IS 1479-4: Methods of test for dairy industry, Part 4: Determination of Freezing point of milk - Thermistor cryoscopoe method (reference method)

2009·7.2 MB·English

by  Bureau of Indian Standards

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IS 1479-4 (2009): Methods of test for dairy industry, Part
4: Determination of Freezing point of milk - Thermistor
cryoscopoe method (reference method) [FAD 19: Dairy
Products and Equipment]
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IS 1479 (Part 4) : 2009
ISO 5764 : 2002

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Indian Standard
METHODS OF TEST FOR DAIRY INDUSTRY
PART 4 DETERMINATION OF FREEZING POINT OF MILK - THERMISTOR
CRYOSCOPE METHOD (REFERENCE METHOD)
( Second Revision)
ICS 67.100.10
©SIS 2009
BUREAU OF INDIAN STANDARDS

MANAK BHAVAN. 9 BAHADUR SHAH ZAFAR MARG
NEWDELHI110002
June 2009 Price Group 7
Da.~ry Products and EquipmentSectional Committee,FAD 19
NATIONALFOREWORD
ThisIndianStandard (Part4)(Second Revision)which isidenticalwithISO 5764 :2002'Milk- Determination
offreezingpoint-Thermistorcryoscopemethod (Referencemethod)'issuedbytheInternationalOrganization
for Standardization (ISO) was adopted by the Bureau of Indian Standards on the recommendation of the
Dairy Products and Equipment Sectional Committee and approval of the Food and Agriculture Division
Council.
Thisstandardwasfirstpublishedin1962andcoveredthemethodfordeterminationoffreezing-pointdepression
ofmilk bythe Hortvetmethod.Itwas subsequently revised in 1977 to includean additional method using a
modified Gerber-Cryoscopefordeterminationoffreezing-point depressionofmilk.Thesecond revisionhas
beenundertaken toalignthestandardwith ISO5764 :2002onthe subjectunderdualnumberingand covers
thedeterminationoffreezing point of milk by thermistorcryoscope method.
The text of ISO Standard has been approved as suitable for publication as an Indian Standard without
deviations. Certainconventions are,however.not identicalto those used in Indian Standards. Attention is
particularlydrawn tothe following:
a) Whereverthewords'InternationalStandard'appearreferringtothis standard,theyshouldbe readas
'IndianStandard'.
b) Comma (.)has been used as adecimalmarker,while in Indian Standards,thecurrentpractice isto
useapoint(.)as thedecimalmarker.
Inthisadopted standard,referencesappearto certain International Standards forwhich Indian Standards
alsoexist. The corresponding Indian Standards,which are to be substituted in their respective places are
listedbelow along with theirdegreeofequivalencefor the editions indicated:
InternationalStandard CorrespondingIndianStandard DegreeofEquivalence
ISO1042:1998Laboratoryglassware IS915:2006Specification forone-mark Technically Equivalent
- One-markvolumetric flasks volumetricflasks(secondrevision)
ISO 3696 :1987 Waterfor analytical IS1070 :1992 Reagentgradewater do
laboratory use - Specification and Specification(thirdrevision)
test methods
ISO 6091 : 1980 Dried milk IS 11765 : 1986 Method for Identical
Determination of titratable acidity determinationoftitratableacidityinmilk
(referencemethod)
powderandsimilarproducts (reference
method)
Inreportir.gtheresult ofatestoranalysismade inaccordancewith thisstandard,ifthe finalvalue,observed
orcal~ulated, isto be rounded off, it shallbe done inaccordance with IS 2 : 1960 'Rules for rounding off
numerical values (rev;sed)'.
IS 1479(Part4) : 2009
ISO 5764: 2002
Indian Standard
METHODS OF TEST FOR DAIRY INDUSTRY
PART 4 DETERMINATION OF FREEZING POINT OF MILK - THERMISTOR
CRYOSCOPE METHOD (REFERENCE METHOD)
( Second Revision)
1 Scope
This International Standard specifies a reference method for the determination of the freezing point of raw,
pasteurized. UHT-treatedor sterilized whole milk, partiallyskimmedmilk and skimmed milk by using a thermistor
cryoscope.
Thefreezingpointcan beusedfor estimatingtheproportionofextraneouswater inmilk.Calculationoftheamount
of extraneous water is complicated by daily variation, seasonal variation. etc. and is not within the scope of this
InternationalStandard.
Resuhsobtainedfrom sampleswith atitratable acidityexceeding20ml of0,1molll sodium hydroxidesolutionper
10gofnon-fatsolidswillnotberepresentativeoftheoriginalmilk.
NOTE Sterilizationandvacuumpasteurizalion canaffectthefreezingpointofmilk(seereference [611.
2 Nonnativereferences
Thefollowingnormative documents containprovisionswhich, throughreferenceinthistext,constituteprovisionsof
this International Standard. For dated references. subsequent amendments to. or revisions of, any of these
publicationsdonotapply.However. partiestoagreementsbasedonthis International Standard areencouragedto
investigate the possibility of applying the most recent editions of the normative documents indicated below. For
undated references. the latest edition of the normative document referred to applies. Members of ISO and IEC
maintainregistersofcurrentlyvalidInternationalStandards.
ISO1042.Laboratoryrjassware- One-marievolumetric"asks
ISO3696,Waterforanalyticallaboratoryuse- Specificationandtest methods
ISO6091,Driedmilk- Detenninationoftitratableacidity(Referencemethod)
3 Tenn and definition
ForthepurposesofthisInternationalStandard,the followingtermanddefinition applies.
3.1
freezing pointofmilk
valueobtainedusingthemethodspecifiedinthisInternationalStandard
NOTE Thefreezingpointisexpressed inmillidegreescetsius(m·C).
4 Principle
A test sample of milk is super-cooled to an appropriate temperature and crystallizatiOn is induced by means
sufficienttocauseaninstantaneous releaseofh eatwithanaccompanyingwarmingofthesampletoatemperature
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IS 1479(Part4) :2009
ISO 5764: 2002
plateau.Theplateauisreachedwhenthetemperature risehasnotexceeded0,5 mOCover the last20 s.The thus
attainedtemperaturecorrespondstothefreezingpointofthemilk sample.
Theinstrumentiscalibrated byadjusting ittogivethe correct readings for two sodium chloride standard solutions,
usingthesameprocedureasfortestportionsofmilk.
5 Reagents
Useonlyreagentsofrecognizedanalyticalgrade,unlessotherwisespecified.
5.1 Water, complying with grade2 in accordance with ISO3696, or water of equivalent quality distilled from
borosilicateglassapparatus.
Thewatershallbe boiledandcooledto20·C ±2"Cshortlybefore use.
5.2 Sodium chloride (NaCI), finely ground, dried in the electric furnace (6.7) at 300"C±25°C for 5h or
alternativelydriedinthedrying oven (6.8)at 130°C±2"Cfor at least 24h,then cooled to room temperature ina
desiccator(6.9).
5.3 Sodiumchloridestandardsolutions
Weigh, to the nearest 0,1mg, the appropriate amount (see Table 1) of prepared dry sodium chloride (5,2) in a
weighing bottle (6.5). Dissolve in water (5.1) and transfer quantitatively to a 1000mione-mark volumetric flask
(66).Dilutetothe1000mlmarkwithwater(5.1)at20°C±2·Candmix.
Alternativelyand preferably, make up the sodium chloride standard solution on a gram per kilogram basis (see
Table1. second column) by weighing the required amount of prepared dry sodium chloride (5.2) to the nearest
0,1mg and dissolving it in exactly 1kg of water (5.1). Store standard solutions at about 5·C in well-stoppered
polyethylenebottles(6.10)ofcapacitynotgreaterthan250mi.
Beforeusingastandardsolution, gentlyinvert androtatethebottle several times to mix its contents thoroughly.At
notimeshouldthestandard solution beagitated viole!'ltly,asthis can lead to incorporation of air.Pour samples of
standardsolutionsfromthebottles.Neverusepipettesforthispurpose. Donot use standardsolutions from bottles
lessthanone-quarterfull,ormorethan2monthsold,orcontaining visible moulds.
Table1- Freezingpointofsodiumchloridestandardsolutions
Naclsolutionat20·C NaCIsolution Freezingpoint
gJ1solution glkgwater m··C
6,731 6,763 - 400,0
6.868 6,901 - 408,0
7,587 7,625 -450,0
8,444 8,489 - 500,0
8,615 8,662 - 510,0
8.650 8,697 - 512,0
8.787 8,835 520,0
8.959 9,008 - 530,0
9.130 9.181 - 540,0
9.302 9,354 550,0
9.422 9,475 - 557,0
10.161 10,220 600,0

