Heterologous expression and characterization of the hydrophobin HFBI in Pichia pastoris and evaluation of its contribution to the food industry.

The class II hydrophobin HFBI from Trichoderma reesei was heterologously expressed by Pichia pastoris using pPIC9 vector under the control of the promoter AOX1. The recombinant HFBI (rHFBI) was purified by ultrafiltration and reverse-phase high performance liquid chromatography. Tricine-SDS-PAGE and Western blotting demonstrated that rHFBI with the expected molecular weight of 7.5 kDa was secreted into the culture medium. X-ray photoelectron spectroscopy and water contact angle measurements indicated that rHFBI could lead to the conversion of the wettability of the hydrophobic siliconized glass and hydrophilic mica surfaces relying on the self-assembly membrane on hydrophobic/hydrophilic interfaces. It was demonstrated that rHFBI had the ability to stabilize oil droplets, which was far excess of the class I hydrophobin HGFI heterologously expressed in P. pastoris (rHGFI) and the typical food emulsifier sodium caseinate. In gushing experiments, it was shown that rHFBI was a strong gushing inducer in beer, whereas rHGFI did not display any signs of gushing. This provided the potential of rHFBI to be used as a novel emulsifying agent and a predictor of gushing risk.