Submitted to: Journal of Food Science and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/25/2006
Publication Date: 11/2/2006
Citation: Carvalho, C.W., Onwulata, C.I., Tomasula, P.M. 2007. Rheological Properites of Starch and Whey Protein Isolate Gels. Journal of Food Science and Technology. 13(3):207-216. Interpretive Summary: Snack foods are made from starches and contain very little protein. Cheese whey protein isolates (WPI) are very nutritious and can be combined with some starches to improve the nutritional content of snack foods. However, whey protein isolates are not compatible with all starches. To understand the interactions between WPI and different starches that may be used to make snack foods, we studied the mixing behavior of WPI with four different starches, corn, Amioca™, cassava, and tapioca. Mixing whey protein isolate with starches reduced the mix paste thickness for all starches. We learned that amylose, one of two main components of starch, makes the most difference in thickness because whey protein isolate interferes with its structure. This effect was seen through the microscope which showed that whey protein did not mix well with amylose. Knowing this, food manufacturers can now reduce the quantity of amylose in starch to allow them produce nutritious foods, which will benefit U.S. consumers.
Technical Abstract: Whey proteins are increasingly being combined with starches and flours to make nutritious extruded snacks. The effect of whey proteins on the rheological properties of starch was investigated. The paste viscosity of starches Amioca (~0.5% amylose), native corn (~27% amylose), Hylon VII (~70% amylose), tapioca (~21% amylose), and their mixture with whey protein isolate (WPI; 50/50) mixtures at varied solid concentration of 2.5, 5, 10, 15 and 20% was determined using two types of visco-analyzers - the Micro ViscoAmylograph (MVA) and the Rapid Visco Analyser (RVA). The rheological properties of the resulting gels were determined along with the microstructure of selected gels, by scanning electron microscopy. RVA paste viscosity of all starches and WPI starch mixtures was greater than those measured by MVA. WPI pastes measured by RVA showed a tremendous increase in viscosity during the cooling cycle at higher concentration than MVA. This finding was supported by SEM microstructure that showed RVA gel formed by uniform network of coarse particles than fine structures in the MVA gel. Inclusion of WPI reduced the paste viscosity of all starches, except for Hylon VII at 20% solid concentration. The gel strength of high amylose content gels, Hylon VII and corn was reduced by WPI. In contrast, gels of tapioca and Amioca showed similar rheological properties to their mixtures with WPI. Gels of WPI/Tapioca and WPI/Amioca had similar rheological properties as their pure starch gels, suggesting that in applications such us extrusion puffing that they may expand similarly.