ISO 7305 pdf download.Milled cereal products — Determination of fat acidity
1 Scope
This International Standard specifies a method for the determination of the “fat acidity” of milled cereal products. It is applicable to flours and semolinas obtained from wheat and durum wheat, and also to pasta. NOTE This method appears to be applicable also to grains, to flours and semolinas obtained from maize, and to rye flour and oat flakes, but a further interlaboratory test is necessary before confirming this extension of the field of application.
2 Normative reference
The following standard contains provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the edition indicated was valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent edition of the standard indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO 71 2:— 1 ) , Cereals and cereal products — Determination of moisture content — Routine reference method .
3 Definition
For the purposes of this International Standard, the following definition applies. 3.1 fat acidity conventional term used to express the quantity of acids, essentially non-esterified fatty acids, extracted according to the procedure described in this International Standard NOTE Fat acidity is expressed in milligrams of potassium hydroxide per 1 00 g of dry matter. It can also be expressed in milligrams of sodium hydroxide per 1 00 g of dry matter (see clause 1 1 ).
4 Principle
Dissolution of the acids in ethanol at room temperature, followed by centrifuging and titration of an aliquot portion of the supernatant liquid against sodium hydroxide. Conversion by calculation of the obtained result to express the result with reference to potassium hydroxide.
5 Reagents
Use only reagents of recognized analytical grade and distilled or demineralized water or water of equivalent purity. 5.1 Ethanol, 95 % (V / V). 5.2 Sodium hydroxide, standard volumetric solution, c(NaOH) = 0,05 mol/l, in 95 % (V / V) ethanol, free of carbonates. The exact concentration shall be known and checked immediately prior to each series of determinations of fat acidity. Use a solution prepared at least 5 days in advance and stored in a brown glass bottle, fitted with a rubber stopper. The solution shall be colourless or straw coloured. If a commercially available solution is not used, it is recommended that the ethanol be purified as follows. Dissolve 5 g to 1 0 g of sodium hydroxide in 1 l of ethanol and add 0,5 g of aluminium turnings. Boil the mixture under reflux for 1 h, then distil the ethanol. Dissolve the required quantity of sodium hydroxide (i.e. to give a concentration of 2 g/l) in the distillate. Leave to stand for 5 days in order to allow the insoluble sodium carbonate to settle out, then use the supernatant solution. 5.3 Phenolphthalein, indicator solution, 1 g per 1 00 ml of 95 % (V / V) ethanol (5.1 ).
6 Apparatus
Usual laboratory apparatus and, in particular, the following. 6.1 Sieves, of wire gauze, of nominal aperture size 1 mm (for flour, if necessary), and 1 60 µm and 500 µm (for semolina and pasta). 6.2 Centrifuge tubes, of borosilicate or neutral glass, of capacity 45 ml, hermetically stoppered. 6.3 Centrifuge, capable of a centrifugal acceleration of 2000 g . 6.4 Pipettes, of capacities 20 ml and 30 ml. 6.5 Conical flask, of capacity 250 ml. 6.6 Microburette, graduated in 0,01 ml divisions. 6.7 Rotary stirrer, capable of 30 r/min to 60 r/min. 6.8 Analytical balance, capable of weighing to an accuracy of ± 0,01 g. 6.9 Grinder, capable of grinding without any appreciable heating (for semolina and pasta). 6.10 Orange filter, photographic-type cellulose acetate filter, blue absorbing (wavelength 440 nm).