The effect of a bread matrix on mastication of hazelnuts

The effect of the degree of nut mastication on bioavailability of their nutrients has been established previously. In contrast, the effect of incorporation of nuts into composite food matrixes on oral processing behaviour and structural breakdown has been studied scarcely. This study aimed to investigate the effect of incorporation of hazelnuts into bread matrixes in comparison with plain hazelnuts on bolus properties and chewing behaviour. Amount of plain hazelnuts was varied to investigate the effect of portion size on bolus properties and chewing behaviour. Bolus particle size distribution was obtained by image analysis of expectorated boli by n = 20 participants. Median bolus particle diameter (d₅₀) and broadness of particle size distribution (b) were quantified by fitting the cumulative area distribution curve with a modified Rosin-Rammler function. Oral processing behaviour (number of chews, chewing time, chewing frequency) was quantified by means of a stopwatch. Mastication of two hazelnuts resulted in smaller d₅₀ than mastication of six hazelnuts or mastication of two hazelnuts in white bread or baguette. Chewing time of two hazelnuts was significantly shorter than chewing time of six hazelnuts or chewing time of two hazelnuts in white bread or baguette, while chewing frequency did not differ between foods. d₅₀ of six hazelnuts did not significantly differ from d₅₀ of two hazelnuts in either bread matrix. Broadness b of the particle size distribution was significantly smaller for six hazelnuts compared to the other foods. We conclude that d₅₀ was affected by bite size or bite volume rather than by incorporation of hazelnuts into bread. We suggest that incorporation of hazelnuts into bread matrixes has a relatively small impact on size of hazelnut bolus particles produced upon mastication.