UGANDA STANDARD 
       US ISO 762
First Edition
2009-mm-dd
 
 Reference numbe r 
     US ISO 762:2003
© UNBS 2009
  
Fruit and vegetable products — Determination of mineral 
impurities content 
 US ISO 762:2003 
 
© UNBS  2009 – All rights reserved Compliance with this standard does not, of itself confer immunity from legal obligations 
A Uganda Standard does not purport to include all necessary provisions of a contract. Users are 
responsible for its correct application  
© UNBS 2009  
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilised in any 
form or by any means, electronic or mechanical, in cluding photocopying and microfilm, without prior written 
permission from UNBS. 
Requests for permission to reproduce this document should be addressed to 
The Executive Director 
Uganda National Bureau of Standards 
P.O. Box 6329 
Kampala  
Uganda 
Tel: 256 41 505 995 
Fax: 256 41 286 123 
E-mail: unbs@infocom.co.ug  
       US ISO 762:2003  
© UNBS  2009 - All rights reserved National foreword 
Uganda National Bureau of Standards (UNBS) is a parastatal under the Ministry  of Tourism, Trade and 
Industry established under Cap 327, of the Laws of Uganda.  UNBS is mandated to co-ordinate the 
elaboration of standards and is  
(a)
 a member of International Organisation for Standardisation (ISO) and  
(b)
 a contact point for the WHO/FAO Codex A limentarius Commission on Food Standards, and  
(c)
 the National Enquiry Point on TBT/SPS Agr eements of the World Trade Organisation (WTO). 
The work of preparing Uganda Standards is carried out through Technical Committees. A Technical 
Committee is established to deliberate on standards in a gi ven field or area and consists of representatives of 
consumers, traders, academician s, manufacturers, governme nt and other stakeholders. 
Draft Uganda Standards adopted by the Technical Committ ee are widely circulated to stakeholders and the 
general public for comments. The committee reviews the comments before recommending the draft standards 
for approval and declaration as Uganda Standards by the National Standards Council. 
This Uganda Standard, US ISO 762:2003, Fruit and vegetable products — Determination of mineral impurities
content, is identical with and  has been reproduced from an International Standard ISO 762:2003, Fruit and
vegetable products — Determin ation of mineral impurities content, and  adopted as a Uganda Standard.
 
This standard was developed by the Food and agricu lture Standards Technical Committee, UNBS/TC 2. 
Wherever the words, "International Standard" a ppear, they should be replaced by "Uganda Standard."  
 
 
  
 Reference numbe r
ISO 762:2003(E)
© ISO 2003
  
 
 INTERNATIONAL 
STANDARD  ISO
762
Second edition
2003 -11-15
Fruit and vegetable products — 
Determination of mineral impurities content 
Produits dérivés des fruits et légumes — Détermination de la teneur en 
impuretés minérales d'origine terreuse 
 ISO 762:2003(E) 
PDF disclaimer 
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed b ut 
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editin g. In 
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Se cretariat 
accepts no liability in this area. 
Adobe is a trademark of Adobe Systems Incorporated. 
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-cr eation 
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bod ies. In 
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below. 
 
©   ISO 2003 
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by an y means, 
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address be low or 
ISO's member body in the country of the requester. 
ISO copyright office 
Case postale 56 • CH-1211 Geneva 20 
Tel.  + 41 22 749 01 11 
Fax  + 41 22 749 09 47 
E-mail  copyright@iso.org Web  www.iso.org 
Published in Switzerland 
 
ii © ISO 2003 — All rights reserved
  ISO 762:2003(E) 
© ISO 2003 — All rights reserved  iii
 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 762 was prepared by Technical Committee ISO/TC 34, Food products , Subcommittee SC 3, Fruit and 
vegetable products . 
This second edition cancels and replaces the first edition (ISO 762:1982), which has been technically revised. 
 INTERNATIONAL STANDARD ISO 762:2003(E)
 
© ISO 2003 — All rights reserved  1
 Fruit and vegetable products — Determination of mineral 
impurities content 
1 Scope 
This international Standard specifies a method for the determination of the mineral impurities content 
(impurities generally originating from the soil) of fruit and vegetable products. 
2 Principle 
Organic matter is separated by flotation and heavy impurities are separated by sedimentation. The sediment is incinerated at approximately 525 °C, and the residue obtained is weighed. 
3 Apparatus 
Usual laboratory equipment and, in particular, the following. 
3.1 Blender . 
3.2 Beakers , of capacities 1 000 ml. 
3.3 Filter paper , Whatman No. 411) or equivalent. 
3.4 Incineration dishes , made of quartz, porcelain or platinum. 
3.5 Muffle furnace , capable of being maintained at 525 °C ± 25 °C. 
3.6 Desiccator , provided with an efficient desiccant. 
3.7 Analytical balance , capable of weighing to the nearest 0,000 2 g. 
3.8 Heater , gas or electric. 
3.9 Sieve , of pore size ca. 1 mm to 2 mm. 
3.10 Stirring rod . 
3.11 Washing equipment , for washing out the impurities (see Figure 1). 
                                                      
