CHARACTERISATION OF NOODLES FROM ORANGE FLESHED SWEETPOTATO FLOUR: EFFECTS OF DRYING METHODS AND STORAGE CONDITIONS

Abstract

ABSTRACT Orange fleshed sweet potato (OFSP) is unstable during processing andpreservation of its quality attributes are required to retain inherent micro-nutrients and optimize it spot entails asabio-fortified crop.In this study, OFSP chips were dried using hot air oven (HAD; at 60-70°C for 7min), micro wave oven (MOD; at 300-500 W for 30-40min) and infrared drying (IFD;250-350 Wfor70-85 min) to determine the effects of processing conditions on quality attributes of its flour. Numerical optimization technique using central composite design of response surface methodology was used to optimize the process variables to obtain the best drying conditions that preserve desirable characteristics of OFSP flour for noodle production. OFSP flour were characterized for colour, moisture and functional properties while optimum drying conditions was established. Optimum OFSP flour samples from each drying technique were made into noodles at 50% and100% levels of inclusion of OFSP flour in wheat while 100% wheatflour served as control. Noodle samples were analysed for proximate, colour, carotenoid and cooking properties prior to storage atroom (28±2 °C) and controlled (18±2 °C) temperatures for four months. Stored samples were analysed for colour, moisture, microbial and textural properties at one month interval. Drying parameters were subjected to analysis of variance and means were separated using Duncan Multiple range test at p≤0.05. Data obtained from stored samples were a factorial of complete block (level of inclusion x storage conditions x storage period) design and analyze dusing SPSS. Mean values of β-carotene and moisture content of flour from HAD, MOD and IRD were 6.39-13.33 mg/100g and 5.8-8.0%; 8.32-10.86 mg/100g and 5.35-10.20%; 2.83-7.38 mg/100g and 5.85-9.25% respectively. The main and quadratic effects of drying time and drying temperature had significant (p≤0.05) effects on the colour, carotenoid and functional properties of the flour samples. Theoptimum drying conditions of HAD, MOD and IRD were 65°C/7h, 300 W/36min and 300 W/78 min, respectively. Noodles samples showed significant (p≤0.05) differences in the proximate, colour, carotenoids, sensory andcooking properties. Total ash and dry matter content of noodles from HAD, MOD and IFD varied from 2.02-3.03%; 24.66-36.41%; 2.04-3.06% and 23.28-35.64%; 1.51-2.52% 26.08-37.12% respectively. The 100% OFSP noodles from all the dryers had the highest total, beta and gamma carotene compared to the control. Values for colour, appearance, taste and overall acceptability were in the range of 5.58-6.58, 5.50-6.35, 4.88-5.88 and 5.40-6.25 respectively. Level of inclusion, storage conditions and duration of storage hads ignificant(p≤0.05) effect on moisture, colour, texture, and microbial load of the noodle samples from the dryers. Noodles stored at room temperature had lower moisture content (4.92,4.98and4.99%) compared to those stored at controlled temperature (5.02,5.09and 5.13%) for HAD, MOD and IFD, respectively. Inconclusion, drying of OFSP at optimum conditions using HAD, MOD and IFD significantly (p<0.05) affected some quality attributes of flour and noodles. Optimum conditions of MOD were found to best preserve β-carotene; an important component of OFSP compared to other drying techniques.