Heat-induced reversible gelation of arachin: kinetics, thermodynamics and protein species involved in the process

Abstract

Arachin forms a heat-reversible gel under certain experimental conditions. The minimal gelling concentration for this sytem is 7.25%. Above minimal gelling concentration calculation of thermodynamic parameters for gelation of arachin revealed a constant ΔH bonding (—1220 cal.mol −1 where ΔS bonding values varied with an increase in protein concentration (ranging from −4.01 e.u. at 7.5% to −3.48 e.u. at 10.0%). The main steps involved in the gelation phenomenon include thermal denaturation of arachin, partial aggregation of heat-denatured protein molecules, setting of protein solution and maturation of the gel formed. Gel maturation process follows first order kinetics and is characterized by a large positive ΔG + + (22030 cal.mol −1). Determination of ΔH + + and ΔS + + for this process reveaed that mostly ΔS + + (—62.9 e.u.) contributes to the large positive ΔG + +, thus decreasing the overall rate of gel maturation process. This large negative ΔS + + value probably arises from a loss of entropy of protein molecules because of their increased involvement in gel network formation. The polymer gel network seems to be primarily contributed by a part of both arachin dodecameric and hexameric species.