BS 4289-5-1989 Method for the analysis of oilseeds - Determination of acidity of fat《油料种子分析方法 第5部分 脂肪酸度测定》.pdf

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1、BRITISH STANDARD BS 4289-5: 1989 Methods for the analysis of Oilseeds Part 5: Determination of acidity of fat UDC 633.85 + 665.3:639.381.3:637.054:541.132.3:001.4:620.1BS4289-5:1989 This British Standard, having been prepared under the direction of the Food and Agriculture Standards Committee, was p

2、ublished under the authority ofthe Board of BSI and comes intoeffect on 28 February 1989 BSI 10-1999 First published March 1968 First revision February 1989 The following BSI references relate to the work on this standard: Committee reference FAC/17 Draft for comment 88/50486 DC ISBN 0580 171183 Com

3、mittees responsible for this British Standard The preparation of this British Standard was entrusted by the Food and Agriculture Standards Committee (FAC/-) to Technical Committee FAC/17, upon which the following bodies were represented: British Food Manufacturing Industries Research Association Dep

4、artment of Trade and Industry (Laboratory of the Government Chemist) FOSFA International Grain and Feed Trade Association International Association of Seed Crushers Intervention Board for Agricultural Produce Ministry of Agriculture, Fisheries and Food National Farmers Union National Institute of Ag

5、ricultural Botany Overseas Development Natural Resources Institute Royal Society of Chemistry Seed Crushers and Oil Processors Association Tropical Growers Association Amendments issued since publication Amd. No. Date of issue CommentsBS4289-5:1989 BSI 10-1999 i Contents Page Committees responsible

6、Inside front cover Foreword ii 1 Scope 1 2 Definitions 1 3 Principle 1 4 Reagents 1 5 Apparatus 1 6 Sampling 1 7 Preparation of test sample 1 8 Procedure 1 9 Expression of results 2 10 Test report 2 Table 1 Expression of acidity 1 Publications referred to Inside back coverBS4289-5:1989 ii BSI 10-199

7、9 Foreword This Part of BS 4289 has been prepared under the direction of the Food and Agriculture Standards Committee and supersedes BS 4289-5:1968 which is withdrawn. It differs from BS 4289-5:1968 in that the determination uses hot ethanol in place of a cold mixture of ethanol and diethyl ether as

8、 solvent with aqueous sodium hydroxide or potassium hydroxide solution as titrant because of the problems associated with the recovery or disposal of diethyl ether and the instability of ethanolic potassium hydroxide solution. Because of the same problems, ISO 729:1988 published by the International

9、 Organization for Standardization has not been implemented as a BritishStandard. 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

10、confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 and2, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicate

11、d in the amendment table on the inside front cover.BS4289-5:1989 BSI 10-1999 1 1 Scope This Part of BS 4289 describes a method for the determination of acidity of fat extracted from oilseeds. In some cases, either by custom or contract, the determination is carried out on cleaned seed and reported a

12、ccordingly. NOTE 1The term “fat” is used to denote any animal or vegetable fat or oil whether solid or liquid. The term “oil” implies that the fat is liquid. NOTE 2The titles of the publications referred to in this Part of BS 4289 are listed on the inside back cover. 2 Definitions For the purposes o

13、f this Part of BS 4289 the following definitions apply. 2.1 acidity the percentage of free fatty acids. According to the type of fat, it can be expressed as indicated in Table 1 Table 1 Expression of acidity 2.2 acid value the number of milligrams of potassium hydroxide required to neutralize the fr

14、ee fatty acids in 1 g of fat 3 Principle A test portion is extracted with technical hexane or light petroleum in accordance with the method described in BS 4289-4. The extract is dissolved in hot ethanol and titrated with sodium hydroxide solution or potassium hydroxide solution. 4 Reagents 4.1 Gene

15、ral. The reagents shall be of a recognized analytical grade. Water complying with grade 3 of BS 3978 shall be used throughout. 4.2 Reagents given in BS 4289-4. 4.3 Ethanol, at least 94% (V/V). NOTEThe ethanol may be replaced by industrial methylated spirits complying with BS 3591 and of equivalent s

