Contrasting impacts of <i>Plantago ovata</i> fibre fractions on corn starch structure and digestibility

Psyllium husk, a dietary fibre derived from <i>Plantago ovata</i> seeds, is widely used in food systems for its gelling ability, water absorption, and texturizing properties. Due to its varying solubility, the fibre can be extracted into fractions with different flow properties. However, limited knowledge exists on how its fractions can be leveraged for food enhancement. Therefore, we isolated two psyllium fractions (F1 and F2) and fabricated starch-fibre gels using starches with varying amylose content (5.9, 37.9, and 63.1% amylose). To fully understand mechanisms between the fractions and starches, we applied three temperature treatments (95, 120 and 140 °C) by utilising high temperature rapid visco analysis (HT-RVA), resulting in 27 starch and starch-fibre gels. F2 increased peak viscosity in all starches, and it significantly changed the profile of high amylose corn starch, while F1 had less effect on the pasting. Texture properties of the gels were mostly influenced by temperature treatments, but amylose leaching and starch hydrolysis by α-amylase were significantly changed by fibre addition. F1 caused an increase of the extent of starch hydrolysis, but F2 reduced it. F1 increased leached amylose, particularly in high amylose corn starch. SEM images have shown changes in the gel microstructure depending on fibre addition and temperature, potentially related to phase separation and fibre impact on ice formation. This work highlights that fibre fractions from the same source have contrasting effects on functional and health-related properties of starch-based food systems, which may be highly valuable for developing healthier food products.