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IS 1479(Part4) :2009
ISO 5764: 2002
For this reference method, only unpreserved sodium chloride standard solutions should be used. For routine
methods.sodium chloride standard solutions with afungicidal or fungistatic agent may be used.For guidance.see
annex B
6 Apparatus
Usuallaboratoryapparatus and.inparticular.thefollowing.
6.1 Cryoscope. consisting of a thermostatically controlled cooling device. a thermistor probe with associated
circuit.aread-outdevice.asampleagitator andacrystallization device(see Figure 1).
6.1.1 Cooling device
Severaltypes ofthermostatedcoolingdevicesmay beused.Thefollowingtypes aregiven asexamples:
immersiontype:acoolingbathwith asuitable buffer capacity;
circulation type:acontinuous stream ofcoolingliquidaround the sample tube;
cooling block type:acooling block with asmallamount ofcooling liquid
After the initiation of freezing. keep the temperature of the cooling liquid around the sample tube constant at
- 7,0°C±0.5°C.
NOTE Asuitablecoolingliquidisa33% (volumefraction)aqueoussolutionofpropyleneglycol.
6.1.2 Measuringdevice,associatedcircuitryand read-outdevice
The thermistor shall be of the glass-probe type with diameter of 1.60mm ±0.4 mm and an electrical resistance of
between 3nand30 kn at0°C.
The type and dimensions of the shank material (including a possible filler) shall not allow a heat transfer into the
sample greater than 2.5" 10-3J/s.underoperating conditions.
When theprobe isinthe measurementposition.thethermistorbead shalllie onthe axisofthe sample andatequal
distances from theinner walls andthe inner bottom ofthetube (see Figure 1).
The thermistor and the associated circuitryshall showadiscrimination of 1mOC orbetter over arange of-400 mOC
to-600mOC.
The linearity ofthe circuit shall be such that noerror greater than 1mOC is introduced at any point within the range
of-400mOCto-600mOCwhen theinstrumentiscorrectly operated.
The read-outdevice shall provideadiscriminationof 1mOCorbetter overarange ofatleast 0mOCto-1000 mOC.
6.1.3 Stirringwire.inert tomilk. used tostirthetest portion during cooling.
The stirringwire shall be adjustable for amplitude and be mounted vertically in accordancewith the manufacturer's
instruction.Thewire shall vibrate laterallywithan amplitudeof2mm to3mm toensure that the temperaturewithin
the test portion remains uniform during cooling.At no time during its normal stirring operation shall the wire strike
theglassprobe orthewall ofthetube.
6.1.4 Device for initiating freezing: any device that. when operated. instantaneously initiates freezing of the
test portionwhen reaching -3.0°C.
The stirringwire (6.13) may be used for this purpose.One method is to inaeasethe amplitudeofvibration for 1s
to2ssuchthatthe stirringwire strikes thewall ofthe sample tube (6.2).

