Rheological characterization of amaranth protein gels

Abstract

Gel forming properties of amaranth proteins at different thermal conditions and protein concentration were studied. Gel point ( G′ and G″ crossover) and gelation kinetics ( G′ vs. time) were analyzed. The type of gel formed from the rheological point of view was studied analyzing the rheograms obtained from frequency sweeps. Texture properties of cold-set gels were analyzed by TPA assays. Minimum conditions for gelation were 7%, w/v and 70 °C. Elasticity of heated dispersions and gels increased with the increase of protein concentration. A high value of the network structure index was observed. This behavior could be related to the great proportion of disulfide bonds formed during amaranth protein gelation. At temperatures above 70 °C (80, 90 and 95 °C), gelation of dispersions (15%, w/v) took place at times less than 5 min. A first order kinetic gelation process with reaction rate specific constant values that increased with the increase of heating temperature was observed. A rapid denaturation of globulins followed by sulfhydryl/disulfide interchange reactions between protein molecules conduced to a gelation phenomenon enhanced by protein aggregation. Gels prepared over critical conditions ( T>70 °C, protein concentration >7%, w/v) presented a strong gel-like behavior. These type of gels were elastic in nature (tan δ<0.1), of high hardness, fracturability and cohesiveness, although presented low adhesiveness. Depending on protein and thermal conditions, amaranth proteins were able to form self-supporting gels that could be applied in different gel-like foods.