1、BRITISH STANDARD CONFIRMED JULY1989 BS1743-6.1: 1983 Methods for Analysis of dried milk and dried milk products Part6: Assessment of the heat class of dried milk Section6.1 Heat number method(reference method) IMPORTANT NOTE. It is essential that this Part be read in conjunction with Part1“General i
2、ntroduction, including preparation of laboratory samples”, published separately. UDC 637.143:664.97:637.133.2.07BS1743-6.1:1983 This British Standard, having been prepared under the directionof the Dairying Standards Committee, was published under the authority ofthe Board of BSI and comesintoeffect
3、 on 29 April1983 BSI 10-1999 The following BSI references relate to the work on this standard: Committee reference DAC/3 Draft for comment 82/52607 DC ISBN 0 580 13222 6 Foreword This Section of Part6 of BS1743, which has been prepared under the direction of the Dairying Standards Committee, describ
4、es one of a new series of methods for the analysis of dried milk and dried milk products. The heat number reference method for assessing the heat class of dried milk is technically the same as that being prepared by a joint working group of the International Dairy Federation(IDF), the International
5、Organization for Standardization(ISO) and the Association of Official Analytical Chemists(AOAC), in which the UK actively participated. The heat number method does not enable Ultra Low Heat dried milk(minimal heat treatment) to be identified, and may be considered unsuitable for routine use. Accordi
6、ngly, further Sections of Part6 of BS1743 will describe a cysteine number reference method for identifying Ultra Low Heat dried milk and also one or more routine methods of heat classification. A British Standard does not purport to include all the necessary provisions of a contract. Users of Britis
7、h Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 to8, an inside back cover and a back cover. Thi
8、s standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No. Date of issue CommentsBS1743-6.1:1983 BSI 10-1999 i Contents Page Foreword Inside front cov
9、er 0 Introduction 1 1 Scope 2 2 Definitions 2 3 Principle 2 4 Reagents 2 5 Apparatus 3 6 Preparation of test sample 3 7 Procedure 3 8 Expression of results 5 9 Test report 5 Appendix A Heat number heat classification scheme for spray-dried milk 6 Appendix B Bibliography 7 Publications referred to In
10、side back coverii blankBS1743-6.1:1983 BSI 10-1999 1 0 Introduction 0.1 The heat treatment applied in the manufacture of spray-dried milk, predominantly in the preheating of the liquid milk, can be varied to produce a product suitable for a particular usage. It is therefore necessary, both for the m
11、anufacturer and the buyer or user, to be able to assess the degreeof overall heat treatment so that a dried milkcan be classified as, for example, Low Heat, Medium Heat, etc. The fact that an increasing proportion of the milk serum protein(whey protein) in milk is denatured(and becomes associated wi
12、th the casein) as the degree of heat treatment increases has provided a basis for heat classification methods. These methods involve either the direct measurement of residual undenatured milk serum protein, or the indirect measurement of denatured milk serum protein, and the concentration found in t
13、he dried milk in relation to the range of possible concentrations indicates heat class. Ideally, because of the small seasonal variations in the concentration and relative proportions of the proteins in raw bulk cows milk, a sample of the original liquid milk should be available for comparison when
14、assessing the heat class of a dried milk but this is only possible for the manufacturer. In practice, heat class is usually assessed solely by examining the dried milk and this inevitably imposes some limitation on the accuracy of all protein-based heat classification methods. The most widely used h
15、eat classification method is probably that published by the American Dry Milk Institute(ADMI)(1971), in which the concentration in the dried milk of undenatured milk serum protein nitrogen (UMSPN) is determined turbidimetrically so that the dried milk can be placed in one of the following heat class
16、es: Low Heat(not less than6.00mg UMSPN/g), Medium Heat(1.51mg to5.99mg UMSPN/g) or High Heat(not more than1.50mg UMSPN/g). But the procedure for determining the so-called “ADMI undenatured whey protein nitrogen value” of dried milk has several drawbacks and alternative procedures utilizing dye-bindi
17、ng have been developed(e.g.Sanderson,1970; McGann, OConnell derived mostly from the DMSP) by the method of de Koning, van Rooijen casein number is the ratio of casein nitrogen content to total nitrogen content multiplied by100 and is useful indiagnosing subclinical mastitis (Rowland White,1980).BS17
