4th International Workshop onInternational Workshop … ¾good dairy manufacturing practice. ......

Freezing point determinations in milkFreezing point determinations in milk 11Brussels, 28Brussels, 28--0303--20062006

44thth International Workshop onInternational Workshop on

Water in FoodWater in Food

Application of Application of Freezing Point Determinations in Milk Freezing Point Determinations in Milk

HarrieHarrie van den van den BijgaartBijgaartNetherlands Milk Control Station Netherlands Milk Control Station -- ZutphenZutphen


Milk compositionMilk composition

Raw cowRaw cow’’s milks milk Drinking milkDrinking milk(no additions)(no additions)

0,10,1--3,5 %3,5 %8787--91 %91 %

0,90,9++ %%

3,43,4++ % % 4,44,4++ %%4,4 % 4,4 % lactoselactose

0,9 % other, mainly salts0,9 % other, mainly salts

87 % 87 % waterwater

3,4 % 3,4 % proteinprotein4,3 % 4,3 % fatfat


Freezing point of liquid milk (1)Freezing point of liquid milk (1)

lactoselactosesaltssalts

waterwater

proteinproteinfatfat

Values for authentic bulk cowValues for authentic bulk cow’’s milks milkrange from range from --0,515 to 0,515 to --0,530 0,530 °°CC

Eventual adulteration can be estimatedEventual adulteration can be estimated



Why controlling water content in liquid milk?Why controlling water content in liquid milk?Combat adulteration with extraneous waterCombat adulteration with extraneous waterAvoiding residues and contaminantsAvoiding residues and contaminants

detergentsdetergentsdisinfectantsdisinfectantsmicrobiological contaminationmicrobiological contamination

In a chainIn a chain--orientedorientedquality assurance approach to promote:quality assurance approach to promote:

good farming practicegood farming practicegood dairy manufacturing practicegood dairy manufacturing practice



Other influencing factors with raw milk:Other influencing factors with raw milk:Species (average value NL goat milk: Species (average value NL goat milk: --0,540 0,540 °°C)C)BreedBreedClimateClimateFeed and water Feed and water


EU demandsEU demands

EU 92/46 EU 92/46 –– Milk Hygiene Directive, art 5.9:Milk Hygiene Directive, art 5.9:HeatHeat--treated cowtreated cow’’s milk must have a freezing point not s milk must have a freezing point not higher than higher than --0,520 0,520 °°C C

EU Council Regulation 2597/97, art. 4 (a):EU Council Regulation 2597/97, art. 4 (a):Drinking milk must have a freezing point close to the Drinking milk must have a freezing point close to the average freezing point for raw milk recorded in the area of average freezing point for raw milk recorded in the area of origin of the drinking milk collectedorigin of the drinking milk collected

EU Regulations 852/2004, 853/2004, 854/2004:EU Regulations 852/2004, 853/2004, 854/2004:Supersede EU 92/46Supersede EU 92/46No demands to freezing point of milkNo demands to freezing point of milk


Analytical methodology (1)Analytical methodology (1)

•• ThermistorThermistor cryoscopy (since 1956!)cryoscopy (since 1956!)T (T (°°C)C)

t (s)t (s)

Attaining equilibriumAttaining equilibrium

SupercoolingSupercooling ((--3 3 °°C)C)Inducement of crystallizationInducement of crystallization

Calibration with salt solutionsCalibration with salt solutions


Analytical methodology (2)Revision of ISO 5764|IDF 108Analytical methodology (2)

Revision of ISO 5764|IDF 108

Period: 1995Period: 1995--20022002

Main shortcomings:Main shortcomings:Insufficient instrument specificationInsufficient instrument specification

apparent from comparison of complete freezing curves apparent from comparison of complete freezing curves with different instrumentswith different instruments

`Cut`Cut--off` point not strictly enough definedoff` point not strictly enough defined



Revision of ISO 5764|IDF 108T (T (°°C)C)

t (s)t (s)

t t afterafter freezingfreezing pulse (s)pulse (s)

T (T (°°C)C)

3030

--0,5220,522

6060

--0,5200,520--0,5180,518

FixedFixed--timetime, 30/60 s, 30/60 s

PlateauPlateau--timedtimed 20 s 20 s ±± 1 1 mm°°CC




Main adaptations:Main adaptations:Test tubes specified in more detailTest tubes specified in more detailTest sample volume: 2,5 mlTest sample volume: 2,5 mlTemperature control cooling mediumTemperature control cooling mediumStandardization of Standardization of thermistorthermistor probe:probe:

position (centred)position (centred)electrical resistanceelectrical resistanceheat conductance of shankheat conductance of shank

`Cut`Cut--off` point reached when rise in off` point reached when rise in temperature during last 20 s temperature during last 20 s <<0,5 0,5 mm°°CC

1 = 1 = mandrelmandrel2 = 2 = samplesample tubetube3 = 3 = stirringstirring wirewire4 = 4 = thermistorthermistor beadbead




Precision characteristics from collaborative study:Precision characteristics from collaborative study:

