BS 684-1 13-1976 Methods of analysis of fats and fatty oils - Physical methods - Determination of cooling curve《脂肪和油脂分析方法 第1部分 物理法 第13节 冷却曲线测定》.pdf

《BS 684-1 13-1976 Methods of analysis of fats and fatty oils - Physical methods - Determination of cooling curve《脂肪和油脂分析方法 第1部分 物理法 第13节 冷却曲线测定》.pdf》由会员分享，可在线阅读，更多相关《BS 684-1 13-1976 Methods of analysis of fats and fatty oils - Physical methods - Determination of cooling curve《脂肪和油脂分析方法 第1部分 物理法 第13节 冷却曲线测定》.pdf（10页珍藏版）》请在麦多课文档分享上搜索。

1、BRITISH STANDARD CONFIRMED APRIL 1993 BS 684-1.13: 1976 Methods of analysis of Fats and fatty oils Part 1: Physical methods Section 1.13: Determination of cooling curve IMPORTANT NOTE. It is essential that this Section be read in conjunction with the information in the “General introduction” to BS 6

2、84, which is published separately. UDC 665.1.014:543:536.332BS684-1.13:1976 This British Standard having been prepared under the direction of the Oils and FAts Standards Committee, was published under the authority of the Executive Board on 29 October 1976 BSI 07-1999 The following BSI references re

3、late to the work on this standard: Committee reference OFC/24 Draft for comment 74/50395 DC ISBN 0 580 09495 2 A British 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 Britis

4、h Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 to 5 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will b

5、e indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No. Date of issue CommentsBS684-1.13:1976 BSI 07-1999 i Contents Page 0 Scope 1 1 Method 1. Preferred method for cocoa butter and similar fats 1 1.1 Field of application 1 1.2 Reference 1 1.3 Princ

6、iple 1 1.4 Apparatus 1 1.5 Sampling and preparation of sample for analysis 3 1.6 Procedure 3 1.7 Expression of results 4 1.8 Test report 4 2 Method 2. For use with samples of less than 80 g 4 2.1 Field of application 4 2.2 Reference 4 2.3 Principle 4 2.4 Apparatus 4 2.5 Sampling and preparation of s

7、ample for analysis 5 2.6 Procedure 5 2.7 Expression of results 5 2.8 Test report 5 Figure 1 Cooling curve apparatus 2 Figure 2 Cooling curve apparatus Method 2 3ii blankBS 684-1.13:1976 BSI 07-1999 1 0 Scope This Section describes two methods for the determination of the cooling curve of cocoa butte

8、r and similar fats. Method 1 describes a procedure requiring a sample of at least 80 g and is preferred. Method 2 requires a sample of only 15 g and describes a procedure that may be used when there is insufficient sample available for method 1. The results of these two procedures are not interchang

9、eable. 1 Method 1. Preferred method for cocoa butter and similar fats 1.1 Field of application The method described is suitable for the determination of the cooling curve of cocoa butter and similar fats. This method is recommended for use when 80 g or more of the fat is available for the test. 1.2

10、Reference The following standards publication is referred to in this method: BS 593, Laboratory thermometers. 1.3 Principle The molten fat is cooled under controlled conditions, solid particles of the fat are introduced and the temperature at which crystallization occurs is noted. 1.4 Apparatus The

11、apparatus illustrated in Figure 1 and consisting of the following items is required (see also BS 684: General introduction). 1.4.1 Test tube, borosilicate glass, of the following dimensions: 1.4.2 Thermometer, complying with the requirements of BS 593 type F50C/100. 1.4.3 Stirrer, a ring stirrer, fa

12、shioned from a borosilicate glass rod, with the following dimensions: 1.4.4 Rubber stopper, of moulded rubber with a central hole to carry the thermometer and a hole accommodating a glass bearing through which the stirrer operates smoothly without contacting the thermometer or the inside of the test

13、 tube. The stopper shall have the following dimensions: 1.4.5 Air jacket, a glass jar (weighted with lead shot) fitted with a bored and recessed cork to accommodate the glass test tube and with the following dimensions: 1.4.6 Water bath, capable of being maintained at a temperature of 55 C to 60 C.

