43-7 |
Rheological properties of soluble leaf protein gels |
B. P. LAMSAL1, R. G. Koegel2, and S. Gunasekaran1. (1) Dept. of Biological Systems Engineering, Univ. of Wisconsin, Madison, Food & Bioprocess Engineering Lab., 460 Henry Mall, Madison, WI 53706-1561, (2) USDA-ARS-U.S. Dairy Forage Research Center, 1925 Linden Dr. W., Madison, WI 53706-1108 Soluble leaf protein (SLP) is a potential source of food protein which has good nutritional and functional properties like solubility, emulsification and foaming. Little information exists with regard to rheological properties of leaf protein concentrate gels. Our objective was to investigate the small-strain rheology of SLP solutions during gelation and large deformation properties of SLP and SLP-whey protein isolate (WPI) mixed gels. SLP concentrates were prepared by freeze-drying of acid precipitated proteins (pH 3.5) from clarified alfalfa juice. SLP solutions (5, 10 and 15% w/v) were prepared by dissolving freeze-dried concentrates in double-distilled water. The solution was stirred for 1 h and centrifuged at 10,000g for 10 min. Storage (G’) and loss (G”) moduli were monitored in a dynamic rheometer with cone and plate geometry during temperature sweep from 25 to 90°C and back to 25°C. Gels were formed by heating SLP solutions and WPI+SLP (at 1:1 and 3:1 ratios) solutions in molds at 90°C for 60 min and cooling overnight at 4°C. The gel samples were tested in compression to 80% deformation to determine the gel strength. The G’ values obtained during temperature sweep ranged from 50 to 180 Pa for 5 to 15% protein solution, which increased to 1 kPa to 2 kPa respectively while cooling back to 25°C. Though gels were weak, they exhibited distinct gelation temperatures of 69, 63, and 61°C for 5, 10, and 15% solutions, respectively. The compression tests also confirmed the weak gel properties of up to 15% SLP solutions. The gel strength improved substantially when WPI was added to SLP. The more the WPI fraction added, the stronger was the gel. In all cases gels were opaque. Results indicate that stable gels could be made in combination with WPI and other protein systems making it easier for incorporation of SLP in food and non-food systems.
Session 43, Food Engineering: Rheology and texture
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