玻璃隔断价格多少钱一平:急件：请问有谁知道那里可以下载电子版的AOAC 方法

33.2.31 - Dairy Products / Milkm
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　　AOAC Official Method 972.16'E8}*a
　　Fat, Lactose, Protein,e1ZX7h
　　and Solids in Milk *71"n
　　Mid-Infrared Spectroscopic Method
　　First Action 1972 j6XG
　　A. Principle.g"&
　　Analysis of milk by IR is based on absorption of IR energy at specific wave numbers by CH groups in fatty acid chains of fat molecules (3.48 µm), by carbonyl groups in ester linkages of fat molecules (5.723 µm), by peptide linkages between amino acids of protein molecules (6.465 µm), and by OH groups in lactose molecules (9.610 µm). Total solids (TS) or solids-not-fat (SNF) are computed by assigning experimentally determined factor to percentage of all other solid milk components, and by adding this amount to appropriate % fat, protein, and lactose, or by direct mulitple regression calculations using instrument signals at combinations of above-mentioned wavelengths. Latter method has been shown to be more accurate method of determining milk solids. Analysis by IR is dependent on calibration against suitable standard method. See "Definitions of Terms and Explanatory Notes," for calculation of regression lines.@E Df
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　　The above wave numbers can be generated by means of (1) series of filters, each absorbing all wave numbers of electromagnetic spectrum but one, or (2) a Michelson interferometer, each wave number of interest selected from the full spectrum by mathematical means.N
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　　B. Performance Specifications_&B=V%
　　Number of firms manufacture various model instruments based upon principle, A. It is imperative that individual instrument utilized meet following performance specifications, based upon analysis of 8 test samples:tH`
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　　Standard deviation of difference between duplicate instrument estimates:x:&
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　　Fat, protein, and lactose 0.02%e06
　　Total solids 0.04%Q*
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　　Mean difference between duplicate instrument estimates:gP!ch4
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　　Fat, protein, and lactose 0.02%m
　　Total solids 0.03%UO
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　　Standard deviation of difference between instrument estimates and values by reference methods:m8vC
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　　Fat [989.05 (see 33.2.26)], protein [991.20 (see 33.2.11)], DHr
　　and lactose [896.01B (see 33.2.21) zwNlo;
　　or 930.28 (see 33.2.22)] 0.06%;cC
　　Total solids [925.23A (see 33.2.09)] 0.12%gZwqW1
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　　Mean difference between instrument estimates and values by reference methods:w
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　　Fat, protein, and lactose 0.05%D#e1<
　　Total solids 0.09%OT$F!x
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　　Calculate standard deviation of difference as in 969.16D (see 33.2.29), where SD = algebraic difference either between duplicate instrument estimates or between instrument estimates and values by reference methods.9
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　　C. Precautions.,RL;
　　Differences in fat readings for homogenized and unhomogenized test portions of same milk should be <0.05% to assure accurate results at high fat levels. If larger differences occur and servicing homogenizer does not correct fault, consult manufacturer. Changes in moisture vapor content within instrument console will cause changes in optical 0 and shift in calibration level. Replace desiccant frequently, preferably at end of each day, as 3-4 h are required to restore equilibrium conditions. For best accuracy, calibrate with type of milk to be analyzed (herd, individual cow, homogenized, unhomogenized, market, etc.). Do not use mixtures of cream and milk for calibration. Avoid abnormal (low lactose) milks for calibration. Single pumping of milk through instrument sample cell should purge 99% of previous test portion. To test purging efficiency, perform fat determinations on H2O and single pasteurized, homogenized whole milk in sequence: H2O, H2O, milk, milk, H2O, etc., until total of 20 determinations have been obtained. CalculateY
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　　Purging efficiency = .e4~[
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　　where M1 and M2 are first and second values for milk and W2 second value for H2O.u b
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　　Instrument must be well maintained and functioning correctly. Malfunctions that influence calibration can cause large errors.>6\vLn
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　　I. FatW9'v\6
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　　D. Calibrationl
　　Before first calibration, check linearity of output signals. Mix accurately measured volumes of H2O and homogenized cream to prepare ca 8 mixtures of known relative fat contents covering required range. Prepare test portions as in 925.21 (see 33.2.02), and pump each mixture into instrument twice, using second readings to prepare plot against relative concentrations. If plot is not linear, adjust as indicated in operating manual. Repeat measurements and adjustments until plot is linear./KVEL
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　　If analyzing unhomogenized milks, check linearity again with ca 4 dilutions of unhomogenized cream or high fat milk. If these mixtures deviate significantly from linearity, see C and check differences between readings for homogenized and unhomogenized milk test portions.g
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　　Determine % fat for series of 8 preanalyzed [989.05 (see 33.2.26) or 905.02 (see 33.2.25)] milk test portions of type to be analyzed (see C). Prepare test portions as in 925.21 (see 33.2.02) and analyze in triplicate. Compare averages of second and third instrument readings with standard values and follow instructions in operating manual for required changes to calibration.CK
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　　Alternatively, for better accuracy, use simple linear regression equation that relates instrument estimates and standard reference values, using latter as dependent variable, to correct these estimates. In earlier instruments, which do not have this capability in instrument software, this calculation must be performed manually. To perform this calculation on calibration data that are collected on successive days or weeks, it is necessary to record instrument estimates as well as final results. Purpose of this alternative, preferred procedure is to avoid adjusting instrument slope controls.T4d
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　　E. Determination*.i
　　Prepare test portion as in 925.21 (see 33.2.02). Operate instrument in accordance with manufacturer's instructions. Use A, B, or A + B filters for measurements when using filter spectrometer; use ester carbonyl, amide II, and hydroxyl spectral information when using interferometric spectrometer.?
