Oral processing of heterogeneous foods : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Science at Massey University, New Zealand

Abstract

Food manufacturers could potentially benefit from foods designed to influence mastication and the breakdown of food into a bolus. Mastication and the properties of the food bolus have been linked to the sensory and nutritional properties of foods. This research aimed to investigate the mastication and particle size distribution of the food bolus of heterogeneous food systems, where one food component is combined with another, with a view to indentifying parameters that influence mastication and the food bolus. A range of matrices of contrasting physical properties, which were embedded with peanut pieces of contrasting physical properties, were investigated. Trials involved serving these heterogeneous foods to subjects standardized by volume (concluded as the most suitable serving method following an investigation of natural bite size). Subjects were asked to chew and expectorate the bolus (where the number of chews and chewing time were recorded) before the matrix of the expectorated bolus was washed away to isolate the peanut particles, and the peanut particle size distributions determined using image analysis. A Rosin-Rammler function was fitted to the cumulative distribution data of each bolus to derive peanut particle size parameters (d50 and broadness (b)). Results demonstrated that in heterogeneous food systems the presence of one food component (the matrices) can alter the breakdown of another food component (the peanuts) embedded inside that matrix. The properties of the matrix influenced mastication, the rate of peanut particle size reduction, and the spread of the distribution of peanut particle size inside the matrix, but did not influence the d50 of the peanut particle size distribution inside the bolus. Peanut properties did not influence mastication, but influenced the d50 of the peanut particle size distribution, the rate of particle size reduction, and the retention of peanuts in the bolus. It is postulated that the properties of the matrices largely influence the probability teeth contact peanut particles (known as the selection function), and the properties of the peanuts largely influence particle fracture per chew (known as the breakage function).