1、BRITISH STANDARD BS 1743:1968 Incorporating Amendment Nos. 1, 2, 3 and 4 Methods for analysis of dried milk and dried milk productsBS1743:1968 This British Standard, having been approved by the Dairying Industry Standards Committee and endorsed by the Chairman of the Chemical Divisional Council, was
2、 published under the authority of the General Council on 19 July 1968 BSI 06-1999 First published May 1951 First revision July 1968 The following BSI references relate to the work on this standard: Committee reference DAC/3 Draft for comment 66/20540 ISBN 580 002543 Co-operating organizations The Da
3、irying Industry Standards Committee, under whose supervision this British Standard was prepared, consists of representatives from the following Government departments and scientific and industrial organizations: The Government departments and scientific and industrial organizations marked with an as
4、terisk in the above list, together with the following, were directly represented on the committee entrusted with the preparation of this standard: Association of Public Analysts* National Farmers Union Chemical Society National Institute for Research in Dairying* Commonwealth Bureau of Science a sui
5、table size is a diameter of about75mm and a depth of about25mm. 3.2 Procedure. Uncover the dish, and place the dish and lid in the oven at102103C for1 hour. Place the lid on the dish, remove from the oven, cool in a desiccator (charged with an efficient desiccant such as silica gel) for30minutes and
6、 weigh. Transfer approximately1g of the well mixed sample to the dish, cover with the lid, and weigh accurately and rapidly. Remove the lid, place both dish and lid in the oven and maintain at102103C for2 hours. With samples of high moisture content this first heating may advantageously be extended
7、to3hours. Replace the lid, remove the dish from the oven, and allow to cool in the desiccator for30minutes; weigh. In the same manner, heat again in the oven for1hour, cool and weigh; repeat this process until the change of mass between succesive weighings does not exceed0.5mg (drying is usually com
8、plete at the end of the first2hours). The maximum loss of mass found is the mass of moisture in the quantity of sample taken, and the percentage of total solids is100minus the percentage of moisture thus found. Calculate the result to the nearest0.1%. 4 Determination of fat content NOTEMethod delete
9、d. Superseded by BS 1743 “Methodsforanalysis of dried milk and dried milk products” Part 11 “Determination of fat content (gravimetric reference method).” 1) BS 2648, “Performance requirements for electrically-heated laboratory drying ovens”.BS1743:1968 2 BSI 06-1999 Figure 1 Fat-extraction tubesBS
10、1743:1968 BSI 06-1999 3 Figure 2 Fat-extraction tube (with siphon fitting)BS1743:1968 4 BSI 06-1999 5 Determination of total nitrogen 5.1 Reagents. All reagents shall be of analytical reagent quality and the water used shall comply with BS 3978 2) . The following reagents shall be used: 1) Potassium
11、 sulphate. 2) Mercuric oxide or mercuric sulphate solution. To prepare the sulphate solution dissolve10g of red mercuric oxide in a solution prepared by adding12ml of sulphuric acid (approximately98% m/m) to92ml of water. (The volume of this solution, when cool, is approximately100ml.) 3) Sulphuric
12、acid, concentrated, approximately98% m/m. 4) Antifoaming agent. A silicone preparation is recommended. 5) Sodium hydroxide/sodium thiosulphate solution. Mix6 volumes of sodium hydroxide solution (40% m/m, approximately14N) and one volume of sodium thiosulphate solution (25% m/v of Na 2 S 2 O 3 .5H 2
13、 O). 6) Sulphuric acid solution, approximately0.1N (Method 1) or boric acid solution, 4% m/v (Method 2). Figure 3 Mojonnier-type-fat-extraction apparatus 2) BS 3978, “Water for laboratory use”.BS 1743:1968 BSI 06-1999 5 7) Indicator solution. Mix equal volumes of a saturated solution of methyl red i
14、n ethanol (95% v/v) and a0.1% solution of methylene blue in ethanol. 8) Sodium hydroxide solution, approximately0.1N, carbonate-free, standardized (Method 1) or sulphuric acid solution, approximately0.1N, standardized (Method 2). 5.2 Procedure. Transfer1g of the dried milk, accurately weighed, to a5
15、00ml Kjeldahl flask containing10g of potassium sulphate and two glass beads. Wash down any dried milk in the-neck of the flask with water and add0.5g of mercuric oxide (or5ml of mercuric sulphate solution) and20ml of concentrated sulphuric acid. Mix the contents of the flask, heat gently until froth
16、ing has ceased, boil gently until the liquid is clear and no particles of carbon remain in the flask and then boil for1 hours, taking care that the flask is not directly heated above the level of the contents. When the digest is cool, add250ml of water, mix, and add a few drops of antifoaming agent
17、and70ml of sodium hydroxide/sodium thiosulphate solution poured down the side of the flask to form a bottom layer. Connect the flask to a splash bulb and an efficient condenser, the tip of which is immersed in40.0ml of sulphuric acid solution (Method 1), or25ml of boric acid solution (Method 2), and
