For avocado a conversion factor of 7.46 should be used (because avocado protein contains 13.4% nitrogen and not 16%). Using a conversion factor of 6.25 …

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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. Remember that you should multiply nitrogen values by the conversion factor to get protein values. If you use a conversion factor that is too low you will underestimate the protein values.

Not right. It is true that this leads to underestimation of the protein values. However, this overestimation is more than 5%. You can figure out the extent of the overestimation by calculating the protein values using each of the conversion factors for 1000 g nitrogen for example.

Right. This lead to underestimation of the protein values of 7.46 - 6.25 = 1.21 gram per g nitrogen. This is 1.21/7.46 = 16%

Not right. It is true that this leads to underestimation of the protein values. However, this overestimation is less than 30%. You can figure out the extent of the overestimation by calculating the protein values using each of the conversion factors for 1000 g nitrogen for example.

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leads to over estimation of protein values of about 5%

leads to over estimation of protein values of about 15%

leads to over estimation of protein values of about 30%

leads to under estimation of protein values of about 5%

leads to under estimation of protein values of about 15%

leads to under estimation of protein values of about 30%

does not affect protein values