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1、BRITISH STANDARD CONFIRMED APRIL 1993 BS 684-2.20: 1977 Methods of analysis of Fats and fatty oils Part 2: Other methods Section 2.20: Determination of carotene in vegetable oils IMPORTANT NOTE. It is essential that this Section be read in conjunction with the information in the “General introductio
2、n” to BS 684, which is published separately. UDC 665.1.014:543:665.3:543.86:547.979.8 Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:25:44 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 684-2.20:1977 This British Standard, having been prepared under the direction of the Oils and Fats Stand
3、ards Committee, was published under the authority of the Executive Board on 31 December 1976 BSI 10-1999 The following BSI references relate to the work on this standard: Committee reference OFC/24 Draft for comment 74/50699 DC ISBN 0 580 09750 9 A British Standard does not purport to include all th
4、e necessary provisions of a contract. Users of British 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, pages i and ii,
5、 pages 1 and 2 and a back cover. This 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 issueComments Licensed Copy: sheffieldun sheffie
6、ldun, na, Wed Dec 06 13:25:44 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 684-2.20:1977 BSI 10-1999i Contents Page 0Introduction1 1Scope1 2Reference1 3Principle1 4Reagent1 5Apparatus1 6Sampling and preparation of the sample for analysis1 7Procedure1 8Expression of results1 9Test report2 Licensed C
7、opy: sheffieldun sheffieldun, na, Wed Dec 06 13:25:44 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ii blank Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:25:44 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 684-2.20:1977 BSI 10-19991 0 Introduction A number of compounds are responsible for
8、colours in crude oils. The colour of the oil is influenced by the method of extraction, maturity and quality of the raw material, improper storage and the temperatures to which the raw material and oil are subjected during extraction. The chemical identity of the colouring components in oils is to a
9、 large extent unknown, but the characteristic yellow-red colour of many natural fats is due to the presence of polyene carotenoid pigments. These derive their colour from the presence in their structure of a sequence of multiple conjugated double bonds which in the solutions concerned absorb light i
10、n the region of 440 nm to 450 nm. Of the vegetable oils widely used, palm oil has the highest concentration of carotenoids, usually about 0.03 % to 0.15 % (m/m) in the crude unbleached oil. Chlorophyll often occurs in small proportions in vegetable oils. Usually its proportion is very small in comme
11、rcial seed oils obtained from mature undamaged seeds. Chlorophyll absorbs light in the 640 nm and 660 nm regions and does not interfere in the spectrophotometric determination of carotenoids. Cottonseed oil is unique among commercial oils in the great complexity of its pigment system, most of the co
12、lour of the crude oil being attributed to pigments of the gossypol type. Gossypol itself absorbs light in the 440 nm region and hence its removal is necessary before the determination of carotenoids in oils or blends containing gossypol pigments. However, gossypol and the related pigments are suffic
13、iently acidic to be removed completely by treatment with alkali. 1 Scope This Section describes a method for the determination of the carotenoid content of vegetable oils by spectrophotometric examination in the visible range of the spectrum. The method described is applicable to vegetable oils if t
14、he greater part of their colour is due to carotenoid pigments and, in particular, to palm oil, which in the crude or unprocessed form usually contains between 300 mg/kg to 1 500 mg/kg, expressed as carotene. 2 Reference The following publication is referred to in this Section: BS 1792, One-mark volu
15、metric flasks. 3 Principle The absorption of a solution of the fatty material in cyclohexane is measured at 445 nm. The percentage content of total carotenoids (m/m) is calculated as beta-carotene. 4 Reagent The following reagent is required (see also BS 684: General introduction). 4.1 Cyclohexane,
16、spectroscopic grade. 5 Apparatus The following items of apparatus are required (see also BS 684: General introduction). 5.1 Spectrophotometer, capable of operating at 445 nm and using matched or paired parallel-sided glass or silica cells of path length about 1 cm. It is essential that the path leng
17、th of the cells is accurately known. 5.2 Volumetric flasks, 100 ml capacity, class B, complying with the requirements of BS 1792. 6 Sampling and preparation of the sample for analysis See BS 684: General introduction. 7 Procedure 7.1 Test portion. Weigh, to the nearest 1 mg, between 0.5 g and 1.0 g
18、of the vegetable oil into the 100 ml volumetric flask (5.2). Dissolve the oil and dilute to the mark with cyclohexane (4.1). 7.2 Determination. Fill a 1 cm glass or silica cell with the solution of the oil and fill a second matched cell with cyclohexane (4.1). Take absorption readings in the spectro
19、photometer at 445 nm. If necessary, dilute the original solution (7.1) to a measured volume and take further readings so that the observed absorptions are between 0.2 and 0.8 optical density. 8 Expression of results Calculate the total carotenoid content of oil as beta-carotene, in milligrams per ki
20、logram, using the following formula: where E is the observed difference in absorption between the sample solution and the cyclohexane 383E l c - Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:25:44 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 684-2.20:1977 2 BSI 10-1999 l is the path len
21、gth of the cell (in cm) c is the concentration used for absorption measurement (in g per 100 ml) 9 Test report See the instructions and recommendations given in BS 684: General introduction. Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:25:44 GMT+00:00 2006, Uncontrolled Copy, (c) BSI bl
22、ank Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:25:44 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 684-2.20: 1977 BSI 389 Chiswick High Road London W4 4AL BSI British Standards Institution BSI is the independent national body responsible for preparing British Standards. It presents th
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