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1、I INTERNATIONAL ORGANIZATION FOR STANDARDIZATION.MEXAYHAPOAHAR OPTAHMJALIIIR il0 CTAHAAPTH3AUHM.ORGANISATION INTERNATIONALE DE NORMALISATION Starch hydrolysis products - Determination of reducing power and dextrose equivalent - Lane and Eynon constant titre method Produits dhydrolyse de lamidon ou d
2、e fa fcule - Dtermination du pouvoir rducteur et de Iquivafent en dextrose - Mthode Lane et Eynon titre constant First edition - 1981-12-15 I - UDC 664.28 : 664.162.036 : 543.24 Ref. No. IS0 5377-1981 (E) z c Descriptors : starches, tests, determination, mass losses, dry matter, titration. Price bas
3、ed on 6 pages COPYRIGHT International Organization for Standardization Licensed by Information Handling Services COPYRIGHT International Organization for Standardization Licensed by Information Handling Services Foreword 5377-81 IS0 (the International Organization for Standardization) is a worldwide
4、 federation of national standards institutes (IS0 member bodies). The work of developing Inter- national Standards is carried out through IS0 technical committees. Every member body interested in a subject for which a technical committee has been set up has the right to be represented on that commit
5、tee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. Draft International Standards adopted by the technical committees are circulated to the member bodies for approval before their acceptance as International Standards by the IS0 Counc
6、il. International Standard IS0 5377 was developed by Technical Committee ISO/TC 93, Starch (including derivatives and by-products), and was circulated to the member bodies in November 1980. It has been approved by the member bodies of the following countries : Australia Netherlands Austria Romania E
7、gypt, Arab Rep. of France USA Iran USSR South Africa, Rep. of No member body expressed disapproval of the document. 0 International Organization for Standardization, 1981 O Printed in Switzerland 4851903 0040103 3 r COPYRIGHT International Organization for Standardization Licensed by Information Han
8、dling Services COPYRIGHT International Organization for Standardization Licensed by Information Handling Services INTERNATIONAL STANDARD I 4853903 o o w o 4 5 c iso53771981(E) 537 7-BL Starch hydrolysis products - Determination of reducing power and dextrose equivalent - Lane and Eynon constant titr
9、e method 1 Scope and field of application This International Standard specifies a Lane and Eynon cons- tant titre method for the determination of the reducing power and dextrose equivalent of all starch hydrolysis products. 2 References IS0 38511, Laboratory glassware - Burettes - Part 1: General re
10、quirements. 1 IS0 38512, Laboratory glassware - Part 2: Burettes for which no waiting t h e is specified.) IS0 648, Laboratory glassware - One-mark pipettes. IS0 1042, Laboratory glassware - One-mark volumetric flasks. IS0 1741, Dextrose - Determination of loss in mass on drying - Vacuum oven method
11、. . IS0 1742, Gucose syrup - Determination of dry matter con- tent - Vacuum oven method. IS0 1743, Glucose syrup and dextrose - Determination of dry matter content - Refractive index method. IS0 1773, Laboratory glassware - Boiling flasks lnarrow- necked). IS0 5809, Starch, including derivatives and
12、 by-products - Determination of sulphated ash.2) 3 Definitions 3.1 reducing power : The content of reducing sugars, ex- pressed as the number of grams of anhydrous D-glucose per 100 g of the sample, when determined by the method specified in this International Standard. 3.2 dextrose equivalent : The
13、 content of reducing sugars, expressed as the number of grams of anhydrous D-glucose per 100 g of the dry matter in the sample, when determined by the method specified in this International Standard. 4 Principle Titration of a prescribed volume of mixed Fehlings solution with a solution of a test po
14、rtion under specified conditions, using methylene blue as internal indicator. 5 Reagents During the analysis, use only reagents of recognized analytical grade and only distilled water or water of equivalent purity. 5.1 Fehlings stock solutions Prepare the following solutions, using apparatus in acco
15、rdance with clause 6. 5.1.1 Stock solution A Copper(l1) sulphate pentahydrate 69,3 9 (CS04.5H20) Water to 1 OO0,O ml 5.1.2 Stock solution B Potassium sodium tartrate tetrahydrate 3460 g (KNaC4H406.4H20) Sodium hydroxide (NaOH) 100.0 g Water to 1 OO0,O ml Before use, decant the clear solution from an
16、y sediment that may form. 5.1.3 Mixed Fehlings solution Transfer into a dry stock glass bottle, in the following order, 100 ml of solution A (5.1.11 and 100 ml of solution B (5.1.21. Mix well. NOTE - Do not keep Fehlings solution. Prepare this mixed solution just before use and standardize it as spe
17、cified in 7.1. 1) At present at the stage of draft. (Revision, in part, of ISO/R 385.) 2) At present at the stage of draft. 1 COPYRIGHT International Organization for Standardization Licensed by Information Handling Services COPYRIGHT International Organization for Standardization Licensed by Inform
18、ation Handling Services IS0 5377-1981 (E) 5.2 requirements : Anhydrous D-glucose, complying with the following a) a solution containing 400 g/l shall be free from haze and sediment and shall show no more colour than the water used in its preparation when examined downwards in 50 ml Nessler tubes (6.