18、 four drops of indicator solution, contained in a500ml conical flask. Gently rotate the Kjeldahl flask to mix its contents thoroughly, and boil, gently at first, so that150ml of distillate are collected in about30minutes. About2 minutes before the end of the distillation, lower the conical flask to
19、bring the tip of the condenser above the acid, and rinse the outside of the tip with water. Repeat the whole procedure with5ml of water in place of the dried milk for a blank determination. Titrate the sample and blank distillates to the same end-point with standardized sodium hydroxide solution (Me
20、thod 1) or standardized sulphuric acid solution (Method 2). When Method 2 is used, the colour of the blank distillate may not enable a blank titration to be obtained; in this case, titrate, the sample distillate to the colour of the blank distillate. Subtract the sample titration from the blank titr
21、ation (Method1), or the blank titration (when obtainable) from the sample titration (Method2), to obtain respectively the volume of standardized sodium hydroxide or sulphuric acid solution equivalent to the total nitrogen in the weight of dried milk taken. Calculate the percentage by weight of total
22、 nitrogen in the milk to three significant figures. 1 ml of 0.1N sodium hydroxide or sulphuric acid solution = 0.0014g of nitrogen. To obtain the percentage by mass of protein in the dried milk, multiply the percentage of total nitrogen by6.38. 6 Determination of ash 6.1 Apparatus. The following app
23、aratus is required: 1) Muffle furnace to operate at525550C. 2) Silica or platinum dishes, 6080 mm diameter. 6.2 Procedure. Heat a silica or platinum dish for60minutes in the muffle furnace at525550C. Cool in an efficient desiccator for60minutes. Accurately weigh about2g of dried milk into the dish,
24、spreading the powder uniformly in the dish before weighing. Heat either at the mouth of the muffle or over a low bunsen flame until the powder is completely charred and smoke is no longer given off 3) . Place the dish in the muffle furnace at525550C and ash for1hour. Remove the dish from the muffle,
25、 cool in the desiccator and moisten the ash with water. Break up the ash with a flat-topped glass rod, wash any particles from the rod back into the dish and evaporate to dryness. The ash shall be further dried at102103C for30minutes to avoid crepitation when it is returned to the muffle. Heat at525
26、550C for a further hour. Cool in a desiccator for60minutes and weigh. Express the result as mass of ash per100g of dried milk as received. 3) Slow, efficient carbonization at this stage facilitates ashing and is essential if the ash is to be used subsequently for the determination of ash alkalinity.
27、BS1743:1968 6 BSI 06-1999 7 Determination of alkalinity of ash 7.1 Reagents. All reagents used shall be of a recognized reagent quality. The following reagents shall be used: 1) 0.2N hydrochloric acid solution. 2) Calcium chloride, neutral, 40% w/v solution. 3) 0.2N sodium hydroxide solution. 4) 0.5
28、% phenolphthalein in50% ethanol. 7.2 Procedure. Ash about2g, accurately weighed, of dried milk as described in Clause6 and using a fine bore pipette or burette add10ml of0.2N hydrochloric acid dropwise to the dish containing the ash, allowing the acid to run from the rim downwards. Grind the ash to
29、a fine powder with a small, flat-ended glass rod and wash the sides of the basin and the rod with a few drops of water complying with BS3978 4) . To obtain a reproducible end point the volume should not exceed15ml. Warm the basin carefully, stirring until the ash is completely dissolved. Cool to air
30、 temperature and run in2ml of40% neutral calcium chloride solution. Stir and add0.5of the phenolphthalein indicator solution. Titrate with 0.2N sodium hydroxide solution until a faint pink coloration remains visible for30seconds on addition of one drop of titrant. Express the result as the volume of
31、0.2N hydrochloric acid solution (in millilitres) required per100g of powder as received, to the nearest whole number. 8 Determination of titratable acidity NOTEMethod deleted. Superseded by BS1743 “Methods for analysis of dried milk and dried milk products” Part7“Determination of titratable acidity
32、of dried milk” Section 7.1:1982 “Reference method” and Section 7.2:1982 “Routine method”. 9 Determination of bulk density 9.1 Apparatus. The following apparatus is required: 1) Balance to weigh to0.05g and weighing scoop. 2) 100 ml measuring cylinder in which the100ml graduation mark is approximatel
33、y150mm above the bottom of the inside, fitted with a cork. 9.2 Procedure. Accurately weigh about20g of the dried milk in a scoop. By means of a funnel transfer the powder to the100ml measuring cylinder. Stand the cylinder on a duster folded about15mm thick (or similar soft pad) and place it between
34、the jaws of a burette clamp so arranged that it will allow the cylinder to be raised by150mm. Lift the cylinder150mm and allow it to drop on the pad ten times. If necessary, level off the powder by tilting and tapping the cylinder. Record the bulk density as grammes of powder per millilitre. 10 Text deleted. 4) BS3978, “Water for laboratory use”.
