1、BRITISH STANDARD BS ISO 2173:2003 Fruit and vegetable products Determination of soluble solids Refractometric method ICS 67.080.01 BS ISO 2173:2003 This British Standard was published under the authority of the Standards Policy and Strategy Committee on 2 December 2003 BSI 2 December 2003 ISBN 0 580
2、 43012 X National foreword This British Standard reproduces verbatim ISO 2173:2003 and implements it as the UK national standard. There has been no UK participation in the preparation of this document. Any enquiries on the text should be sent to the Head of Standards International Content. Cross-ref
3、erences The British Standards which implement international publications referred to in this document may be found in the BSI Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards
4、 Online. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its 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, a
5、n inside front cover, the ISO title page, pages ii and iii, a blank page, pages 1 to 8, an inside back cover and a back cover. The BSI copyright notice displayed in this document indicates when the document was last issued. Amendments issued since publication Amd. No. Date Comments Reference number
6、ISO 2173:2003(E) OSI 3002INTERNATIONAL STANDARD ISO 2173 Second edition 2003-12-01 Fruit and vegetable products Determination of soluble solids Refractometric method Produits drivs des fruits et lgumes Dtermination du rsidu sec soluble Mthode rfractomtrique BSISO2173:2003IS:3712 O3002(E) DPlcsid Fre
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12、tandardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the ri
13、ght to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Internationa
14、l Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as
15、an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO
16、 2173 was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 3, Fruit and vegetable products. This second edition cancels and replaces the first edition (ISO 2173:1978), which has been technically revised. BSISO2173:2003blank BSISO2173:2003INTENRATIONAL TSANDADR IS:3712 O3002(
17、E)I SO 3002 All irhgts seredevr 1Fruit and vegetable products Determination of soluble solids Refractometric method 1 Scope This International Standard specifies a refractometric method for the determination of the soluble solids in fruit and vegetable products. This method is particularly applicabl
18、e to thick products, to products containing suspended matter, and to products rich in sugar. If the products contain other dissolved substances, the results will be only approximate; nevertheless, for convenience the result obtained by this method can be considered conventionally as the soluble soli
19、ds content. NOTE For the determination of the soluble solids in fruit juices (not containing suspended matter) and in concentrated juices (clarified), the pyknometric method specified in ISO 2172 is applicable. 2 Terms and definitions For the purposes of this document, the following terms and defini
20、tions apply. 2.1 soluble solids determined by the refractometric method concentration of sucrose in an aqueous solution which has the same refractive index as the product analysed, under specified conditions of preparation and temperature NOTE This concentration is expressed as a mass fraction in pe
21、rcent. 3 Principle The refractive index of a test solution is measured at 20 C 0,5 C using a refractometer. The refractive index is correlated with the amount of soluble solids (expressed as sucrose concentration) using tables, or by direct reading on the refractometer of the mass fraction of solubl
22、e solids. 4 Reagents Use only reagents of recognized analytical grade. 4.1 Water The water used shall have been distilled twice in borosilicate glass apparatus, or shall be water of at least equivalent purity. 5 Apparatus Usual laboratory apparatus and, in particular, the following. BSISO2173:2003IS
23、:3712 O3002(E) 2 I SO 3002 All irhgts seredevr5.1 Refractometer Use one of the following. 5.1.1 Refractometer indicating the refractive index, by means of a scale graduated in 0,001, in order to allow readings to be estimated to 0,000 2. This refractometer shall be adjusted so that at 20 C 0,5 C it
24、registers a refractive index of 1,333 0 for distilled water. 5.1.2 Refractometer indicating the mass fraction of sucrose, by means of scale graduated in 0,10 %. This refractometer shall be adjusted so that at 20 C 0,5 C it registers a mass fraction of soluble solids (sucrose) of zero for distilled w
25、ater. 5.2 Means for circulating water, to maintain the temperature of the prisms of the refractometer (5.1.1 or 5.1.2) constant to within 0,5 C, in the neighbourhood of 20 C, which is the reference temperature (see 8.1). 5.3 Beaker, of capacity 250 ml. 6 Sampling It is important that the laboratory
26、receive a sample which is truly representative and has not been damaged or changed during transport or storage. 7 Procedure 7.1 Preparation of test solution 7.1.1 Clear liquid products Thoroughly mix the laboratory sample and use it directly for the determination. 7.1.2 Semi-thick products (purees,
27、etc.) Thoroughly mix the laboratory sample. Press a part of the sample through a gauze folded in four, rejecting the first drops of the liquid and reserving the remainder of the liquid for the determination. 7.1.3 Thick products (jams, jellies, etc.) Weigh into the tared beaker (5.3), to the nearest
28、 0,01 g, a suitable quantity (up to 40 g) of the laboratory sample and add 100 ml to 150 ml of water. Heat the contents of the beaker to boiling and allow to boil gently for 2 min to 3 min, stirring with a glass rod. Cool the contents and mix thoroughly. After 20 min, weigh to the nearest 0,01 g, th
29、en filter through a fluted filter or a Bchner funnel into a dry vessel. Reserve the filtrate for the determination. 7.1.4 Frozen products After thawing the sample and removing, if necessary, stones, pips and hard seed-cavity walls, mix the product with the liquid formed during the thawing process an
30、d proceed as described in 7.1.2 or 7.1.3 as appropriate. BSISO2173:2003IS:3712 O3002(E) I SO 3002 All irhgts seredevr 37.1.5 Dried products Cut a part of the laboratory sample into small pieces. Remove, if necessary, stones, pips and hard seed-cavity walls, and mix carefully. Then weigh into a tared
31、 beaker, to the nearest 0,01 g, 10 g to 20 g of the sample. Add 5 to 10 times this mass of water and place on a boiling water bath for 30 min, stirring from time to time with a glass rod. If necessary, prolong the heating time until a homogeneous mixture is obtained. Cool the contents of the beaker
32、and mix well. After 20 min, weigh to the nearest 0,01 g, then filter into a dry vessel. Reserve the filtrate for the determination. If the test solution is too dark to be read in the refractometer, dilute the test solution with concentrated sugar solution; never use water for this purpose. Mix weigh
33、ed amounts of the solution under examination and a solution of pure sugar of about the same strength(see reference 1). 7.2 Determination Adjust the water circulation (5.2) in order to operate at the required temperature (between 15 C and 25 C) and allow it to flow to bring the prisms of the refracto
34、meter (5.1.1 or 5.1.2) to the same temperature, which shall remain constant to within 0,5 C during the determination. Bring the test solution (7.1) to the measuring temperature. Put a small quantity of test solution (2 or 3 drops are sufficient) onto the fixed prism of the refractometer (5.1.1 or 5.