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IS 1471(Part4) : 2009
ISO 5714: 2002
Dimensionsinmillirnetres
1
2
..
N
ei
3
U"I
o'
U"I
.13.1to,l
~16 to,2
Key
1 Mandrel 3 Stirringwire
2 Samplelube 4 Thermistorbead
Figure1- Detail ofthennistorcryoscope
6.2 Sample tubft, symmetncal, made of borosilicate glass,.of length 50,Smm ±0,2mm, external diameter
16,0mm±0,2mm,andinternal diameter13,7mm±0.3mm(seeFigure 1).
Thewallthicknessthroughout thetube shallnotvarybymorethan0,1 mm.
The tubes shall be equally shaped so that equal freezing points are obtained for equal volumes of the same
solution.Checkonequality beforeusingthetubes.
6.3 Main powersupply,capable ofoperatingwithinthernanutacturer'sspecifications.
6.4 Analyticalbalance, capable ofweighingtothenearest 0,1mg.
6.5 Weighingbottle
6.6 OnHnaft(volumetric flasks,ofcapacity 1000m l,complying with therequirementsonsa 1042,class A.
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IS 1479(Part4) : 2009
ISO 5764: 2002
6.7 Electricfurnace, capableofbeingcontrolledat3oO·C ±25·C.
6.8 Dryingoven,capableofbeingcontrolledat130·C ±2·C.
6.9 Desiccator
6.10 Polyethylenebottles,ofmaximumcapacity250ml,withasuitablestopper.
7 Sampling
Sampling is not part of the method specified in this International Standard. A recommended sampling method is
giveninISO707.
It is important that the laboratory receive a sample that is truly representative and has not been damaged or
changedduringtransportorstorage.
Ifnecessary,thetestsamplesmaybe storedatatemperatureofbetween0·C and6·C.
Itispreferabletotestthesamplesimmediatelyuponarrivalatthelaboratory.
8 Calibration ofthe thermistorcryoscope
Ensurethat thecryoscope (6.1)is in workingcondition inaccordance with the manufacturer's instructions.Check
the positionof the probe,the amplitude of vibration of the stirringwire andthe temperature of the cooling device
(6.1.1).
Select two sodium chloride standard solutions (see Table1) which closely bracket the expected value of the
freezing point of the milk to be tested. The difference in the freezing points between the two selected sodium
chloridestandardsolutions shallnotbelessthan100m·C.Takecarethatthetemperatures oftheselectedsodium
chloridestandardsolutionsandthatofthetestsamplearesimilar.
Pour2,5ml±0,1ml ofthe sodiumchloride standardsolutions intoclean,dry sample tubes (6.2)andcalibratethe
instrumentasindicatedby the manufacturer. Usesampletubes(6.2)ofthesame typeasthose beinguseddunng
testingofthesample.Thereafter, thethermistorcryoscopeisreadyforuse.
9 Preparation oftestsample
9.1 Preparation
If necessary,remove any visible foreign bodies or solid butterfatfrom the test sample by filtering into aclean dry
vessel.Mixthesamplegently.Useafinerthatisinerttomilkandeffectivewhenusedatlaboratorytemperature.
Test the samples at their storage temperature or after having reached the laboratory temperature before
commencmgthedetermination.However,thetestsamplesandthesodiumchloride standardsolutionsshouldhave
thesametemperaturewhen commencingthedetermination(seealsoclause8).
9.2 Samplecondition
If doubts exist about the sample condition, determine the titratable acidity of the test sample by the method
specifiedinISO6091asfaraspossibleatthesametimeasdeterminingthefreeZingpoint.
Resultsobtained from testsampleswith atitratableaCidity exceeding20ml of0,1moUl sodium hydroxidesolution
per 109ofnon-fatsolidswillnotberepresentativeoftheonginalmilk.

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