SIST ISO 2173:2011

Fruit and vegetable products -- Determination of soluble solids -- Refractometric method

ISO 2173:2003 specifies a refractometric method for the determination of the soluble solids in fruit and vegetable products.
This method is particularly applicable to thick products, to products containing suspended matter, and to products rich in sugar. If the products contain other dissolved substances, the results will be only approximate; nevertheless, for convenience the result obtained by this method can be considered conventionally as the soluble solids content.

Produits dérivés des fruits et légumes -- Détermination du résidu sec soluble -- Méthode réfractométrique

Sadni in zelenjavni proizvodi - Določanje topnih snovi - Refraktometrična metoda

Ta mednarodni standard določa refraktometrično metodo za določanje topnih snovi v sadnih in zelenjavnih proizvodih.
Ta metoda še posebej velja za goste proizvode, za proizvode, ki vsebujejo zadržane snovi, in za proizvode, bogate s sladkorjem. Če proizvodi vsebujejo druge raztopljene snovi, bodo rezultati samo približni; kljub temu se rezultat, pridobljen s to metodo, lahko uporabi in se običajno šteje za vsebnost topnih snovi.
OPOMBA: Za določanje topnih snovi v sadnih sokovih (ki ne vsebujejo zadržanih snovi) in koncentriranih sokovih (čistih) velja piknometrična metoda, določena v ISO 2172.

General Information

• Status: Published
• Public Enquiry End Date: 09-May-2011
• Publication Date: 15-May-2011
• ICS: 67.080.01 - Fruits, vegetables and derived products in general
• Technical Committee: KŽP - Agricultural food products
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 06-May-2011
• Due Date: 11-Jul-2011
• Completion Date: 16-May-2011
• Ref Project: ISO 2173:2003 - Fruit and vegetable products - Determination of soluble solids - Refractometric method

Relations

• Replaces: SIST ISO 2173:1995 - Fruit and vegetable products -- Determination of soluble solids content -- Refractometric method
• Effective Date: 01-Jun-2011

Overview

ISO 2173:2003 specifies a refractometric method for determining the soluble solids content of fruit and vegetable products. The method correlates the refractive index of a prepared test solution to a mass fraction of sucrose (expressed as % by mass) and is especially suitable for thick products, products containing suspended matter, and sugar‑rich items. Results are conventionally reported as soluble solids even when other dissolved substances are present (in which case results are approximate).

Key topics and requirements

• Principle: Measure refractive index at the reference temperature (20 °C ± 0.5 °C) and convert to sucrose concentration using tables or direct-read refractometer scales.
• Apparatus:
  • Refractometer with refractive index scale (readable to 0.001; adjusted to 1.3330 for distilled water at 20 °C).
  • Refractometer with sucrose (mass fraction) scale (readable to 0.10 %; zeroed on distilled water).
  • Temperature control for prism assemblies to ±0.5 °C.
• Sample preparation: Procedures provided for:
  • Clear liquids (use directly)
  • Semi‑thick products (press through gauze)
  • Thick products (dilute, boil 2–3 min, filter)
  • Frozen products (thaw, remove stones, then follow semi‑thick or thick procedure)
  • Dried products (rehydrate with water, heat on water bath ~30 min, filter)
• Corrections and calculations:
  • Temperature corrections (formula or table adjustments) when measurements are not at 20 °C.
  • Salt correction for added NaCl (linear correction factor).
  • Acid correction for highly acidic citrus products (additive table based on total acidity).
  • Formulas for converting diluted or sugar‑diluted samples back to original soluble solids (%).
• Quality & reporting:
  • Repeatability: two single test results on identical material should differ by ≤ 0.5 g soluble solids per 100 g in most cases.
  • Test report must identify sample, sampling method, method reference (ISO 2173), operating details and results.

Applications and users

ISO 2173:2003 is used for routine laboratory and production quality control where soluble solids (sugar content proxy) are critical:

• Fruit and vegetable processing plants (jams, jellies, purees)
• Juice and concentrate producers (when samples contain suspended matter)
• Food control laboratories and regulatory agencies
• R&D and product development teams monitoring sweetness and consistency

Keywords: ISO 2173:2003, soluble solids determination, refractometric method, refractometer, refractive index, mass fraction of sucrose, fruit and vegetable products, quality control, temperature correction.

