1、BRITISH STANDARD CONFIRMED FEBRUARY1991 BS 770-5:1976 Methods for Chemical analysis of cheese Part 5: Determination of pH value NOTEThis Part should be read in conjunction with Part 1: General introduction, published separately. UDC 637.322:543.247.1BS770-5:1976 BSI 08-1999 ISBN 0 580 08747 6 A Brit
2、ish Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a fron
3、t cover, an inside front cover, pages i and ii, page 1 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No. Date CommentsBS
4、770-5:1976 BSI 08-1999 i Contents Page 1 Scope 1 2 References 1 3 Definition 1 4 Principle 1 5 Buffer solutions 1 6 Apparatus 1 7 Procedure 1 8 Expression of result 1 9 Repeatability 1 10 Test report 1ii blankBS770-5:1976 BSI 08-1999 1 1 Scope This Part of BS 770 describes a method for the determina
5、tion of pH value applicable to all cheeses and to processed cheese products made from cheese with the addition of emulsifying salts only. 2 References The following British Standards are referred to in this Part: BS 1647, pH scale. BS 2586, Glass electrodes for measurement of pH. 3 Definition For th
6、e purposes of this Part the following definition applies: pH value the result of the pH measurement made according to the procedure described 4 Principle A pH meter is used to determine the pH value of the cheese itself, if soft enough, or otherwise of a suspension of the cheese in water: 5 Buffer s
7、olutions Use at lease two buffer solutions, one with a higher pH value and one with a lower pH value than that of the sample under test. NOTESuitable buffer solutions are described in BS 1647. 6 Apparatus Usual laboratory apparatus is required and, in particular, the following. 6.1 pH meter, with a
8、suitable glass electrode complying with BS 2586, and with a saturated calomel or other standard reference electrode. The pH meter shall be capable of being read to the nearest 0.01 pH unit. NOTEThe apparatus shall be operated in accordance with the manufacturers instructions. 7 Procedure 7.1 Calibra
9、tion check. Before carrying out the determination, check the electrodes against two buffers, one higher and one lower in pH than the expected pH range of the samples to be measured. Ensure that the buffers and the cheese suspension are at the same temperature, preferably laboratory temperature. 7.2
10、pH measurement 7.2.1 If the cheese sample consists of cores, plugs, or cut portions of the cheese, determine the pH value as soon as possible and within 6 h of sampling. Proceed as described in 7.2.2 if possible, but if the cheese is too hard to allow this procedure, proceed instead as described in
11、7.2.3. During testing check the pH meter calibration against one of the buffer solution every 30 min, or after testing every six samples (whichever is the most frequent). 7.2.2 Press the electrodes into the cheese and read the pH value to the nearest 0.01 unit, using the pH meter. Note the temperatu
12、re of measurement. 7.2.3 Using non-absorbent apparatus (e.g. a glazed or glass mortar and pestle), mix 10 g of the sample with 6 ml of water to form a fine suspension. Using the pH meter, determine the pH value of the suspension to the nearest 0.01 unit, as soon as possible and within 30 min of prep
13、aring the suspension. Note the temperature of measurement. 7.3 Cleaning of electrodes. Clean the electrodes after each determination with a jet of water from a wash bottle and wipe them with tissue paper. Clean the glass electrode daily by swabbing with a 1 % (V/V) solution of a non-ionic detergent
14、followed by rinsing with water. 8 Expression of result Express the result as the pH value of the cheese, stating the temperature of measurement and whether or not the sample was mixed with water as described in 7.2.3. 9 Repeatability The difference between the results of two determinations carried o
15、ut simultaneously, or in rapid rapid sucession, by the same analyst should not exceed 0.05 pH unit. 10 Test report See Part 1. BS 770-5:1976 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsInstitution BSI is the independent national body responsible for preparing BritishStandards. It pre
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