1) Whatman No. 41 is an example of a suitable product available commercially. This information is given for the 
convenience of users of this International Standard and does not constitute an endorsement by ISO of this product. ISO 762:2003(E) 
2 © ISO 2003 — All rights reserved
 4 Preparation of test sample 
4.1 General case 
Before taking the test portion, thoroughly mix the entire laboratory sample using, if necessary, the blender 
(3.1). Allow frozen or deep frozen products to thaw in a closed vessel and add the liquid formed during this process to the product before mixing. 
4.2 Dried products 
Mix the laboratory sample well. Weigh 20 g ± 0,1 g of the product, transfer it to a beaker (3.2) and add 400 ml 
of filtered tap water. Bring to the boil, then leave overnight at room temperature to allow the product to rehydrate. 
5 Procedure 
5.1 Test portion 
5.1.1 General case 
Rapidly weigh 100 g ± 1 g of the test sample (4.1) into a beaker (3.2). If the mass of this sample is less than 
100 g, weigh all of it. 
5.1.2 Dried products 
Use all of the product taken in 4.2 as the test portion. 
5.2 Determination 
5.2.1 Separation of sediments Add filtered tap water to the beaker containing the test portion (4.1 or 4.2) until the beaker is almost 
completely full. Mix by agitating, if necessary using a stirring rod (3.10). 
Allow the suspension to stand for 5 min, then put the beaker under the water tube as shown in Figure 1. 
The important part of the washing equipment (3.11) is the water tank equipped with a leak tube for equalizing 
the pressure. In the tank, the water level shall be constant and 13 cm high; the overflow leaves the tank 
through the leak tube. One or more glass tubes, with 0,4 cm internal diameter, are connected to the bottom of the tank by rubber tubes. Their end parts are extruded. The distance between the bottom of the tank and the top end of the glass tube shall be 55 cm, the extruded part shall be 1 cm long and its internal diameter shall be 0,2 cm. The opening and closing of the stream is controlled by a clamp. Keeping these conditions, the flow rate through one glass tube shall be 200 ml/min. Put a glass tube filled loosely with cotton- or glass-wool 
between the tap and the tank to retain floating impurities. 
Immerse the glass tube in the beaker containing the suspension in such position that the tip of it is 6 cm from 
the bottom of the beaker. Open the stream and continue the washing for 35 min to 40 min. During this time the fine fragments of plant fibre are washed out, while the sand, other mineral impurities and the larger fragments of seeds and skins settle, and the water becomes colourless and transparent in the beaker. ISO 762:2003(E) 
© ISO 2003 — All rights reserved  3
 Dimensions in centimetres 
 
Key 
1 water tank 
2 leak tube 
3 glass tube 
4 end part of glass tube 
5 clamp 
6 cotton- or glass-wool 
7 beaker containing the suspension 
8 water 
Figure 1 — Washing equipment ISO 762:2003(E) 
4 © ISO 2003 — All rights reserved
 5.2.2 Determination 
If, after the washing-out procedure (5.2.1), there are no visible fragments of plant but only the sand on the 
bottom of the beaker, remove the glass tube from the beaker. Wait for 3 min then decant carefully most of the water, avoiding any agitation of the settled fragments. Quantitatively filter the residue through a filter paper (3.3). 
If, after the washing-out procedure (5.2.1), there remains a lot of plant fibres and larger fragments of seeds 
and plant skins on the bottom of the beaker, decant most of the water. Transfer the residue to a sieve (3.9) 
which is placed on a porcelain dish having an appropriate size. Wash the sand into the dish with water. Pour the water in 100 ml portions to separate the sand from the fragments of skin, seed and fibre. About 1 000 ml water are needed for this purpose. 
5.2.3 Preparation of the dish 
Heat the empty incineration dish (3.4) in the muffle furnace (3.5) set at 525 °C. Allow it to cool in the 
desiccator (3.6) and weigh to the nearest 0,000 2 g. Repeat until a constant mass is achieved. 
5.2.4 Incineration 
Transfer the filter paper and residue to the prepared incineration dish (5.2.3). 
Heat the incineration dish for a few minutes using the heater (3.8), then transfer it to the muffle furnace (3.5) 
set at 525 °C. Incinerate it for 1 h. Cool in the desiccator (3.6) and weigh to the nearest 0,000 2 g. Repeat until a constant mass is achieved. 
5.2.5 Number of determinations 
Carry out at least two determinations of the same sample. 
6 Expression of results 
6.1 Calculation 
The mineral impurities content, expressed as a percentage by mass, is given by the formula 
()21
0100% mmm−×  
where 
m0 is the mass, in grams, of the test portion (5.1); 
m1 is the mass, in grams, of the empty dish (5.2.3); 
m2 is the mass, in grams, of the dish and incinerated residue (5.2.4). 
Take as the result the arithmetic mean of the values obtained in two determinations, provided that the 
requirement for repeatability (6.2) is satisfied. 
Report the result to two decimal places. ISO 762:2003(E) 
© ISO 2003 — All rights reserved  5
 6.2 Repeatability 
The absolute difference between two independent single test results, obtained using the same method on 
identical test material in the same laboratory by the same operator using the same equipment within a short 
interval of time, will in not more than 5 % of cases be greater than 3 % of the mean value. 
7 Test report 
The test report shall specify: 
a) all information necessary for the complete identification of the sample; b) the sampling method used, if known; c) the test method used, with reference to this International Standard; 
d) all operating details not specified in this International Standard, or regarded as optional, together with 
details of any incidents which may have influenced the test result(s); 
e) the test result(s) obtained or, if the repeatability has been checked, the final quoted result obtained. 
 ISO 762:2003(E) 
ICS  67.080.01 
Price based on 5 pages 
© ISO 2003 — All rights reserved