Physiological measures related to crispness perception of extruded snacks : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Albany, New Zealand

Published research for understanding crispness perception has relied on correlations of sensory results to objective measurements. This research was undertaken to evaluate the contribution of physiological responses to the perception of crispness of corn based puffed snacks. Predictive models published in literature relate crispness perception to instrumental force and sounds produced during biting and compression. These models were used as the basis for this research. Air-conducted and bone-conducted sounds were measured using both consumer and trained panelists. A novel analysis technique, fractal analysis, was used to analyse the jagged sound wave patterns produced during biting into extruded snacks. A specialised bite force apparatus was designed for measuring bite forces produced by the incisors. All physiological results were then related to panelists' perception of crispness. To minimise sample variability, extruded snack samples were prepared and used throughout the entire trial. A range of crispness levels were achieved by equilibrating the extrudates over various water activities. Consumer panelists and trained panelists consistently agreed on the relative crispness of the extruded snacks. Air-conducted sounds and bite force showed significant correlations with crispness, while bone-conducted sounds did not. Bite force measures were also shown to relate to instrumental measures of force. For statistical validity, the physiological data from the 39 consumers were used to develop predictive equations for crispness. Analysis of the data showed no significant correlation between the physiological data and crispness. Therefore, it was not possible to develop a predictive equation for crispness based on the physiological measures collected from consumers. While there are reports linking crispness to various instrumental measures, this is the first time in-vivo physiological measures have been collected from a large group of individuals for development of statistically viable models for crispness. The lack of a relationship between crispness and physiological measures indicates that crispness perception across consumers is complex and not adequately explained by bite force and sounds alone