ISO 5518:2007

Fruits, vegetables and derived products - Determination of benzoic acid content - Spectrophotometric method

ISO 5518:2007 specifies a method for determining the benzoic acid content of fruits, vegetables and derived products. As chlorobenzoic acids are resistant to oxidation, the method cannot be applied in the presence of p-chlorobenzoic acid, as the absorption spectrum of this acid is close to that of benzoic acid. Neither can it be used in the presence of cinnamic acid, which is transformed into benzoic acid by chromic acid oxidation.

Fruits, légumes et produits dérivés — Détermination de la teneur en acide benzoïque — Méthode spectrophotométrique

Sadje, zelenjava in sadni ter zelenjavni proizvodi - Določevanje benzojske kisline - Spektrofotometrična metoda

Ta mednarodni standard opredeljuje metodo za določevanje benzojske kisline v sadju, zelenjavi in sadnih ter zelenjavnih proizvodih.
Ker so klorobenzojske kisline odporne proti oksidaciji, se metoda ne more uporabljati v prisotnosti p-klorobenzojske kisline, ker je absorpcijski spekter te kisline blizu absorpcijskega spektra benzojske kisline. Ne more se uporabljati niti v prisotnosti cimetove kisline, ki se pretvori v benzojsko kislino z oksidacijo s kromovo kislino.
OPOMBA: Cimetova kislina, ki se v tej metodi določi kot benzojska kislina, v splošnem v zelenjavi obstaja le v sledovih in torej nima učinka na dobljene rezultate, razen pri cimetovem lubju, ki vsebuje večje količine.

General Information

• Status: Published
• Publication Date: 17-Jan-2007
• ICS: 67.080.01 - Fruits, vegetables and derived products in general
• Technical Committee: ISO/TC 34/SC 3 - Fruits and vegetables and their derived products
• Drafting Committee: ISO/TC 34/SC 3 - Fruits and vegetables and their derived products
• Current Stage: 9093 - International Standard confirmed
• Start Date: 26-Aug-2024
• Completion Date: 13-Dec-2025
• Ref Project: SIST ISO 5518:2011 - Fruits, vegetables and derived products -- Determination of benzoic acid content -- Spectrophotometric method

Relations

• Revised: SIST ISO 5518:1995 - Fruits, vegetables and derived products -- Determination of benzoic acid content -- Spectrophotometric method
• Effective Date: 12-May-2008
• Revises: ISO 5518:1978 - Fruits, vegetables and derived products - Determination of benzoic acid content - Spectrophotometric method
• Effective Date: 15-Apr-2008

Overview

ISO 5518:2007 specifies a precise spectrophotometric method for determining the benzoic acid content in fruits, vegetables, and derived products. Benzoic acid is commonly used as a preservative, making its quantification crucial for food safety, quality control, and regulatory compliance. This international standard provides laboratories with a reliable procedure to extract, purify, and measure benzoic acid concentration accurately. However, the method excludes samples containing p-chlorobenzoic acid or cinnamic acid due to their interference with the determination process.

Key Topics

• Scope and Limitations:
  • Applicable to fruits, vegetables, juices, jams, and other derived food products.
  • Not suitable if p-chlorobenzoic acid or cinnamic acid is present because of overlapping absorption spectra and chemical transformations during oxidation.
• Method Principle:
  • The sample is homogenized, acidified, and benzoic acid is extracted using diethyl ether.
  • Alkaline re-extraction and purification by oxidation with acidified potassium dichromate remove interfering substances.
  • Purified benzoic acid is then quantified by UV spectrophotometry, measuring absorbance at key wavelengths (267.5 nm, 272 nm, 276.5 nm).
• Sample Preparation:
  • Liquid, pulpy, thick, and solid products have tailored preparation steps, ensuring representative sampling and accurate analysis.
  • Neutralization with sodium hydrogen carbonate prevents benzoic acid loss by volatilization during processing.
• Reagents and Equipment:
  • Use analytical grade reagents such as tartaric acid, sodium hydroxide, potassium dichromate, and diethyl ether.
  • Essential apparatus includes volumetric flasks, separating funnels, spectrophotometer (UV range), water bath, and analytical balance.
• Calibration and Calculation:
  • Establishes a calibration curve using standard benzoic acid solutions to correlate absorbance with concentration.
  • Results expressed in milligrams per liter (mg/L) or milligrams per kilogram (mg/kg) depending on sampling method.
• Performance and Repeatability:
  • Method offers repeatability with absolute differences not exceeding 10 mg/L or mg/kg in 95% of cases, ensuring reliable routine use.

