Kinetic compensation effect in depolymerisation of food polysaccharides

The thermal depolymerisation kinetics of agarose and kappa-carrageenan in w ater were investigated by measurement of intrinsic viscosity ([eta]) An iso kinetic relationship (IKR) revealing a kinetic compensation effect in polys accharide depolymerisation was then discovered from the obtained kinetic da ta and those reported in the literature. Generally, the Arrhenius frequency factor, k(0), and activation energy, E-a, of depolymerisation of agarose, kappa/lambda-carrageenan, kappa-carrageenan and schizophyllan, under common ly used thermal conditions (high temperature, in water or pH-7 solvents, wi thout deaeration and in disordered conformation), were in the ranges of 1.8 x10(7)-7.8x10(10) s(-1) and 97-126 kJ mol(-1), respectively. These two vari ables showed parallel increases when using solvents of lower pH values (esp ecially in k(0)) or with deaeration, and polysaccharides in ordered conform ation or at lower concentrations. The IKR for the polysaccharide depolymeri sation was: In k(0)/s(-1) = 0.379.E-a/kJ mol(-1)-18.5 (R-2=0.906), giving a n isokinetic temperature (T-iso) of 317 K. Conclusively, the depolymerisati on mechanism was the same for all polysaccharide systems examined. (C) 1999 Elsevier Science Ltd. All rights reserved.