/hr
Elecrem 110g/hr
Past outlet (skim milk)
Skimmed milk
29
<100 Mallinson 110gal/hr
Elecrem 110g/hr
Separator cream spout
Double cream
1536.4
100 Mallinson 110gal/hr
Elecrem 110g/hr
Past outlet pipe to sep
Whole milk
229.8
1500 Mallinson 110gal/hr
Past outlet pipe to sep
Skimmed milk
149.4
600 Mallinson 110gal/hr
Separator cream spout
Double cream
345.6
300 Mallinson 110gal/hr
Past outlet pipe to sep
Whole milk
161.8
100 ALFA LAVAL Microtherm ELECREM 5
Separator outlet (skm) milk Skimmed milk
193.5
<100 ALFA LAVAL Microtherm ELECREM 5
Separator cream spout
Double cream
521.2 Reactivated
<100 ALFA LAVAL Microtherm ELECREM 5
Past outlet pipe to sep
Whole milk
645.4 Reactivated
<100 Mallinson 1 gallon/8 min
Elecrem 5
100 Mallinson 1 gallon/8 min
Elecrem 5
<100 Mallinson 1 gallon/8 min
Elecrem 5
Separator outlet (skm) milk Skimmed milk
Separator cream spout
Equivocal
49.2
Double cream
1247.6
10
Equivocal
LAK Sami
LAK Sami
LAK Sami
LAK Sami
Alfa Laval 120-180
(restricted to 110gal/hr)
Alfa Laval 120-180
(restricted to 110gal/hr)
Alfa Laval 120-180
(restricted to 110gal/hr)
P03.00145
23/10/2003 33.K
Farm P
P03.00145
23/10/2003 32.C
Farm P
P03.00145
23/10/2003 34.J
Farm P
P03.00164
16/12/2003 49.F
Farm Q
P03.00164
16/12/2003 50.E
Farm Q
P03.00164
16/12/2003 51.Y
Farm Q
P03.00144
22/10/2003 88.J
Farm R
P03.00144
22/10/2003 89.B
Farm R
P03.00144
22/10/2003 90.C
Farm R
P03.00156
25/11/2003 01.E
Farm K
P03.00155
25/11/2003 99.M
Farm K
P03.00137
01/10/2003 66.L
Farm E
P03.00137
01/10/2003 65.X
Farm E
P04.00054
26/04/2004 24.X
Farm S
P04.00054
26/04/2004 25.X
Farm S
P04.00054
26/04/2004 26.X
Farm S
Past outlet pipe to sep
Whole milk
Separator outlet (skm) milk Skimmed milk
Separator cream spout
Double cream
Past outlet pipe to sep
Whole milk
Separator outlet(skm milk
Skimmed milk
Separator cream spout
Single cream
Past outlet pipe to sep
Whole milk
35.9
100 Alfa Laval 130 gals/hr
Electra 100 gals/hr
40
200 Alfa Laval 130 gals/hr
Electra 100 gals/hr
144.4
<100 Alfa Laval 130 gals/hr
Electra 100 gals/hr
1003.9
Residual
<100 Read Mallinson
Read Mallinson
622
Equivocal
100 Read Mallinson
Read Mallinson
<100 Read Mallinson
Read Mallinson
69.9
1900 Alfa Lavel 120gl per hr
West Failure 120gl per hr
41.8
1000 Alfa Lavel 120gl per hr
West Failure 120gl per hr
West Failure 120gl per hr
1550.2 Reactivated
Separator outlet (skm) milk Skimmed milk
Separator cream spout
Double cream
258.4
100 Alfa Lavel 120gl per hr
Past outlet pipe to sep
Skimmed milk
34.5
5000 Mallinson 200 gals/hour
Gaulin 200 gals /hour
Separator cream spout
Single cream
184.3
700 Mallinson 200 gals/hour
Gaulin 200 gals /hour
Past outlet (skim milk)
Skimmed milk
25.7
Separator cream spout
Double cream
2408
Past outlet to sep
Whole milk
33.6
Alfa Laval 200g/hr
Nagima
28.0
Alfa Laval 200g/hr
Nagima
Alfa Laval 200g/hr
Nagima
Pasteuriser outlet (skimmed
milk)
Skimmed milk
Separator cream spout
Double cream
505.2
11
100 Alfa Laval 220g/hr
Residual
Residual
<100 Alfa Laval 220g/hr
Appendix 2: Sampling protocol
LANCASHIRE FOG/GREATER MANCHESTER FLG/PRESTON PHLS
PILOT SURVEY
Examination of skimmed milk and cream to compare levels of phosphatase and
microbiological contamination
PROTOCOL SURVEY NO: 304007
SURVEY DATES: APRIL – JUNE 2003
BACKGROUND
The pasteurisation of milk is an essential process in the production of milk which is safe
and free from pathogens. The Dairy Products (Hygiene) Regulations 1995 specify the
temperature milk must be heated to and the length of time it must be held, to ensure that it
is adequately pasteurised. The Regulations specify a temperature of 71.7ºC for a period of
15 seconds or an equivalent method.
