Dietary fibre yields an additional benefit in terms of stabilisation of food structure or nutritional value, but may alter sensory properties in fibre-enriched foods. This study aims to investigate the impact of pectin-rich orange fibre on rheological, sensory and tribological properties of yoghurt gels. More specifically, the effect of the fibre particle size (coarse and fine) and fibre concentration (0.1 and 1.0%) is evaluated. Both, coarse and fine fibre accelerate structure formation during lactic acid fermentation. At low concentration fibre-enriched yoghurts exhibit rheological properties similar to the plain yoghurt and syneresis is decreased. At high concentration coarse fibre considerably reduces gel firmness whereas fine fibre additionally stabilises the casein network as a filler. This stabilising effect might be favoured by pectin, which leaches from orange fibre during mechanical and thermal pre-treatment and subsequently supports the bridging of casein micelles due to its calcium sensitivity. Depending on the criteria for classification of gels, fibre-enriched yoghurts show either strong or weak gel properties. Fibre addition causes alterations in sensory perception. A slight decrease in overall acceptance compared to the plain yoghurt is mainly related to a more compact texture and an increased particulate mouthfeel. Tribological data reveal that increased friction is mainly related to a reduced ability of coarse fibre yoghurt to immobilise water at high strain and that the protein (casein) network dominates lubrication properties in plain yoghurt.
