EFFECTS OF MICROWAVE AND SUN DRYING ON THE CHEMICAL COMPOSITION, FUNCTIONAL, AND BISCUIT MAKING PROPERTIES OF SWEET ORANGE PEEL FLOUR

Abstract

Objective: The broad objective of the study was to determine the effects of microwave and sun drying on the chemical composition, functional, and biscuit making properties of sweet orange peel flour.

Methods: Peels were prepared from sweet orange fruits and cut into thin pieces. The peel pieces were dried in a domestic microwave oven at power outputs of 200, 400, 600, and 800 W. Flour samples were prepared from the dried peel pieces, evaluated for chemical composition and functional properties, and compared with of the sun dried sweet orange peel flour. Each of the flours was used to substitute 10% wheat flour in biscuits, which were assessed for the chemical composition, physical, and sensory properties.

Results: The microwave oven dried sweet orange peel flour contained higher amounts of ash, fat, fiber, and carbohydrate than the sun dried peel flour. The microwave drying decreased the total phenol content of the flour from 2.04 to 0.78 mg/g and the flavonoids content from 1.17 to 0.71 mg/g. The water absorption capacity, oil absorption capacity, and swelling capacity increased with the intensity of the microwave drying. The ash, crude fat, carbohydrate, fiber, and total phenol and flavonoids contents of the biscuits containing microwave dried peel flour were slightly (p>0.0.5) higher than those of the biscuits containing sundried peel flour. The diameter and height of the biscuits were not significantly (p>0.05) affected by the microwave oven drying. The spread ratio of the biscuit containing sun dried peel flour was 9.15 and decreased to a range of 7.530–5.595 for the biscuits containing microwave oven dried flour. The break strength and the weight of the biscuits increased with the power output of the microwave oven. The scores for flavor, texture, and overall acceptability of the biscuits containing sweet orange peel flour dried at 200 and 800 W were not significantly different (p>0.05). However, the scores for color and taste were higher for the biscuit containing the peel dried at higher power out puts (600 and 800 W) than the biscuits containing the peels dried at low power outputs (200 and 400 W).

Conclusion: It is concluded that microwave oven drying at 200 W improved the proximate composition and phytochemical contents but decreased the functional properties of the sweet orange flour. The biscuit containing sweet orange peel flour dried at 200 W was preferred to the others for the chemical composition, physical, and sensory properties.