Phosphatase is an enzyme which is naturally present in milk, but is destroyed by heat
treatment. As such, the “phosphatase test” is used to indicate whether milk has been
adequately pasteurised. The maximum level of phosphatase permitted in pasteurised milk
and cream is detailed in the Regulations. Fluorimetric assay is a method used widely to
measure phosphatase levels. The maximum level using this test, which is equivalent to
that specified in the Regulations is 500mU/L.
Skimmed milk and cream are produced by the separation (skimming) of whole milk. In
large industrial dairies, the products may be pasteurised separately, however in many
small “on farm” dairies, pasteurised whole milk is separated to produce pasteurised
skimmed milk and pasteurised cream.
It has been noted that on occasions, skimmed milk and cream which have originated from
a individual dairy on the same date have given significantly different phosphatase results,
with the phosphatase level in the cream significantly higher that that in the skimmed milk.
This has resulted in situations where the skimmed milk has passed the phosphatase test,
while the cream has a result above the legal limit. This is despite the fact that both
products have originated from whole milk which has apparently undergone the same
pasteurisation process.
It has been suggested that the phosphatase enzyme is “attached” to the butterfat within
the milk and that when the milk is separated to produce skimmed milk and cream, the
phosphatase is concentrated within the cream, leading to the pattern of results described
above. This may lead to a situation where skimmed milk which has been inadequately
pasteurised could pass the phosphatase test, or conversely cream which has been
adequately pasteurised could be above the legal limit. It is also suggested that any
bacteria within the milk may be similarly redistributed.
12
OBJECTIVES
5. To compare the levels of phosphatase in farm pasteurised skimmed milk and cream
with that of the whole milk from which it originated.
6. To compare the levels of bacteria in farm pasteurised skimmed milk and cream, which
has originated from the same batch of pasteurised milk.
7. To investigate the hypothesis that phosphatase present in milk is attached to the
butterfat within the milk and that when pasteurised milk is separated to produce
skimmed milk and cream, the phosphatase is concentrated within the cream.
8. To investigate whether when pasteurised milk is separated to produce skimmed milk
and cream, any bacteria present are equally distributed between the skimmed milk and
the cream, or whether they are concentrated within either product.
9. To determine whether the current legal limit for phosphatase which applies equally to
all types of milk and cream is appropriate and provides adequate protection in relation
to the safety of each of these products.
DEFINITIONS
Pasteurised milk: milk which has been subject to the pasteurisation process detailed in the
Dairy Products (Hygiene) Regulations 1995, (a temperature of 71.7ºC for a period of 15
seconds, or an equivalent method).
Phosphatase test: the test specified in Schedule 11 of the Dairy Products (Hygiene)
Regulations 1995 or an equivalent method.
Premises to be sampled are farms producing skimmed milk and cream by the separation
(skimming) of pasteurised milk.
SAMPLING DETAILS
Sampling must be carried out by sampling officers who have been suitably trained and
who are familiar with the pasteurisation/separation process.
To ensure that suitable samples can be obtained by the sampling officer, suitable
premises which produce skimmed milk and cream from pasteurised milk should be
identified. Samples must not be obtained where skimmed milk and cream are separated
from raw milk and then pasteurised separately.
Samples should be taken from as many different premises as possible. The premises
must be contacted to confirm the days and times at which the separation of milk takes
place to ensure that the samples will be available.
Samples should be taken using sterile “honey jars” supplied by PHLS. A minimum of 150g
of each product must be obtained.
13
Three samples must be taken as follows:
1. One sample of pasteurised whole milk, prior to separation. This should be taken at a
point immediately before the milk enters the separator. For example, from the end of
the take-off pipe from the pasteuriser which feeds the separator. It is important that
where this sample is taken, no changes are made to the equipment (e.g. opening of
take off valves or dismantling of pipework) as this may affect the flow rate of the
equipment and the level to which the milk is pasteurised. If it is not possible to obtain a
sample of whole milk without making such changes, this sample should be ignored;
2. One sample of cream. This must be taken directly from the “cream spout” of the
separator;
3. One of sample of skimmed milk. This should be taken either from the separator outlet
or from closest point to the outlet of the pasteuriser (normally the pipe which feeds the
bottling machine or storage tank);
The samples must be taken with as little time interval between the samples as possible.