Related standards

• ISO 2172 - Soluble solids by pycnometric method (clarified juices)
• ISO 750 - Titratable acidity (used for acid corrections)
• EN 12143 and AOAC methods referenced for comparable refractometric procedures and practices.

Standards Content (Sample)

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Produits dérivés des fruits et légumes -- Détermination du résidu sec soluble -- Méthode réfractométriqueFruit and vegetable products -- Determination of soluble solids -- Refractometric method67.080.01Sadje, zelenjava in njuni proizvodi na splošnoFruits, vegetables and derived products in generalICS:Ta slovenski standard je istoveten z:ISO 2173:2003SIST ISO 2173:2011en01-junij-2011SIST ISO 2173:2011SLOVENSKI
STANDARDSIST ISO 2173:19951DGRPHãþD

Reference numberISO 2173:2003(E)© ISO 2003
INTERNATIONAL STANDARD ISO2173Second edition2003-12-01Fruit and vegetable products — Determination of soluble solids — Refractometric method Produits dérivés des fruits et légumes — Détermination du résidu sec soluble — Méthode réfractométrique
©
ISO 2003 All rights reserved. Unless otherwise specified, 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 either ISO at the address below 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
[e-mail] Web
www.iso.org Published in Switzerland
ii © ISO 2003 — All rights reserved
INTERNATIONAL STANDARD ISO 2173:2003(E) © ISO 2003 — All rights reserved 1 Fruit and vegetable products — Determination of soluble solids — Refractometric method 1 Scope This International Standard specifies a refractometric method for the determination of the soluble solids in fruit and vegetable products. This method is particularly applicable to thick products, to products containing suspended matter, and to products rich in sugar. If the products contain other dissolved substances, the results will be only approximate; nevertheless, for convenience the result obtained by this method can be considered conventionally as the soluble solids content. NOTE For the determination of the soluble solids in fruit juices (not containing suspended matter) and in concentrated juices (clarified), the pyknometric method specified in ISO 2172 is applicable. 2 Terms and definitions For the purposes of this document, the following terms and definitions apply. 2.1 soluble solids determined by the refractometric method concentration of sucrose in an aqueous solution which has the same refractive index as the product analysed, under specified conditions of preparation and temperature NOTE This concentration is expressed as a mass fraction in percent. 3 Principle The refractive index of a test solution is measured at 20 °C ± 0,5 °C using a refractometer. The refractive index is correlated with the amount of soluble solids (expressed as sucrose concentration) using tables, or by direct reading on the refractometer of the mass fraction of soluble solids. 4 Reagents Use only reagents of recognized analytical grade. 4.1 Water The water used shall have been distilled twice in borosilicate glass apparatus, or shall be water of at least equivalent purity. 5 Apparatus Usual laboratory apparatus and, in particular, the following. SIST ISO 2173:2011
...

INTERNATIONAL ISO
STANDARD 2173
Second edition
2003-12-01
Fruit and vegetable products —
Determination of soluble solids —
Refractometric method
Produits dérivés des fruits et légumes — Détermination du résidu sec
soluble — Méthode réfractométrique

Reference number
©
ISO 2003
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©  ISO 2003
All rights reserved. Unless otherwise specified, 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 either ISO at the address below 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 [e-mail]
Web www.iso.org
Published in Switzerland
ii © ISO 2003 — All rights reserved

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 2173 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 2173:1978), which has been technically revised.

INTERNATIONAL STANDARD ISO 2173:2003(E)

