ISO 3656:2011 動物性および植物性の油脂—特定のUV吸光度として表される紫外線吸光度の測定 | ページ 2

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 committees. 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 International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. 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 least 75 % of the member bodies casting a vote.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights.

ISO 3656 was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 11, Animal and vegetable fats and oils.

This fourth edition cancels and replaces the third edition (ISO 3656:2002), which has been technically revised.

Introduction

This International Standard describes a method for the determination of the absorbance of light in the ultraviolet (UV) spectrum by fats and oils. Changes in absorption in the UV region are used as quality, purity, and authenticity criteria for fats and oils. Refining causes the formation of conjugated dienes and trienes and increased values of K₂₃₂ and K₂₆₈, which then indicate the presence of refined oils. The oxidation of linoleic and linolenic acids results in the formation of hydroperoxides in which the double bonds become conjugated. Furthermore, the formation of either carbon-carbon bonds or carbon-oxygen bonds (α,β-unsaturated carbonyl compounds) as secondary autoxidation products are observed. These compounds all lead to an increase of the absorption in the region between 225 nm and 325 nm.

The third edition of this International Standard allowed the determination of the UV absorbance at 232 nm and 268 nm using three different solvents (isooctane, cyclohexane or n-hexane). However, it is known that the solvents themselves have an effect on the UV absorbance between 260 nm and 276 nm in vegetable oils. Recent investigations have shown that the measurement of K₂₆₈ and K₂₇₀ for the same oil in isooctane or in cyclohexane give significantly different results. In isooctane, the maxima appear at 267 nm to 268 nm whereas in cyclohexane, the maxima appear at 268 nm to 269 nm. In the IOC standards for the determination of the ultraviolet absorbance of (virgin) olive oils, the specified wavelengths are 232 nm and 270 nm.

Taking into account the above, the fourth edition of this International Standard specifies measurement at 268 nm when isooctane is used and measurement at 270 nm when cyclohexane is used. Moreover, the variation of the specific extinction, ∆K, for olive oils has been introduced. Precision data from a new collaborative trial have also been taken into consideration for this revision.

1 Scope

This International Standard specifies a method for the determination of the absorbance at ultraviolet wavelengths of animal and vegetable fats and oils.

2 Normative references

The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

3 Terms and definitions

For the purposes of this document, the following terms and definitions apply.

Bibliography