In a paper you have found total protein data for a range of almond varieties. In the methods section it is mentioned that a conversion factor of 6.25 has been used. However, you know that the nitrogen fraction in almond protein is 19.3%. What would you do with these data?

Title of page

Therefore Jones et al (1941) proposed food specific conversion factors to account for differences in amino acid composition in foods (see table).

Besides, foods contain also (a small) non protein nitrogen (NPN) fraction: substances such as nucleic acids, urea, ammonia, nitrates, certain phospholipids etc. contain also nitrogen. The following products are examples of products that contain a high amount of NPN:

• Cow’s milk (5-6% of the total nitrogen)

• Seafood (many shellfish and crustaceans)

• Human breast milk (15 % of the total nitrogen)

The Jones’ factors are based on protein nitrogen only and do not include NPN.

Proteins differ with respect to nitrogen contents because of differences in amino acids composition. Consequently, it is reasonable to use food specific conversion factors instead of a factor of 6.25 for all foods.

Not right. If you use these data, you will use protein values that are too high.

Right. The conversion factor should be 100/19.3 = 5.18. Thus data based on a conversion factor of 6.25 are 6.25/5.18 = 1.2 times too high. Therefore you should recalculate the data by multiplying with 5.18/6.25 = 0.83.

Not right. If you use a conversion factor of 6.25 you will use protein values that are too high. Thus you have to recalculate the data, but not by multiplying with 6.25/(100/19.3). This will only make the protein value higher.

a
b
c

Use these data as given

Recalculate these data by multiplying with (100/19.3)/6.25

Recalculate these data by multiplying with 6.25/(100/19.3)