The whole milk sample should be taken first, followed by the cream and then the skimmed
milk. The reason for this is that after separation, the skimmed milk may return to the
pasteuriser to continue cooling. Taking the samples in this order will ensure that they have
come from milk which has been separated within the shortest time possible.
Whilst taking the samples, no adjustments whatsoever should be made to the equipment
(pasteuriser, separator etc) as this could lead to a difference in the level of pasteurisation
achieved.
Immediately after sampling, the sample jars must be securely lidded, labelled with the
name and address of the premises, description of the product and the date and time of
sampling. The samples must then be placed in a cool box containing eight 400g or four
1000g ice packs. As the cream may still be warm, no more than two cream samples
should be placed in a single cool box.
Samples must be delivered to PHLS on the day of collection in accordance with normal
methods. A separate copy of the submission form attached at Appendix 1 must
accompany each sample.
During the pilot study, Rochdale MBC and Preston CC will each submit 10 sets of 3
samples during the period April – June 2003. Samples should be submitted on Monday
Tuesday, Wednesday or Thursday.
EXAMINATION
Samples will be examined for Aerobic Colony Count (30ºC) and for phosphatase levels
using the Fluorimetric assay method.
The presence of residual phosphatase indicates inadequate pasteurisation or
contamination with raw product.
14
Cream samples which fail the phosphatase test will also be tested to establish the origin of
the phosphatase. The presence of microbial and reactivated phosphatase can give false
positive results.
INTERPRETATION OF RESULTS
Phosphatase results will be considered in relation to the legal limit contained in the Dairy
Products Regulations (500mU/L). In addition, results between 100 and 500mU/L will be
reported as “of concern”. Follow-up action for samples, which exceed 100mU/L, should be
taken following the “Guidance Note for the Examination of Milk and Cream”.
ACC results will be considered for survey purposes only.
ENQUIRIES
The following contacts are available to answer queries relating to this project:
Allan Watson,
Alan Walker,
Kevin Williamson,
Trudi Allen
Rochdale MBC,
Preston CC,
Preston PHLS,
Preston PHLS,
01706 864147
01772 906160
01772 522115
01772 522115
15
Appendix 3. Sample submission Form
Public Health Laboratory
Liverpool Rd,
Chester CH2 1UL
Tel 01244 366770
Fax 01244 3667771
PUBLIC HEALTH LABORATORY SERVICE
Food and Environmental Service Laboratories
Public Health Laboratory
Royal Preston Hospital
PO Box 202, Sharoe Green Lane
Preston PR2 9HG
Tel 01772-710100
Fax 01772-713681
CPA Accredited
a UKAS TESTING Laboratory No 1496; Group
REQUEST FOR MICROBIOLOGICAL EXAMINATION OF DAIRY PRODUCT
SKIMMED MILK/CREAM PHOSPHATASE SURVEY
Survey No 304007
SENDERS REF NUMBER:
.............................................
LAB REF NUMBER:
SENDERS ADDRESS:
..............................................
DATE OF SAMPLING:
..............................................
TIME OF SAMPLING:
..............................................
SAMPLING OFFICER:
SAMPLE DETAILS
...........................................
...
...........................................
...
...........................................
...
Place of sampling: ...........................................................
Conditions of storage and transport since sample taken:
.............................................................................................
......................................................................................
TICK ONE BOX ONLY
Approval No:.......................................................................
Separator cream spout
Separator outlet (skimmed milk)
Pasteuriser outlet (skimmed milk)
Other (specify):
PRODUCT
TICK ONE BOX ONLY
SAMPLING POINT
Comments/additional information (if appropriate):





(Make/Model/Throughput (Gals/hr))
EQUIPMENT DETAILS
Pasteuriser outlet pipe leading to separator
Pasteurised whole milk
Skimmed milk
Double cream
Whipping cream
Single cream
Other (Specify):






Pasteuriser:
Separator:
Please insert any additional information as appropriate, or details of difficulties encountered during sampling:
EXAMINATION REQUIRED
Phosphatase (Fluorimetric assay)
Aerobic Colony Count (30ºC/48hrs)
Samples should be transported to the laboratory at 0-4oC and delivered preferably within 4h on the day of collection.
Sterile sample containers are available from any of the PHLS North West Laboratories.
_____________________________________________________________________________________________________________________________ _______________________________________________________________________________________________________________________
LABORATORY USE ONLY
Temperature on receipt:
.............................oC
R
I
Date received:
............................................. Time received:
..............................................
Received by:
............................................. Received from:
..............................................
.
Sample receipt:
SATISFACTORY
/ UNSATISFACTORY*
.
*Details if relevant: ………………………………………………………………………………………………….....
106750374
PROTECTING THE POPULATION FROM INFECTION
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