1、 Collection of SANS standards in electronic format (PDF) 1. Copyright This standard is available to staff members of companies that have subscribed to the complete collection of SANS standards in accordance with a formal copyright agreement. This document may reside on a CENTRAL FILE SERVER or INTRA
2、NET SYSTEM only. Unless specific permission has been granted, this document MAY NOT be sent or given to staff members from other companies or organizations. Doing so would constitute a VIOLATION of SABS copyright rules. 2. Indemnity The South African Bureau of Standards accepts no liability for any
3、damage whatsoever than may result from the use of this material or the information contain therein, irrespective of the cause and quantum thereof. ISBN 978-0-626-21428-9 SANS 5235:2008Edition 2SOUTH AFRICAN NATIONAL STANDARD Standard test method for the determination of the diastatic power of malts
4、prepared from sorghum including bird-proof varieties, and from millet Published by SABS Standards Division 1 Dr Lategan Road Groenkloof Private Bag X191 Pretoria 0001Tel: +27 12 428 7911 Fax: +27 12 344 1568 www.sabs.co.za SABS SANS 5235:2008 Edition 2 Table of changes Change No. Date Scope Foreword
5、 This South African Standard was approved by National Committee SABS SC 1024B, Yeast and sorghum products Sorghum products, in accordance with procedures of the SABS Standards Division, in compliance with annex 3 of the WTO/TBT agreement. This document was published in December 2008. This document s
6、upersedes SABS SM 235:1977 (first edition as modified by amendment 1:1970). SANS 5235:2008 Edition 2 1 Standard test method for the determination of the diastatic power of malts prepared from sorghum including bird-proof varieties, and from millet 1 Scope This standard specifies a method for the det
7、ermination of the diastatic power of malts prepared from sorghum and from millet. 2 Principle The malt is ground to a standard fineness and an aqueous peptone extract of it is made and filtered. This extract is allowed to act on a standard buffered starch solution for 30 min at 30 C. At the end of t
8、his period, the action is stopped by the addition of sodium hydroxide solution. The sugars that have been produced by the malt extract are estimated by boiling an aliquot of the solution with ferricyanide and determining the unchanged ferricyanide by titration. A blank is carried out in order to mak
9、e allowance for preformed sugar, i.e. that is already present in the malt extract. The diastatic power is then calculated in accordance with the formula given in clause 7. 3 Reagents 3.1 General Unless otherwise stated, reagents used shall be of recognized analytical reagent quality. 3.2 Peptone Dis
10、solve 10 g peptone in 500 mL water. 3.3 Starch 3.3.1 General The starch used shall be any starch which, when tested in parallel with the reference starch, will give results that differ by not more than 5 % from those obtained with the reference starch. Starches with results that differ by more than
11、5 % from those obtained with the reference starch shall not be used. SANS 5235:2008 Edition 2 2 3.3.2 Reference starch The reference starch shall comply with the following requirements: a) Solubility, minimum: 1 part in 50 parts of water. b) Dextrins: shall be absent. c) Reducing substances, maximum
12、: 0,75 % (calculated as maltose). d) Moisture content (determined as described in clause 6): 10 % to 12 %. 3.4 Buffered starch solution 3.4.1 Weigh out a quantity of starch representing 2 g of dry starch per 100 mL of final solution. 3.4.2 Macerate the starch with a little water to form a smooth, th
13、in paste. 3.4.3 Pour this with constant stirring into boiling freshly-distilled water that represents approximately 75 % of the final volume of the starch solution, and at such a rate that boiling does not cease. 3.4.4 Continue boiling for 2 min after the final paste has been introduced, then add an
14、 additional 10% of the final volume of cold freshly-distilled water and transfer to a glass-stoppered 250 mL volumetric flask. 3.4.5 Mix by inverting the flask several times, wash down the neck, cool to 30 C, add 2 mL of buffer solution (see 3.5) for each 100 mL of the final solution and make up to
15、volume. 3.4.6 Mix again and store at 30 C. 3.5 Buffer solution for starch Dissolve 68 g of chemically pure sodium acetate trihydrate (CH3COONa3H2O) in 500 mL of acetic acid and dilute to 1 L with distilled water. (The pH value of this solution is approximately 4.7.) 3.6 Sodium hydroxide solution (0,
16、5 N) for stopping diastasis Dissolve 20 g sodium hydroxide in distilled water and make up to 1 L. 3.7 Reagents for sugar determination 3.7.1 Alkaline ferricyanide solution (0,05 N) 3.7.1.1 Dissolve 16,5 g potassium ferricyanide and 22 g anhydrous sodium carbonate in distilled water and dilute to 1 L
