Department of Animal and Wildlife Sciences, University of Pretoria, Pretoria, South Africa.
Food Chem. 2013 Oct 1;140(3):608-12. doi: 10.1016/j.foodchem.2012.08.046. Epub 2012 Sep 13.
In most cited food composition studies and tables, the proximate system measures protein as total nitrogen (N) (determined by Kjeldahl or Dumas method) multiplied by a specific factor. A factor of 6.25 is used for determining total protein from total N (Jones, Munsey, & Walker, 1942). Although more expensive, it is considered more accurate to base protein content of foods on amino acid data (Greenfield & Southgate, 2003). A study on the nutrient composition of beef analysed the full amino-acid profile of fifteen retail cuts from three age groups and six fat codes, as well as determined total nitrogen content to determine proximate protein composition. For all cuts, the correlation coefficient of total amino acids to protein (N×6.25) was 0.635. This indicates a poor correlation for predicting actual protein content (as determined by total amino acid count), based on the nitrogen factor of 6.25. On average, the sum of amino acids per cut amounted to 91% of total determined protein (N×6.25) for the same cut.
在大多数被引用的食物成分研究和表中，近侧系统将蛋白质作为总氮 (N)（通过凯氏或杜马斯法测定）乘以特定因子来测量。总氮（Jones、Munsey 和 Walker，1942）用于确定总蛋白的因子为 6.25。虽然更昂贵，但基于氨基酸数据确定食物的蛋白质含量被认为更准确（Greenfield 和 Southgate，2003）。一项关于牛肉营养成分的研究分析了来自三个年龄组和六个脂肪代码的十五个零售切块的完整氨基酸谱，以及测定总氮含量以确定近侧蛋白质组成。对于所有切块，总氨基酸与蛋白质（N×6.25）的相关系数为 0.635。这表明，根据 6.25 的氮因子，用总氨基酸计数来预测实际蛋白质含量的相关性很差。平均而言，每个切块的氨基酸总和占同一切块总测定蛋白质（N×6.25）的 91%。
