Colour and rheological properties of non-conventional grapefruit jams: Instrumental and sensory measurement

• Alternative heating methods and bamboo fibre to obtain grapefruit jams are studied.
• Heating methods include osmotic dehydration (OD) and/or microwave energy (MW).
• OD and bamboo fibre allow obtaining jams closer in colour to fresh fruit.
• Microwaves (MW) and bamboo fibre increase the consistency of the jams.
• Jams obtained by combining OD and MW processes are sensory preferred.

Alternative methods with which to obtain grapefruit jams have been applied. These include the use of osmotic dehydration (OD) and/or microwave energy (MW), as an alternative to conventional heating, and the incorporation of bamboo fibre together with pectin in order to increase the jam's consistency. Colour, consistency and rheological behaviour were measured and sensory evaluation was carried out to compare product quality. When compared to the fresh fruit, the greatest colour changes took place in those jams processed by MW and conventional heating, both of them showing lower L*, a*, b* and chrome values than the rest of the samples obtained by applying osmotic dehydration. By adding bamboo fibre, the colour of OD samples approaches that of fresh fruit. The higher yield stress, greater consistency and more viscoelastic behaviour was displayed by jams obtained by combining OD and MW processes. In the sensory analysis, the judges awarded this sample a better score. The sensory attribute product coverage in mouth was closely related to viscosity at a shear rate of 120 s−1 and consistency.