Modification and Molecular Interactions of a Soy Protein Isolate
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2007-06-27
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Abstract
Soy is a nutritional protein source with gelation and emulsification abilities that have expanded its use in the food industry. This research aimed to further the capabilities of soy protein by producing a readily reconstituted isolate capable of gelling at ambient temperatures. The modified soy protein isolate would have application in food systems requiring a high quality vegetarian protein and gelation ability without reaching required denaturation temperatures. Foods where the isolate may find use include a shelf stable soy protein based powder that may be used "on the go" to form a pudding type of dessert upon the addition of water.
Soy protein was modified with a heat treatment that denatured the protein at a concentration required for gelation (8% w⁄w). The resulting soy protein isolate demonstrated immediate dispersibility and gelation in water, as well as heat stability during subsequent rheological thermal scans. The heat modified soy protein also remained two orders of magnitude higher in viscosity than an isolate that was originally denatured below a concentration required for gelation, after both of the isolates received a second thermal treatment at 8% protein (w⁄w). The viscosity difference between the two isolates demonstrates the importance of concentration at the point of denaturation, as irreversible denaturation may prevent interactions leading to preferable functionality at a later point.
The molecular interactions governing the gelation of the heat modified soy protein isolate were also investigated, as it is important to understand the network providing functionality for potential improvement. It was determined that while hydrophobic interactions contribute to a majority of the network influencing final viscosity, intermolecular disulfide bonds must initiate network formation.
The heat modified soy protein isolate demonstrated an ability to conjugate to dextran (100-200 kDa) via Maillard reaction during a dry heat procedure. However, the conjugation of dextran (100-200 kDa) to the native soy protein isolate displayed a viscosity several orders of magnitude higher than the heat modified soy protein conjugate. The native soy protein isolate also showed a higher viscosity and greater ability as an emulsifier when conjugated to higher molecular weight polysaccharides such as dextran (100-200 kDa) than when conjugated to small molecular weight sugars such as mannose. Therefore, the heat modified soy protein isolate demonstrated gelation at ambient temperatures, whereas the high molecular weight soy protein conjugate demonstrated better emulsifying capabilities.
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Keywords
emulsifying properties, hydrophobic interactions, disulfide bonds, gelation, soy protein isolate
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Degree
MS
Discipline
Food Science