18 labs18 labs rr((mm°°CC))

RR((mm°°CC))

Raw milkRaw milk(n=6)(n=6) 3,63,6 6,56,5

UHT whole milkUHT whole milk(n=6)(n=6) 4,14,1 6,16,1

UHT UHT skimmilkskimmilk(n=6)(n=6) 3,13,1 4,24,2




Coming from:Coming from:Different instrument specificationsDifferent instrument specificationsOperating with different Operating with different ‘‘cutcut--offoff’’ pointspointsDifferent temperature scales (Different temperature scales (°°C, C, °°H)H)

Annexes with guidance on:Annexes with guidance on:Keeping linkage between revised reference method and Keeping linkage between revised reference method and inin--house applied methodology, i.e. establishing correction house applied methodology, i.e. establishing correction factors for equipment/method/product combinationsfactors for equipment/method/product combinations

(with demands to n and max (with demands to n and max ssdiffdiff))Adjusting earlier established values for genuine milkAdjusting earlier established values for genuine milk




Published in 2002Published in 2002Next revision underway:Next revision underway:addition of precision addition of precision characteristics for goat and characteristics for goat and sheep milk (ISO/DIS stage)sheep milk (ISO/DIS stage)


Milk-based reference materials (1)Milk-based reference materials (1)

Calibration with salt solutions:Calibration with salt solutions:SimpleSimpleEasy to standardizeEasy to standardizeFunctions well in practiceFunctions well in practice‘‘ShorterShorter’’ freezing curvesfreezing curves


Milk-based reference materials (2)Milk-based reference materials (2)

Use of milkUse of milk--based reference materials:based reference materials:Potential strengthsPotential strengths

supporting harmonized measurement levelssupporting harmonized measurement levelscryoscopiccryoscopic behaviour more similar to test samplesbehaviour more similar to test samples

Potential weaknesses Potential weaknesses stability (stability (detoriationdetoriation, salt equilibriums, gas), salt equilibriums, gas)variation due to shipment/storage conditionsvariation due to shipment/storage conditionspossible influence of water quality with reconstitutionpossible influence of water quality with reconstitution

Preferably also applicable with alternative methodsPreferably also applicable with alternative methods


Application of IR spectrometry (1)Application of IR spectrometry (1)

Principle first described by:Principle first described by:KoopsKoops, J. , J. KerkhofKerkhof MogotMogot, M.H. & van , M.H. & van HemertHemert, H., H.1989. 1989. NethNeth. Milk Dairy J. 43:3. Milk Dairy J. 43:3--16 16

Using mid IRUsing mid IR--signal (lactose!) in combination with signal (lactose!) in combination with measurement of conductivity (salts!),measurement of conductivity (salts!),

producing producing ““freezing point equivalentsfreezing point equivalents””In practice combined with highIn practice combined with high--capacity capacity compositional analysiscompositional analysis



Performance characteristics:Performance characteristics:Repeatability r: 2Repeatability r: 2--3 3 mm°°CC ((rrcryosopycryosopy: 4 : 4 mm°°CC))In case of a parallel measurement with the In case of a parallel measurement with the reference method in singular, the difference will in reference method in singular, the difference will in 95% of the cases be smaller than 595% of the cases be smaller than 5--6 6 mm°°CC

((RRcryoscopycryoscopy: 6 : 6 mm°°CC))

(van (van CrombruggeCrombrugge, J. 2003. IDF Bull. 383:16, J. 2003. IDF Bull. 383:16--22)22)



Strong points in application with raw milk:Strong points in application with raw milk:Attractive performance characteristicsAttractive performance characteristicsCheap and easy in routine testingCheap and easy in routine testingAllows continuous monitoring + trend analysisAllows continuous monitoring + trend analysis-->>

signalling irregularities!signalling irregularities!Fits perfectly in integratedFits perfectly in integratedchain quality control concepts!chain quality control concepts!

Microsoft Office Excel-werkblad



Considerations with application for checkingConsiderations with application for checkingcompliance with official limits:compliance with official limits:

Attractive performance characteristicsAttractive performance characteristicsEventual selective confirmationEventual selective confirmation

with reference methodwith reference methodExceptional differences:Exceptional differences:

unlikely at the (herd) bulk milk levelunlikely at the (herd) bulk milk levellikely related to other compositionallikely related to other compositional

abnormalitiesabnormalities…………


ConclusionsConclusions

There is sound based and up to date analytical There is sound based and up to date analytical methodology available for the detection of methodology available for the detection of extraneous water in liquid milk extraneous water in liquid milk For the checks on the different control points in For the checks on the different control points in the production chain, choices from the analytical the production chain, choices from the analytical toolbox are to be based on:toolbox are to be based on:

performance characteristicsperformance characteristics(legislative) demands(legislative) demandscapacity, convenience, costcapacity, convenience, costpotential to provide additional information for quality potential to provide additional information for quality management purposesmanagement purposes


Thanks for your attention!Thanks for your attention!

4th International Workshop onInternational Workshop … ¾good dairy manufacturing practice. ......

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