UGANDA STANDARD 
         US ISO 751
First Edition
2009-mm-dd
 
 Reference numbe r
    US ISO 751:1998
© UNBS 2009
  
Fruit and vegetable products — Determination of water-
insoluble solids  
 US ISO 751:1998 
 
© 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 751:1998  
© 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 751:1998, Fruit and vegetable products — Determination of water-insoluble
solids, is identical with and  has been reproduced from an International Standard ISO 751:1998, Fruit and 
vegetable products — Determination of water-insoluble solids, 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." A Reference numbe r
ISO 751:1998 (E)INTERNATIONAL
STANDARDISO
751
Second edition
1998-08-01
Fruit and vegetable products —
Determination of water-insoluble solids
Produits dérivés des fruits et légumes — Détermination du résidu sec
insoluble dans l’eauISO 751:1998(E)
©   ISO 1998
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 the publisher.
International Organization for Standardization
Case postale 56 • CH-1211 Genève 20 • Switzerland
Internet iso@iso.ch
Printed in Switzerland
iiForeword
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 technicalcommittees. Each member body interested in a subject for which a technical committee has been established hasthe right to be represented on that committee. International organizations, governmental and non-governmental, inliaison with ISO, also take part in the work. ISO collaborates closely with the International ElectrotechnicalCommission (IEC) on all matters of electrotechnical standardization.
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.
International Standard ISO 751 was prepared by Technical Committee ISO/TC 34
, Agricultural food  products,
Subcommittee SC 3, Fruit and vegetable products .
This second edition cancels and replaces the first edition (ISO 751:1981), which has been technically revised.INTERNATIONAL STANDARD    © ISO ISO 751:1998(E)
1Fruit and vegetable products — Determination of water-insoluble
solids
1 Scope
This International Standard specifies a method for the determination of the content of water-insoluble solids in the
edible parts of fruit and vegetable products.
2 Principle
The water-soluble matter in a test portion is dissolved in water, followed by filtration, drying of the residue andweighing.
3 Apparatus
Usual laboratory apparatus and, in particular, the following.
3.1   Beakers, of capacity 250 ml or 400 ml.
3.2   Buchner funnel .
3.3   Filter paper , medium texture.
3.4   Indicator paper .
3.5   Weighing vessel .
3.6   Desiccator , containing an efficient desiccant.
3.7   Oven, capable of being maintained at 103 °C ± 2 °C.
3.8   Centrifuge .
3.9   Analytical balance, capable of weighing to the nearest 0,001 g.
4 Sampling
It is important the laboratory receive a sample which is truly representative and has not been damaged or changed
during transport or storage.
Sampling is not part of the method specified in this International Standard. As there is no specific International
Standard dealing with fruit and vegetable products, it is recommended that the parties concerned come to anagreement on the subject.ISO 751:1998(E) © ISO
25 Preparation of test sample and of apparatus
5.1 Preparation of test sample
Separate and remove from the laboratory sample stalks, stones, hard seed-cavity walls and, whenever possible,
pips (after thawing in the case of frozen or deep-frozen products). Mix the sample thoroughly.
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.
If it is desired to express the result in terms of the sample as received, weigh the latter before removing stalks,
stones, etc. Weigh these after washing and drying and take them into account in the expression of results (see 8.2).
5.2 Preparation of apparatus
Place a filter paper (3.3) in the weighing vessel (3.5) and dry in the oven (3.7) set at 103 °C for 30 min. Cool in the
desiccator (3.6) and weigh to the nearest 0,001 g.
6 Procedure
NOTE   If it is required to check whether the repeatability requirement (clause 9) is met, carry out two single determinations in
accordance with 6.1 to 6.2.
6.1 Test portion
Weigh, to the nearest 0,01 g, into a 250 ml beaker (3.1) (400 ml in the case of sweetened products) 10 g to 100 g of
the test sample (5.1), according to the consistency of the product and the expected content of water-insolublesolids; for example:
 tomato concentrates 10 g
 jam, fruit preserves 25 g
 pulpy products 50 g
 fruit and vegetable juices 100 g
NOTE   For liquid products, it is also possible to take the test portion by volume.
6.2 Determination
Add 100 ml to 150 ml of distilled water or water of equivalent purity to the beaker containing the test portion (6.1).
Stir with a glass rod until a homogeneous mixture is obtained. Heat to boiling (in the case of sweetened products,see 7.3).
Pour the contents of the beaker quantitatively onto the dried filter paper (see 5.2) placed in the Buchner funnel (3.2)
and filter (see 7.4). Wash the filter paper with a little hot water.
Transfer the filter paper and its contents quantitatively to the weighing vessel (see 5.2) and dry in the oven (3.7), set
at 103
°C, to constant mass; i.e. until the difference between two consecutive weighings, after 30 min in the oven
followed by cooling in the desiccator for about 20 min, does not exceed 0,001 g. Carry out the weighings to thenearest 0,001 g.© ISO ISO 751:1998(E)
37 Special cases
7.1 Grape juice
If crystals of potassium hydrogen tartrate are found to be present in grape juice, the quantity should be determined.
For this purpose, using another test portion, collect the crystals on a filter, wash them with the same juice and then
with 50 % ( V/V) ethanol solution saturated with potassium hydrogen tartrate.
Dry and weigh the crystals. The mass of the crystals of potassium hydrogen tartrate shall be recorded in the test
report.
7.2 Citrus products
A similar procedure should be followed when crystals of hesperiden or naringin are present in citrus products.
7.3 Sweetened products
For the analysis of sweetened products, add about 250 ml of water. Bring to the boil and boil gently for 5 min to10 min.
7.4 Products difficult to filter
If it proves difficult to filter the product (products with high contents of pectin or protein), or in the case of productshaving high sugar contents (fruit preserves, jam, etc.), separate the solid matter by means of a centrifuge (3.8).Decant the clear liquid, recover the residue (deposit) with hot water and again centrifuge. Repeat these operationsseveral times, until the washings are free from sugars, salts, acids, etc., then collect the residue obtained bycentrifuging on the filter, as described in 6.2.
8 Expression of results
8.1   The content of water-insoluble solids in the edible parts of fruit and vegetable products, expressed as a
percentage by mass, is equal to
(m2 − m1) 3 100
0m
where
m0is the mass, in grams, of the test portion (6.1);
m1is the mass, in grams, of the weighing vessel and dried filter paper (5.2);
m2is the mass, in grams, of the weighing vessel, filter paper and residue after drying (6.2).
8.2   It is also possible to express the result in relation to the sample as received (see 5.1) or, for liquid products, in
grams per 100 ml for a test portion taken by volume.
9 Repeatability
The absolute difference between two independent single test results, obtained using the same method on identicaltest 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 0,1 g of water-insoluble solids per 100 g of sample.ISO 751:1998(E) © ISO
410 Test report
The test report shall specify:
 all information necessary for the complete identification of the sample;
 the sampling method used, if known;
 the test method used, together with reference to this International Standard;
 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);
 the test result(s) obtained;
 if the repeatability has been checked, the final quoted result obtained.ISO 751:1998(E) © ISO
ICS  67.080.01
Descriptors:  agricultural products,  food products,  plant products,  fruit and vegetable products,  tests,  determination of content,  inso luble
matter,  solids.
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