ISO 16624:2020 pdf download Wheat flour and durum wheat semolina — Determination of colour by diffuse reflectance colorimetry
1 Scope
This document specifies a method for the determination of colour in durum wheat semolina and wheatflour by diffuse reflectance colorimetry.
lt is applicable to industrial semolina and flour.
The method can be applicable to flour obtained from experimental mill.
2Normative references
There are no normative references in this document.
3Terms and definitions
For the purposes of this document, the following terms and definitions apply.
IS0 and IEC maintain terminological databases for use in standardization at the following addresses:- ISo online browsing platform: available at https://www.iso.org/obp
—IEC Electropedia: available at http://www.electropedia.org/
3.1
colour metric space
expression of the colour of an object or of a light source by some parameters expressed by figures3.2
illuminant
light source characterized by a spectral curve, where the energy relative distribution is defined in thefield of wavelengths that are able to influence the object colour vision
4 Principle
The principle is based on the measurement of colour directly on semolina and flour by a reflectancecolorimeter.
The colour of wheat milling product (semolina and flour) is due to the pigments naturally present inwheat grains. These pigments (xanthophyl’s and carotenoids) are responsible for the colour visuallyperceived in milling products.
5 Apparatus
5.1 Reflectance colorimeter
1) with head of measurement suitable for carrying out measurements of absolute chromaticity. Consists of a setting system and a cell samples-driver. The colorimeter shall be characterized by the following technical characteristics:
— system of measurement with pulsed xenon lamp diffused to the light and receipt of the radiation reflected to 0° (geometry d/0°);
— circular surface of measurement;
— measurements of chromaticity expressed as L*, a*, b* (see CIE 1976) with the use of the illuminant CIE D 65 (illuminant D 65 : representing one of the relative spectral distribution of the day-light energy that corresponds to a proximal colour temperature similar to 6 504 K);
— time of measurement 1 s;
— possibility of calibration with reference plate; — repeatability within a DE * 0,6 (30 measurements effected to an interval of 10 s on the reference plate).
5.2 Accessory samples-driver and cell for the measurement of granular materials. The dimensions of the cell that defines the quantity of sample submitted to the test are: external diameter = 60 mm, diameter inside hole = 22 mm, thickness = 9 mm. 5.3 Reference plate in porcelain for the initial setting of the colorimeter.
6 Sample preparation
Before the analysis, the samples shall be carefully homogenized. Sampling is not part of the method specified in this document. A recommended sampling method is given in ISO 24333.
7 Procedure
7.1 General Before each series of measurements, the apparatus shall be calibrated. The colorimeter calibration shall be made through opaque stable materials (as ceramics, glaze etc.) samples supplied by manufacturers. When the colorimeter (5.1) is used, a further calibration for better measurement accuracy can be performed using a reference material similar to the colour of the samples to be measured. Before the calibration, verify the integrity of the reference plate (5.3) used as a reference (e.g. for the absence of linings or colour not homogeneous). Also, for the setting, verify that the coordinates are those reported on the reference standard
7.2 Setting of the colorimeter To set the colorimeter (5.1), put the head of measurement on the centre of the reference plate (5.3) and select the colour metric space y, x, z with illuminant D 65 in the system CIE Lab. At the end, return in the colour metric space L*, a*, b*, and therefore prepare the colorimeter to the reading of the samples. The reference plate shall carefully be cleaned after every setting, being careful to avoid any rubbing or lining. After the setting, the plate shall be stored in the dark.
7.3 Colorimetric determination From a homogeneous sample of at least 100 g, withdraw a share, fill with care the cell for granular samples and measure. Every determination shall be performed twice. The cell has to be emptied completely and cleared between two determinations. The sample shall be mixed each time.ISO 16624:2020 pdf download