ISO INTERNATIONAL STANDARD 9648 First edition 1988-12-15 INTERNATIONAL ORGANIZATION FOR STANDARDIZATION ORGANISATION INTERNATIONALE DE NORMALISATION MEKAYHAPOAHAA OPIAHM3ALMA O CTAHAAPTM3ALMM Sorghum - Determination of tannin content Sorgho - Dosage des tanins Reference number ISO 9648 : 1988 (E) Not for Resale d without license from IHS ISO 9648 : 1988 (E) Foreword 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, govern- mental 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. 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 Council. They are approved in accordance with ISO procedures requiring at least 75 % approval by the member bodies voting. International Standard ISO 9648 was prepared by Technical Committee ISO/TC 34, Agricultural food products. ? International Organization for Standardization, 1988 Printed in Switzerland Copyrihtlinternatinal organizationfor Standadization Not for Resale license from IHS INTERNATIONAL STANDARD ISO 9648 : 1988 (E) Sorghum -- Determination of tannin content Scope is recommended in order to permit inter-laboratory comparison of results. This International Standard specifies a universal method for the determination of tannin content in sorghum grains. This solution can be kept for 1 week. It is not specific for one single type of polyphenols. Its 4.2Ammonia, solution of 8,0 g/l NH3. usefulness, meanwhile, is justified by the good negative cor- relation observed between the metabolizable energy of sorghum grain, measured using animal experiments on cocks, 4.3 Dimethylformamide, 75 % (V/ V) solution. and the results obtained using this method. Introduce 75 ml of dimethyiformamide into a 100 ml volumetric flask. Dilute with water, allow to cool and make up to the mark. 2 Normative references WARNING -- Dimethylformamide may be harmful to the The following standards contain provisions which, through health when inhaled or allowed to come into contact reference in this text, constitute provisions of this International with the skin. It is also irritating to the eyes. Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to 4.4 Ferric ammonium citrate, having an iron content be- agreements based on this International Standard are encour. tween 17 % (m/m) and 20 % (m/m), 3,5 g/l solution, aged to investigate the possibility of applying the most recent prepared 24 h before use. editionsofthestandardslistedbelow.MembersofIECandiSO maintain registers of currently valid International Standards. Since the iron content of the citrate has an influence on the ISo 712 : 1985, Cereals and cereals products -- Determination results, this content shall be respected imperatively. of moisture content (Routine reference method). ISO 950 : 1979, Cereals - Sampling (as grain). 5 Apparatus Usual laboratory apparatus and, in particular, the following. 3Principle 5.1 Mechanical crusher, capable of producing particles Extraction of tannins by shaking with dimethylformamide After centrifuging, addition of ferric ammonium citrate and am- which pass completely through the sieve (5.2). moniatoanaliguotpartofthesupernatantliguidanaspec trometric determination, at 525 nm, of the absorbance of the 5.2 Sieve, having apertures of size 0,5 mm. solution thus obtained. Determination of the tannin content using a calibration curve prepared using tannic acid. 5.3 Centrifuge, capable of producing a centrifugal accel