Experimental design and statistical analysis
The experimental design and corresponding response values as a function of different independent variable with coded variables are summarized in Table 1. Lack of fit test for all the models were observed insignificant which describe the adequacy of models to predict responses (Table 2). CV was < 6% in case of all the responses, indicating that the experiments were carried out with adequate precision. Fig 1 represents the response surface graphs obtained from experimental data.
Hardness
Hardness is a measure of firmness of the vermicelli. The hardness value was observed in the range from 5.70 to 8.30 (based on 9-point hedonic scale) as shown in Table 1. The results of the regression model showed that the hardness first decreases with increase in BMF and RF level up to 59.18% and 14.84% respectively, whereas further increase showed the opposite results as shown in Fig 1(a).
BMF and RF had a negative significant (p<0.05) effect at quadratic level (Table 2).
Shukla and Srivastava (2014) also reported a reduction in hardness of noodles fortified with millet flour. The hardness effect due to the amylose component of rice starch as observed by
Araki et al., (2016) which bind to each other to form a matrix and thus increases hardness whereas lower amylose content causes less retrogradation of starch during gel formation and consequently weaker gel structure (
Afifah and Ratnawati, 2017). The interactive effect showed slight negative significant (p<0.05) for BMF and RF (Table 2).
Stickiness
Stickiness is a measure of adhesiveness of vermicelli and is negatively related to vermicelli quality. The stickiness value was observed in the range from 4.40 to 7.40 (based on 9-point hedonic scale) as shown in Table 1. The results of the regression model showed that stickiness decreases with increase in BMF level up to 66.28%, while further increase showed the opposite results, whereas increase in RF level showed the decrease in stickiness (Fig 1b).
XG and BMF had a significant (p<0.05) negative effect on stickiness at linear and quadratic level respectively (Table 2).
Mudgil et al., (2016) reported that on supplementation of partially hydrolyzed guar gum to noodles bound the free water and thus stickiness decreased in the cooked noodles. Similarly,
Low et al., (2019) observed that the use of mono-glyceride and amylose molecules inhibit swelling of starch as a result of which stickiness in noodles is substantially reduced.
Color
Color value was observed in the range from 6.50 to 8.50 (based on 9-point hedonic scale) as shown in Table 1. The results of the regression model showed that with increase in BMF and RF level up to 59.18% and 14.84% respectively, there was increase in acceptability for product color, whereas further increase showed the opposite results (Fig 1c).
Chandraprabha et al., (2017) reported that barnyard millet vermicelli prepared from barnyard millet flour, whole wheat flour and
Ekanayakam root barks, showed decrease in sensory score for color with when level of BMF exceeds beyond 40%.
BMF had a significant (p <0.05) positive effect on color at linear level whereas slightly negative effect at quadratic level (Table 2).
Gull et al., (2015) reported that incorporation of millet decreases the lightness of pasta at linear level due to the pigments present in pericarp, aleuronic layer and in endosperm region.
Flavor
Flavor value was observed in the range from 6.00 to 8.40 (based on 9-point hedonic scale) as shown in Table 1. The results of the regression model showed that with increase in BMF level up to 59.18%, there is increase in product flavor while further increase showed the opposite results, whereas increase in RF level showed increase in flavor (Fig 1d). Similarly,
Chandraprabha et al., (2017) reported the decrease in sensory score of flavor in barnyard millet vermicelli prepared from barnyard millet flour, whole wheat flour and
Ekanayakam root barks when BMF level exceeds beyond 40%.
BMF and RF had a significant (p<0.05) positive effect on flavor at linear level. XG showed the insignificant (p>0.10) negative effect at all three levels (Table 2).
Masticability
Masticability, also defined as chewiness is the energy needed to break down the vermicelli to the swallowing state. Masticabilityvalue was observed in the range from 5.10 to 8.10 (based on 9-point hedonic scale) as shown in Table 1. The regression model showed that masticability increases with increase in BMF and RF level up to 59.18% and 14.84% respectively, while, further increase showed the opposite results as shown in Fig 1(e).
BMF had a significant (p<0.05) positive effect on masticability at linear level. BMF, RF and XG showed the significant (p<0.05) negative effect at quadratic level (Table 2). The incorporation of XG into a rice starch system mimic the visco-elastic properties of gluten
(Hymavathi et al., 2019) thereby leading to improved texture of the product as reported by
Srikaeo et al., (2018) and
Low et al., (2019). BMF and RF had a significant (p<0.05) negative effect at interactive level.
Optimization of product formulation and model validation
Optimum values of processing variable and responses are shown in Table 3. The optimized solutions for the BMV wereobserved as BMF (64.25%), RF (22.32%) and XG (2.36%). The model predicted value (µ
0) and the observed experimental value (µ
1) obtained after manufacturing optimized product are tabulated in Table 4. No significant difference (p<0.10) was observed between the predicted and experimental values.
Proximate analysis
Nutrient composition of BMF, RF, flour mix (optimized) and refined wheat flour revealed that the fat, protein and carbohydrates of the BMF, RF and optimized flour mix significantly differed (p< 0.05) from the refined wheat flour (Fig 2a).
Nutrient composition of control vermicelli and BMV has been presented in Fig 2b. The protein and carbohydrate content in BMV were observed to be differed significantly (p<0.05) from the control vermicelli. The protein was 8.8% higher in BMV whereas, the fat content is reduced by 10.50%. The content of iron and beta-carotene in BMV was found to be 3.81mg/100g and 1039µg/100g respectively.