D. D. Hamann

Polyacrylamide gels as elastic models for food gels

Abstract The physical properties of Polyacrylamide gels (10% w/v) were evaluated by dynamic oscillatory testing, stress relaxation and torsional fracture analysis. Gels had a linear relationship between shear stress and strain when deformed to fracture; thus small strain (storage modulus, G′) and large strain (fracture modulus, Gf) moduli were equivalent. Non-fracture and fracture tests showed that gels maintained an entropy (rubber) elastic response over all testing temperatures (10–80°C). Shear stress at fracture was independent of temperature, whereas shear strain at fracture decreased as temperature increased. This was associated with increased thermal motion strains decreasing the amount of mechanically induced strain required for fracture. Our results have shown that Polyacrylamide gels are a suitable elastic model for understanding the molecular mechanisms of food texture.

Fracture properties of konjac mannan gel: effect of gel temperature

Abstract Fracture properties of 2% konjac mannan (KM) gels were determined by torsion testing at several temperatures. Two treatments were evaluated: 3:1 and 2:1 ratios of alkali:KM (v/w). Capstan geometry gels were equilibrated to 5, 20, 35, 50, 65 or 80°C. Shear stress at fracture was invariant with test temperature. This response suggests a permanently bonded network. However, there were no covalent links believed to be present in stabilization of KM gels. Shear strain at failure decreased linearly with increasing temperature, a typical response of entropy elastic gels. It is observed that the ‘total’ strain at fracture, the sum of mechanically produced strain and internal thermal motion strain, remains constant throughout the range of test temperatures. Total strain was estimated at ~3.4 by extrapolation to absolute zero. KM gels, although probably not covalent in nature, respond to mechanical deformation as permanently bonded systems during the short stress times involved in the present study.