BS 5752-15-1997 Methods of test for coffee and coffee products - Instant coffee determination of free and total carbohydrate contents by high performance anion-exchange chromatogra.pdf

1、BRITISH STANDARD BS 5752-15: 1997 ISO 11292: 1995 (corrected and reprinted 1997) Methods of test for Coffee and coffee products Part 15: Instant coffee: determination of free and total carbohydrate contents by high performance anion-exchange chromatography ICS 67.140.20BS5752-15:1997 This British St

2、andard, having been prepared under the directionof the Consumer Products and Services Sector Board, was published under theauthority of the Standards Board and comes into effect on 15May1997 BSI 09-1999 ISBN 0 580 27262 1 National foreword This British Standard reproduces verbatim ISO11292:1995 (cor

3、rected and reprinted in1997) and implements it as the UK national standard. It supersedes BS5752-15:1995 which is withdrawn. This new edition includes new informative references inAnnex B. The International Standard has been amended to reflect the technical content of the 1995 British Standard. This

4、 standard embodies an agreement, to which the UK was a party, reached in Subcommittee15, Coffee, of Technical Committee34, Agricultural food products, of ISO. The UK participation in its preparation was entrusted to Technical Committee AW/15, Coffee, which has the responsibility to: aid enquirers to

5、 understand the text; present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed; monitor related international and European developments and promulgate them in the UK. A list of organizations represent

6、ed on this committee can be obtained on request to its secretary. Cross-references The British Standards which implement international or European publications referred to in this document may be found in the BSI Standards Catalogue under the section entitled “International Standards Correspondence

7、Index”, or using the “Find” facility of the BSI Standards Electronic Catalogue. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself c

8、onfer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii theISOtitle page, pages ii to iv, pages 1to 10 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This wil

9、l be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No. Date CommentsBS5752-15:1997 BSI 09-1999 i Contents Page National foreword Inside front cover Foreword iii Text of ISO 11292 1ii blankBS5752-15:1997 ii BSI 09-1999 Contents Page Foreword iii

10、1 Scope 1 2 Normative references 1 3 Definitions 1 4 Principle 1 5 Reagents 1 6 Apparatus 2 7 Sampling 2 8 Procedure 2 9 Calculation 3 10 Precision 4 11 Test report 4 Annex A (informative) Results of an interlaboratory test 5 Annex B (informative) Bibliography 10 Table 1 Preparation of column 3 Tabl

11、e 2 Conditions for analysis 3 Table 3 Coefficient of variation of reproducibility and repeatability 4 Table A.1 Determination of mannitol content for instant coffees 6 Table A.2 Determination of arabinose content for instant coffees 6 Table A.3 Determination of galactose content for instant coffees

12、7 Table A.4 Determination of glucose content for instant coffees 7 Table A.5 Determination of mannose content for instant coffees 8 Table A.6 Determination of fructose content for instant coffees 8 Table A.7 Determination of xylose content for instant coffees 9 Table A.8 Determination of sucrose con

13、tent for instant coffees 9BS5752-15:1997 BSI 09-1999 iii Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committee

14、s. Each member body interested in a subject for which a technical committee has been established has the right 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 Inter

15、national Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least75% of the member bod

16、ies casting a vote. International Standard ISO11292 was prepared by Technical Committee ISO/TC34, Agricultural food products, Subcommittee SC15, Coffee. Annex A andAnnex B of this International Standard are for information only. Descriptors: Agricultural products, plant products, coffee, chemical an

17、alysis, determination of content, carbohydrates, high performance liquid chromatography.iv blankBS5752-15:1997 BSI 09-1999 1 1 Scope This International Standard specifies a method for the determination of free and total carbohydrate contents in instant coffee using high-performance anion-exchange ch

18、romatography. In particular, it determines the content of individual monosaccharides, sucrose and mannitol. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the e

19、ditions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO maintain registers of curren

20、tly valid International Standards. ISO 1042:1983, Laboratory glassware One-mark volumetric flasks. ISO 3509:1989, Coffee and its products Vocabulary. ISO 3726:1983, Instant coffee Determination of loss in mass at70 C under reduced pressure. 3 Definitions For the purposes of this International Standa

