Final Examination for the Degree of PhD - Madhu Sharma

Date and Time


Location: Webex meeting - Invitation will be sent to email lists 


Examining Committee  
Dr. Donald Mercer, Chair
Dr. Lisa Duizer, Advisor
Dr. Alexandra Grygorczyk, Advisory Committee Member
Dr. Douglas Goff, Department Member
Dr. Jianshe Chen, Zhejiang Gongshang University, External Examiner



Texture perception is a dynamic process which occurs when food is orally processed. The contribution of oral processing to perception has yet to be explored in a semisolid real food matrix. There are many aspects to oral processing and the aim of this research was to understand the effect of saliva on dynamic textural perceptions of pureed foods and find relationships between instrumental measures and perceptions. Pureed foods are the compensatory semisolid foods recommended for people with swallowing difficulties. Nine pureed carrot matrices made with starch (0.4, 0.8 w/w%), xanthan (0.2, 0.4 w/w%), their blends and a control were characterized for instrumental (with and without saliva) and dynamic sensory properties. In vitro bolus characterisation was done after adding fresh stimulated saliva to the sample. Perceived textural evolution measured using dynamic sensory techniques of Temporal Dominance Sensations and Temporal Check-All-That-Apply indicated that 3-4 attributes were perceived for each sample during the entire oral processing time. Both tests gave similar results about texture dynamics and divided samples into two groups based on graininess. Control and starch-only samples were perceived as grainy and the remaining products were perceived as smooth. Instrumental measures of viscosity showed that, at a shear rate of 10 s-¹ viscosity decreased with hydrocolloid addition and saliva incorporation. Storage modulus varied between samples based on hydrocolloid and its concentration. In comparison to the control, friction measurements increased for all samples and also increased with addition of saliva. Oral starch breakdown measured in terms of maltose released, for control and starch samples (0.4, 0.8 w/w%), although not statistically significant, showed variation with starch concentration and oral processing times. Perceived thickness measured at different time-points of oral processing increased with starch concentration and decreased at a constant rate among these three samples.

Findings from this work showed that it is important to include saliva in instrumental measurements to understand the dynamics of texture during oral processing of a semisolid food. Changes in oral starch hydrolysis due to the action of salivary amylase, from ingestion to swallowing, can help explain the decrease in perceived viscosity in a starch-based texture modified food.

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