1、October 2009DEUTSCHE NORM English price group 13No part of this standard may be reproduced without prior permission ofDIN Deutsches Institut fr Normung e. V., Berlin. Beuth Verlag GmbH, 10772 Berlin, Germany,has the exclusive right of sale for German Standards (DIN-Normen).ICS 67.100.10!$ZC“1553257w
2、ww.din.deDDIN EN ISO 5764Milk Determination of freezing point Thermistor cryoscope method (Reference method) (ISO 5764:2009)English version of DIN EN ISO 5764:2009-10Milch Bestimmung des Gefrierpunktes Thermistor-Kryoskop-Verfahren (Referenzverfahren) (ISO 5764:2009)Englische Fassung DIN EN ISO 5764
3、:2009-10SupersedesDIN EN ISO 5764:2002-09www.beuth.deDocument comprises 24 pagesDIN EN ISO 5764:2009-10 2 National foreword This standard has been prepared by Technical Committee ISO/TC 34 “Food products” (Secretariat: AFNOR, France), Subcommittee SC 5 “Milk and milk products” (Secretariat: NEN, Net
4、herlands) in collaboration with Technical Committee CEN/TC 302 “Milk and milk products Methods of sampling and analysis” (Secretariat: NEN, Netherlands). The responsible German body involved in its preparation was the Normenausschuss Lebensmittel und landwirtschaftliche Produkte (Food and Agricultur
5、al Products Standards Committee), Technical Committee NA 057-05-13 AA Milch und Milchprodukte Probenahme- und Untersuchungsverfahren. Based on the results of parallel voting, ISO 5764:2009 has been adopted as a European Standard. In this standard, the unit “mC” (millidegree Celsius) is used. It shou
6、ld, however, be noted that the Gesetz ber Einheiten im Messwesen (German Law on units in metrology) prohibits the use of the unit “mC” for official and commercial purposes in Germany. Non-SI unit SI unit The DIN Standards corresponding to the International Standards referred to in this document are
7、as follows: ISO 707 DIN EN ISO 707 ISO 1042 DIN EN ISO 1042 ISO 3696 DIN ISO 3696 ISO 5725-1 DIN ISO 5725-1 ISO 5725-2 DIN ISO 5725-2 Amendments This standard differs from DIN EN ISO 5764:2002-09 as follows: a) Clause 1 “Scope” has been extended to include ovine and caprine milk. b) The results of i
8、nterlaboratory tests on raw ovine and caprine milk have been included. c) The standard has been revised in form and substance and brought in line with the current rules of presentation. Previous editions DIN 10319: 1970-10, 1989-10 DIN EN ISO 5764: 2002-09 mC 10 C 3 DIN EN ISO 5764:2009-10 3 Nationa
9、l Annex NA (informative) Bibliography DIN EN ISO 707, Milk and milk products Guidance on sampling DIN EN ISO 1042, Laboratory glassware One-mark volumetric flasks DIN ISO 3696, Water for analytical laboratory use Specification and test methods DIN ISO 5725-1, Accuracy (trueness and precision) of mea
10、surement methods and results Part 1: General principles and definitions DIN ISO 5725-2, Accuracy (trueness and precision) of measurement methods and results Part 2: Basic method for the determination of repeatability and reproducibility of a standard measurement method DIN EN ISO 5764:2009-10 4 This
11、 page is intentionally blank EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN ISO 5764 May 2009 ICS 67.100.10 Supersedes EN ISO 5764:2002English Version Milk - Determination of freezing point - Thermistor cryoscope method (Reference method) (ISO 5764:2009) Lait - Dtermination du point de conglat
12、ion - Mthode au cryoscope thermistance (Mthode de rfrence) (ISO 5764:2009) Milch - Bestimmung des Gefrierpunktes - Thermistor-Kryoskop-Verfahren (Referenzverfahren) (ISO 5764:2009) This European Standard was approved by CEN on 13 April 2009. CEN members are bound to comply with the CEN/CENELEC Inter
13、nal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN Management Centre or to any CEN memb
14、er. This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as the official versions. CEN membe
15、rs are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, S
16、witzerland and United Kingdom. EUROPEAN COMMITTEE FOR STANDARDIZATION COMIT EUROPEN DE NORMALISATION EUROPISCHES KOMITEE FR NORMUNG Management Centre: Avenue Marnix 17, B-1000 Brussels 2009 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref.