14、1.4.7 Water bath, comprising a 4 litre low form beaker of borosilicate glass of the following dimensions and capable of being maintained at a temperature of 16.5 C to 17.0 C. 1.4.8 Stopwatch Inside diameter Outside diameter Length 38 mm 43 mm 0.25 mm 190 mm Diameter of glass rod Diameter of ring 5.2

15、5 mm 0.25 mm 25 mm (centre of ring to centre of rod, see Figure 1) Length of stirrer 350 mm 5 mm Top diameter Bottom diameter Length 43 mm 38 mm 38 mm Outside diameter Height 100 mm 228 mm Outside diameter of neck Inside diameter of neck Length of neck 57 mm 50 mm 50 mm Outside diameter Height 160 m

16、m 230 mmBS684-1.13:1976 2 BSI 07-1999 Figure 1 Cooling curve apparatusBS 684-1.13:1976 BSI 07-1999 3 1.5 Sampling and preparation of sample for analysis Heat a minimum quantity of 80 g of the fat in a beaker to 60 C and maintain at this temperature for 5 min. See also BS 684: General introduction. 1

17、.6 Procedure 1.6.1 Test portion. Transfer 75 g of the liquid sample into the glass test tube which has been warmed to 45 C to 50 C. Insert the stopper carrying the thermometer and stirrer. It is essential that the thermometer is equidistant from the vertical sides of the tube and that the centre of

18、the bulb is located 40 mm from the upper surface of the fat. 1.6.2 Stabilization of the test portion. Place the test tube with the contents for a minimum of 15 min in a water bath maintained at a temperature of 55 C to 60 C. During this time destroy any crystal nuclei which may be present. Figure 2

19、Cooling curve apparatus Method 2BS684-1.13:1976 4 BSI 07-1999 1.6.3 Determination. Conduct the determination in a draught-free area with an air temperature of 19 C to 21 C, avoiding a high relative humidity. Place the air jacket in the water bath maintained at a temperature of 16.5 C to 17.0 C. Adju

20、st the level of the water in the bath so that it is level with the midpoint of the shoulder of the air jacket. Leave for at least 30 min before proceeding with the test. 1.6.3.1 Remove the test tube from the stabilizing bath (see 1.6.2). Wet the stirrer bearing with the fat by raising the stirrer ar

21、m. Allow to cool in air to 40 C, while gently stirring continuously, just breaking the surface of the fat with the ring of the stirrer. Secure the test tube in the air jacket by means of the recessed cork (see Figure 2). 1.6.3.2 Allow the test portion to cool to 35 C without stirring. Start the stop

22、watch; at each 5 s, 20 s, 35 s and 50 s past the minute make one stirrer stroke (up and down). This should be firm in action, raising the stirrer ring 25 mm to 40 mm above the surface of the fat. (This ensures that crystals formed in the bearing are carried down to the bulk of the test portion to ac

23、hieve positive “seeding”.) 1.6.3.3 When the temperature falls to 32 C (or immediately above or below) record the temperature at the start of each minute and continue to record the temperature at one minute intervals until the test is completed. 1.6.3.4 Record the temperature at which fat crystals fi

24、rst appear in the main bulk of the sample as the “point of first crystals” (Jenson supercooling limit). The temperature will continue to fall until the “minimum” point is reached after which it will commence to rise. Continue stirring as describe described in 16.3.2, ensuring that the stirring strok

25、e is sufficiently firm to ensure thorough mixing of the test portion. Discontinue the stirring when the temperature rise becomes less than 0.1 C per minute or when the solidifying fat becomes so stiff that a risk of breakage is incurred. A further small rise in temperature will occur. Continue recor

26、ding until the temperature commences to fall or until five consecutive readings are constant. Record the highest temperature reached as the “maximum”, the “temperature rise” (maximum minus minimum) and the “total time” (the number of minutes taken to reach the maximum after commencing to take temper

27、ature readings at 32 C). 1.7 Expression of results Plot the recorded temperatures against time with temperature on the ordinate and time on the abscissa so that 0.1 C N 1 min = 2 min. 1.8 Test report See the general instructions and recommendations given in BS 684: General introduction and include t

28、he following information: a) the method used; b) graph of temperature against time; c) temperature at which stirring was discontinued; d) temperature at which the first crystals were observed; e) minimum temperature; f) maximum temperature; g) temperature rise i.e. e) to f); h) time taken from 32 C