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　　II. Protein!
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　　F. CalibrationG5
　　Proceed as in D, first and third paragraph, substituting calcium propionate solution (dissolve 15.0 g pure calcium propionate·H2O in H2O and dilute to 1 L with H2O at 20°C) for homogenized cream to prepare mixtures of known relative concentrates from 0 to required maximum for protein. Determine % protein for series of 8 preanalyzed [991.20 (see 33.2.11)] milk test portions having range of protein content approximately that of population of milks to be analyzed. Prepare test portions as in 925.21 (see 33.2.02) and analyze in triplicate. Compare averages of second and third instrument readings with standard values and follow directions in operating manual for making required adjustments to calibration.OkC
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　　Alternatively, for better accuracy, use simple linear regression equation that relates instrument estimates and standard reference values, using latter as dependent variable, to correct these estimates. In earlier instruments, which do not have this capability in instrument software, this calculation must be performed manually. To perform this calculation on calibration data that are collected on successive days or weeks, it is necessary to record instrument estimates as well as final results. Purpose of this alternative, preferred procedure is to avoid adjusting instrument slope controls.SEzJM=
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　　G. DeterminationkD
　　Prepare test portion as in 925.21 (see 33.2.02). Operate instrument according to manufacturer's instructions. When using interferometric spectometer, use ester carbonyl, amide II, and hydroxyl spectral information.%-
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　　III. LactoseeK]d$\
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　　H. CalibrationJ]U
　　Proceed as in D, paragraph 1, substituting lactose solution (dissolve 50.00 g lactose·H2O and 0.25 g HgCl2 in H2O and dilute to 1 L with H2O at 20°C) for homogenized cream to prepare mixtures of known relative concentrates ranging from 0 to required maximum for lactose. Determine lactose for series of 8 preanalyzed [896.01B (see 33.2.21) or 930.28 (see 33.2.22)] milk test portions having range of lactose content approximately that of population of milks to be analyzed.wZ
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　　Prepare test portions as in 925.21 (see 33.2.02) and analyze in triplicate. Use averages of second and third values for each test portion in estimating calibration requirements. Adjust instrument controls, as directed in operating manual, to make L = L, where L = instrument readings for lactose and L = values from reference method.pY
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　　Alternatively, for better accuracy, multiply instrument estimates by L/L to obtain final results. In earlier instruments, which do not have this capability in instrument software, this calculation must be performed manually. To perform this calculation on calibration data that are collected on successive days or weeks, it is necessary to record instrument estimates as well as final results. Purpose of this alternative, preferred procedure is to avoid adjusting instrument slope controls.~ty
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　　I. DeterminationB
　　Prepare test portion as in 925.21 (see 33.2.02). Operate instrument according to manufacturer's instructions. When using interferometric spectrometer, use ester carbonyl, amide II, and hydroxyl spectral information.dc
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　　IV. Solids (Total)oKwtO
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　　J. CalibrationdUHe]@
　　Use standard method 925.23A (see 33.2.09) to determine % total solids for series of 8 milks. Determine % fat, % protein, and % lactose. Calculate mean difference for total solids (TS) - F - P - L = a, where F, P, and L are estimates of fat, protein, and lactose, respectively. For routine control of calibration, analyze additional series of milks and adjust value for mean difference in accordance with accumulated data.j/Ed
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　　Calculate % total solids = a + F + P + LAg%-
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　　Alternatively, calibrate by multiple regression to calculate equation for estimation of either TS or SNF as function of fat, protein, and lactose uncorrected signals. For recalibration, use simple linear regression equation which relates regression estimates and standard reference values, using latter as dependent variable, to correct these estimates and obtain final result. In earlier instruments, which do not have this capability in instrument software, this calculation must be performed manually. To perform this calculation on calibration data that are collected on successive days or weeks, it is necessary to record regression estimates as well as final result. This alternative, preferred method has been demonstrated to be more accurate.P0=@.y
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　　(Note: For products that are fortified or diluted, both original multiple regression and simple regression calculations must be based on regression that forces calibration line through origin. First calculation procedure in this section, paragraph 1, cannot be used successfully with these products.)H-hU
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　　K. Computer-Based Calibration and ControlU@jk:?
