Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/23/2007
Publication Date: 7/10/2007
Citation: Liu, K., Fu-Hung, H. 2007. Protein-Protein Interactions in high moisture-extruded meat analogs and heat-induce soy Protein Gels. Journal of the American Oil Chemists' Society. 84(8):741-748
Interpretive Summary: This work was not an ARS funded project. It dealt with extrusion of plant proteins, mainly soy proteins and gluten, into fibrous meat analogs under a high moisture and high temperature condition, using a twin screw extruder. High moisture extrusion is a promising and emerging technology in producing meat alternatives having structure similar to muscle meat. The objective of the study was to investigate protein-protein interaction during extrusion. The rationale for this objective was that, based on literature review, the mechanism of protein-protein interactions during extrusion has not been well understood. On the practical aspect, by knowing the mechanism, we can improve production efficiency and end product quality. To achieve the objective, we compared protein-protein interaction during extrusion with that of heat-induced protein gel formation. Our hypothesis was that both soy protein gels and extrudates have the same types of chemical bonds, namely covalent disulfide bonds and non-covalent interactions. What sets the two apart from each other in terms of thermal reversibility and structure rigidity is the relative proportion of each type of bonds in their structures. Protein gels primarily consist of non-covalent bonds, but the disulfide bond is also partially responsible; whereas for forming the fibrous structure of soy protein extrudates, both non-covalent bonds and covalent disulfide bonds are important. The significance of this study is that the results supported our hypothesis and thus gave us better understanding of protein-protein interaction during high moisture extrusion.
Technical Abstract: Two commercial soy protein isolates were made into fibrous meat analogs by high moisture extrusion or into gels by heating and cooling, at varying concentrations and/or temperatures. Protein-protein interactions by extrusion or gelation were investigated through protein solubility studies of raw and finished products. All samples except for extrudates exhibited similar patterns of solubility in four selected extractants. Phosphate buffer (PB) extracted the least amount of protein. Addition of dithiothreitol (DTT) to PB improved protein solubility, indicating the presence of disulfide bonds. PB+Urea and PB+Urea+DTT gave the highest and almost equal amount of extractable proteins from all samples, except that extrudates from which protein could not be extracted effectively by PB+Urea, implying that disulfide bonding was more pronounced during extrusion than gelation. The results support our hypothesis that soy protein gels and extrudates both have the same types of chemical bonds, namely covalent disulfide bonds and non-covalent interactions. It is the relative proportion of each type of bonds in their structures that differentiates the two with respect to reversibility and structure rigidity. In forming protein gels during heat-induced gelation, non-covalent bonds play a dominant role over disulfide bonds; whereas for forming the fibrous structure of protein extrudates, non-covalent bonds and covalent disulfide bonds are both important.