The high level of protein content reported in insects for food and feed is overestimated

The potential of insects as a source of protein for future food and feed is widely admitted in the last couple years and is the object of numerous studies. The Kjeldahl method is widely used to quantify the crude protein content of insects which ranges from 8 to 70% of dry mass. This procedure evaluates the total concentration of Nitrogen (N), which is converted to protein by multiplying it by the nitrogen-to-protein conversion factor (N-factor) for meat (6.25). Giving that the insect cuticle contents large amounts of fibrous chitin, a polysaccharide rich in N, and proteins tightly embedded in its matrix, and is not digested by humans or domesticated animals, using the Kjeldahl method overestimates the digestible protein content of insects. We propose to evaluate digetible nitrogen by quantifying N in the cuticle and sustraiting it from the total nitrogen content, and to calculate a new N conversion factor which should be similar for all the insects species and their development stages.