University of Arkansas, Fayetteville Division of Agriculture


The co-product of soybean after oil extraction is the meal, which is rich in protein. From this meal, protein concentrate and protein isolate are prepared and are commercially available as functional ingredients. Thermal treatment is the most common step applied to foods during processing. Changes in structural and functional properties can be affected by thermal or chemical treatments. The objective of this study was to evaluate the effect of heat on surface hydrophobicity, gelling properties, and viscosity of soy meal (SM), soy protein concentrate (SPC), and soy protein isolate (SPI). The soy products were subjected to heat at varying temperatures and heating times. Viscosity of soy protein products treated with heat increased for SM when temperature and heating times increased, but decreased for SPC and SPI. This may be due to the polysaccharides present in SM that could form starch gelation and increase meal viscosity. The surface hydrophobicity of the soy products increased when the proteins were treated with heat, possibly due to heat exposing the hydrophobic amino acids buried within the protein molecule making them become more hydrophobic on the surface of the molecule. When 8% suspensions (protein basis) were heated at 100°C, all soy products formed firm gels, indicating that protein plays an important role in gel network formation. Precaution must be taken to maintain functionality when heat processing is applied to food systems that contain soy protein products as functional ingredients.