AOAC Official Method 976
|
ID： |
B56F6A78E0004890BBBF630490401148 |
|
文件大小(MB)： |
0.07 |
|
页数： |
1 |
|
文件格式： |
|
|
日期： |
2016-2-28 |
|
购买： |
文本摘录（文本识别可能有误，但文件阅览显示及打印正常，pdf文件可进行文字搜索定位）：
32.1.35,AOAC Of fi cial Method 976.13,Al pha-Amylase,in Flour, Meal, and Malted Ce reals,Falling Number (FN) Determina tion Method,First Ac tion 1976,Fi nal Ac tion 1994,AACC–AOAC Method,(Ap pli ca ble to both meal and flour of wheat, rye, bar ley, and other,grains, and malted ce re als. Not ap pli ca ble to de ter mi na tion of,a-am y lase ac tiv ity from fun gal sources.),A. Prin ci ple,a-Am y lase liq ue fies starch gel. Ac tiv ity of en zyme is mea sured,by fall ing num ber (FN), de fined as time in s re quired to stir and let,stir rer fall mea sured dis tance through hot aque ous flour gel,un der go ing liq ue fac tion.,B. Apparatus,(a) FN ap pa ra tus.—Avail able from Perten In stru ments (PO,Box 5101, S-14105, Huddinge, Swe den). Spec ify test tube,tol er ances: id ±0.2 mm, od ±0.3 mm, length ±0.3 mm. Check weight,of tubes, and use those that agree most closely with mean value.,(b) Mill.—Must pro duce meal with par ti cle size dis tri bu tion as,fol lows: >500 mm, 0–10%; >210 but <500 mm, 25–40%; <210 mm,75–50%. Use ei ther of fol low ing: Weber Pulverizer with 0.5 mm,sieve (Hosokawa Mi cron Pow der Sys tems, Inc., 10 Chat ham Rd,Sum mit, NJ 07901, USA); Udy Cy clone with 0.024 in sieve (Udy,Corp., 201 Rome Ct, Ft. Col lins, CO 80524, USA); or equiv a lent.,(c) Au to matic pipet.—Cal i brated to de liver 25 ± 0.3 mL.,(d) Thermome ter.—NIST or equiv a lent, cal i brated in 0.1°C and,cer ti fied ac cu rate to ±0.3°C.,C. Preparation of Test Sam ple,Grind ca 250 g grain test sam ple in mill. Mois ture con tent of grain,should be within range of ca 8–16%. Add H2O to grain with <8%,mois ture, and air- or vac uum-dry grain with >16% mois ture.,D. Temperature Adjustment of FN Apparatus,Con stant tem per a ture water bath of FN ap pa ra tus must be,main tained at 100.0°C. Pre pare as fol lows: Fill res er voir with H2O,to H2O-level con trol fixed at 2.5 cm be low cover. Place rub ber,stop per con tain ing ther mom e ter in tube well and let re main un til,tem per a ture is con stant. If bath tem per a ture is be tween 98.0 and,99.8°C, ad just it to 100.0°C with amount eth yl ene gly col or glyc erol,in di cated in Ta ble 976.13.,If bath tem per a ture is <98.0°C, do not at tempt tem per a ture,re ad just ment be cause of dan ger of boil ing out con tents of FN tube.,In stead, de ter mine FN at ob served bp, e.g., 96.0°C, as in E. Then,ad just tem per a ture to 97.5°C by add ing 13.6% eth yl ene gly col and,de ter mine FN again. Plot both val ues against tem per a ture on,graph pa per and ex trap o late to 100.0°C. Read FN from graph at,this point.,If bath tem per a ture is >100.2°C, add 0.1% isopropanol to H2O for,each 0.1 of ex cess tem per a ture above 100.0°C. Ob serve,ther mom e ter-immersion point, and if stem cor rec tion is ap pli ca ble,use fol low ing for mula:,Stem cor rec tion = K ′ n ′ (T - t),where K = 0.00016 for Hg, n = num ber of de grees Hg col umn is,above stoppered water bath, T = bath tem per a ture, and t = Hg,tem per a ture above stop per (room tem per a ture).,E. De ter mi na tion,Weigh 7.00 g [or ap pro pri ate weight test portion cal cu lated to,14% H2O ba sis = 7.00(100 - 14)/(100 - x), where x = ac tual,per cent H2O] test por tion into dry FN tube and tip to 45° an gle.,Add 25 mL H2O with au to matic pipet. In sert rub ber stop per and,shake in up right po si tion 10 times (up and down), mak ing sure all,solids are sus pended by up end ing. Scrape down up per part of tube,with viscometer–stir rer. Re move stop per from bath well.,Si mul ta neously start timer; place tube in bath and lock into,po si tion, tak ing ￡5 s. Stir test so lu tion with viscometer–stirrer at,rate of 2 strokes/s (down and up is 1 stroke) un til clock reaches,60 s, for to tal of 110 strokes. Stop with stir rer in up po si tion. If,au to matic timer is used, set wire against stir rer so that buzzer and,shut-off mech a nism will be ac ti vated at con clu sion of test. Let,stir rer drop by its own weight. Stop buzzer by push ing small top,knob, which con trols con tact wire, coun ter clock wise. Re cord,time in s (stir ring plus drop ping time). Quickly re move test tube,from bath and in sert stop per or an other empty test tube to pre vent,H2O evap o ra tion. Hold tube un der run ning water and re move,viscometer–stir rer. Re move starch gel from tube by means of,spat ula with ex tended han dle. Clean viscometer–stir rer with test,tube brush. Use air jet to re move any re main ing gel and H2O from,or i fice.,FN (14% mois ture ba sis) = FNas is (100 - 14)/(100 - M),where M = percent mois ture in test sam ple.,Ref er ence: AACC Method 56-81B.,CAS-9000-90-2 (a-am y lase),Ta ble 976.……
……