INFLUENCE OF CARROT FLOUR SUBJECTED TO DIFFERENT DRYING TECHNIQUES ON THE NUTRITIONAL AND ANTIOXIDANT PROPERTIES OF RICE-BASED DOUGH MEAL

Abstract

Rice flour was supplemented with carrot flour subjected to sun, oven and freeze drying in order to enrich the nutritional and bioactive components qualities of the rice-carrot composite flour. Experimental design was carried out using optimal mixture design of response surface methodology which generated fifteen formulations. The functional properties, carotenoid contents, and colour characteristics of the composite flour were evaluated leading to ultimate selection of three samples for further analysis; the pasting properties, minerals composition, starch contents and antioxidants activities. The selected blends were 100% Rice flour + 0% Carrot flour; 93.7% Rice flour + 6.3% Carrot flour; and 75% Rice flour + 25% Carrot flour. The Glycemic index of the formulated rice-carrot dough meal was also investigated. Freeze dried samples, RCFD1 (93.7% rice flour + 6.3% carrot flour) and RCFD3 (81.25% rice flour + 18.75% carrot flour) had the same bulk density with the control sample, R (100% rice) of 0.97 g/ml. The sun dried and oven dried samples also had the best oil absorption capacity at 12.5% incorporation of carrot flour. Freeze dried samples had the best oil absorption capacity at 25% incorporation of carrot flour. Sun dried samples had the best water absorption capacity at 25% incorporation of carrot flour while oven dried and freeze dried samples had their best values at 12.5% carrot flour incorporation. Addition of carrot flour caused increased in swelling capacity and the same trends were observed in the three drying methods with obvious significance differences. Increase in carrot flour incorporation increased the emulsification capacity. Freeze dried flour blend had the best carotenoids content at 25% carrot flour incorporation. Sun-dried sample RCSD1 (93.7% rice flour + 6.3% carrot flour) had the best peak viscosity (557.00Cp) and final viscosity (939.00cP), oven dried sample RCOD1 (93.7% rice flour + 6.3% carrot flour) had the lowest breakdown (74.00Cp) and pasting time (4.8 min) while sample RCFD4 (75% Rice flour + 25% Carrot flour) had the lowest setback (78.00cP) viscosity. However, free-dried sample, RCFD4 (75% Rice flour + 25% Carrot flour) had the lowest pasting temperature (94.75 oC). Incorporation of carrot flour increased amylose contents, in vitro starch digestibility and resistant starch but a decrease in amylopectin content. Antioxidant properties increased in the flour blends as the carrot flour level increased. The best values were observed at 25% carrot flour incorporation. The same trends were observed for the minerals contents. The formulated dough meal had the lowest glycemic index at 25% carrot flour incorporation. The values ranged from 48-50%. The sensory evaluation showed that rice dough meal (100% rice) was the most acceptable while freeze dried sample at 25% carrot flour incorporation was the second most preferred. Freeze drying technique gave the best sample, followed by oven drying and sun drying. Overall, carrot flour inclusion resulted in rice-carrot flour with improved antioxidants, minerals and carotenoids contents.