17、. 3.7.1.2 Store in an amber bottle away from light. Standardization a) Add 25 mL of acetic acid-salt solution (see 3.7.4), 1 mL potassium iodide solution (see 3.7.6) and 2 mL of starch indicator (see 3.7.3) to 10 mL of the potassium ferricyanide solution. b) Titrate with sodium thiosulfate solution
18、(see 3.7.2) until the blue starch-iodine colour is discharged. SANS 5235:2008 Edition 2 3 3.7.2 Sodium thiosulfate solution (0,05 N) Dissolve 12,41 g pure pea crystals of sodium thiosulfate (Na2S2O35H2O) and 3,8 g of borax (as preservative) in water and dilute to 1 L. Standardization a) Dissolve 0,1
19、000 g pure dry reagent-grade potassium dichromate in water and make up to 50 mL. b) Add 2 g potassium iodide and 8 mL concentrated hydrochloric acid, mix thoroughly and titrate with the thiosulfate until the colour changes to yellow-green. c) Add a few millilitres of starch indicator (see 3.7.3) and
20、 titrate to a light-green shade when the colour of the starch-iodine is discharged. d) Use the relationship, 1 mL 0,05 N sodium thiosulfate 0,00245 g potassium dichromate, to calculate the normality of the sodium thiosulfate solution. 3.7.3 Starch indicator 3.7.3.1 Prepare a paste of 1 g of soluble
21、starch with a little water. 3.7.3.2 Pour the paste with constant stirring into boiling water. 3.7.3.3 Cool and make up to 100 mL. 3.7.3.4 Prepare a fresh solution for each series of standardizations. 3.7.4 Acetic acid-salt solution Dissolve 200 mL of glacial acetic acid, 70 g potassium chloride and
22、20 g zinc sulfate (ZnSO47H2O) in distilled water and dilute to 1 L. 3.7.5 Concentrated sodium hydroxide solution 3.7.5.1 Dissolve 50 g sodium hydroxide in 50 mL of water. 3.7.5.2 Cool before use. 3.7.6 Potassium iodide solution 3.7.6.1 Dissolve 50 g potassium iodide in water, add one or two drops of
23、 concentrated sodium hydroxide solution (see 3.7.5) and dilute to 100 mL. 3.7.6.2 The solution should be colourless. 4 Apparatus 4.1 Mill: Standardization of setting 4.1.1 Pass about 70 g of malt through the mill. 4.1.2 Mix well and then sieve 50 g of the ground sample through a sieve of nominal ape
24、rture size 500 m. SANS 5235:2008 Edition 2 4 4.1.3 Shake the sieve, lid and pan by hand in a horizontal plane for 5 min, tapping it on a table top every 15 s. 4.1.4 Remove the pan and cover and shake the sieve for a short while over a sheet of paper until no further malt passes through the sieve. 4.
25、1.5 The mill shall be considered as having a standardized setting when the portion of ground malt remaining on the sieve is between 4,5 g and 5,5 g (i.e. 9 % to 11 %). 4.1.6 The mill shall be standardized at 6-monthly intervals. 4.2 Glassware All glassware shall be cleaned in chromic acid cleaning s
26、olution, rinsed with tap water not less than four times and finally rinsed with distilled water. The glassware shall be dried in a hot-air oven. 5 Method 5.1 Preparation of the malt extract 5.1.1 Take about 35 g of the sample after grinding in a standardized mill (see 4.1). 5.1.2 Weigh accurately an
27、 amount of 25 g 0,05 g of the ground malt and transfer quantitatively to an extraction flask. (Use the remaining malt for the determination of moisture in accordance with clause 6.) Avoid delays which could alter the moisture content of the malt. 5.1.3 Add 500 mL of freshly prepared peptone solution
28、 (see 3.2) to the extraction flask and let the infusion stand for 2 h at 30 C 0,2 C. 5.1.4 Agitate by gentle rotation at intervals of 20 min. 5.1.5 Do not mix by inverting the flask. Gentle swirling without splashing will give sufficient mixing. 5.1.6 At the end of 2 h, filter the infusion by transf
29、erring the entire charge on to a 320 mm fluted filter paper in a funnel with a diameter of 175 mm. 5.1.7 Return the first 50 mL of the filtrate to the filter. 5.1.8 Collect the filtrate until 3 h have elapsed from the time that the peptone solution and ground malt were first mixed. 5.1.9 Prevent eva
30、poration during the filtration period as far as possible by placing watch glass over the funnel and a suitable cover to rest on the neck of the receiver around the stem of the funnel. 5.2 Diastasis 5.2.1 Using an accurately graduated measuring cylinder, transfer 200 mL of buffered starch solution to
31、 a 250 mL volumetric flask. 5.2.2 Add distilled water in such a quantity that the volume of this water plus that of the malt extract to be added is equal to 10 mL (see table 1). 5.2.3 Place the flask in a waterbath of which the temperature is maintained at 30 C 0,2 C. SANS 5235:2008 Edition 2 5 5.2.
