Abstract

Various alfalfa soluble leaf protein concentrates were prepared by freeze-drying acid-precipitated proteins (pH 3.5), resolubilized proteins (pH 7), and membrane-concentrated clarified alfalfa juice. Dilute leaf protein solutions were prepared by dissolving these concentrates in water. Storage modulus (G. ) of soluble leaf protein solutions as they gel was monitored with a cone-and-plate probe during temperature sweep from 25°C to 90°C and back to 25°C. G. values during the heating phase ranged from 5 to 120 Pa for 1.6% to 4% protein solutions. They increased to 3 kPa for 4% protein solution while cooling back to 25°C. Although resulting gels were weaker, they exhibited distinct gelation temperatures of 77°C, 68°C, 66°C, and 60°C for 1.6%, 2.7%, 3.6%, and 3.9% acid-precipitated SLP solutions, respectively. Apparent viscosities of solutions were also studied as a function of temperature and shear rate. Similar tests were conducted for soluble leaf protein and whey protein isolate biopolymer systems at different ratios. At 1:3 ratio, leaf proteins interacted with whey proteins to increase G. during heating and cooling. The compressive failure force of standing gels produced from soluble leaf proteins and whey protein mixtures correlated well with their G. values from solution rheology. Results indicated that stable soluble leaf protein gels could be made in combination with whey protein isolates, presenting the possibilities to incorporate them in food and non-food systems.

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