Influence of mechanical and thermal treatment on particle structure, leaching of alcohol insoluble substances and water binding properties of pectin-rich orange fibre

Abstract

Mechanical and thermal processings may affect the composition and the techno-functional properties of dietary fibre as a part of a complex food system. The aim of this study was to investigate the impact of a mechanical and thermal treatment alone or in combination on alcohol insoluble substance (AIS), the content of galacturonic acid (GalA), the water retention capacity (WRC) and the microstructure by scanning electron microscopy (SEM). Two samples of orange fibre with different particle size (coarse and fine) were investigated in an experimental design and evaluated with regard to particle size (d50) after treatment and their impact on network formation. Our study highlights a more pronounced susceptibility of the coarse fibre towards mechanical stress compared to the fine fibre with regard to particle size reduction. High-pressure homogenization (HPH) represents the crucial step regarding AIS release and the increase of WRC for both fibres. A mechanical treatment with additional thermal treatment maximises AIS release. GalA, as a marker for pectin in AIS, was detected in various amounts depending on the intensity of the treatment. Highest values for WRC were achieved for the coarse fibre as a consequence of both, particle size reduction and the formation of a stable network on a microstructural level.