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1、BRITISH STANDARD BS 684-2.32: 1979 Incorporating Amendment No. 1 Methods of analysis of Fats and fatty oils Part 2: Other methods Section 2.32: Determination of rancidity index IMPORTANT NOTE. It is essential that this Section be read in conjunction with the information in the “General Introduction”
2、 to BS 684, which is published separately. UDC 665.1.014:543:535.653:665.112.2 Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:25:44 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 684-2.32:1979 This British Standard, having been prepared under the direction of the Oils and Fats Standards Co
3、mmittee was published under the authority of the Executive Board and comes into effect on 31 August 1979 BSI 07-1999 The following BSI references relate to the work on this standard: Committee reference OFC/24 Draft for comment 74/50699 DC ISBN 0 580 10837 6 A British Standard does not purport to in
4、clude 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 confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pag
5、es i and ii, page 1 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 3258December 1979 Indicated b
6、y a sideline in the margin Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:25:44 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 684-2.32:1979 BSI 07-1999i Contents Page 0Introduction1 1Scope1 2Principle1 3Reagents1 4Apparatus1 5Sampling and preparation of the sample for analysis1 6Procedure
7、1 7Expression of results1 8Test report1 Table 1 Equivalence of CIE colour coordinates to Lovibond units1 Licensed Copy: 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,
8、 Uncontrolled Copy, (c) BSI BS 684-2.32:1979 BSI 07-19991 0 Introduction The method described is a modified form of the Kreis test and is regarded as the best available at present for this determination. 1 Scope This Section describes a method for the detection and assessment of the degree of rancid
9、ity of fats. 2 Principle The sample is reacted with phloroglucinol in diethyl ether solution. When the products are extracted with hydrochloric acid a red aqueous solution is obtained if the material is rancid. The colour is measured by means of a colour comparator or colorimeter1), and the results
10、are expressed in red units on the Lovibond scale. 3 Reagents The following reagents are required. 3.1 Phloroglucinol solution, 1 g/l in diethyl ether. It is essential to prepare the solution on the day of use. 3.2 Hydrochloric acid, concentrated, 36 % (m/m), 11N. 4 Apparatus The following apparatus
11、is required. 4.1 Colour comparator or colorimeter1) NOTEIt is essential to maintain the colour-matching apparatus in good condition in accordance with the manufacturers instructions. 4.2 Glass cell, 1 in (25.4 mm) light path. 5 Sampling and preparation of the sample for analysis See BS 684: General
12、introduction. 6 Procedure Weigh, to the nearest 0.01 g, 9.8 g to 10.2 g of the sample into a 100 ml beaker. Melt the sample on a water bath to a temperature not more than 10 C above its melting point and whilst stirring gently add 20 ml of the phloroglucinol solution (3.1) to dissolve the sample, ta
13、king care because of the flammable nature of the warm solvent. Transfer the solution to a 100 ml separating funnel, add 10 ml of hydrochloric acid (3.2) and shake well. Allow the mixture to settle into two phases, then run off the acid phase into a 1 in (25.4 mm) glass cell. CAUTION. Take great care
14、 when shaking and handling mixtures of warm ether and hydrochloric acid. Wear eye goggles and perform the operations behind a safety screen. Read the colour of the solution in the comparator using yellow, red, and, if necessary, blue slides in order to obtain the best match. 7 Expression of results
15、Express the rancidity index as units on the red Lovibond scale; the equivalent CIE (Commission Internationale de lEclairage) colour co-ordinates using CIE standard illuminant B are as shown in Table 1. Table 1 Equivalence of CIE colour coordinates to Lovibond units A very faint red colour does not n
16、ecessarily denote rancidity. A colour up to 3 red units is considered to indicate incipient rancidity. A colour between 3 and 8 red units is considered to indicate rancidity towards the end of the induction stage. Over 8 red units is considered to indicate definite rancidity. For dark-coloured or gr
17、een fats the above does not necessarily apply because of interference by water-soluble colouring matter in the material. Before judging a fat, it is advantageous to have some knowledge of the history of the material under test. NOTERancidity develops rapidly; therefore once the induction period is w
18、ell established, it is necessary to adhere to an agreed time of testing when comparing results obtained by sellers and buyers. All deliveries should be tested immediately on arrival at a buyers premises and the date and time noted on the test certificate. The seller should be notified the same day.
19、8 Test report See the general instructions and recommendations given in BS 684: General introduction. 1) The Lovibond tintometer with standard colour slides available from The Tintometer Ltd, Waterloo Road, Salisbury, England is suitable. Lovibond units CIE co-ordinates xyz 0.1 red 3.0 red 8.0 red 0
20、.348 0.380 0.430 0.351 0.327 0.262 0.300 0.293 0.308 20.0 red 20.0 yellow 10.0 blue 0.543 0.449 0.201 0.298 0.494 0.184 0.159 0.057 0.615 Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 13:25:44 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 684-2.23: 1979 BSI 389 Chiswick High Road London W4
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