Food oral processing: Exploring the relationship between texture perception and bolus rheology

Abstract

Food oral processing alters bolus structure, mechanical and rheological properties, and perceived texture. A greater understanding of the relationships between these areas is valuable for the food industry. Possible applications include instrumental measurement of perceived texture and specialised food design. This thesis aimed to use a biscuit-based model food for advancement of the current understanding of oral processing. Masticatory behaviour was measured by timing mastication, counting chews, and calculating chewing frequency. Bolus composition and structure were monitored using visual inspection and a gravimetric analytical technique for moisture content determination. Bolus mechanical and rheological properties were quantified using back extrusion and consecutive double compression. Texture perception was followed using both conventional and discrete point temporal dominance of sensations. The single subject utilised different breakdown pathways when chewing three biscuit recipes with differing initial sensory and instrumental hardness and moisture content. In the early stages of mastication, perceived textural intensities reflected differing initial fracture properties. During the middle stages of mastication, a transition from fracture to rheological properties dominating perception occurred. This corresponded to changes in bolus structure, moisture content, and mechanical and rheological properties. Biscuit recipes reached swallow points which differed in terms of sensory intensity and some of the mechanical and rheological parameters; but were similar in terms of sensory dominance, bolus moisture content, and other mechanical and rheological parameters. Thus, the subject’s swallowing threshold was dependent on biscuit recipe; a “cohesiveness” trigger was not found. Five subjects utilised different breakdown pathways when chewing one biscuit recipe. Inter-individual differences in masticatory behaviour and sensory texture perception were observed. These corresponded to differing bolus moisture content and mechanical and rheological properties. A universal swallowing threshold was not found; there was not agreement across the panel in: bolus structure and composition, mechanical and rheological properties, nor perceived texture. However, there was agreement between several individuals. Thus, consumers may be categorised based upon swallowing thresholds. This study also indicated instrumental adhesiveness and cohesiveness were not direct measures of sensory stickiness intensity. This project provides further evidence of the subjective nature of food texture perception. Individuals used the same sensory terms (and intensities) to describe boluses with different structures and mechanical and rheological properties, and vice versa.