High pressure processing in jam manufacture: effects on textural and colour properties

High hydrostatic pressure-treated strawberry jam samples were examined with respect to their textural and colour properties, the aim being to establish the relationship between pectin concentration, texture and colour. Samples were prepared with varying amounts of pectin (0.1, 0.5, 2.5, 5, 7.5 and 10% w/w) and were processed using the same parameters (400 MPa, for 5 min at 25°C). After preparation, the samples were rheologically tested using a cone and plate configuration on a Creep Viscometry Oscillation rheometer. A colour spectrophotometer was used to monitor (at 505 nm) the changes in colour during storage. Comparing these experimental samples with commercially available samples of high pressure and traditional strawberry jams, it was found that the best texture was achieved when the pectin concentration was between 2.5 and 5% w/w. With increasing pectin concentration, the storage and loss moduli (indicators of liquid- and solid-like characteristics) were increased. Colour was found to be affected by the increasing pectin concentration, as the absorbance intensity was decreased, suggesting a relation between pectin and anthocyanin degradation.