ISO INTERNATIONAL STANDARD 5518 Second edition 2007-02-01 Fruits, vegetables and derived products Determination of benzoic acid content s Spectrophotometric method Fruits, legumes et produits derives-Determination de la teneur en acidebenzoique-Méthodespectrophotométrique Reference number ISO 5518:2007(E) ISO := Foreword Electrotechnical Commission (IEC)onall matters of electrotechnical standardization. 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. ISO5518was prepared byTechnical Committee ISO/TC34,Food products, Subcommittee SC 3,Fruit and vegetableproducts. This second edition cancels and replaces the first edition (isO 5518:1978), which has been technically revised ii 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 antiseptics have been used. Moreover, purification increases the sensitivity of the method. This improved technique was also more rapid. iv Fruits, vegetables and derived products Determination of benzoicacidcontentSpectrophotometricmethod 1 Scope 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 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 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)2COOH], crystalline. 3.2 Sodium hydroxide (NaOH), approximately 1 mol/l solution. 3.3 Potassium dichromate (K2Cr2O7), solution containing 33 g/l to 34 g/l. 3.4 Dilute sulfuric acid (H2sO4), obtained by diluting 2 volumes of concentrated sulfuric acid (P2o = 1,84 g/ml) with 1 volume of water. 3.5 Diethyl ether [(CHgCH2)2O], recently distilled. 3.6 Benzoic acid (CHsCOOH), standard solution in diethyl ether containing 0,100 g/l 3.7 Sodium hydrogen carbonate (NaHCO3),crystalline 4 Apparatus Usual laboratory apparatus and, in particular, the following 4.1 Volumetric flasks, of capacities 50 ml and 1 000 ml. 4.2Beakers, of capacities 50 ml and 100 ml. 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. 4.7Water bath, capable of being controlled at a temperature of 70 °C to 80 °C. 4.8 Homogenizerormortar,as appropriate. 4.9 Spectrophotometerfor determination in the ultraviolet range, equipped with a monochromator allowing 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 dam