Sensory Texture and Fundamental Rheology of Agar and Agarose Gels

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Title: Sensory Texture and Fundamental Rheology of Agar and Agarose Gels
Author: Barrangou, Lisa
Advisors: MaryAnne Drake, Committee Member
Christopher R. Daubert, Committee Co-Chair
Den Truong, Committee Member
E. Allen Foegeding, Committee Chair
Abstract: Texture properties of foods are an important component of food quality perception and acceptability. In order to design specific textures with predictable sensory attributes, a molecular understanding of food structures and their corresponding texture is necessary. Fundamental rheological methods are valuable tools for investigating structural mechanisms because they are based on physical and chemical theory, and when combined with descriptive sensory analysis, structure-function relationships can be established. The overall objective of this research was to utilize model food systems to further elucidate how physical properties of foods relate with the dynamic sensory perception of texture. Agar and agarose gels were used as model food gel systems. Initially, rheological profiles of agarose gels were developed, including linear, non-linear and fracture properties. Gel properties were examined under conditions of varying agarose concentration, solvent conditions, and strain rate. Increasing concentrations of agarose produced an increasingly stronger, more brittle network, while increasing concentrations of glycerol produced an increasingly stronger, more deformable network. All fracture properties and non-linear behaviors increased with increasing strain rate in a similar manner, suggesting a general mechanism responsible for strain rate effects that is similar for non-linear and fracture behavior. Additionally, a new model was proposed to reliably describe and quantify non-linear behavior. Descriptive analysis was used to quantify the perceived hand texture characteristics of agarose gels, and results were compared with fundamental rheological profiles to determine if structure-function relationships could be established. Sensory small-strain and fracture causing forces were capable of differentiating the gels equally as well, indicating that relative gel strength was perceived similarly with non-destructive and fracture causing deformations. Surprisingly, hand force terms correlated more highly with fracture modulus (fractures stress / fracture strain) values (r ≥ 0.98, p ≤ 0.001) than fracture stress values (r = 0.76-0.82, p ≤ 0.05), suggesting sensory perception of force includes a coupling of stress and strain. Additionally, sensory deformation perceived at fracture correlated highly with fracture strain values (r = 0.98, p ≤ 0.001). Small-strain rheological tests could not distinguish gels as sensitively as fracture properties, indicating that fracture properties relate to sensory texture better than small-strain rheology. Descriptive sensory analysis and fundamental large-strain rheological methods were also used to characterize texture characteristics of agar gels. Gels were differentiated in the same manner by sensory texture analysis in the mouth and rheological properties (p ≤ 0.05), and significant correlations between sensory and rheological properties were reported. First bite and chew-down sensory terms highly correlated with each other and with fracture properties. Specifically, the first bite sensory term of force required to cause fracture correlated well with the chew-down sensory term chewiness (r > 0.99, p ≤ 0.0001), and both of these sensory terms highly correlated with the fundamental rheological property, fracture modulus (r > 0.94, p ≤ 0.05). The first bite sensory term deformability perceived at fracture highly correlated with fracture strain values (r = 0.88, p ≤ 0.05), while the chew down property of particle breakdown negatively correlated with fracture stress values (r = -0.97, p ≤ 0.05). Additionally, the sensory properties that contribute to perception of strain-hardening were determined, and were found to correlate with non-linear rheological behavior, which is an important first step in understanding how non-linearity influences sensory perception of texture. These findings clearly demonstrate that fundamental large-strain rheological properties give valuable information toward the understanding of sensory perception of physical properties of foods.
Date: 2006-01-18
Degree: PhD
Discipline: Food Science
URI: http://www.lib.ncsu.edu/resolver/1840.16/5543


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