Chemical Composition, Health Promoting Potentials and Storage Properties of Biscuits Supplemented with Orange Peel and Pulp Flours

Abstract

Sweet orange (Citrus sinensis) fruits were washed, peeled manually, the juice extracted and the seeds were removed. The peels and pulps were sliced into thin slices of about 2 cm thick, sun dried at 30 ± 2°C to constant weight, milled and sieved to obtain orange peel and orange pulp flours, respectively. The orange peel and pulp flours, respectively were used to substitute wheat flour 5, 10 and 15 % respectively. The flours were analyzed for their chemical composition. Biscuits were prepared from the flour blends and evaluated for their chemical composition, sensory and storage properties. Antioxidant activities of water and ethanol extracts of flours and biscuits were determined. Bioassay study in which five weeks old Wistar rats weighing between 80 and 90 grams were divided into four groups containing six rats each was carried out. Groups 1,2,3 and 4 were fed biscuits containing 10 % orange peel flour, 10 % orange pulp flour, 100 % wheat flour, and normal feed (growers mash), respectively. Feed intake, water intake, changes in body weight, blood sugar and lipid profile of the rats were determined. Biscuit samples were stored for six months at 30 ± 2°C and 80 to 90 % relative humidity. Changes in pH, moisture and peroxide value of the biscuits were assessed monthly. The sensory properties of the stored biscuits were also evaluated after every two months of storage. The results showed that the orange pulp flour was significantly higher (p<0.05) in fibre, ash and moisture but lower in fat and carbohydrate contents than the orange peel flour. The mineral contents of the flours were not significantly different (p>0.05).The orange peel flour contained more tannins than the pulp flour, but the flours were not significantly different in their oxalates contents. However, orange peel flour was significantly higher (p<0.05) than the pulp flour in alkaloids, flavonoids, anthocyanins and carotenoids. The biscuit samples containing 10 % orange pulp had higher fibre content than the biscuit containing 10 % peel flour. The mineral contents did not differ significantly (p>0.05) among the biscuits. Baking reduced all the antinutrients of the biscuit samples. The highest antioxidant activity was shown by the ethanol extracts of the flours and biscuit samples in relation to the water extracts. Body weights of all the rats in all the groups increased during the study period. The rats fed biscuits containing 10 % peel and pulp flours showed least increase in body weight. There were increases in the high density lipoprotein and total cholesterol contents in all the rat groups. However, the low density lipoprotein (bad cholesterol) of the rat groups decreased. The triglyceride contents increased in all the rat groups except for the group fed biscuit containing 100 % wheat flour. The rats fed 10 % orange peel and pulp flour biscuits also showed lower blood glucose levels than the other groups. There were no significant differences (p>0.05) between the peel and pulp biscuits in colour and texture at the end of six months storage. However, the biscuits containing orange peel had higher ratings for flavour, but lower ratings for taste and overall acceptability. Moisture contents of biscuits fluctuated during storage, values ranged between 5.56 and 8.85 %. The peroxide values of the biscuits increased slightly after 4 months of storage.