Moisture, temperature affect protein-protein interactions.

Extrusion-cooking peanut flour creates unusual qualities in the end product. These characteristics are caused by the severe shear forces and high temperatures to which the flour is subjected. However, it is difficult to understand the behavior and conformational changes that the proteins in the flour undergo when they are extruded.

Researchers have been able to examine protein-protein interactions by determining the solubility of proteins with different buffers and their chromatographic elution, depending on their aggregation state. The focus of research at the University of Georgia was to determine the effect of extrusion on peanut protein interactions. They found that extrusion strongly affects the solubility of peanut proteins. Moisture and temperature conditions play a major role in protein-protein interactions. These conditions can have significance in optimizing extrusion parameters.

Scientists sequentially extracted unextruded peanut flour and two samples of 50% peanut flour-50% corn starch. They used chromatography to determine the differences in aggregation and protein composition of the various aggregates. Their results showed a marked difference in the solubility of the samples. There was a high amount of disulfide interactions in some samples. This was reconfirmed by size-exclusion chromatography of the extracts.

However, non-covalent interactions were predominant in a high moisture-lower temperature extruded sample, compared with a lower moisture-high temperature extruded sample. Ion-exchange chromatography revealed the elution of three main peaks along with a large amount of unbound proteins.

Further information. Dick Phillips, Department of Food Science and Technology, University of Georgia, 1109 Experiment St., Griffin, GA 30223; phone: [phone]; email: [e-mail].