Evaluation of the ultrafiltration method to obtain a high-value protein concentrate from the edible insect Tenebrio molitor

The fractionation of edible insects is one of the major topics related to using insects as food. Developing adequate protein recovery methods is essential to guarantee acceptable incorporation of insect protein fractions into functional food products, which in turn is essential to the development of insect-based products with higher consumer acceptance. This research aimed to produce high-purity protein concentrates from Tenebrio molitor larvae with favourable techno-functional properties, through membrane ultrafiltration with a 50 kDa cut-off, while also comparing with protein concentrates obtained through isoelectric point precipitation (IP). The protein fractions were evaluated for extraction efficiency (protein content, yield, and recovery rate), protein profile (size exclusion chromatography), and techno-functional properties (colour, foaming, and emulsifying properties, and water/oil absorption capacities). The >50 kDa fraction had a protein content above 80% (although lower than the IP fraction), while the <50 kDa fraction only had a protein content of 44.2%. Despite its high protein content, the >50 kDa fraction only attained a protein recovery rate of 27.9%, comparable to the IP fraction recovery rate. The >50 kDa fraction had higher (lightness) and (yellowness) colour than the IP, defatted fraction and powder samples (dried and ground T. molitor). However, all the obtained protein fractions presented a higher Browning Index than the defatted fraction. Additionally, the protein fractions presented better techno-functional properties than the powder or defatted samples, with the >50 kDa fraction presenting better properties than commercial protein concentrates (whey or pea protein). The protein isolation method based on ultrafiltration led to a protein concentrate with high purity and acceptable techno-functional properties, presenting itself as an alternative to the more common method based on isoelectric point precipitation.