Fruit and vegetable products — Determination of soluble
solids — Refractometric method
1 Scope
This International Standard specifies a refractometric method for the determination of the soluble solids in fruit
and vegetable products.
This method is particularly applicable to thick products, to products containing suspended matter, and to
products rich in sugar. If the products contain other dissolved substances, the results will be only approximate;
nevertheless, for convenience the result obtained by this method can be considered conventionally as the
soluble solids content.
NOTE For the determination of the soluble solids in fruit juices (not containing suspended matter) and in
concentrated juices (clarified), the pyknometric method specified in ISO 2172 is applicable.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
soluble solids determined by the refractometric method
concentration of sucrose in an aqueous solution which has the same refractive index as the product analysed,
under specified conditions of preparation and temperature
NOTE This concentration is expressed as a mass fraction in percent.
3 Principle
The refractive index of a test solution is measured at 20 °C ± 0,5 °C using a refractometer. The refractive
index is correlated with the amount of soluble solids (expressed as sucrose concentration) using tables, or by
direct reading on the refractometer of the mass fraction of soluble solids.
4 Reagents
Use only reagents of recognized analytical grade.
4.1 Water
The water used shall have been distilled twice in borosilicate glass apparatus, or shall be water of at least
equivalent purity.
5 Apparatus
Usual laboratory apparatus and, in particular, the following.
5.1 Refractometer
Use one of the following.
5.1.1 Refractometer indicating the refractive index, by means of a scale graduated in 0,001, in order to
allow readings to be estimated to 0,000 2.
This refractometer shall be adjusted so that at 20 °C ± 0,5 °C it registers a refractive index of 1,333 0 for
distilled water.
5.1.2 Refractometer indicating the mass fraction of sucrose, by means of scale graduated in 0,10 %.
This refractometer shall be adjusted so that at 20 °C ± 0,5 °C it registers a mass fraction of soluble solids
(sucrose) of zero for distilled water.
5.2 Means for circulating water, to maintain the temperature of the prisms of the refractometer (5.1.1 or
5.1.2) constant to within ± 0,5 °C, in the neighbourhood of 20 °C, which is the reference temperature (see 8.1).
5.3 Beaker, of capacity 250 ml.
6 Sampling
It is important that the laboratory receive a sample which is truly representative and has not been damaged or
changed during transport or storage.
7 Procedure
7.1 Preparation of test solution
7.1.1 Clear liquid products
Thoroughly mix the laboratory sample and use it directly for the determination.
7.1.2 Semi-thick products (purees, etc.)
Thoroughly mix the laboratory sample. Press a part of the sample through a gauze folded in four, rejecting the
first drops of the liquid and reserving the remainder of the liquid for the determination.
7.1.3 Thick products (jams, jellies, etc.)
Weigh into the tared beaker (5.3), to the nearest 0,01 g, a suitable quantity (up to 40 g) of the laboratory
sample and add 100 ml to 150 ml of water. Heat the contents of the beaker to boiling and allow to boil gently
for 2 min to 3 min, stirring with a glass rod. Cool the contents and mix thoroughly.
After 20 min, weigh to the nearest 0,01 g, then filter through a fluted filter or a Büchner funnel into a dry vessel.
Reserve the filtrate for the determination.
7.1.4 Frozen products
After thawing the sample and removing, if necessary, stones, pips and hard seed-cavity walls, mix the product
with the liquid formed during the thawing process and proceed as described in 7.1.2 or 7.1.3 as appropriate.
2 © ISO 2003 — All rights reserved

7.1.5 Dried products
Cut a part of the laboratory sample into small pieces. Remove, if necessary, stones, pips and hard seed-cavity
walls, and mix carefully. Then weigh into a tared beaker, to the nearest 0,01 g, 10 g to 20 g of the sample.
Add 5 to 10 times this mass of water and place on a boiling water bath for 30 min, stirring from time to time
with a glass rod. If necessary, prolong the heating time until a homogeneous mixture is obtained. Cool the
contents of the beaker and mix well.
After 20 min, weigh to the nearest 0,01 g, then filter into a dry vessel. Reserve the filtrate for the determination.
If the test solution is too dark to be read in the refractometer, dilute the test solution with concentrated sugar
solution; never use water for this purpose. Mix weighed amounts of the solution under examination and a

solution of pure sugar of about the same strength (see reference [1]).
7.2 Determination
Adjust the water circulation (5.2) in order to operate at the required temperature (between 15 °C and 25 °C)
and allow it to flow to bring the prisms of the refractometer (5.1.1 or 5.1.2) to the same temperature, which
shall remain constant to within ± 0,5 °C during the determination.
Bring the test solution (7.1) to the measuring temperature. Put a small quantity of test solution (2 or 3 drops
are sufficient) onto the fixed prism of the refractometer (5.1.1 or 5.1.2) and immediately adjust the movable
prism. Suitably illuminate the field of view. The use of a sodium vapour
...