　　Program computer to:WaFe|?
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　　(1) Calculate S2 = S1 + [(S2 - S1)/PF], where S2 is purge-corrected signal; S2 is signal at any instrument channel; S1 is same signal for previous test portion; and PF is predicted purge fraction = purging efficiency/100 (see C). Apply correction to all signals received from instrument.~H"e
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　　(2) Calculate (CS2)/10, where CS2 is purge-corrected control milk signal. Sum control milk signals at each channel for 10 control samples, and average. At time of calibration, store and designate as required control milk samples.b
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　　(3) Calculate S = S2 + CSE, where S is purge- and drift-corrected signal; CSE is control signal error = (required control signal average) - (determined control signal average) for any check on control milk. Apply value to all except control milks.M
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　　(4) Calculate estimates from purge- and drift-corrected signals using calibration signals, and store. Equation type is Estimate = A + B (main equation). Initially, A = 0 and B = 1.I|z
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　　(5) Calculate calibration equations and store.fI)HJ*
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　　(6) Store random test portion signals, estimates, and standard method reference results.H_
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　　(7) Calculate and store mean difference, standard deviation of difference, limits for mean difference, and population standard deviation of difference for statistical quality control.N
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　　(8) Store results for checks on purging efficiency tests, homogenization efficiency tests, linearity tests, and repeatability tests.s>ke
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　　L. Instrument Controls@|)SZr
　　For instrument with secondary slope controls, operate in uncorrected mode. For instruments without secondary slope controls, reduce interference correction coefficients to 0.yZ2JeA
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　　M. Control Milk3|d
　　Prepare adequate supply of pasteurized, homogenized, preserved milks with % fat about that of population average. Transfer amounts for single tests to test sample containers and keep refrigerated. Zero-adjust instrument channels. Heat 11 test samples to 40°C, and pump each through instrument, collecting signals. Average last 10 results for each signal to calculate required signal. Record required control milk signals to 4 decimals to prevent rounding errors in continuous control situation.$&
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　　N. Setting Primary Slope Controls4
　　For filter IR spectrometers, determine % fat, protein, and lactose on series of 8 preanalyzed [e.g., 989.05 (see 33.2.26), 905.02 (see 33.2.25), 991.20 (see 33.2.11), 896.01A (see 33.2.21), or 984.15 (see 33.2.24)] milks of type to be analyzed by instrument. Warm test samples to 40°C, mix thoroughly, and pump through instrument, collecting and correcting signals for purge and drift. For each signal calculate regression equation of type S = aF + bP + cL, where S is signal and F, P, and L are results for standard. At fat channel, adjust slope amplification by 1/a. At protein and lactose channels, adjust by 1/b and 1/c, respectively. Check success of attempt to obtain coefficient of 1 for main components by repeating test. Readjust slope amplifications if necessary. Lock slope controls and do not change settings thereafter. Warm 11 test samples of control milk and redetermine required control milk values as indicated above./j
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　　For interferometric spectrometers, re-zero by collecting background spectrum of thermostated distilled water. Ratio test sample emittance spectrum against water background emittance spectrum.2F6cWf
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　　O. First Calibration~
　　Obtain 20 milk test samples by random selection from population to be tested, and analyze by standard reference method for components to be estimated by IR method. Key standard results into computer. Warm and prepare 11 control milk samples and the calibration samples. Pump through instrument and collect and store signals. Computer applies purge correction, calculates control signal correction values, applies these to calculate milk signals, and stores these values in matrix with standard reference values. Select equation that is applicable to instrument from following main equation types.j6
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　　For filter IR spectometers:l@e]w
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　　Components.
　　SignalszCT^$
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　　FB©食品论坛 -- 关注食品安全，探讨食品技术，汇聚行业英才，推动行业发展。 vKOC
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　　1. F, P, L, TS, SNFf
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　　2. F, P, L, TS, SNFD!]0\g
　　*10(l
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