ABSTRACT

This study was carried out to investigate the effect of incorporating local rice (Oryza sativa L.) flour and wateryam (Dioscorea alata) flour on wheat (Triticum aestivum) flour at different concentrations on the quality of instant noodle samples. Another different component proportions of the local rice (Oryza sativa L.), wateryam, and soybeans (Glycine max) flour was also used to develop flakes. In both studies, the mixture experimental designs were used to generate the 3-Dimensional graphs (response surfaces) and fitting the regression models where necessary. The proximate, amylose, functional and pasting properties were performed on the flour samples to establish the characteristics of the raw material samples used for the study. Significant (P<0.05) differences were observed in the crude protein (5.58-12.4%), amylose content (16.92 - 27.75 %), bulk density (0.77 - 0.93g/ml), gelatinization temperature (64 – 69 ⁰C), and breakdown viscosity (34.27 - 88.12 RVU). The local rice flour had the highest bulk density, gelatinization temperature, and breakdown viscosity, but had the least amylose content. Cooking quality, chemical (proximate, free fatty acid, and peroxide value), mineral composition, water soluble vitamins, pH, microbial load, and sensory properties of the instant noodle samples were analyzed. The cooking time of the instant noodle samples (5.25 - 7.05 min), cooked weight (3.08 - 3.99 g), and cooking loss (0.11 - 0.6 g/g) varied significantly (p<0.05). The major factor that affected the cooking quality of the instant noodle samples was the increase in the rice flour component of the mixture components. The protein content (3.07 - 7.42 %) of the noodle samples decreased significantly with increase in the water yam component of the blends. The mixture response surfaces of the sensory analysis depicted a progressive decrease in preference for appearance, flavor, mouthfeel, taste, and overall acceptability with increase in the rice and water yam components of the mixture. However noodle samples made from 100:0:0 (wheat flour) was not statistically (p>0.05) different from noodle samples made from 75:25 (wheat: rice) composite flour in all the sensory attributes except for the taste preference. The coefficient of the components implied that the local rice flour was a better substitute for wheat than water yam in the production of instant noodles. For the flake samples, the blending of rice flour with soybeans and wateryam flour improved significantly (p<0.05) the nutritional quality of the flake samples. The saponin, tannins, flavonoid, phenol values ranged from 0.00 - 17.50 mg/100g, 0.50 - 3.25 mg/100g, 2.15 - 9.8mg/100g, and 0.00 - 4.95 mg/100g respectively. The phenol content increased as the component of soybean increased. The sensory analysis conducted showed that the flake samples made from 100:0:0 (local rice); 83.33:8.33:8.33 (rice: wateryam: soybean), 75:0:25 (rice: soybean), were the best in terms of appearance, aroma, taste, texture, and overall acceptability, and their scores were not statistically different (p>0.05). Therefore, flake samples made from 70:0:25 (rice: soy bean) composite flour is recommended for the production of rice flake due to its relative high protein and fibre contents. Overall, the present study revealed that Nigerian local rice has the potential of becoming an important industrial raw material, by incorporating 25 % of its flour in noodles production, as well as blending it with 25 % soy flour to produce nutritious flakes.