Nitrogen-to-Protein Conversion Factors for Edible Insects on the Swiss Market: T. molitor, A. domesticus, and L. migratoria.

Samy Boulos,Anina Tännler,Laura Nyström

doi:10.3389/fnut.2020.00089

Abstract

With an increasing worldwide demand for animal protein, insects are becoming a promising sustainable option for meat protein replacement. However, reported protein contents of insects are often overestimated when calculated as “crude protein” = 6.25 × nitrogen content (N), compared to true protein contents quantified from the sum of amino acid (AA) residues. In this study, the main two types of usual nitrogen-to-protein conversion factors kp and kA were determined on the basis of true protein/total nitrogen and true protein/protein nitrogen, respectively, with focus on the three insect species legally sold on the Swiss food market. T. molitor (mealworm larvae), A. domesticus (house crickets), and L. migratoria (locusts) from various breeders were analyzed for total and amide nitrogen, chitin, and AA composition. Careful control experiments of insect samples spiked with a protein standard were conducted to establish the recovery of true protein, which was with >95% excellent. Mealworms, crickets, and locusts exhibited similar AA-profiles and true protein contents of 51, 55, and 47 g/100 g (dry weight basis), respectively. Specific conversion factors kp showed little variability between the three insect species with 5.41, 5.25, and 5.33 for mealworms, crickets, and locusts, respectively, and confirmed an average ~17% overestimation of protein contents when using 6.25 × N. The determined average kp of 5.33 is supported by extracted literature data and is suggested for general use instead of 6.25 × N to calculate more accurate insect protein contents, whereas the average pure protein conversion factor kA of 5.6 is proposed for use in the case of insect protein isolates.

Highlights

The worldwide demand for animal protein increased over the past years and is presumed to continue to increase by over 50% until 2050, mainly driven by the population growth and increasing wealth
While insects are already consumed in many parts of the world, a new food law was only recently introduced to Switzerland in May 2017 which allows three insect species, namely Tenebrio molitor, Acheta domesticus, and Locusta migratoria, to be bred and sold as food products without requiring a permission [4]
The protein content is calculated by multiplying the nitrogen content with the nitrogen-to-protein conversion factor

Summary

Introduction

The worldwide demand for animal protein increased over the past years and is presumed to continue to increase by over 50% until 2050, mainly driven by the population growth and increasing wealth. Factors published by Jones [5] are used, who proposed as factor for animal proteins and as default factor for unknown proteins the value 6.25. This corresponds to an average nitrogen content of 16% in the pure protein (100%: 16% = 6.25) [6]. The high levels of protein contents reported in insects are often overestimated [8] It is not conclusively settled if a (partial) correction is possible by subtracting the non-protein nitrogen contained in the chitin exoskeleton from the total nitrogen content before calculating crude protein by N×6.25. Amino acid analysis is the only method to give reliable, accurate results for protein contents [9], and if not possible, use of an accurate, specific conversion factor for the food item is suggested [6]

Objectives

Methods

Results