Interfacial/foaming properties and antioxidant activity of a silkworm (Bombyx mori) pupae protein concentrate

The current consumer demand for healthier diets, the growing interest in the search for new sources of protein, and the desire to reduce the negative effects on the environment have increased interest in the study of insect proteins. The present study focused on the technofunctional characteristics (interfacial and foaming properties) and the in-vitro antioxidant activity of a protein concentrate obtained from silkworm (Bombyx mori) pupae (SPC). The isoelectric point of the SPC was close to pH 4.0-5.0 as determined by protein solubility and z potential analysis. Given that the SPC had solubilities of similar to 50% and z potentials of similar to 20 mV at pH 2.0 and 8.0, it was decided to further study SPC properties at these pH values. The supernatant obtained after adjustment of SPC to pH 8.0 showed higher (p < 0.05) antioxidant activity than that at pH 2.0 when analysed by the ferric reducing antioxidant power (FRAP) assay (168.0 +/- 3.0 V. 43.5 +/- 8.1 mu mol Trolox Eq. center dot g(-1) protein). However, no significant differences in antioxidant activity were found between pH 2.0 and 8.0 when using the oxygen radical absorbance capacity (ORAC) assay (1826.0 +/- 131.9 vs. 1659.2 +/- 46.8 mu mol Trolox Eq. g(-1) protein). The interfacial properties of SPC were determined at pH 2.0 and 8.0 during protein adsorption and after reaching the pseudo equilibrium state by means of dilatational and interfacial shear rheology following by foaming capacity and stability analyses. Faster adsorption kinetic values were obtained at pH 8 (k(D)* <1/4> 69.2 +/- 0.4 Vs. 29.5 +/- 0.9 mN/m.s(-1/2) at pH 2.0). However, lower kinetic values at pH 2.0 increased the elastic behaviour of the viscoelastic interfacial film formed (E'(s) similar to 30 mN/m at pH 2.0 V. E'(s) similar to 20 mN/m at pH 8.0), which can be related with the higher protein sizes found at pH 2.0. These rearrangements of the SPC components appeared to increase its foaming capacity, whereas the foaming capacity of SPC adjusted to pH 8.0 was minimal.