Non-conventional techniques to obtain grapefruit jam

Different grapefruit jams obtained by conventional, osmotic dehydration (OD) without thermal treatment and microwave (MW) techniques were compared. A kinetic study was previously carried out to characterize the fruit OD process in order to manufacture OD jams. Fibres from bamboo, apple and orange were incorporated into OD jams. Soluble solids, moisture, water activity, pH, consistency, flow properties and colour were evaluated for all jams. The jams obtained by the OD process had a colour more similar to the fresh fruit than the heated ones, but the addition of fibre was necessary to improve the consistency. However, the MW procedure affects colour in a similar way to conventional heating but increases the consistency of the samples.Industrial relevanceThe consumption of grapefruit may be as fresh fruit, juice or jam. The application of prolonged heat treatments to the fruit, such as in the case of jams and juices, can lead to important losses of the beneficial properties of this citrus fruit. Osmotic dehydration at mild temperature is a technique that could be used to obtain jam without being so aggressive to the fruit. On the other hand, the use of microwave energy has been proposed as an alternative to traditional heat pasteurisation in order to better preserve the natural organoleptic characteristics and essential thermolabile nutrients of grapefruit juice, due to the shorter processing time required. In this work the quality of different grapefruit jams obtained by applying alternative procedures to the conventional one has been compared. Osmotic dehydration and microwave energy were applied as alternatives to conventional heating and bamboo, apple and orange fibres were added and compared with conventional pectin. The osmotic dehydration procedure used produces jams with lower sugar content but with a colour very similar to that of the fresh fruit. Nevertheless, fibre should be added to improve the consistency of the samples, bamboo exhibiting the flow properties most similar to conventional jam. On the other hand, microwaves affect the colour of the product in a similar way to conventional heating but increase the consistency of jams.