29、to the maximum temperature. 2 Method 2. For use with samples of less than 80 g 2.1 Field of application The method described is suitable for the determination of the cooling curve of cocoa butter and similar fats but should only be used when the sample is less than 80 g. 2.2 Reference See 1.2. 2.3 P

30、rinciple See 1.3. 2.4 Apparatus The apparatus illustrated in Figure 2 and consisting of the following items is required (see also BS 684: General introduction). 2.4.1 Glass test tube, thin-walled, 150 mm long and 25 mm in diameter, fitted with a bung bored with holes to accommodate a thermometer, gr

31、ipped firmly and a stirrer. The bung is required to be an easy sliding fit for the test tube. 2.4.2 Thermometer, complying with the requirements of BS 593, type F50C/100. 2.4.3 Stirrer, of 4 mm diameter borosilicate glass rod with a loop of suitable diameter so that it is approximately midway betwee

32、n the thermometer bulb and the wall of the test tube when the apparatus is assembled. 2.4.4 Beaker, 1 litre, tall form (diameter approximately 85 mm), weighted with lead shot, and with a felt plug to accommodate the test tube. 2.4.5 Water bath, capable of being maintained at 17 0.2 C. The bath shoul

33、d be a glass vessel, or a vessel with a glass window, to enable the contents of the test tube to be observed. 2.4.6 StopwatchBS 684-1.13:1976 BSI 07-1999 5 2.5 Sampling and preparation of sample for analysis See BS 684: General introduction. 2.6 Procedure 2.6.1 Preparation of flakes of well grained

34、fat for seeding. Melt a portion of the sample in an oven at a temperature between 55 C to 60 C. Filter at this temperature through a dry filter paper. Cool the filtered fat, with occasional stirring, until the temperature falls to within 32 C to 34 C and then stir continuously either by hand or mech

35、anically until the fat has the consistency of a paste. Immediately transfer the fat to a vessel previously kept at a temperature of 15 C to 22 C, and allow to stand at this temperature for not less than 24 h. Shave or scrape the fat with a cool sharp blade (e.g. scalpel or razor blade), taking care

36、to avoid melting of the sample, to obtain fine flakes for seeding the bulk of the fat during the determination (see 2.5.3). 2.6.2 Test portion. Weigh, to the nearest 0.1 g, 15 g of the fat into the test tube and melt the test portion at 50 C. 2.6.3 Determination. Assemble the apparatus as shown in F

37、igure 2 with the thermometer bulb positioned at the centre of the test portion. Place the apparatus in the water bath at 17 C so that the water surface is 20 mm below the top of the tall form beaker air bath and stir the test portion occasionally until the thermometer reading indicates a temperature

38、 of 35 C. From this stage note the temperature readings at 1 min intervals, stirring the test portion by gentle strokes of the stirrer at intervals of 15 s, taking care not to break the surface of the fat with the stirrer loop. At 28 C, add 0.03 g to 0.04 g of the flakes of well grained fat (2.6.1).

39、 Stop stirring when the increase in temperature has just passed its maximum. For samples of cocoa butter, readings may be stopped conveniently when the temperature has remained constant for two consecutive minutes after the rise in temperature. For fats whose properties are not known, continue to ta

40、ke readings beyond the maximum point. Record the temperature at which the first definite sign of crystallization appears. NOTEShould the sample under examination have solidification properties differing widely from those of cocoa butter, some modification to the procedure may be required. In particu

41、lar, if crystallization first occurs at a temperature above 28 C, the seed crystals should be added 2 C or 3 C above the crystallization temperature. The temperature at which regular stirring and reading are commenced may also need to be altered. 2.7 Expression of results Plot the recorded temperatu

42、res against time, with temperature on the ordinate and time on the abscissa so that 0.1 C N 1 min = 2 mm. 2.8 Test report See the general instructions and recommendations given in BS 684: General introduction and include the following information: a) the method used; b) graph of temperature against

43、time; c) temperature at which stirring was discontinued; d) temperature at which the first crystals were observed; e) minimum temperature; f) maximum temperature; g) temperature rise i.e. e) to f); h) time taken from 32 C to the maximum temperature.BS 684-1.13: 1976 BSI 389 Chiswick High Road London

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