17、No. EN ISO 5764:2009: EContents 2 DIN EN ISO 5764:2009-10 EN ISO 5764:2009 (E)Page Foreword .3 1 Scope4 2 Normative references4 3 Terms and definitions .4 4 Principle .5 5 Reagents 5 6 Apparatus.6 7 Sampling 7 8 Calibration of the thermistor cryoscope.7 9 Preparation of test sample .8 9.1 Preparatio
18、n.8 9.2 Sample condition.9 10 Procedure.9 10.1 Preliminary checks9 10.2 Routine calibration check.9 10.3 Determination 9 11 Calculation and expression of results 10 11.1 Calculation .10 11.2 Expression of results10 12 Precision 10 12.1 Interlaboratory test10 12.2 Repeatability 10 12.3 Reproducibilit
19、y 10 13 Test report11 Annex A (informative) Interlaboratory trial on bovine milk 12 Annex B (informative) Interlaboratory trial on raw ovine and caprine milk14 Annex C (informative) Guidelines for the application of routine thermistor cryoscope methods .16 Annex D (informative) Adjustment of the fre
20、ezing point value used as the reference for genuine milk19 Bibliography20 3 Foreword This document (EN ISO 5764:2009) has been prepared by Technical Committee ISO/TC 34 “Agricultural food products“ in collaboration with Technical Committee CEN/TC 302 “Milk and milk products - Methods of sampling and
21、 analysis” the secretariat of which is held by NEN. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by November 2009, and conflicting national standards shall be withdrawn at the latest by November 2
22、009. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN and/or CENELEC shall not be held responsible for identifying any or all such patent rights. This document supersedes EN ISO 5764:2002. According to the CEN/CENELEC Internal
23、Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
24、Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom. Endorsement notice The text of ISO 5764:2009 has been approved by CEN as a EN ISO 5764:2009 without any modification. DIN EN ISO 5764:2009-10 EN ISO 5764:2009 (E) 1 Scope This Inter
25、national Standard specifies a reference method for the determination of the freezing point of raw bovine milk, heat-treated whole, reduced fat and skimmed bovine milk, as well as raw ovine and caprine milk, by using a thermistor cryoscope. The freezing point can be used to estimate the proportion of
26、 extraneous water in milk. Calculation of the amount of extraneous water is subject to daily and seasonal variations, and is not within the scope of this International Standard. Results obtained from samples with a titratable acidity exceeding 20 ml of 0,1 mol/l sodium hydroxide solution per 10 g of
27、 non-fat solids are not representative of the original milk. NOTE 1 Sterilization and vacuum pasteurization can affect the freezing point of milk (see Reference 5). NOTE 2 The method uses plateau-timed instruments. For routine measurements, other thermistor cryoscope methods, i.e. fixed time procedu
28、res, can be used. Guidelines for the application of other procedures are given in Annex C. NOTE 3 The limit value mentioned for the titratable acidity in Clause 1 and 9.2 applies to bovine milk. It is possible that the limit values for ovine and caprine milk are higher. 2 Normative references The fo
29、llowing referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 3696, Water for analytical laboratory use Specifica
30、tion and test methods ISO 6091, Dried milk Determination of titratable acidity (Reference method) 1)3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 freezing point of milk temperature value obtained using the method specified in this Internati
31、onal Standard NOTE The freezing point is expressed in millidegrees Celsius. 1) Equivalent to IDF 86. 4 DIN EN ISO 5764:2009-10 EN ISO 5764:2009 (E) 4 Principle A test sample of milk is supercooled to an appropriate temperature. Crystallization is induced by means sufficient to cause an instantaneous
32、 release of heat with an accompanying warming of the sample to a temperature plateau. The plateau is reached when the temperature rise has not exceeded 0,5 mC over the previous 20 s. The temperature thus attained corresponds to the freezing point of the test sample. The instrument is calibrated by a
33、djusting it to give the correct readings for two sodium chloride standard solutions, using the same procedure as for test portions of milk. 5 Reagents During the analysis, unless otherwise stated, use only reagents of recognized analytical grade. 5.1 Water, in accordance with ISO 3696 grade 2 or wat
34、er of equivalent quality distilled from borosilicate glass apparatus. Boil the water and cool it to 20 C 2 C shortly before use. 5.2 Sodium chloride (NaCl), finely ground, dried in the electric furnace (6.7) at 300 C 25 C for 5 h or, alternatively, dried in the drying oven (6.8) at 130 C 2 C for at
