1、BRITISH STANDARD CONFIRMED NOVEMBER1992 BS684-2.42: 1989 ISO7366:1987 Methods of analysis of Fats and fatty oils Part2: Other methods Section2.42 Determination of1-monoglycerides and free glycerol contents IMPORTANT NOTE. It is essential that BS684-0, which is published separately, be read in conjun
2、ction with this Section. UDC 665.1.014:543:547.426.1+547.426.21BS684-2.42:1989 This BritishStandard, having been prepared under the directionof the Food and Agriculture Standards Committee,was published underthe authority of the BoardofBSI and comes into effect on 31 March1989 BSI11-1999 First publi
3、shed November1986 First revision March1989 The following BSI references relate to the work on this standard: Committee referenceFAC/18 Draft announced in BSI News March 1986 ISBN 0 580 17193 0 National foreword This revision of Section2.42 of BS684 has been prepared under the direction of the Food a
4、nd Agriculture Standards Committee. It is identical with ISO7366:1987 “Animal and vegetable fats and oils Determination of1-monoglycerides and free glycerol contents” published by the International Organization for Standardization (ISO) and in the preparation of which the UK played a full part. This
5、 revision does not differ technically from BS684-2.42:1986, which it supersedes and which is withdrawn, but the Table in8.2 has been expanded to give a wider range of approximate masses of the test portion, and editorial modifications have been made. Terminology and conventions. The text of the Inte
6、rnational Standard has been approved as suitable for publication as a BritishStandard without deviation. Some terminology and certain conventions are not identical with those used in BritishStandards; attention is drawn especially to the following. The comma has been used as a decimal marker. In Bri
7、tishStandards it is current practice to use a full point on the baseline as the decimal marker. The symbol “l” has been used to denote litre (and in its submultiples). In BritishStandards it is current practice to use the symbol “L”. In BritishStandards it is current practice to use the spelling “su
8、lphur”, etc. instead of “sulfur”, etc. Wherever the words “International Standard” appear, referring to this standard, they should be read as “Section of BS684”. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for
9、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 to4, an inside back cover and a back cover. This standard has been updated (see
10、 copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Cross-reference International Standard Corresponding British Standard ISO5555:1983 BS627:1982 Methods for sampling animal and vegetable fats and oils (Technically equiv
11、alent) Amendments issued since publication Amd. No. Date of issue CommentsBS684-2.42:1989 BSI 11-1999 i Contents Page National foreword Inside front cover 1 Scope 1 2 Field of application 1 3 Reference 1 4 Principle 1 5 Reagents 1 6 Apparatus 1 7 Sampling 1 8 Procedure 1 9 Expression of results 3 10
12、 Test report 3 Table 1 Publication referred to Inside back coverii blankBS684-2.42:1989 BSI 11-1999 1 1 Scope This International Standard specifies a method for the determination of1-monoglycerides content and of free glycerol content consecutively on the same test portion. 2 Field of application It
13、 is applicable to animal and vegetable fats and oils and to interesterified products of oils, fats and fatty acids with glycerol. It is not applicable when the sample contains a) in addition to1-monoglycerides: chloroform-soluble polyhydric substances with two or more adjacent hydroxyl groups; b) in
14、 addition to free glycerol: water-soluble polyhydric substances with two or more adjacent hydroxyl groups. 3 Reference ISO5555, Animal and vegetables fats and oils Sampling. 4 Principle Dissolution of a test portion in chloroform. Extraction of free glycerol from this solution with acetic acid solut
15、ion. Oxidation of1-monoglycerides in the chloroform solution by an excess of periodic acid solution. Addition of potassium iodide and titration of the liberated iodine with a sodium thiosulfate standard volumetric solution. Oxidation of free glycerol in the aqueous solution by an excess of periodic
16、acid solution. Addition of potassium iodide and titration of the liberated iodine with a sodium thiosulfate standard volumetric solution. 5 Reagents All reagents shall be of recognized analytical grade. The water used shall be distilled water or water of at least equivalent purity. 5.1 Chloroform 5.
