Microwave dehydration of three citrus peel cultivars: Effect on water and oil retention capacities, color, shrinkage and total phenols content

The aim of this work is to investigate the effect of microwave dehydration (100, 180, 300, 450 and 600 W) on the physico-chemical (shrinkage, total phenols and color) and technological properties (water and oil retention capacities) and the drying behaviour of three citrus peel cultivars (thompson navel, mandarin and lemon).The fresh citrus peel of thompson navel, mandarin and lemon are characterized by high moisture (3.140 ± 0.159; 3.798 ± 0.070 and 3.010 ± 0.143 kg water/kg db) and fiber (41.644 ± 1.891; 27.894 ± 2.358 and 39.135 ± 1.250 g/100 g db) contents. As excepected, whatever the citrus cultivar, the microwave power level has a significant effect on drying time of the citrus peel (drying time ranges from 51.5 ± 2.828 min to 79 ± 0.707 min at 100 W and from 8.75 ± 0.353 min to 12 ± 0.707 min at 600 W). Shrinkage of volume does not depend on the peel cultivar variety and on the microwave drying level but on the quantity of evaporated moisture. Microwave drying induces a significant increase of the water retention capacities of the three citrus peels. The microwave powers lower than 450 W were in favour of the best water retention capacities. Microwave drying decreases significantly the oil retention capacities of all citrus peels and the total phenolic contents of mandarin and lemon peels. The maximal peel phenolic contents were preserved for drying microwave power higher than 450 W. Also, microwave drying does not have a significant effect on color parameter (L*, a*, b*) of thompson and mandarin peels howerver it induces a significant decrease of the parameter b* and an increase of the global color difference, ΔE, of lemon peels.

► The citrus peel cultivars studied are mandarin, thompson and lemon.
► Their microwave drying time depends on microwave power levels and on cultivars.
► The initial colors were preserved at the low microwave power levels. Drying at 100 and 300 W gives the maximal water retention capacities.
► Microwave drying at 450 and 600 W preserves the highest total phenolic contents.