(TSO 6557/2 International Standard INTERNATIONAL ORGANIZATION FOR STANDARDIZATIONGME XAYHAPOAHAA OPTAHM3ALWR nO CTAHAAPTW3ALWM-ORGANISATION INTERNATIONALE DE NORMALISATION Fruits, vegetables and derived products - Determination of ascorbic acid content Part 2: Routine methods Fruits, legumes et produits derivés - Détermination de la teneur en acide ascorbique -- Partie 2: Methodes pratiques First edition -- 1984-11-15 ISO 6557/2-1984 (E) UDC 634.1/635.6 : 543.24 : 547.475.2 Ref. No. 1SO 6557/2-1984 (E) Descriptors : agricultural products, fruits and vegetable products, tests, determination of content, ascorbic acid. Price based on 4 pages No reproduction or networking permited without license from IHS Not for Resale Foreword Iso (the tnternationat Organization for Standardization) is a worldwide federation of national standards bodies tisO member bodies). The work of preparing international body interested in a subject for which a technical comrmittee has been established has the right to be represented on that committee. International organizations, govern- mental and non-governmental, in liaison with Iso, also take part in the work. Draft International Standards adopted by the technical committees are circulated to the member bodies for approval before their acceptance as International Standards by the ISo Councit. They are approved in accordance with ISO procedures requiring at ieast 75 % approval by the member bodies voting. International Standard ISO 6557/2 was prepared by Technicat Committee: ISO/TC 34, Agricultural food products. sewithISO No reproduction or networking permitted without license from IHS Not for Resale INTERNATIONAL STANDARD ISO 6557/2-1984 (E) Fruits, vegetables and derived products -- Determination of ascorbic acid content Part 2: Routine methods Scope and field of application 2.2.2 2,6-dichlorophenolindophenol, dyestuff solution. 1 This part of Iso 6557 specifies two routine methods for the 50 mg of the sodium salt of 2,6-dichioro- Dissolve determination of the ascorbic acid content1) of fruits, phenolindophenot in 150 ml of hot (50 to 60 °C) water contain- vegetables and derived products: ing 42 mg of sodium hydrogen carbonate in a 200 ml one-mark volumetric flask, make up to the mark with water and filter. 2,6-dichiorophenolindophenol titrimetric Store the solution in a dark brown bottle in a refrigerator. method A: method; As the dyestuff decomposes with time, fresh solution should method B: 2,6-dichlorophenolindophenol spectrometric be prepared periodically. method after extraction with xylene. 2.2.3 Ascorbic acid, 1 g/l standard solution. Method A can only be used in the absence of certain in- terferences (see 2.6). Weigh, to the nearest 0,01 mg, 50 mg of ascorbic acid which has been stored in a desiccator, transfer quantitatively to a Method B is applicable to derived fruit and vegetable products 50 ml one-mark volumetric flask and make up to the mark with in strongly coloured solutions. the extraction solution (2.2.1). Method A: 2,6-dichlorophenolindophenol Apparatus 2.3 titrimetric method Usual laboratory equipment, and 2.1 Principle 2.3.1 Analytical balance. Extraction of the ascorbic acid from a test portion using either oxalic acid sotution or metaphosphoric acid-acetic acid solu- tion. Titration with 2,6-dichlorophenolindopheno! dyestuff until 2.3.2 Mixer. a salmon pink colour is obtained. Burette, of capacity 10 to 50 ml. 2.3.3 2.2 Reagents All reagents shall be of recognized analytical grade. The water 2.4 Procedure used shalt be distiled water or water of at least equivalent purity. 2.4.1 Preparation of the test sample Extraction solution. 2.2.1 If necessary, remove seeds and hard seed-cavity walls and then thoroughiy mix the sampte. Filter, and proceed with the deter- Use either a 2 % (m/m) oxatic acid solution or a metaphos- mination on the filtrate. phoric acid/acetic acid solution prepared as follows. Allow frozen or deep frozen products to thaw in a closed vessel Dissolve 15 g of