32、4 When the temperature of the contents of the flask has reached the temperature of the waterbath, add the malt extract (also at 30 C), mix the solutions by rotating the flask during the addition, and at the same time start a stopwatch. 5.2.5 Stop the reaction after exactly 30 min by adding 20 mL of
33、0,5 N sodium hydroxide and mix thoroughly. 5.2.6 Make up to a volume of 250 mL and shake. Table 1 Malt extract preparation 1 2 3 Diastatic power of malt Volume of malt extract to be used Volume of water to be added SDU per gram mL mL 30 or above 2 8 20 to 29 5 5 0 to 19 10 0 NOTE SDU refers to the s
34、orghum diastatic units. 5.3 Determination of sugars 5.3.1 Pipette 5 mL of the buffered starch solution (see 3.4) into a 125 mL Erlenmeyer flask. 5.3.2 Add 10 mL alkaline ferricyanide solution (see 3.7.1), mix well and immerse the flask in a vigorously boiling waterbath for exactly 20 min (timed with
35、 a stopwatch) so that the level of the boiling water is slightly above the level of the mixture in the flask. 5.3.3 Cool under running water and add 25 mL of the acetic acid-salt solution (see 3.7.4) and 1 mL of potassium iodide solution (see 3.7.6). 5.3.4 Mix and titrate with 0,05 N sodium thiosulf
36、ate solution (see 3.7.2) until the blue colour of the starch-iodine complex is discharged. 5.3.5 Use a 10 mL semi-micro burette for the titration. 5.3.6 Note the number of millilitres of 0,05 N sodium thiosulfate solution used and designate this volume as A. 5.4 Determination of blank 5.4.1 Prepare
37、a blank by proceeding exactly as described in 5.2 but add the sodium hydroxide before adding the malt extract. 5.4.2 Pipette 5 mL of this blank into a 125 mL Erlenmeyer flask, then add 10 mL of alkaline ferricyanide solution (see 3.7.1). 5.4.3 Boil, cool and titrate as described in 5.3. 5.4.4 Design
38、ate the number of millilitres of 0,05 N sodium thiosulfate solution used as B. SANS 5235:2008 Edition 2 6 6 Determination of moisture in malt 6.1 Apparatus 6.1.1 Weighing bottle The weighing bottle may be of glass or aluminium, and shall be provided with a tight-fitting cover. It should have a diame
39、ter of approximately 40 mm for a 5 g sample or 55 mm for a 10 g sample. 6.1.2 Oven 6.1.2.1 The oven shall be provided with a thermo-regulator capable of keeping the temperature to within 0,5 C of the temperature required. 6.1.2.2 The oven shall be of such a size that all samples can be accommodated
40、on one shelf in order to give comparable results on duplicate samples. 6.1.2.3 The thermometer bulb shall be at the level of the shelf. Standardization a) Place weighed duplicate samples in the oven at 103 C to 104 C, allow to cool and dry for 3 h. Weigh and dry again for 1 h. b) If the moisture con
41、tent has increased by more than 0,1 %, raise the temperature of the oven with 1 C and test again with new duplicate samples. The lowest temperature below 106 C that gives a moisture content which, after a 3 h drying, is within 0,1 % of the value obtainable at the same temperature within 4 h, shall b
42、e taken as standard for the oven concerned. c) The ventilators on the oven shall be left open during the entire experiment, and the door shall be kept closed during all drying periods. 6.2 Procedure Determine the moisture content of the malt on duplicate 5 g or 10 g samples in accordance with the pr
43、ocedure followed in the standardization of the oven (see 6.1.2), but omit the reheating of the samples. 7 Calculation of results Express the diastatic power (DP) of the malt in sorghum diastatic units (SDU) per gram, one SDU taken as the amount of enzymatic activity which, under the conditions of te
44、st described in clause 6, produces a quantity of sugar equivalent to 0,5 mL of 0,05 N sodium thiosulfate solution. Calculate the result as follows: DP = 40 (B A) VF M100100where DP is the diastatic power, expressed in SDU per gram; B is the sodium thiosulfate solution used for the determination of a
45、 blank (see 5.4), in millilitres; SANS 5235:2008 Edition 2 7 A is the sodium thiosulfate solution used for the determination of sugars (see 5.3), in millilitres; F is the standardized value of the normality of the sodium thiosulfate solution (see 3.7.2), in mililitres; V is the malt extract used for diastasis (see 5.2), in millilitres; M is the moisture in the malt sample used (see 6.2), expressed as a percentage. SABS
