EN 1133-1994 pdf download.Fruit and vegetable juices – Determination of the formol number.
This EN 1133 specifies a method for the determination of the formol number of fruit and vegetable juices and related products.
2 Normative references
This European Standard incorporates by dated or undated reference, provisions from other publications. These normative references are cited at the appropriate places in the text and the publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the publication referred to applies. ISO 5725:1986, Precision of test methods — Determination of repeatability and reproducibility for a standard test nwthod by inter-laboratory tests. ISO 3696:1987, Water for analytical laboratory use — Specification and test methods.
3 Definitions and symbols For the purposes of this standard, the following definition applies:
formol number
the number of inillimoles of sodium hydroxide consumed per litre of test sample according to the method described below. For conformity with existing methods (see Annex A), the formol number is reported as the number of inilh metres of sodium hydroxide solution. c (NaOH) = 0,1 molfl required per 100 ml of test sample
for the purposes of this standard, the following symbols apply:
c Substance concentration;
p Mass concentration.
4 Principle
Upon addition of formaldehyde solution to the test sample, one H i-ion is liberated per molecule of amino acid present. This ion is then treated potentiometrically with sodium hydroxide solution. The formol number is thus a measure of the amino acid content of the test sample, with the following provisions: the secondary amino group of histidine does not react; those of proline and hydroxyproline react to about 75 %. Tertiary nitrogen and guanidine groups undergo no reaction.
5 Reagents
5.1 General
Use only reagents of recognized analytical grade
and only water in accordance with at least grade 3
of ISO 3696:1987.
5.2 Sodiu in hydroxide so lii lion,
c (NaOH) = 0,25 mol/l.
5.3 Formaldehyde solution, pH 8,1.
Formaldehyde solution, w (CH2O) = at least 350 gIl,
adjusted precisely to pH 8,1 on the pH meter
with 0,25 moIII sodium hydroxide (5.2.). This
solution shall be prepared freshly on the day of use.
5.4 Hydrogen peroxide, w(H202) = 300 gIl.
6 Apparatus
Usual laboratory equipment and, in particular, the following:
6.1 pH meter. accurate to at least 0,05 pH units.
6.2 pH glass elect rode
6.3 Reference electrode, for example calomel
electrode.
6.4 Gombinat ion pH glass electrode (alternative to 6.2 arid 6.3). The pH meter and electrode(s) shall he calibrated and serviced according to the manufacturer’s instructions.
7 Procedure
7.1 Preparation of the test sample
Normally products shall not be pretreated and their analysis by this method shall be on a volumetric basis, results being expressed per 100 millilitres of sample. The analysis of concentrated products may also he carried out on a volumetric basis, after dilution to a known relative density. In this case, the relative density shall be indicated. Based on a weighed sample and taking the dilution factor for analysis into account, the results may also be expressed ier 100 grams of product. In products with high viscosity andlor very high content of cells (for example pulp), determination on the basis of a weighed test sample is the usual procedure.
In the case of lemon juice or other high acidic juices, take 5 ml of juice and 20 ml water and continue as below. If the sample contains sulfur dioxide, it shall be treated with a few drops of hydrogen peroxide solution (5.4) before titration.
7.2 Determination
While stirring, adjust 25 ml of test sample in a beaker to pH = 8,1 using solution (5.2) and the pH meter. Add 10 En1 solution (5.3) and continue stirring. Leave to stand for 1 minute, then titrate the solution to pH = 8,1 using solution (5.2). while continuing stirring. Note the number of ml (n) of solution (5.2) required for the tiration. If the number of ml required exceeds 20 ml, repeat the titration using 15 ml solution (5.3) in place of 10 ml. Use only sodium hydroxide solution c (NaOH) = 0,25 molll (5.2) for the determination, irresj)ective of the formol number of the test sample.
8 Calculation
Calculate the formol number as foflows:
Formnol number = 10 X
Any additional dilution and the relation of the value to mass or volume (see 7.1) shall be taken into account if applicable. If a concentrated product, has been diluted to single strength, report the relative density of the single strength sample. The formol number can be calculated per 100 g of test sample, taking into account the relative density.
Report the forinol number in millimetres of sodium hydroxide solution c (NaOH) = 0,1 molll per 100 ml of test sample, to one decimal place.
9 Precision
Details of the interlaboratory test on the precision of the method are summarized in Annex B. EN 1133-1994 pdf download.