Analysis revealed that avocado protein contains 13.4% nitrogen (and not 16 %). For avocado, which conversion factor should be used to convert nitrogen to protein?

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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. Avocado protein consists of 13.4% nitrogen. This means that the nitrogen contents should be multiplied by 100/13.4 = 7.46 to get the protein contents.

Not right. The conversion factor is only 6.25 if the nitrogen contents of protein is 16%. However, the nitrogen contents of avocado protein is lower; consequently the conversion factor should be higher.

Right. Avocado protein consists of 13.4% nitrogen. This means that the nitrogen contents should be multiplied by 100/13.4 = 7.46 to get the protein contents.

a
b
c
d
e

0.134 (i.e. 13.4/100)

0.84 (i.e. 13.4/16)

2.14 (i.e. 13.4 * 16%)

still 6.25

7.46 (i.e. 100/13.4)