Gel properties of potato protein and the isolated fractions of patatins and protease inhibitors – Impact of drying method, protein concentration, pH and ionic strength

Abstract

The use of plant protein in food products is increasing. Potato protein gelation is scarcely documented, therefore potato protein gel properties were tested for two whole protein isolates (freeze dried or spray dried) and the purified sub-fractions, protease inhibitors and patatins. The effects of protein concentrations, 8 or 15% (w/w), pH-range of 3.0–7.5, and 2 different levels of ionic strength; low (15 mM NaCl) or high (200 mM NaCl) on heat induced gel properties was studied by oscillatory rheology and by uniaxial compression. Spray drying did not impair gel properties of the whole protein isolates, with the spray dried isolate actually showing higher gel strength at most conditions.For whole protein isolates, gel strength expressed as the storage modulus (G′) had a minimum at pH 4.7 at both high and low salt. The isolated patatin fraction showed a similar trend at low salt, but at high salt the gel strength was very low at pH 3, with progressively higher values at pH 5 and pH 7.5. The protease inhibitor fraction gelled best at low salt and pH values below pH 3.3, while higher pH resulted in very weak gels with a 10-fold decrease in G’. Gel appearance was affected by protein sample, pH, and ionic strength. Both whole protein isolates and the protease inhibitor fraction formed translucent gels at pH 3.0 and ionic strength 15 mM, while patatin formed translucent gels at both pH 3.0 and pH 7.5 at low salt concentration. All other conditions resulted in opaque gels.