19、5) filled to the marks; b) the sulphated ash content shall be not greater than 0,Ol % (rn/rn) when determined by the method specified in IS0 5809 amended as follows : 1) the mass of the test portion shall be increased to 20 g, 2) only a platinum dish shall be used for incineration, 3) the platinum d
20、ish shall be weighed to the nearest 0,l mg before and after the incineration; c) the maltose and/or isomaltose content shall not exceed 0,l % rn/rn) and no sugar of greater relative molecular mass shall be detected. 5.3 D-glucose, standard reference solution. 5.3.1 D-glucose by the method specified
21、in IS0 1741. Determine the dry matter content of the anhydrous 5.3.2 Weigh, to the nearest 0,l mg, a mass of the anhydrous D-glucose (5.2) containing 0,600 g of solids, dissolve it in water, transfer the solution quantitively into a 100 ml one-mark volumetric flask (6.4), dilute to the mark with wat
22、er and mix. Prepare this solution freshly on each day of use. 5.4 aqueous solution. Methylene blue (C,GH18CIN3S.2HO), indicator, 1 g/l 6 Apparatus Ordinary laboratory apparatus and in particular 6.1 plying with the requirements of IS0 1773. Narrow-necked boiling flask, of capacity250 ml, com- 6.2 Bu
23、rette, of capacity 25 ml, graduated in subdivisions of 0,05 ml, complying with the requirements of IS0 385/2, class A. 6.3 plying with the requirements of IS0 648, class A. One-mark pipettes, of capacity 1 ml and 25 ml, com- 6.4 One-mark volumetric flasks, of capacity 100 ml, 500 ml and 1 o00 ml, co
24、mplying with the requirements of IS0 1042, class A. 6.5 Nessler tubes, of capacity 50 ml. 6.6 Heating device, suitable for maintaining boiling as re- quired in 7.1.4 whilst enabling the colour change at the end- 5377-83 3 4853983 8040L05 7 p point of the titration to be observed without the flask ha
25、ving to be removed from the heating device. 6.7 Stop-watch. 7 Procedure NOTES 1 ensure freedom from super-heating. 2 A boiling aid (for example glass beads) may be added, if desired, to Shield the burette from the source of heat (6.6) at all times. 7.1 solution (5.1.31 Standardization of the mixed F
26、ehlings 7.1.1 tion (5.1.3) in the clean, dry boiling flask (6.1). Using a pipette (6.3), place25,O ml of the Fehlings SOIU- 7.1.2 standard reference solution (5.3). Fill the burette (6.2) to the zero mark with the D-glucose 7.1.3 Run into the boiling flask from the burette, 18,O ml of the D-glucose
27、solution (5.3). Swirl the flask to mix the con- tents. 7.1.4 Place the boiling flask on the heating device (6.61, previously adjusted so that the boiling commences in 120 k 15 s as timed by the stop-watch (6.7). Do not adjust the heating device subsequently. This ensures that once boiling has commen
28、ced the evolution of steam is brisk and continuous throughout the whole of the titration pro- cess, thus preventing to the maximum possible extent the en- trance of air to the titration flask with consequent re-oxidation of its contents. 7.1.5 Bring the contents of the flask to the boil and continue
29、 boiling for 120 s (timed by the stop-watch). Add 1 ml of the methylene blue solution (5.4) towards the end of this period. After expiry of the 120 s period, commence adding the D-glucose solution to the flask from the burette in 0,5 ml in- crements until the colour of the methylene blue is discharg
30、ed, boiling being continued during the whole titration. Note the total volume of the D-glucose solution ( V ml), added up to and including the penultimate 0,5 ml increment. NOTE - The disappearance of the colour of the methylene blue is best seen by looking at the upper layers and the meniscus of th
31、e contents of the titration flask, as these will be relatively free from the precipitated, red copper(l) oxide. The colour disappearance is more easily seen when indirect lighting is used. A white screen behind the titration flask is helpful. 7.1.6 Repeat7.1.1 and 7.1.2. 7.1.7 the D-glucose solution
32、 equal to ( V - 0,3) ml. From the burette run into the boiling flask a volume of 7.1.8 Repeat 7.1.4. 2 COPYRIGHT International Organization for Standardization Licensed by Information Handling Services COPYRIGHT International Organization for Standardization Licensed by Information Handling Services
33、 7.1.9 Bring the contents of the flask to the boil and continue boiling for 120 s (timed by the stop-watch). Add 1 ml of the methylene blue solution towards the end of this period. After expiry of the 120 s period, commence adding the D-glucose solution to the flask from the burette, initially in 0,
34、2 ml in- crements and finally drop by drop, until the colour of the methylene blue (5.4) is just discharged, boiling being continued during the whole titration. Towards the end of this action, add the successive increments of the D-glucose solution at intervals of 10 to 15 s. Complete these addition
