Seed proteins come naturally packaged in highly folded conformations that reduce functional properties. Therefore, environmental conditions can be modified to break non-covalent bonds that hold native proteins in their folded conformations. This presentation will illustrate the structure-function effects of the manipulation of environmental conditions using pea and rapeseed proteins. Subjecting pea proteins to 600 MPa led to significant protein unfolding as reflected in the reduction in intrinsic fluorescence intensity when compared to the untreated protein. The effect of this high pressure treatment on pea protein functionality was more evident at pH 3.0 where the mean oil droplet size of emulsions was reduced by about 50% when compared to pH 5.0 and 7.0. Foam forming ability was also significantly enhanced by high pressure treatment at pH 3.0 with foam volumes that were 30-60% bigger than those formed at pH 5.0 and 7.0. In contrast, heat pretreatment of pea proteins led to significant losses in emulsion and foam formation capacities at pH 3.0 and 5.0 but not pH 7.0. This was attributed to the more extensive protein denaturation as revealed by the quenched intrinsic fluorescence at pH 3.0 and 5.0. Mean oil droplet size was smallest at pH 7.0 when compared to pH 3.0 and 5.0, irrespective of temperature of heat treatment. For rapeseed proteins, high pressure or heat treatments led to decreases in the content of free sulfhydryl groups while the surface hydrophobicity was significantly enhanced. Theses structural changes were reflected in the increased denaturation temperature and reduced heat of denaturation (enthalpy change) of the rapseed proteins from 98<sup>o</sup>C in the native to 104<sup>o</sup>C and 10.25 J/g to 3.72 J/g, respectively after 400-600 MPa treatment. Interestingly, high pressure treatment resulted in rapeseed proteins with reduced α-helix and random fractions, which indicate a more ordered structural conformation when compared to the untreated protein. Gelling ability of the rapeseed proteins was significantly enhanced by high pressure treatment with least gelation concentration decreasing from 15% (w/v) in the untreated to 6% (w/v) after 600 MPa treatment. The high pressure treatment led to formation of harder gels with increased springiness and chewiness. These studies confirm that significant improvements in the structure-function properties of food proteins can be achieved through simple controls of pH, temperature and pressure.

Modulation of the structure-function properties of plant proteins by pH, temperature and high pressure

ACS Fall 2021

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