35、1.2) and immediately adjust the movable prism. Suitably illuminate the field of view. The use of a sodium vapour lamp allows more precise results to be obtained (especially in the case of coloured and dark products). Bring the line dividing the light and dark parts of the surface into the field of v
36、iew to the crossing of the threads. Read the value of the refractive index or the mass fraction of sucrose, according to the instrument used (5.1.1 or 5.1.2). 8 Expression of results 8.1 Corrections 8.1.1 If the determination has been carried out at a temperature other than 20 C 0,5 C, the following
37、 corrections are required. a) For the scale indicating the refractive index (5.1.1), apply the formula: () 20 0,0013 20 t DD nn t =+ where 20 D n is the refractive index at 20 C; t D n is the refractive index at the temperature of measurement; t is the temperature of measurement, in degrees Celsius.
38、 b) For the scale indicating the mass fraction of sucrose (5.1.2), correct the result according to Table A.1. 8.1.2 If the determination has been carried out for the products with added salt, correct the refractometer reading, expressed as a concentration of sucrose at 20 C 0,5 C, for added salt by
39、the following formula (see reference 2): S = (R N) 1,016 BSISO2173:2003IS:3712 O3002(E) 4 I SO 3002 All irhgts seredevrwhere S is the mass fraction of soluble solids, in percent, as sucrose, corrected for added NaCl; R is the refractometer reading, as a mass fraction in percent, as sucrose; N is the
40、 total chloride content, as a mass fraction in percent, expressed as NaCl; 1,016 is the correction factor for added salt. 8.1.3 If the determination has been carried out for the highly acidic products, such as citrus juices and concentrated citrus juices, correct the refractometer reading, expressed
41、 as a masss fraction of sucrose at 20 C 0,5 C, by making the following addition to the refractometric reading (see reference 3): 0,012 + 0,193 M 0,000 4 M 2where M is the total acidity expressed in grams per 100 g, at pH = 8,1, expressed as anhydrous citric acid (see reference 4). The calculated val
42、ues for this expression are given in Table A.2. 8.2 Calculation method 8.2.1 Refractometer with refractive index scale 8.2.1.1 Read from Table A.3 the mass fraction of soluble solids corresponding to the value read in accordance with 7.2, corrected if necessary in accordance with 8.1.1 a). In the ca
43、se of liquid or semi-thick products (7.1.1 or 7.1.2), the mass fraction of soluble solids is equal to the number found. If the determination has been carried out on a diluted solution (7.1.3 or 7.1.5), the mass fraction of soluble solids, in percent, is equal to ( ) 10 / Pmm where P is the mass frac
44、tion of soluble solids in the diluted solution, in percent; m 0is the mass, in grams, of the sample before dilution (7.1.3 or 7.1.5); m 1is the mass, in grams, of the sample after dilution (7.1.3 or 7.1.5). 8.2.1.2 If the determination has been carried out on a dark solution (see 7.1.5) that has to
45、be diluted with concentrated sugar solution, the mass fraction of soluble solids, in percent, is equal to (see reference 1) () WB B W mmCm D m + where m Wis the mass, in grams, of the sample diluted with sugar solution; m Bis the mass, in grams, of sugar solution used in the dilution; C is the mass
46、fraction of soluble solids, in percent, in the mixture (m W+ m B ), obtained from the refractive index; D is the mass fraction of soluble solids, in percent, in the pure sugar solution, obtained from its refractive index. Express the result to one decimal place. BSISO2173:2003IS:3712 O3002(E) I SO 3
47、002 All irhgts seredevr 58.2.2 Refractometer with sucrose scale In the case of liquid or semi-thick products (7.1.1 or 7.1.2), the mass fraction of soluble solids, in percent, as sucrose, is equal to the value read in accordance with 8.1.1 b). If the determination has been carried out on a diluted s
48、olution (7.1.3 or 7.1.5), calculate the mass fraction of soluble solids by means of the formula given in 8.2.1.1, or the formula in 8.2.1.2 for a dark solution diluted with a sugar solution (see 7.1.5). Express the result to one decimal place. 9 Repeatability The absolute difference between two inde
49、pendent single test results, obtained using the same method on identical test material in the same laboratory by the same operator using the same equipment within a short interval of time, will in not more than 5 % of cases be greater than 0,5 g of soluble solids per 100 g or per 100 ml of product. 10 Test report The test report shall specify: all information necessary for the compl
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