21、rd, the definitions given in ISO3509 and the following definitions apply. 3.1 free carbohydrate content content of each individual monosaccharide (arabinose, fructose, galactose, glucose, mannose), and the sucrose and mannitol contents, determined under the conditions described (method A). Content i

22、s expressed as a percentage by mass on a dry basis 3.2 total carbohydrate content content of each individual monosaccharide (arabinose, galactose, glucose, mannose, xylose) and the mannitol content, determined under the conditions described, which includes a strong hydrolysis step (method B). Conten

23、t is expressed as a percentage by mass on a dry basis 4 Principle 4.1 Method A Dissolution of a test portion in water. Separation of the carbohydrates present in the filtered extract byion chromatography on a high-performance anion-exchange column (HPAEC) using pure water as eluent. Electrochemical

24、detection of the eluted compounds by means of a pulsed amperometric detector (PAD) and quantification by comparison with peak areas given by standard solutions. 4.2 Method B Hydrolysis of a test portion with aqueous hydrochloric acid. Analysis of the carbohydrates present in the filtered hydrolysed

25、solution as described in method A. 5 Reagents Use only reagents of recognized analytical grade, unless otherwise specified, and distilled or demineralized water or water of equivalent purity. 5.1 Sodium hydroxide (NaOH), 50 % (m/m) aqueous solution. The reagent should contain the minimum amount of s

26、odium carbonate and mercury. Do not shake or stir the solution before use. 5.2 Hydrochloric acid (HCl), 1,00mol/l standard volumetric solution. 5.3 Eluent 1 (S1), demineralized water (18 M7cm). Filter the demineralized water through0,24m membrane filters. Degas by sparging with helium for between20m

27、in and30min. 5.4 Eluent 2 (S2), sodium hydroxide (NaOH),300mmol/l solution. To 985 ml of degassed water (5.3), pipette15,6ml of the sodium hydroxide solution (5.1). CAUTION It is extremely important to remove dissolved carbon dioxide from the eluents prior to use. Carbonate will act as a strong “pus

28、her” on the column, resulting in a drastic reduction in resolution and efficiency. Prepare the solution the day before the analysis. 5.5 Carbohydrate standard solutions Prepare fresh solutions of arabinose, fructose, galactose, glucose, mannose, sucrose and mannitol. Weigh, to the nearest0,1mg, appr

29、oximately100mg of each carbohydrate into separate100ml volumetric flasks (6.2) and dilute to the mark with water (stock standard solutions of1000mg/l).BS5752-15:1997 2 BSI 09-1999 Mixed standard solutions can also be prepared from separate stock solutions once the retention time of each carbohydrate

30、 is known under the prevailing chromatographic conditions. Further dilute the standard solutions to reach carbohydrate concentrations similar to those found in the non-hydrolysed or hydrolysed instant coffee sample solutions. The resolution of rhamnose from arabinose is difficult to achieve. If thes

31、e two monosaccharides coelute, do not add rhamnose in a mixed standard solution. 6 Apparatus Usual laboratory apparatus and, in particular, the following. 6.1 Analytical balance, capable of weighing to an accuracy of 0,1mg. 6.2 One-mark volumetric flasks, of capacity100ml (in accordance with class A

32、 of ISO1042). 6.3 Graduated cylinders, of capacities1000ml and50ml, tall form. 6.4 Vacuum filtration system 6.5 Folded filter papers, medium fast, qualitative. 6.6 Disposable C18 filter cartridges 1) , to be used according to the manufacturers recommendations. 6.7 Disposable membrane filters, 0,24m

33、pore size. 6.8 Water bath, capable of being maintained at100 C 5 C. 6.9 Metal-free liquid chromatograph 2) , with a high-performance anion-exchange column 3)filled with pellicular polystyrene-divinylbenzene resin and precolumn (guard column) 4)and postcolumn delivery system. 6.10 Pulsed amperometric

34、 detector (PAD) with gold electrode 5) . 6.11 Integrator chromatography data station 6) . 6.12 Disposable cartridges 7) , to be used according to the manufacturers recommendations. 7 Sampling It is important that the laboratory receive a sample which is truly representative and has not been damaged

35、or changed during transport or storage. Sampling is not part of the method specified in this International Standard. A recommended sampling method is given in ISO6670:1983, Instant coffee in cases with liners Sampling. When the instant coffee is not in cases with liners, take a well-mixed representa