35、s within 60 s to give a total time of boiling not longer than 180 s. A third titration with a slightly larger, appropriately adjusted, in- itial addition of the D-glucose solution may be necessary to achieve this. 7.1.10 Note the volume of the D-glucose solution used up to the end-point of the final
36、 titration. 7.1.11 It is essential that the titre is between 19,0 and 21,O ml of the D-glucose solution. If it is outside these limits, adjust the concentration of the Fehlings solution A (5.1 .I) appropriately and repeat the standardization process. 7.1.12 Repeat 7.1.6 to 7.1.10 and calculate the m
37、ean of the two titres Vl ml). 7.1.13 For the day-to-day standardization of the mixed Fehl- ings solution, as Vl is known with accuracy, a single titration only is necessary, using an initial addition of (VI - 0,5) ml of the D-glucose solution. NOTE - As there is a personal factor involved, it is ess
38、ential that each operator carries out his own standardization titration and uses his own value of VI in the calculation (8.1.1). 7.2 Determination 7.2.1 Preparation of test sample If the sample is in powder or crystalline form, remove it from its container, break down any lumps, mix in an appropriat
39、e man- ner and place in a suitable airtight container. If the sample is in massive, solid form, e.g. starch sugar (solid glucose), melt it in a closed container immersed in a hot water bath at 60 to 70 OC, allow to cool to ambient temperature and shake a number of times without removing the closure,
40、 in order to mix any condensed moisture on the interior into the sample. If the sample is in liquid form, mix it by stirring it in its con- tainer, after removing any skin that may have formed on its sur- face. 7.2.2 If the reducing sugar content of the sample is unknown, obtain an approximation to
41、its value by prior trial titrations, in general as specified in 7.1.1 to 7.1.5, but with the following modifications : a) Add 10,O ml of the test solution in place of the D-glucose solution added in 7.1.3. b) After 7.1.4 1) Immediately boiling starts, add 1 ml of the methylene blue solution and comm
42、ence adding the test solution to the flask from the burette in 1,0 ml in- crements at intervals of approximately 10 s until the.blue colour of the methylene blue is discharged. If the blue colour is discharged before the addition of any 1,0 ml in- crements of test solution, decrease the concentratio
43、n of the test solution and repeat the titration. 2) ed up to and including the penultimate.increment. Note the total volume of test solution (v ml), add- V shall not be greater than 50 ml. If it is, increase the concentration of the test solution and repeat the titra- tion. 3) The approximate reduci
44、ng power (see 3.1) (ARP) of the test sample is given by the formula F x 1 0 0 x 5 0 0 v x mo ARP = 300 x v, x mo - - where = 0,006 x v, mo is the mass, in grams, of the test portion in 500 ml of test solution. The mass, in grams, of the test portion to be taken is 100 x 3 300 ARP ARP - - - 7.2.3 Tes
45、t portion Weigh, to the nearest 1 mg, a mass of the test sample (m g) containing between 2,85 and 3,15 g of reducing sugars (ex- pressed as anhydrous D-glucose). 7.2.4 Test solution Dissolve the test portion (7.2.3) in water, transfer the solution quantitively to a 500 ml one-mark volumetric flask (
46、6.41, dilute to the mark with water and mix. 7.2.5 Titration 7.2.5.1 place of the D-glucose solution (5.3). Repeat 7.1.1 to 7.1.9 using the test solution (7.2.4) in 3 COPYRIGHT International Organization for Standardization Licensed by Information Handling Services COPYRIGHT International Organizati
47、on for Standardization Licensed by Information Handling Services IS0 5377-1981 (E) 7.2.5.2 Note the volume V2) of the test solution (7.2.4) used up to the end-point of the final titration. 7.2.5.3 It is essential that V2 is between 19,0 and 21,O ml of the test solution (7.2.4). If V2 lies outside th
48、ese limits, adjust the concentration of the test solution appropriately and repeat 7.2.5.1 and 7.2.5.2. 7.2.5.4 Carry out two determinations on the same test sample. 7.3 Dry matter content Determine the dry matter content DMC % (rn/m)l of the test sample as follows : a) IS0 1742. For dried glucose s
49、yrup, by the method specified in b) For dextrose (anhydrous and monohydrate), by the method specified in IS0 1741. c) For glucose syrup, by the method specified in IS0 1743. 8 Expression of results 8.1 Method of calculation and formulae 8.1.1 Reducing power (Lane and Eynon) (see 3.1) 0,600 x v, 500 100 100 v2 m 300 x v, RP = x - x - - - V2 x rn 8.1.2 Dextrose equivalent (Lane and Eynon) (see 3.2) RP x 100 DMC DE = 4 where VI is the volume, in millilitres, of the D-glucose solution (5.3) used in the standardization of the mixed Fehlings solu- tion (7.11; V2