Applications

• Food Quality Control:
  • Accurate detection of benzoic acid levels in fresh and processed fruits and vegetables to ensure compliance with food safety limits.
• Regulatory Compliance:
  • Enables producers and regulatory agencies to verify preservative concentrations per national and international food legislation.
• Research and Development:
  • Supports studies on preservative efficacy, food shelf life, and formulation improvements in fruit and vegetable products.
• Food Industry Laboratories:
  • Ideal for routine testing of juices, jams, sauces, and frozen products for benzoic acid content to maintain product integrity and consumer safety.

Related Standards

• ISO 2951 - Fruit and vegetable products - Determination of sorbic acid content - Spectrophotometric method
• ISO 6636 - Fruit and vegetable products - Determination of sulphur dioxide content
• ISO 7507 - Fruit and vegetable products - Determination of ascorbic acid content
• Codex Alimentarius - General standards for food additives, including maximum levels for benzoic acid in foods

By following ISO 5518:2007, laboratories ensure the accurate and consistent quantification of benzoic acid, supporting food safety, quality assurance, and regulatory adherence in the international food supply chain.

Standards Content (Sample)

SLOVENSKI STANDARD
01-junij-2011
1DGRPHãþD
SIST ISO 5518:1995
6DGMH]HOHQMDYDLQVDGQLWHU]HOHQMDYQLSURL]YRGL'RORþHYDQMHEHQ]RMVNHNLVOLQH
6SHNWURIRWRPHWULþQDPHWRGD
Fruits, vegetables and derived products -- Determination of benzoic acid content --
Spectrophotometric method
Fruits, légumes et produits dérivés -- Détermination de la teneur en acide benzoïque --
Méthode spectrophotométrique
Ta slovenski standard je istoveten z: ISO 5518:2007
ICS:
67.080.01 Sadje, zelenjava in njuni Fruits, vegetables and
proizvodi na splošno derived products in general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

INTERNATIONAL ISO
STANDARD 5518
Second edition
2007-02-01
Fruits, vegetables and derived
products — Determination of benzoic acid
content — Spectrophotometric method
Fruits, légumes et produits dérivés — Détermination de la teneur en
acide benzoïque — Méthode spectrophotométrique

Reference number
©
ISO 2007
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but shall
not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
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-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the
unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.
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 2007 – 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 5518 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 5518:1978), which has been technically revised.
©
ISO 2007 – All rights reserved iii

Introduction
A method for determining the benzoic acid content of fruits, vegetable and derivatives, described in 1959, was
based on the technique of peak emergence. The advantage of this method was that it was specifically intended
for benzoic acid, with one exception: p-chlorobenzoic acid.
However, it was necessary to make a modification, consisting of purifying the ethereal extract by chromic acid
oxidation. This results in the elimination of the effects of colouring substances in certain vegetable products
containing anthocyanins, and also all the oxybenzoic acids and sorbic acid which may be present if several
antiseptics have been used. Moreover, purification increases the sensitivity of the method. This improved
technique was also more rapid.
©
iv ISO 2007 – All rights reserved

