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1、INTERNATIONAL STANDARD IS0 6731 First edition 1989-05- 15 Milk, cream and evaporated milk - Determination of total solids content (Reference method) Lait, c see 7.1). 6 Sampling See IS0 707. 7 Preparation of the test sample 7.1 Milk Bring the sample to a temperature of 20 OC to 25 OC. Mix thoroughly
2、 to ensure a homogeneous distribution of the fat throughout the sample. Avoid agitating so vigorously as to cause frothing of the milk or churning of the fat. If it is found difficult to disperse the cream layer, warm slowly to 35 OC to 40 OC on a water-bath (5.6.1) with careful mixing and incor- po
3、rate any cream adhering to the container. Cool the sample quickly to 20 OC to 25 OC. If desired, a homogenizer may be used to assist the dispersion of the fat. NOTE - Correct results cannot be expected if the sample contains separated liquid fat or separate visible irregularly shaped white particles
4、 adhering to the walls of the container. 7.2 Cream Warm the sample slowly to a temperature of 35 OC to 40 OC on a water-bath (5.6.1). Mix or stir the cream thoroughly but not so vigorously as to cause frothing or churning. Cool the sample 1 Copyright International Organization for Standardization Pr
5、ovided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/26/2007 19:33:00 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 6731 :I989 (E) quickly to 20 OC to 25 OC. In order to reduce the evaporation of water to a minimum dur
6、ing mixing, the container should be uncovered for as short a time as possible. 8.3.4 Again heat the dish, with its lid alongside, in the oven but for only 1 h. Place the lid on the dish and immediately transfer to the desiccator. Allow to cool as in 8.3.3 and weigh to the nearest 0,l mg. NOTE - Corr
7、ect results cannot be expected if adequate mixing of the sample is not achieved or if the sample shows any evidence of churning or any other signs of abnormality. 8.3.5 Repeat the operations described in 8.3.4 until the differ- ence in mass between two consecutive weighings does not ex- ceed 1 mg. R
8、ecord the lowest mass. 7.3 Evaporated milk Shake the container thoroughly with frequent inversion. Open this container and pour the milk slowly into another container made of glass or other suitable material, provided with an air- tight lid, taking care to incorporate in the sample any fat or other
9、constituents adhering to the walls of the original con- tainer. Stir vigorously and close the container. 9 Expression of results 9.1 Method of calculation The total equal to content, expressed as a percentage by mass, is Heat the closed container in a water-bath (5.6.2) at 40 OC to 60 OC. Remove and
10、 shake the container vigorously every 15 min. After 2 h, remove the container and cool to 20 OC to 25 OC. Remove the lid and mix thoroughly by stirring the milk with a spoon or spatula. In2 - no x 100 ml - m() where NOTE - If the fat separates, correct results cannot be expected. m0 is the mass, in
11、grams, of the dish and lid (see 8.1); 8 Procedure ml is the mass, in grams, of the dish, lid and test portion (see 8.2); 8.1 Preparation of the dish 1n2 is the mass, in grams, of the dish, lid and dried test portion (see 8.3.5). Heat a dish (5.51, with its lid alongside, in the oven (5.4) for at lea
12、st 1 h. Place the lid on the dish and immediately transfer to the desiccator (5.2). Round the value obtained to the nearest 0,Ol % (I/IKJ). Allow to cool to room tern to the nearest 0, 1 mg. perature (at least 30 min) and weigh 9.2 Precision NOTE - The values for repeatability and reproducibility ar
13、e expressed at the 95 % probability level and were derived from the results of an inter-laboratory test (see STEIGER, G. and MARTENS, R. Bulletin of the international Dairy Federation, 1986, No. 207) carried out in accor- dance with IS0 5725 : 1986, Precision of test methods - Determina- tion of rep
14、eatability and reproducibility for a standard test method by inter-laboratory tests. 8.2 Test portion Quickly weigh, to the nearest 0,l mg, 1 g to 5 g of the prepared test sample (depending on the expected solids con- tent) into the prepared dish (8.1). In the case of milk or cream, tilt the dish to
15、 spread the test portion evenly over the bottom of the dish. In the case of evaporated milk, add 3 ml to 5 ml of distilled water or water of at least equivalent purity, tilt the dish to mix and spread the test portion evenly over the bottom of the dish. 9.2.1 Repeatability The difference between two
16、 single results found on identical test material by one analyst using the same apparatus within a short time interval will exceed the following values of total solids per 100 g of product on average not more than once in 20 cases in the normal and correct operation of the method: 8.3 Determination 8
17、.3.1 Place the dish without lid on the vigorously boiling water-bath (5.3) in such a way that the bottom of the dish is maximally exposed to and directly heated by the steam. Leave for 30 min. - for milk OJO g - for cream 020 g - for evaporated milk Of30 g 8.3.2 Remove the dish from the water-bath a
18、nd then heat it, with its lid alongside, in the oven (5.4) for 2 h. Place the lid on the dish and immediately transfer to the desiccator (5.2). 9.2.2 Reproducibility 8.3.3 Allow the dish to cool to room temperature 30 min) and weigh to the nearest 0,l mg. (at least The difference between two single
19、and independent results foun d by two operators working in different laboratories on 2 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/26/2007 19:33:00 MDTNo reproduction or networking p
20、ermitted without license from IHS -,-,- IS0 6731 :1989 (E) identical test material will exceed the following values of total solids per 100 g of product on average not more than once in 20 cases in the normal and correct operation of the method: - for milk 020 g - for cream 0,35 g - for evaporated m
21、ilk 0,50 g 10 Test report The test report shall show the method used and the result ob- tained. It shall also mention any operating details not specified in this International Standard, or regarded as optional, together with details of any incidents likely to have influenced the result. The test rep
22、ort shall include all the information necessary for the complete identification of the sample. 3 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/26/2007 19:33:00 MDTNo reproduction or ne
23、tworking permitted without license from IHS -,-,- This page intentionally left blank Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/26/2007 19:33:00 MDTNo reproduction or networking per
24、mitted without license from IHS -,-,- This page intentionally leff blank Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/26/2007 19:33:00 MDTNo reproduction or networking permitted witho
25、ut license from IHS -,-,- IS0 6731 :1989(E) UDC 1637.12 + .14.07 : 543.82 Descriptors: agricultural products, food products, dairy products, milk, creams, condensed milk, determination of content, solids, dry matter. Price based on 3 pages Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/26/2007 19:33:00 MDTNo reproduction or networking permitted without license from IHS -,-,-