Compositional, functional and sensory properties of protein ingredients

Soy protein products are gaining importance as ingredients in the food industry. A number of soybean meals have been investigated as starting materials for the production of soy protein ingredients. Hexane-extracted and flash-desolventized soybean meals, known as white flakes (WF), are most commonly used, but have disadvantages of containing solvent residue and being too expensive for processing identity-preserved soybeans. Gas-supported screw pressing (GSSP) is a new soybean oil-extraction process that combines screw pressing with injecting carbon dioxide (CO2) under pressure. The objective of the present research was to investigate GSSP meal and its protein products by determining yields, composition, functional properties, preservation methods and sensory properties. The properties of GSSP meal proteins were compared to traditional soy protein products produced from WF. For the laboratory-scale study, analytical, chemical and functionality tests were performed on the starting materials and isolated soy proteins. Soy protein isolate (SPI) prepared from GSSP meal had higher protein yield, fat content, water-holding capacity (WHC) and viscosity, and better emulsification and fat-binding properties than SPIs prepared from WF. The SPIs produced in the pilot plant were analyzed for composition and functionality. Hydrogen peroxide (H2O2) treated SPIs were compared to jet-cooked SPIs. GSSP SPIs did not differ in functionality from SPIs prepared from WF, except for having lower solubility and poorer foaming properties. H2O2 used as a preservative improved solubility, emulsification and foaming properties and reduced glycinin and β–conglycinin (β–con) denaturation. A descriptive sensory panel study with 12 trained panelists evaluated the aroma, flavor and mouthfeel of SPI and glycinin–rich (gly–rich) and β–conglycinin–rich (β–con–rich) soy protein fractions extracted from both GSSP meal and WF. Protein products prepared from GSSP meal were similar to protein products prepared from WF except for having greater mouthcoating. Regardless of starting material, the gly–rich and β–con–rich fractions had stronger fishy aroma, less floury aroma, less raw beany aroma and less floury flavor than the SPIs. Hunter color LAB data indicated GSSP meal was more yellow (higher b* value) in color compared to WF. SPIs were darker (lower L* value) than than the gly–rich and β –con–rich fractions. Overall, protein products prepared from GSSP meal were similar in composition, functional and sensory properties to protein products prepared from WF. These findings demonstrate that the GSSP process can produce defatted meals suitable for manufacturing soy protein ingredients. Because GSSP plants can be profitable at low capacity (50 mt/day) compared to solvent extraction (3000 mt/day), GSSP is suitable for processing identitypreserved soybeans that contain value-added traits. Additional benefits are that there are no concerns over residual organic solvents and the process complies with “organic“ definitions