杜马斯燃烧法测定油料作物中粗蛋白质含量的 方法优化及其与凯氏定氮法的比较研究

目的建立杜马斯燃烧法测定油料作物中粗蛋白质含量的方法,并与凯氏定氮法进行比较。方法以芝麻、大豆、油菜和花生为研究对象,对杜马斯燃烧法的称样量和氧气系数进行优化。分别用杜马斯燃烧法和凯氏定氮法测定4种样品的粗蛋白含量,并对2种测试方法的结果进行比较分析。结果杜马斯燃烧法的测定值略高于凯氏定氮法,但2种方法的测定值间没有显著性差异(P0.05),杜马斯燃烧法比凯氏定氮法的测定精密度和准确度更高。测定结果的相关性分析表明两种方法的测定值呈显著相关(r~2=0.9988)。结论杜马斯燃烧法的精密度和准确度更好,可以替代凯氏定氮法测定油料作物的粗蛋白质含量。     

杜马斯燃烧法测定煤炭中氮含量

采用杜马斯燃烧法,利用氮分析仪对煤炭中的氮含量进行测定。试样在一个分析周期中分为3个阶段：冲洗、燃烧和分析。结果表明,用杜马斯燃烧法测定煤炭中氮含量与传统湿法分析相比,操作方法简便容易掌握,快速分析的同时确保了准确性,符合工业生产与试验分析的要求。     

Comparison of kjeldahl and dumas methods for determining protein contents of soybean products

The Kjeldahl and Dumas methods for quantifying nitrogen content were compared using nine soybean products having protein contents ranging from 0.5 to 90%. In addition to comparing day-to-day variability of the Dumas method, differences between and variabilities of two Kjeldahl systems and Kjeldahl operators were also evaluated. The Kjeldahl method gave slightly, but significantly, lower values than did the Dumas method. Both the Kjeldahl and Dumas methods had equivalent variabilities (same SD about the means). The ratios between the means for the Kjeldahl and Dumas (K/D) protein values ranged from 0.66 to 1.03. The conversion equation y=−0.00536+0.97188x (R ²=0.9997) was developed and validated to convert from Dumas to kjeldahl protein concentrations.     

Determination of the Total Soluble Nitrogen Content of Malt and Beer by the Dumas Combustion Method: Collaborative Trial

The determination of the total soluble nitrogen content of malt and beer, by the Dumas procedure, has jointly been collaboratively tested by the Analysis Committee of the Institute of Brewing (IOB) and the European Brewery Convention (EBC). Five samples of beer (range 362 to 1159 mg/l) and five samples of malt (range EBC 0.598 to 0.798 %m/m (dry basis) and IOB 0.534 to 0.706 %m/m (dry basis)) were distributed to eighteen participating laboratories for analysis. Precision values were judged to be independent of the mean soluble nitrogen content for malt by both IOB and EBC methodologies. Values for r₉₅ and R₉₅ were 0.047 and 0.136%m/m for EBC laboratory wort and 0.039 and 0.144 %m/m for IOB laboratory wort respectively. Precision values for beer were judged to be dependent upon the mean nitrogen content (m) in the case of r₉₅ and independent of the mean nitrogen content in the case of R₉₅. Values for r₉₅ and R₉₅ were 0.074m and 120 mg/l respectively.     

Comparison of analytical and predictive methods for water,protein, fat,sugar, and gross energy in marine mammal milk

Mammalian milks may differ greatly in composition from cow milk, and these differences may affect the performance of analytical methods. High-fat, high-protein milks with a preponderance of oligosaccharides, such as those produced by many marine mammals, present a particular challenge. We compared the performance of several methods against reference procedures using Weddell seal (Leptonychotes weddellii) milk of highly varied composition (by reference methods: 27–63% water, 24–62% fat, 8–12% crude protein, 0.5–1.8% sugar). A microdrying step preparatory to carbon-hydrogen-nitrogen (CHN) gas analysis slightly underestimated water content and had a higher repeatability relative standard deviation (RSD_r) than did reference oven drying at 100°C. Compared with a reference macro-Kjeldahl protein procedure, the CHN (or Dumas) combustion method had a somewhat higher RSD_r (1.56 vs. 0.60%) but correlation between methods was high (0.992), means were not different (CHN: 17.2 ± 0.46% dry matter basis; Kjeldahl 17.3 ± 0.49% dry matter basis), there were no significant proportional or constant errors, and predictive performance was high. A carbon stoichiometric procedure based on CHN analysis failed to adequately predict fat (reference: Röse-Gottlieb method) or total sugar (reference: phenol-sulfuric acid method). Gross energy content, calculated from energetic factors and results from reference methods for fat, protein, and total sugar, accurately predicted gross energy as measured by bomb calorimetry. We conclude that the CHN (Dumas) combustion method and calculation of gross energy are acceptable analytical approaches for marine mammal milk, but fat and sugar require separate analysis by appropriate analytic methods and cannot be adequately estimated by carbon stoichiometry. Some other alternative methods—low-temperature drying for water determination; Bradford, Lowry, and biuret methods for protein; the Folch and the Bligh and Dyer methods for fat; and enzymatic and reducing sugar methods for total sugar—appear likely to produce substantial error in marine mammal milks. It is important that alternative analytical methods be properly validated against a reference method before being used, especially for mammalian milks that differ greatly from cow milk in analyte characteristics and concentrations.     

