Effects of Sugars on Syneresis of Agarose Gel

Syneresis Phenomena of Foods Part 3

Abstract

By analysing the rate of syneresis and measuring storage modulus of agarose gel and sugar-agarose gel (monosaccharide: fructose, glucose, disaccharide: maltose, sucrose), the following results were obtained. (1) Syneresis increased gradually with increasing overall pressure, namely the sum of the endogenous pressure, the pressure caused by weight of gel and external pressure. (2) Syneresis decreased as storage modulus of the gel was higher. Sugars added increased storage modulus of the gel. (3) Syneresis increased gradually with time and then reached an equilibrium position. The rate of syneresis is expressed as dM/dt=k(1-M)², where M=m/m_∞ (m: syneresis at holding time, t, m_∞: the equilibrium syneresis) and k is the rate constant of syneresis. (4) m_∞ of agarose gel decreased with an increase in concentration of agarose and sugar added. On the other hand, k of agarose gel increased with increasing concentration of agarose, while k of sugar-agarose gel decreased with increasing amount of sugar added. (5) The apparent activation energies of syneresis were 1.7kJ⋅mol^-1 for agarose gel, 2.5kJ⋅mol^-1 for fructose-agarose gel, 8.1kJ⋅mol^-1 for sucrose-agarose gel, respectively. (6) Storage modulus of the gels decreased as syneresis increased. It can be considered that loose network structure in agarose and sugar-agarose gels, caused by syneresis, is responsible for the decrease in storage modulus.