18、43-6.1:1983 2 BSI 10-1999 NOTEIt is expected that the Kjeldahl procedure described in7.2 of this standard, but with the volume of sulphuric acid(4.9) reduced from30mL to25mL(in7.2.1), and consequently the volumes of water and sodium hydroxide solution(4.10) increased to250mL and reduced to60mL respe
19、ctively(in7.2.3) will be adopted in revised British Standards for the analysis of milk and milk products. 1 Scope This Section of Part6 of BS1743 describes a reference method, incorporating a Kjeldahl method, based on the determination of heat number, for assessing the heat class of dried whole milk
20、, dried partly skimmed milk and dried skimmed milk manufactured by the spray process. The method is also applicable to all types of instant dried milk. The heat number heat classification scheme and its relation to the ADMI heat classification scheme are described in Appendix A. The literature refer
21、ences quoted for background information are listed inAppendix B. NOTEThe titles of the publications referred to in this standard are listed on the inside back cover. 2 Definitions For the purposes of this Section of BS1743, the following definitions apply. 2.1 heat number (of dried milk) ratio of ac
22、id-insoluble(pH4.8) protein nitrogen content to total nitrogen content, multiplied by100 NOTEThe acid-insoluble protein is casein plus heat-denatured milk serum protein. 2.2 heat class a description assigned to dried milk to indicate the overall degree of heat treatment applied in the conversion of
23、the liquid milk to dried milk(seeAppendix A) 3 Principle The casein plus heat-denatured milk serum protein in a certain volume of reconstituted dried milk is precipitated at a final pH of approximately4.8 by adding acetic acid solution and then sodium acetate solution. The precipitate is collected a
24、nd washed, and its nitrogen content(in terms of the equivalent volume of a standard volumetric solution) determined by a Kjeldahl method. The total nitrogen content of the same volume of the reconstituted dried milk is similarly determined. The heat number of the dried milk is calculated directly fr
25、om the two volumes of standard volumetric solution, after correction of each by an appropriate blank Kjeldahl determination. The heat class of the dried milk is derived from the heat number according to a heat classification scheme consisting of four heat classes, namely Low Heat, Medium(1) Heat, Me
26、dium(2) Heat, and High Heat. NOTE 1The acetic acid/sodium acetate procedure used is that developed by Rowland(1938a,b) for the precipitation of casein or casein plus heat-denatured milk serum protein, in determining the nitrogen distribution in cows milk. The buffered reaction mixture, whether conta
27、ining milk or reconstituted dried milk, has a pH(glass electrode) at20 C of approximately4.8, not approximately4.6 as commonly supposed. NOTE 2The Low Heat class and the High Heat class of the heatnumber heat classification method are equivalent to the Low Heat class and the High Heat class respecti
28、vely of the ADMI(1971) heat classification method but the Medium(1) Heat class and the Medium(2) Heat class correspond to subdivisions of the ADMI Medium Heat class, as indicated in Appendix A. 4 Reagents 4.1 General. During the analysis use only reagents of recognized analytical grade and only dist
29、illed water complying with BS3978. 4.2 Antifoaming agent. Octan-2-olcapryl alcohol; at least97%(m/m) or a silicone preparation, e.g.a30%(m/m) aqueous emulsion. 4.3 Acetic acid solution. Add25.00g of acetic acidat least99.7%(m/m) to200mL of water and dilute to250mL(20 C) in a volumetric flask. 4.4 So
30、dium acetate solution. Dissolve34.02g of sodium acetate trihydrate at least99.0%(m/m) in water and dilute to250mL(20 C) in a volumetric flask. To delay mould growth,0.5mL of chloroform may then be added. 4.5 Washing solution. Add6.0mL of acetic acid solution(4.3) and14.0mL of sodium acetate solution
31、(4.4) to1L of water and mix. Check that the pH of the washing solution, measured with a pH meter, is4.80 0.05 (at20 C) and adjust if necessary by adding more acetic acid solution or sodium acetate solution as appropriate. 4.6 Sucrose, nitrogen content not more than0.002%(m/m). 4.7 Potassium sulphate
32、 4.8 Copper sulphate solution. Dissolve5.0g of copper(II) sulphate pentahydrate in water and dilute to100mL in a volumetric flask. 4.9 Sulphuric acid, at least98.0%(m/m) density approximately1.84g/mL at20 C. 4.10 Sodium hydroxide solution, 47%(m/m) (704g/L at20 C). NOTE 1The sodium hydroxide need no
33、t be of recognized analytical grade. NOTE 2A less concentrated sodium hydroxide solution may be used, e.g.40%(m/m)(572g/L at20 C) or30%(m/m)(399g/L at20 C). (Seenote to7.2.3).BS1743-6.1:1983 BSI 10-1999 3 4.11 Boric acid solution. Dissolve40g of boric acid in1L of hot water, allow to cool, and store
34、 in a borosilicate glass bottle. 4.12 Indicator solution. Mix equal volumes of methyl red solution(0.2g/100mL ethanol) and methylene blue solution(0.1g/100mL ethanol); the ethanol shall be at least94%(V/V). 4.13 Standard volumetric solution, c(1/2H 2 SO 4 ) orc(HCI)=approximately0.1mol/L. NOTEThe ex