35、least 24 h, then cooled to room temperature in a desiccator (6.9). 5.3 Sodium chloride standard solutions. Preferably, make up the sodium chloride standard solution on a gram per kilogram basis (see Table 1, leftmost column) by weighing the required amount of prepared dry sodium chloride (5.2) to th
36、e nearest 0,1 mg and dissolving it in 1 000 g 0,1 g of water (5.1). Store standard solutions at about 5 C in well-stoppered polyethylene bottles (6.10) of capacity not greater than 250 ml. Alternatively, weigh, to the nearest 0,1 mg, the appropriate amount (see Table 1, middle column) of prepared dr
37、y sodium chloride (5.2) in a weighing bottle (6.5). Dissolve in water (5.1) and transfer quantitatively to a 1 000 ml one-mark volumetric flask (6.6). Dilute to the 1 000 ml mark with water (5.1) at 20 C 2 C and mix. Table 1 Freezing point of sodium chloride standard solutions NaCl solution g/kg NaC
38、l solution at 20 C g/l Freezing point mC 6,763 6,731 400,0 6,901 6,868 408,0 7,625 7,587 450,0 8,489 8,444 500,0 8,662 8,615 510,0 8,697 8,650 512,0 8,835 8,787 520,0 9,008 8,959 530,0 9,181 9,130 540,0 9,354 9,302 550,0 9,475 9,422 557,0 10,220 10,161 600,0 5 DIN EN ISO 5764:2009-10 EN ISO 5764:200
39、9 (E) Before using a standard solution, gently invert and rotate the bottle several times to mix its contents thoroughly. Do not agitate the standard solution violently at any time, as this can lead to incorporation of air. Pour samples of standard solutions from the bottles; never use pipettes for
40、this purpose. Do not use standard solutions from bottles less than one-quarter full, or more than 2 months old, or containing visible moulds. Only use unpreserved sodium chloride standard solutions for this reference method. For routine methods, sodium chloride standard solutions with a fungicidal o
41、r fungistatic agent may be used. For guidance, see Annex C. 6 Apparatus Usual laboratory apparatus and, in particular, the following. 6.1 Cryoscope, consisting of a thermostatically controlled cooling device, a thermistor probe with associated circuit, a read-out device, a sample agitator and a crys
42、tallization device (see Figure 1). 6.1.1 Cooling device. Several types of thermostatically controlled cooling devices can be used, e.g.: a) immersion type: a cooling bath with a suitable buffer capacity; b) circulation type: a continuous stream of cooling liquid around the sample tube; c) cooling bl
43、ock type: a cooling block with a small amount of cooling 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 A suitable cooling liquid is a 33 % (volume fraction) aqueous solution of propylene glycol. 6.1.2 Measuri
44、ng device, associated circuitry and read-out device. The thermistor shall be of the glass probe type with diameter of 1,60 mm 0,4 mm and an electrical resistance of between 3 and 30 k at 0 C. The type and dimensions of the shank material (including a possible filler) shall not allow a heat transfer
45、into the sample greater than 2,5 103J/s, under operating conditions. When the probe is in measurement position, the thermistor bead shall lie on the axis of the sample tube and at equal distances from the inner walls and the inner bottom of the tube (see Figure 1). The thermistor and the associated
46、circuitry shall show a discrimination of 1 mC or better over a range of 400 mC to 600 mC. The linearity of the circuit shall be such that no error greater than 1 mC is introduced at any point within the range of 400 mC to 600 mC when the instrument is correctly operated. The read-out device shall pr
47、ovide a discrimination of 1 mC or better over a range of at least 0 mC to 1 000 mC. 6.1.3 Stirring wire, inert to milk, used to stir the test portion during cooling. The stirring wire shall be adjustable for amplitude and mounted vertically in accordance with the manufacturers instructions. The wire
48、 shall vibrate laterally with an amplitude of 2 mm to 3 mm to ensure that the temperature within the test portion remains uniform during cooling. At no time during its normal stirring operation shall the wire strike the glass probe or the wall of the tube. 6 DIN EN ISO 5764:2009-10 EN ISO 5764:2009
49、(E) 6.1.4 Device for initiating freezing, that, when operated, instantaneously initiates freezing of the test portion when reaching 3,0 C. The stirring wire (6.1.3) may be used for this purpose. One method is to increase the amplitude of vibration for 1 s to 2 s such that the stirring wire strikes the wall of the sample tube (6.2). 6.2 Sample tubes, symmetrical, made of borosilicate glass, of length 50,5 mm 0,2 mm, of external diameter 16,0 mm 0,2 mm and of internal di