17、2 Acetic acid,5%(V/V) solution. 5.3 Periodic acid,2,7g/l solution. Weigh2,7g of periodic acid (H 5 IO 6 ) in a1litre volumetric flask and dissolve in50ml of water. Make up to the mark with glacial acetic acid and mix thoroughly. Store in the dark. 5.4 Potassium iodide,150g/l solution, not containing
18、 free iodine or iodates. 5.5 Sodium thiosulfate, standard volumetric solution, c(Na 2 S 2 O 3 )=0,1mol/l. 5.6 Starch, indicator solution,10g/l. Dissolve1g of soluble starch in100ml of water by stirring and heating. Add0,1g of salicylic acid to preserve the indicator solution and boil for3min. Cool t
19、o room temperature. 6 Apparatus Usual laboratory equipment and in particular 6.1 Conical flasks, of capacity500ml, with ground-glass stoppers. 6.2 Magnetic stirrer 7 Sampling See ISO5555. 8 Procedure 8.1 Preparation of the test sample 8.1.1 Solid samples in flake or in powder form Mix the sample tho
20、roughly without melting. 8.1.2 Other solid or semi-solid samples Melt the sample at not more than10 C above its melting point, mix thoroughly. CAUTION The sample shall not be subjected to excessive temperatures. At temperatures above80 C the1-monoglycerides content may decrease as a result of intere
21、sterification and/or intraesterification. 8.1.3 Liquid samples Mix the sample thoroughly. 8.2 Test portion Weigh accurately into a50ml beaker the appropriate mass of the test portion as indicated in the Table. Table Expected content of 1-monoglycerides or of glycerol Approximate mass of the test por
22、tion Weighing accuracy %(m/m) g g 100 75 50 40 30 20 15 10 5 3 or less 0,3 0,4 0,6 0,7 1,0 1,5 2,5 3,0 6,0 10,0 0,0001 0,0001 0,0001 0,0001 0,001 0,001 0,001 0,001 0,001 0,001 NOTEIf the contents of1-monoglycerides and glycerol are very different and therefore an intermediate test portion mass is no
23、t possible, two test portions are necessary, one for the1-monoglycerides and the other for the glycerol.BS684-2.42:1989 2 BSI 11-1999 8.3 Extraction 8.3.1 Take three separating funnels of capacity250ml and label them1,2 and3. Use separating funnel1 to collect aqueous solutions and separating funnels
24、2 and3 for washing the solutions. When shaking is required, this is performed vigorously for about1min, releasing pressure from time to time through the tap and avoiding the formation of emulsions. Take two volumetric flasks of capacity100ml and label them A and B. Use flask A for the chloroform sol
25、ution of1-monoglycerides and flask B for the aqueous solution of glycerol. 8.3.2 Dissolve the test portion(8.2) in chloroform(5.1), dispersing any free glycerol. Pour quantitatively into separating funnel1, using successive small quantities of chloroform to aid the transfer until the volume reaches4
26、5 to50ml. 8.3.3 Rinse the used50ml beaker with about25ml of acetic acid solution(5.2) to dissolve any remaining glycerol. Transfer the rinsings to separating funnel1. Stopper, shake and allow to separate. Run the chloroform (lower) layer into separating funnel2. Wash the50ml beaker with25ml of aceti
27、c acid solution and pour into separating funnel2. Stopper, shake and allow to separate. Run the chloroform layer into separating funnel3 and run the aqueous solution into separating funnel1. 8.3.4 Wash the beaker and separating funnel2 with a further25ml of acetic acid solution and run this into sep
28、arating funnel3. Stopper, shake and allow to separate. Run the chloroform layer into the100ml volumetric flask A. Run the aqueous layer into separating funnel1. Rinse separating funnels2 and3 successively with two20ml volumes of chloroform and run the chloroform into separating funnel1. Stopper, sha
29、ke and allow to separate. 8.3.5 Run the chloroform layer into the100ml volumetric flask A and make up to volume with chloroform. Stopper and mix. 8.3.6 Run the aqueous layer into the100ml volumetric flask B. Rinse the separating funnel1 with acetic acid solution, add the rinsings to flask B and make
30、 up to volume with acetic acid solution. Stopper and mix. 8.4 Determination of1-monoglycerides Using a pipette, transfer50ml of the chloroform solution from flask A(8.3.5) into the500ml conical flask(6.1), add50ml of periodic acid solution(5.3) with a pipette, mix and stopper. Allow to stand for30mi
31、n in the dark. Carry out a blank test under the same conditions, using50ml of chloroform(5.1) and50ml of periodic acid solution(5.3). After the30min period add20ml of potassium iodide solution(5.4) both to the test solution and to the blank. Stopper the flasks, mix and allow to stand for1min longer.