35、act value for the concentration of this solution is not required for the calculation of heat number(8.1) but seenote to clause7. 5 Apparatus 5.1 Balance, capable of weighing to0.01g. 5.2 Conical flask, of capacity150mL, with rubber stopper. 5.3 Thermometer, complying with BS1704, range5 C to+105 C,
36、graduated at each1 C. 5.4 Graduated measuring cylinder, complying with BS604, of capacity100mL. 5.5 Glass stirring rods, one plain and one rubber tipped. 5.6 Pipettes, one-mark, complying with BS1583(class A or B), two of capacity1mL and oneof capacity10mL. 5.7 Glass beaker, of capacity150mL, low fo
37、rm with spout. 5.8 Filter funnel, of top internal diameter75mm. 5.9 Filter papers 1) , of diameter125mm, routine ashless quantitative, medium speed and retention. 5.10 Wash bottles, of capacity500mL, for use with water and washing solution(4.5) respectively. 5.11 Kjeldahl flasks, of capacity500mL. 5
38、.12 Glass balls, of diameter approximately5mm. 5.13 Burette or automatic pipette, for delivering1.0mL portions of copper sulphate solution(4.8). 5.14 Graduated measuring cylinders, complying with BS604, of capacities50mL,100mL and250mL respectively. 5.15 Digestion apparatus, to hold Kjeldahl flasks(
39、5.11) in an inclined position (approximately45 ), with electric heaters or gas burners that do not heat the flasks above the level of their contents, and with a fume extraction system. 5.16 Distillation apparatus, borosilicate glass, to which a Kjeldahl flask (5.11) can be fitted, consisting of a sp
40、lash head connected to a condenser (with straight inner tube; jacket of length at least300mm) with an outlet tube attached to its lower end. The connecting tubing and stopper(s) shall be close fitting and preferably made of neoprene. 5.17 Pipette or automatic pipette, for delivering0.10mL portions o
41、f indicator solution(4.12). 5.18 Conical flasks, of capacity500mL, graduated at200mL. 5.19 Burette, complying with BS846(class A), of capacity50mL. 5.20 Magnifying lens, for reading the burette(5.19). 6 Preparation of test sample Thoroughly mix the laboratory sample(seeBS1743-1), which should be at
42、laboratory temperature, by repeatedly rotating and inverting the container. If the container is too full to allow thorough mixing, transfer all the laboratory sample to a clean, dry, air-tight container of adequate capacity and mix as described. With instant dried milk, the mixing shall be gentle to
43、 avoid reducing the particle size of the sample. 7 Procedure NOTEThe total nitrogen content of the test sample can be calculated from the values for V 2and V 3 (see8.1) if: a) the mass of the reconstituted milk is obtained (bydifference) by weighing the empty stoppered conical flask and the stoppere
44、d conical flask containing the reconstituted milk(7.1.1); b) the mass of the reconstituted milk delivered by the10mL pipette, when used as described in 7.1.4, is determined; c) if the exact value for the concentration of the standard volumetric solution(4.13) is known. 7.1 Initial procedure 7.1.1 We
45、igh into a conical flask(5.2) a test portion of14.00g of dried whole milk or dried partly skimmed milk, or10.00g of dried skimmed milk, from the test sample. 1) Whatman No.40 filter papers have been found to be suitable.BS1743-6.1:1983 4 BSI 10-1999 Transfer100mL of water at40 C to a measuring cylin
46、der(5.4) and add10mL of the water to the test portion so as to wash any of the test portion on the walls of the flask down to the bottom of the flask. Stir the mixture with a plain stirring rod(5.5) to disperse any lumps and to form a paste. Add the remainder of the water in successive small portion
47、s, with stirring, rinsing the stirring rod and the neck of the flask with the final portions of water. Close the flask with a rubber stopper, swirl the contents of the flask to mix thoroughly and allow the flask to stand for30min, periodically gently swirling and inverting it. 7.1.2 Prepare four Kje
48、ldahl flasks(5.11) by adding15g of potassium sulphate(4.7) and three glass balls(5.12) to each flask. 7.1.3 Remove the stopper from the conical flask, add1 drop of antifoaming agent(4.2) to the reconstituted milk, restopper the flask and mix its contents by gentle swirling and inversion. 7.1.4 Trans
49、fer10mL of the reconstituted milk by means of a10mL pipette (5.6), filled so that the top level of the milk is coincident with the mark, to the first of the Kjeldahl flasks. Wash down the reconstituted milk on the neck of the Kjeldahl flask with a little water and set aside the flask. 7.1.5 Using the same pipette in exactly the same way, transfer10mL of the reconstituted milk to a beaker(5.7). Using the measuring cylinder, add75mL of water at40 C to the reconstituted milk in the beaker and then add with a1mL pipette(5.6)1.0mL of acetic acid solution(4.3