36、tive sample from single packed units. 8 Procedure 8.1 Determination of dry matter Calculate the dry matter determined on a portion of the laboratory sample in accordance with ISO3726. 8.2 Preparation of sample for analysis Method A Weigh, to the nearest0,1mg, approximately300mg of the laboratory sam

37、ple directly into a100ml volumetric flask (6.2). Add, using a graduated cylinder (6.3), 70ml of water and shake until dissolution is complete. Dilute to the mark with water. Filter5ml to10ml of this solution through a cartridge (6.6). Discard the first few millilitres. 8.3 Preparation of sample for

38、analysis Method B Weigh, to the nearest 0,1mg, approximately300mg of the laboratory sample directly into a100ml volumetric flask (6.2). Add50ml of the hydrochloric acid (5.2) and swirl. Place the flask in a boiling water bath (6.8) for150min. Keep the level of the sample solution always below that o

39、f the water in the bath. Swirl the solution by hand every30min. Cool to room temperature by passing the flask under tap water. Dilute to the mark with water and filter the solution through a folded filter paper (6.5). Pass3ml of the filtrate through a disposable cartridge (6.12). Discard the first m

40、illilitre. 1) Sep-Pack C18 (Waters) and Supelclean LC-18 (Supelco) are examples of suitable products available commercially. This information is given for the convenience of users of this International Standard and does not constitute an endorsement by ISO of these products. 2) The BioLC system (Dio

41、nex) consisting of a model GPM-II quarternary gradient pump (Dionex) with a model SP8875 autosampler (Spectra Physics) filled with a204l loop, model EDM-II eluent degas module (Dionex) and reagent reservoir for NaOH postcolumn addition (Dionex) are examples of suitable, equipment available commercia

42、lly. 3) CarboPac PA1 (104m,250mm 4mm) (Dionex) is an example of a suitable analytical column available commercially. 4) CarboPac PA (Dionex) is an example of a suitable precolumn available commercially. 5) Model PAD-II (Dionex) is an example of suitable equipment available commercially. 6) Model Aut

43、olon Al-450 is an example of suitable equipment available commercially. 7) On Guard-AG (Dionex) is an example of a suitable cartridge commercially available. This information is given for the convenience of users of this International Standard and does not constitute an endorsement by ISO of these p

44、roducts.BS5752-15:1997 BSI 09-1999 3 Table 1 Preparation of column Table 2 Conditions for analysis 8.4 Chromatographic analysis Set up the chromatograph (6.9), detector (6.10) and integrator (6.11). Allow the chromatograph to equilibrate. Filter the standard solutions (5.5) and the test solutions (8

45、.2 or8.3) through0,24m membrane filters (6.7). Inject the same volume of filtered standard and test solutions into the chromatograph and separate carbohydrates under the conditions given in Table 1 andTable 2. Identify and quantify carbohydrates in the sample solution by comparison with retention ti

46、mes and areas of corresponding peaks obtained using the standard solution. Inject a standard solution every four injections, in order to account for any changes in retention times or peak integrations. 9 Calculation The carbohydrate content, , expressed as a percentage by mass, is equal to where Tak

47、e as the result the arithmetic mean of the two determinations. Express the result either as free (method A) or total (method B) carbohydrate content to the nearest 0,01% (m/m) for each carbohydrate of interest, or the total of all carbohydrates detected. Eluent Time Eluent S1 Eluent S2 Procedure min

48、 ml ml Isocratic 0 100 0 Start data acquisition 50,0 100 0 Stop data acquisition 50,1 0 100 Start clean-up 65,0 0 100 Stop clean-up 65,1 100 0 Start re-equilibrium 80,0 100 0 Stop re-equilibrium NOTE 1Retention times tend to vary from one column to another. Start clean-up only when the last monosacc

49、haride (ribose) has been eluted. NOTE 2It may be necessary to perform two or three injections of standard solution or to increase the re-equilibrium time in order to achieve a good separation of sucrose and xylose. Injection 20 4l Flowrate 1,0ml/min Postcolumn addition Eluent S2 (5.4) at a flowrate of0,6ml/min Temperature Ambient Detector Fill up the reference cell with Eluent S2 (5.4). Use the optimum conditions given lay the manufacturer. A is the peak area of the individual carbohydrate in the test solution (8.4);