杜马斯燃烧法测定食品中总氮含量

以各类食品为试验材料,分析了各种参数对杜马斯燃烧法测定含氮量结果的影响,并比对了杜马斯法和凯氏法的测定结果。结果表明,当通氧量为110～200min/mL,反应炉温度设定900℃以上,样品量在100～150mg时,测定结果理想。大部分食品样品杜马斯和凯氏法无显著性差别。但杜马斯法结果RSD较凯氏法稍大。另改进前处理方法,杜马斯法还可以用于测定液体食品中的氮含量,结果准确。     

Could the Dumas Method Replace the Kjeldahl Digestion for Nitrogen and Crude Protein Determinations in Foods?

Increased demand for determinations of nitrogen (N), and hence crude protein (CP), has led to wider use of the Dumas method in place of the traditional Kjeldahl methods. Although Kjeldahl N (KN) and Dumas N (DN) represent different N fractions, published studies on infant formula, animal feed and meat products have indicated that DN could replace KN with little practical impact on the reliability of the N values obtained. This study was conducted to establish whether DN determination could replace that of KN in a broader range of foods for CP calculation. Statistical analysis was performed on in-house assayed KN and DN values together with published KN and DN values for selected food products. In the range 0·05–6·8% N, KN may be estimated from DN with the equation: KN=1·00^(P<0·01)×DN-0·09^(P=0·50) (n=101, R²=0·98, P-regression<0·01). Because N levels in individual groups of food did not span the entire range of N contents, KN: DN ratios were calculated for each food group. KN: DN ratios differed significantly (R²=0·25, P<0·01) from group to group. Ratios of 1·01 for dairy, 1·00 for oilseeds, 0·99 for feed, 0·98 for infant formulas, 0·95 for cereals, 0·94 for meats, 0·89 for vegetables, 0·80 for fish and 0·73 for fruits were valid for the estimation of KN and CP using DN data. CP was independently calculated as CP1=H×KN or CP2=H×KN: DN×DN, where H is the nitrogen to protein conversion factor for the food group. Mean differences between CP1 and CP2 values were 0% for dairy, oilseeds, feed, infant formulas and baby foods, cereals, meat and meat products, vegetables and vegetable products and fruit, and 1% for fish. These results suggest that DN may replace KN for the determination of N and CP in selected food groups when appropriate coefficients are used. © 1997 SCI.     

杜马斯燃烧定氮法在农产品品质检测中的应用

测定农产品中全氮的凯氏定氮法在许多国家已被杜马斯然烧定氮法所代替，对比了杜马斯燃烧定氮法与凯氏定氮法的特点，介绍了杜马斯定氮法的原理及其在国内外农产品领域中的应用。     

杜马斯燃烧法测定大豆水溶性蛋白含量的方法研究

通过优化大豆水溶性蛋白的提取条件,采用杜马斯燃烧定氮法,建立了一种大豆水溶性蛋白的测定方法,并探讨了杜马斯燃烧定氮仪的试验条件。结果表明,最佳试验条件为:20℃恒温振荡提取,提取时固液比1∶30,提取次数2次,提取时间40 min;提取液蒸发、干燥时吸取量3～4 m L,电热板温度150℃;杜马斯燃烧定氮仪氧气流速300 m L/min,氧气因子1. 4 m L/mg。在最佳试验条件下,本方法的试验精密度符合GB/T 27404—2008“检测方法确认过程中实验室变异系数(CV)”的技术要求,与现行凯氏定氮法的测定结果无显著性差异(P=0. 89)。本方法属于环境友好型化学分析方法,可以满足大豆水溶性蛋白的无污染、快速、准确检测工作。