16、trength. In the UK the use of industrial methylated spirits is governed by the Methylated Spirits Regulations, 1983 (S.I. 1983 No. 252). It is not permissible to use duty-free ethanol, received under the provisions of the Alcoholic Liquors Duties Act 1972, Section 10, for purposes for which industri

17、al methylated spirits is an acceptable alternative. 4.4 Sodium hydroxide or potassium hydroxide, standard volumetric solution, c(NaOH) or c(KOH)=0.1 mol/L. 4.5 Sodium hydroxide or potassium hydroxide, standard volumetric solution, c(NaOH) or c(KOH)=0.5 mol/L. 4.6 Phenolphthalein indicator, 10 g/L in

18、 95% (V/V) ethanol. NOTEIn determinations on fats giving dark coloured solutions, observation of the end point of the titration may be facilitated by either substitution of the phenolphthalein indicator by thymolphthalein or alkali blue 6B or addition of 1 mL of a 1 g/L solution of methylene blue to

19、 each 100 mL of the phenolphthalein indicator solution before the titration. 5 Apparatus Apparatus as given in BS 4289-4. 6 Sampling The laboratory sample shall be taken in accordance with BS 4146. 7 Preparation of test sample Prepare a representative sample from the laboratory sample in accordance

20、with BS 4289-4. 8 Procedure 8.1 Extraction of fat Extract the fat from the test sample in accordance with BS 4289-4, and record the total mass of the extracts. Determine the acidity without delay (see8.3). 8.2 Neutralization of ethanol Heat to boiling point 50 mL of the ethanol (4.3). While the temp

21、erature of the ethanol is still higher than 70 C, neutralize with the sodium hydroxide or potassium hydroxide solution (4.4) using 0.5 mL of the indicator (4.6). Type of fat Expressed as Relative molecular mass Coconut oil, palm kernel oil and similar oils Lauric acid 200 Palm oil Palmitic acid 256

22、All other fats and oils Oleic acid 282BS4289-5:1989 2 BSI 10-1999 8.3 Determination of acidity On completion of the extraction of fat (see 8.1) transfer any extract from flask B to flask A using the neutralized ethanol (see 8.2) and dissolve the extract in flask A. Heat to boiling and titrate with t

23、he sodium hydroxide or potassium hydroxide solution (see 4.4) mixing vigorously during the titration. The end point is reached when the addition of one drop of the sodium hydroxide or potassium hydroxide solution produces a slight but definite colour change lasting for at least 15 s. If the titratio

24、n exceeds 10 mL, repeat the procedure using the more concentrated sodium hydroxide or potassium hydroxide solution (see 4.5). 8.4 Number of determinations Carry out two determinations using two separate test portions from the same test sample. 9 Expression of results 9.1 Acidity The acidity, express

25、ed as a percentage by mass, is given by the following expression: Take as the result the arithmetic mean of the two determinations. 9.2 Acid value The acid value is given by the following expression: where V, c and m are as defined in 9.1. Take as the result the arithmetic mean of the two determinat

26、ions. 10 Test report The test report shall state the following: a) the method used, i.e. BS 4289-5:1989, and the results obtained; b) whether the determination was carried out on cleaned samples or samples as received; c) whether the results are expressed on the sample as tested or on the cleaned se

27、ed with the results expressed on the material as received; d) any operating conditions not described in this Part of BS 4289 or regarded as optional and any circumstances that may have influenced the results; e) all details required for the complete identification of the sample. where V is the volum

28、e of the standard volumetric sodium hydroxide or potassium hydroxide solution used to titrate the test portion (inmL); c is the exact concentration of the standard volumetric sodium hydroxide or potassium hydroxide solution used (in mol/L); M is the relative molecular mass of the acid chosen for exp

29、ression of the result (see Table 1); m is the mass of the extracts (8.1) (in g). Vc M 10m - 56.1V c m -BS4289-5:1989 BSI 10-1999 Publications referred to BS 3978, Specification for water for laboratory use. BS 4146, Methods for sampling oilseeds. BS 4289, Methods for the analysis of oilseeds. BS 428

30、9-4, Determination of hexane extract (or light petroleum extract) called “oil content”. ISO 729, Oilseeds Determination of acidity of oils 1) . 1) Referred to in the foreword only.BS4289-5: 1989 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsInstitution BSI is the independent national b

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