Relationships Between Physical, Chemical, and Functional Properties of Enzymatically-Modified and Unmodified Soy Protein (Nmr, Plasteins, Denaturation, Extrusion)
The principal objective of this study was to investigate and establish relationships between various physical, chemical, functional, and gross conformational properties of enzymatically-modified and unmodified soy protein isolate (SPI). Systems were analyzed for average molecular weight (AMW), TCA and water solubility, functionality, process performance, (twin-screw extrusion), and high-resolution pulsed proton magnetic resonance (PMR). The effects of solvent state, pH (pD), and extent of hydrolysis (EH) on gross conformational properties of SPI were studied by PMR (360 MHz) using novel spectral analysis techniques. Spectral resonance peak width at half height (PW) and "peak intensity ratios" (PIR) were, in many cases, found to correlate strongly with physical/chemical properties of hydrolyzed and unhydrolyzed SPI. The methyl proton resonance PW (assigned to Leu, Ile and Val) and PIR calculated as the ratios of "hydrophilic" divided by "hydrophobic" resonance peak heights were found to be markedly affected by EH, solvent composition, and pD level. PIR calculated from ratios of CH resonance zones (the so-called "end"/"coil" PIR) were also strongly related to EH. PMR results suggest that proteolysis, solvent denaturation, and alteration in solution pD levels induced gross conformational changes in SPI molecules possible due to dissociation, unfolding, and/or swelling in solution. Results also imply that hydrophobic interaction may be the principal stabilizing force in soy proteins. The PMR technique, thus, may represent a powerful new analytical tool for the qualitative and quantitative assessment of gross physical state of complex food proteins in solution. A separate study investigated how protein texturization was influenced when various mixtures of hydrolyzed and unhydrolyzed soy proteins were twin-screw extruded. Feed hydrolysate levels strongly affected feed properties, extrusion conditions, and product characteristics, often in a highly linear fashion. Another set of experiments explored relationships between AMW, TCA and water solubility of plasteins formed under variable incubation substrate concentration and using several different proteases. Results indicated that plasteins were low in molecular weight and that substrate concentration, AMW, TCA and water solubility were highly intercorrelated in most cases. Other results showed that the TCA solubility test could be used to gauge the effects of nonprotein substances on plastein and hydrolysate formation.
Agriculture, Food Science and Technology
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign