ISO INTERNATIONAL STANDARD 1842 Second edition 1991-12-01 Fruit and vegetable products -- Determination of pH Produits derivés des fruits et legumes -- Mesurage du pH Reference number ISO 1842:1991(E) No reproductic n or networking permitted without license from IHS Not for Resale ISO 1842:1991(E) 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, govern- mental and non-governmental, in liaison with isO, also take part in the work. iso collaborates closely with the International Eiectrotechnical Commission (IEC) on all matters of electrotechnical standardization. Draft International Standards adopted by the technicai committees are national Standard requires approval by at least 75 % of the member bodies casting a vote. International Standard IsO 1842 was prepared by Technical Committee ISO/TC 34, Agricultural food products, Sub-Committee SC 3, Fruit and vegetableproducts. s second edition cancels and replaces the first edition (Iso This 1842:1975), of which its constitutes a technical revision. C ISO1991 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the publisher. International Organization for Standardization Case Postale 56· CH-1211 Geneve 20 · Switzerland Printed in Switzerland Copyright International Organization for Standardization Not for Resale sefromIHS ISO 1842:1991(E) INTERNATIONAL STANDARD Fruit and vegetable products --- Determination of pH 1 Scope Preparation of the test sample 4 This International Standard specifies a potentio- metric method of measuring the pH of fruit and veg- 4.1 Liquid products and easily filtrable products etabie products. (e.g. juices, liquids from compotes or from pickles, brines, fermented liquids, etc.) Principle 2 Mix the laboratory sample carefully until it is homo- geneous. Measurement of the potential difference between two electrodes dipped in the liquid to be tested. 4.2 Thick or semi-thick products and products from 3 Apparatus which it is difficult to separate the liquid (e.g. syrups, jams, purées, jellies, etc.) Usual laboratory apparatus and. in particular, the Mix a part of the laboratory sample and grind it, if following. necessary, in a blender or mortar; if the product obtained is still too thick, add an equal mass of dis- 3.1 pH meter, with a scale graduated in units of tilled water and, if necessary, mix well with a 0,05 pH or, preferably, less. blender or mortar. If a temperature correction system is not provided, the scale shall apply to measurements at 2o °c. 4.3 Frozen products 3.2 Electrodes (alternative to 3.3). Thaw the product and remove stones and hard seed-cavity walls. Proceed as described in 4.1 or 3.2.1 Glass electrode 4.2, as appropriate. Glass electrodes of different geometrical shapes may be used. They shall be stored in water. 4.4 Dried products 3.2.2 Calomel electrode, containing saturated pot- Cut a part of the laboratory sample into small assium chloride solution. pieces, and remove stones and hard seed-cavity Store the calomel electrode according to the in- walls. Put the pieces into a beaker, add two to three structions of the manufacturer; if these are not times their mass of distilled water (or more if re- available, the electrode shall be stored in saturated quired to give a suitable consistency) and heat in a potassium chloride solution. water-bath for 30 min,mixing fromtime to time with a glass rod. Then grind the product in a blender or mortar. 3.3 Combined-electrode system (alternative to 3.2) The calomel and glass electr