Mariotti François, Tomé Daniel, Mirand Philippe Patureau
AgroParisTech, INRA, UMR914 Nutrition Physiology and Ingestive Behavior, Paris, France.
Crit Rev Food Sci Nutr. 2008 Feb;48(2):177-84. doi: 10.1080/10408390701279749.
The protein content in foodstuffs is estimated by multiplying the determined nitrogen content by a nitrogen-to-protein conversion factor. Jones' factors for a series of foodstuffs, including 6.25 as the standard, default conversion factor, have now been used for 75 years. This review provides a brief history of these factors and their underlying paradigm, with an insight into what is meant by "protein." We also review other compelling data on specific conversion factors which may have been overlooked. On the one hand, when 6.25 is used irrespective of the foodstuff, "protein" is simply nitrogen expressed using a different unit and says little about protein (s.s.). On the other hand, conversion factors specific to foodstuffs, such as those provided by Jones, are scientifically flawed. However, the nitrogen:protein ratio does vary according to the foodstuff considered. Therefore, from a scientific point of view, it would be reasonable not to apply current specific factors any longer, but they have continued to be used because scientists fear opening the Pandora's box. But because conversion factors are critical to enabling the simple conversion of determined nitrogen values into protein values and thus accurately evaluating the quantity and the quality of protein in foodstuffs, we propose a set of specific conversion factors for different foodstuffs, together with a default conversion factor (5.6). This would be far more accurate and scientifically sound, and preferable when specifically expressing nitrogen as protein. These factors are of particular importance when "protein" basically means "amino acids," this being the principal nutritional viewpoint.
食品中的蛋白质含量是通过将测定的氮含量乘以氮与蛋白质的换算因子来估算的。琼斯针对一系列食品提出的换算因子，包括作为标准默认换算因子的6.25，至今已使用了75年。本综述简要介绍了这些因子及其背后的范式，并深入探讨了“蛋白质”的含义。我们还回顾了其他可能被忽视的关于特定换算因子的有力数据。一方面，无论食品种类如何都使用6.25时，“蛋白质”仅仅是以不同单位表示的氮，对蛋白质本身（按干物质计）说明甚少。另一方面，针对特定食品的换算因子，如琼斯提出的那些，在科学上存在缺陷。然而，氮与蛋白质的比例确实会因所考虑的食品种类而异。因此，从科学角度来看，不再应用当前的特定因子是合理的，但它们仍在继续使用，因为科学家们担心打开潘多拉魔盒。但是，由于换算因子对于将测定的氮值简单转换为蛋白质值从而准确评估食品中蛋白质的数量和质量至关重要，我们提出了一组针对不同食品的特定换算因子，以及一个默认换算因子（5.6）。这将更加准确且在科学上合理，并且在将氮具体表示为蛋白质时更可取。当“蛋白质”基本上意味着“氨基酸”时，这些因子尤为重要，这是主要的营养观点。
