Effect of pre-treatment and drying method on physico-chemical properties and dry fractionation behaviour of mealworm larvae (Tenebrio molitor L.)

Edible insects have emerged as an alternative source for feed and food. Fractionation is considered as a promising strategy to produce standardised insect-based intermediates to augment industrial applicability and consumer acceptance. So far, mainly wet fractionation techniques were studied to separate insect components and concentrate protein. This study investigated a dry fractionation approach to yield protein-enriched and differently composed fractions of mealworm larvae (Tenebrio molitor). The influence of post-harvest procedures including different pre-treatments (blanching, freezing, etc.), drying methods (oven drying, fluidized bed drying, freeze-drying, etc.), and defatting on physico-chemical properties of the larvae were studied. Furthermore, the impact of pre-processing on disintegration of larvae during roller milling was investigated via sieve classification. Applied post-harvest process chain significantly affected the colour, dimensions, apparent density, and hardness of dried larvae with an impact on fractionation behaviour and characteristics of the obtained fractions. Drying at elevated temperatures caused pronounced darkening and shrinkage due to browning reactions and tissue collapse. Mechanical properties were affected as well leading to heterogeneous particle size distributions after milling and sieving. A large fraction of particles < 500 A mu m was determined for samples exhibiting low mechanical hardness such as freeze-dried and defatted larvae. Significant differences in macro-nutrient composition of the sieving fractions were found deviating in chitin (3.6-16.1%db), protein (52.5-58.2%db) and fat (21.4-26.6%db) content. Highest protein recovery of max 72% was determined in the particle size fraction 500-1000 A mu m. Concluding, these results provide insights into physico-chemical characteristics of mealworms affected by pre-treatment and drying. The potential of dry fractionation techniques for protein enrichment and delivery of a variety of differently composed mealworm fractions was demonstrated and may provide an interesting potential to optimize water and energy consumption during insect fractionation.