INTERNATIONAL STANDARD ISO 5518:2007(E)
Fruits, vegetables and derived products — Determination of
benzoic acid content — Spectrophotometric method
1Scope
This International Standard specifies a method for determining the benzoic acid content of fruits, vegetables
and derived products.
As chlorobenzoic acids are resistant to oxidation, the method cannot be applied in the presence of
p-chlorobenzoic acid, as the absorption spectrum of this acid is close to that of benzoic acid. Neither can it be
used in the presence of cinnamic acid, which is transformed into benzoic acid by chromic acid oxidation.
NOTE The cinnamic acid determined as benzoic acid in this method exists generally only in the form of traces in
vegetables, and therefore has no effect on the result obtained, except in the case of cinnamon bark, which contains higher
quantities.
2 Principle
The test sample is homogenized, followed by dilution and acidification of a test portion. The benzoic acid is
extracted by diethyl ether, then this acid undergoes alkaline re-extraction and purification by oxidation using
acidified potassium dichromate. The purified benzoic acid dissolved in diethyl ether is determined by
spectrophotometry.
3Reagents
Use only reagents of recognized analytical quality and distilled water or water of at least equivalent purity.
3.1 Tartaric acid [COOH(CHOH) COOH], crystalline.
3.2 Sodium hydroxide (NaOH), approximately 1 mol/l solution.
3.3 Potassium dichromate (K Cr O ), solution containing to .
33 g/l 34 g/l
2 2 7
3.4 Dilute sulfuric acid (H SO ), obtained by diluting 2volumes of concentrated sulfuric acid
2 4
(ρ = 1,84 g/ml) with 1 volume of water.
3.5 Diethyl ether [(CH CH ) O], recently distilled.
3 2 2
3.6 Benzoic acid (C H COOH), standard solution in diethyl ether containing 0,100 g/l.
6 5
3.7 Sodium hydrogen carbonate (NaHCO ), crystalline.
4 Apparatus
Usual laboratory apparatus and, in particular, the following.
4.1 Volumetric flasks, of capacities 50 ml and 1 000 ml.
4.2 Beakers, of capacities 50 ml and 100 ml.
©
ISO 2007 – All rights reserved 1

4.3 Graduated pipettes, of capacities 10 ml, 20 ml and 50 ml.
4.4 Flasks, of capacity 250 ml, having ground-glass stoppers and made of borosilicate glass.
4.5 Separating funnels, of capacities 100 ml and 500 ml.
4.6 Evaporating dish, of diameter about 10 cm.
◦ ◦
4.7 Water bath, capable of being controlled at a temperature of 70 C to 80 C.
4.8 Homogenizer or mortar, as appropriate.
4.9 Spectrophotometer for determination in the ultraviolet range, equipped with a monochromator allowing
measurement to the nearest 0,5 nm, with silica cells of optical path length 10 mm or 20 mm (preferably 20 mm
so as to increase sensitivity), equipped with ground glass covers.
4.10 Analytical balance.
5 Sampling
A representative sample should have been sent to the laboratory. It should not have been damaged or changed
during transport or storage.
6 Procedure
6.1 Preparation of test sample
6.1
...

INTERNATIONAL ISO
STANDARD 5518
Second edition
2007-02-01
Fruits, vegetables and derived
products — Determination of benzoic acid
content — Spectrophotometric method
Fruits, légumes et produits dérivés — Détermination de la teneur en
acide benzoïque — Méthode spectrophotométrique

Reference number
©
ISO 2007
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but shall
not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
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-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the
unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.
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 2007 – 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 5518 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 5518:1978), which has been technically revised.
©
ISO 2007 – All rights reserved iii

Introduction
A method for determining the benzoic acid content of fruits, vegetable and derivatives, described in 1959, was
based on the technique of peak emergence. The advantage of this method was that it was specifically intended
for benzoic acid, with one exception: p-chlorobenzoic acid.
However, it was necessary to make a modification, consisting of purifying the ethereal extract by chromic acid
oxidation. This results in the elimination of the effects of colouring substances in certain vegetable products
containing anthocyanins, and also all the oxybenzoic acids and sorbic acid which may be present if several
antiseptics have been used. Moreover, purification increases the sensitivity of the method. This improved
technique was also more rapid.
©
iv ISO 2007 – All rights reserved

