Stress Relaxation Analysis of Food Gels according to the Cooperative Flow Theory

Abstract

A personal computer was interfaced with a compressing-tensiling digital rheometer so that stress relaxation analysis could be performed and analyzed automatically. This equipment eliminated time consuming measurements and analysis of viscoelasticity of hydrogels of food stuffs. In addition, simulation results of stress relaxation phenomenon according to a cooperative flow theory could be shown on either a system display or on a printer. The rheometrical system was suitable for gels with a lower limit of 0.3s for the relaxation time. The rheological properties of hydrogels of agar (1%), low methoxyl pectin (LMP, 2%), κ-carrageenan (1%) and gelatin (3%) were analyzed by a cooperative flow theory. The data for the time dependence of the relaxation function suggested the existence of two separate flow processes for gels of agar, LMP and κ-carrageenan. One process occurred at early times (10-1-10s) and the other occurred at late times (10-103 or 10-104s). For gelatin gel, a flow process only at late times (<104s) was found. Typically the observed half relaxation time was longer for the gels which had a more dense by packed microstructure than that of the gels which had a three-dimensional network structure. But a cooperative flow theory may not be adaptable for agar gels in stress relaxation analysis.