32、 Add100ml of water to each. Titrate with sodium thiosulfate standard volumetric solution(5.5) whilst stirring continuously using the magnetic stirrer(6.2) in order to ensure thorough mixing. Towards the end of the titration, when the brown iodine colour has almost disappeared from the aqueous layer,
33、 add about2ml of starch solution(5.6) as indicator. Continue the titration dropwise until the end-point is reached (disappearance of the blue iodo-starch colour from the aqueous layer). Vigorous agitation is essential for complete removal of iodine from the chloroform layer. If the volume used to ti
34、trate the test solution is not more than80% of the volume used to titrate the blank, repeat the determination using a smaller test portion or taking a smaller aliquot of the chloroform solution (to ensure an adequate excess of periodic acid). 8.5 Determination of free glycerol Filter the aqueous sol
35、ution from flask B(8.3.6). Using a pipette, transfer50ml of the filtrate into a500ml conical flask(6.1), add50ml of periodic acid solution(5.3) with a pipette, mix and stopper. Allow to stand for30min in the dark. Carry out a blank test under the same conditions, using50ml of acetic acid solution(5.
36、2) and50ml of periodic acid solution(5.3). After the30min period add20ml of potassium iodide solution(5.4) both to the test solution and to the blank. Stopper the flasks, mix and allow to stand for1min longer. Add100ml of water to each. Titrate with sodium thiosulfate standard volumetric solution(5.
37、5) adding2ml of starch solution(5.6) when the brown colour of the iodine has almost disappeared. If the volume used to titrate the test solution is not more than80% of the volume used to titrate the blank, repeat the determination using a smaller test portion or taking a smaller aliquot of the aqueo
38、us solution (to ensure an adequate excess of periodic acid). 8.6 Number of determinations Carry out two determinations on the same test sample.BS684-2.42:1989 BSI 11-1999 3 9 Expression of results 9.1 Method of calculation and formulae 9.1.1 Calculation of1-monoglycerides content The1-monoglycerides
39、 content, expressed as a percentage by mass, is equal to where V 0 is the volume, in millilitres, of the sodium thiosulfate standard volumetric solution required for the titration of the blank; V 1 is the volume, in millilitres, of the sodium thiosulfate standard volumetric solution required for the
40、 titration of the test solution; c is the concentration, expressed in moles per litre, of the sodium thiosulfate standard volumetric solution; M r is the relative molecular mass of a particular1-monoglyceride, the choice depending on the composition of the fatty acids (when the results are expressed
41、 as glyceryl monostearate, M r =358); m is the mass, in grams, of the test portion; r is the ratio of the volume(100ml) of the chloroform phase to the volume(50ml or less) of this phase taken for the determination. Express the result to one decimal place. 9.1.2 Calculation of free glycerol content T
42、he free glycerol content, expressed as a percentage by mass, is equal to where V 2 is the volume, in millilitres, of the sodium thiosulfate standard volumetric solution required for the titration of the blank; V 3 is the volume, in millilitres, of the sodium thiosulfate standard volumetric solution
43、required for the titration of the test solution; c is the concentration, expressed in moles per litre, of the sodium thiosulfate standard volumetric solution; M r is the relative molecular mass of glycerol (M r =92,1); m is the mass, in grams, of the test portion; r is the ratio of the volume(100ml)
44、 of the aqueous phase to the volume of this phase(50ml or less) taken for the determination. Express the result to one decimal place. 9.2 Repeatability The difference between the results of two determinations carried out simultaneously or in rapid succession by the same analyst under the same condit
45、ions on the same test sample shall not exceed the values given in9.2.1 and9.2.2. 9.2.1 For1-monoglycerides 0,5%(m/m) at contents from15 to25% (m/m) 2% (relative) of the average value at contents from25 to50%(m/m) 1%(m/m) at contents greater than50%(m/m) 9.2.2 For free glycerol 0,1%(m/m) 10 Test repo
46、rt The test report shall show the method used and the results obtained. It shall also mention any operating details not specified in this International Standard, or regarded as optional, together with details of any incidents likely to have influenced the results. The test report shall include all t
47、he information necessary for the complete identification of the sample. V 0 V 1 () crM r 20 m - V 2 V 3 () crM r 40 m -4 blankBS684-2.42:1989 BSI 11-1999 Publication referred to See national foreword.BS684-2.42: 1989 ISO7366:1987 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsInstitutio
48、n BSI is the independent national body responsible for preparing BritishStandards. It presents the UK view on standards in Europe and at the international level. It is incorporated by Royal Charter. Revisions BritishStandards are updated by amendment or revision. Users of BritishStandards should mak
49、e sure that they possess the latest amendments or editions. It is the constant aim of BSI to improve the quality of our products and services. We would be grateful if anyone finding an inaccuracy or ambiguity while using this BritishStandard would inform the Secretary of the technical committee responsible, the identity of which can be found on the inside front cover. Tel:02089969000. Fax:02089967400. BSI offers members an individual updating service called PLUS which ensures that sub