INTERNATIONAL STANDARD ISO 5518:2007(E)
Fruits, vegetables and derived products — Determination of
benzoic acid content — Spectrophotometric method
1Scope
This International Standard specifies a method for determining the benzoic acid content of fruits, vegetables
and derived products.
As chlorobenzoic acids are resistant to oxidation, the method cannot be applied in the presence of
p-chlorobenzoic acid, as the absorption spectrum of this acid is close to that of benzoic acid. Neither can it be
used in the presence of cinnamic acid, which is transformed into benzoic acid by chromic acid oxidation.
NOTE The cinnamic acid determined as benzoic acid in this method exists generally only in the form of traces in
vegetables, and therefore has no effect on the result obtained, except in the case of cinnamon bark, which contains higher
quantities.
2 Principle
The test sample is homogenized, followed by dilution and acidification of a test portion. The benzoic acid is
extracted by diethyl ether, then this acid undergoes alkaline re-extraction and purification by oxidation using
acidified potassium dichromate. The purified benzoic acid dissolved in diethyl ether is determined by
spectrophotometry.
3Reagents
Use only reagents of recognized analytical quality and distilled water or water of at least equivalent purity.
3.1 Tartaric acid [COOH(CHOH) COOH], crystalline.
3.2 Sodium hydroxide (NaOH), approximately 1 mol/l solution.
3.3 Potassium dichromate (K Cr O ), solution containing to .
33 g/l 34 g/l
2 2 7
3.4 Dilute sulfuric acid (H SO ), obtained by diluting 2volumes of concentrated sulfuric acid
2 4
(ρ = 1,84 g/ml) with 1 volume of water.
3.5 Diethyl ether [(CH CH ) O], recently distilled.
3 2 2
3.6 Benzoic acid (C H COOH), standard solution in diethyl ether containing 0,100 g/l.
6 5
3.7 Sodium hydrogen carbonate (NaHCO ), crystalline.
4 Apparatus
Usual laboratory apparatus and, in particular, the following.
4.1 Volumetric flasks, of capacities 50 ml and 1 000 ml.
4.2 Beakers, of capacities 50 ml and 100 ml.
©
ISO 2007 – All rights reserved 1

4.3 Graduated pipettes, of capacities 10 ml, 20 ml and 50 ml.
4.4 Flasks, of capacity 250 ml, having ground-glass stoppers and made of borosilicate glass.
4.5 Separating funnels, of capacities 100 ml and 500 ml.
4.6 Evaporating dish, of diameter about 10 cm.
◦ ◦
4.7 Water bath, capable of being controlled at a temperature of 70 C to 80 C.
4.8 Homogenizer or mortar, as appropriate.
4.9 Spectrophotometer for determination in the ultraviolet range, equipped with a monochromator allowing
measurement to the nearest 0,5 nm, with silica cells of optical path length 10 mm or 20 mm (preferably 20 mm
so as to increase sensitivity), equipped with ground glass covers.
4.10 Analytical balance.
5 Sampling
A representative sample should have been sent to the laboratory. It should not have been damaged or changed
during transport or storage.
6 Procedure
6.1 Preparation of test sample
6.1.1 Liquid products (e.g. juices, pulpy fluid products, syrups)
Thoroughly mix the laboratory sample.
6.1.2 Thick products (e.g. marmalades, jams)
Homogenize the laboratory sample after having carefully mixed it.
6.1.3 Solid products (e.g. fruits, vegetables)
Cut a part of the laboratory sample into small pieces and remove seeds, stalks and carpellary cells, if
necessary. Carefully homogenize approximately 40 g of the sample.
6.1.4 Frozen or deep-frozen products
After thawing the sample in a closed container and removing, if n
...