Root and tuber flours to improve nutritional quality in instant noodles

The instant noodle (IN) consumption increased significantly among the pasta. The use of regional products may increase the economic value chain, besides the increase of final product functional properties. The aim of this work was to evaluate the partial replacement of refined wheat flour by purple sweet potato, beet and carrot in IN production. The IN were evaluated regarding the fat content (after frying and rehydration), cooking properties, instrumental texture, antioxidant capacity and glycemic index. The results showed that is possible to do the replacement the wheat flour, between the studied conditions, and achieve an IN with similar characteristics to standard sample, but with higher antioxidant capacity and low glycemic index.


Introduction
Instant noodles (IN) were originated in Japan in the 1950s and are currently produced in 80 countries. In 2019, approximately 106.4 billion servings of instant noodles have been consumed worldwide, where Asian countries correspond to nearly 80% of instant noodles consumed (WINA, 2020). The consumption of IN is increasing every year due the affordability, convenience and palatability.
Nowadays, there are several researches to improve the quality of IN through fortification to obtain noodles with high nutritional and desirable eating qualities (Parvin et al., 2020), for example the improvement of flavor and color. One possible alternative might be the use of regional products to provide sensory characteristics to noodles, aside from the addition of functional properties. The use of the roots and tubers reduce waste belong the agro-industrial chain.
The use of ingredients rich in bioactive compounds can be an alternative for the nutritional improvement of foods (Neves et al., 2021;Vilar et al., 2021;Wahanik et al., 2021). Besides the economic value added, the use of roots and tubers in instant noodles may contribute to enrich the population diet by the increase of bioactive compounds in this product, such as with antioxidant capacity. Examples of roots and tubers with high content in antioxidant compounds are purple sweet potato, rich in phenolic compounds with acts on the prevention of chronic noncommunicable diseases (Rodriguez-Amaya et al., 2008); the beetroot which contains the betalain that can act on the cancer prevention and the carrot, rich in β-carotene (carotenoid). Besides the antioxidant compounds, these roots and tubers are rich in dietary fibers, which prevent diabetes type 2, since they help to reduce the glycemic index (Mello & Laaksonen, 2009).
The aim of this work was to analyze the technical and nutritional feasibility of the partial refined wheat flour replacement through 5 or 10% purple sweet potato, beet or carrot flour in instant noodles production in order to analyze the product feasibility.

Raw material
Wheat flour and palm fat were donated by Moinho Paulista (Santos, Brazil) and Bunge (São Paulo, Brazil), respectively. The beet, purple sweet potato and carrot were purchased from the local market in the whole form and processed into flour.

Processing of beet, purple sweet potato and carrot flours
The tuber and roots were washed in potable water, sanitized by immersion in chlorated water (100ppm/20min) and washed in potable water again. Pieces with uniform sizes (approximately 50x10 mm) were cut and blanched in boiling water for 5 minutes for poliphenoloxidase inactivation. The blanching process was confirmed by guaiacol test, in the presence of hydrogen peroxide. The material was cooled as the method described by Ortolan (2015). The dehydration was carried out in a LP820 freeze-dryer (Liotop, São Carlos, BRA) for 72 hours. The material was ground in an OBL10/2 Blender (OXY, Santana de Parnaíba, BRA), at 35000 rpm until particle size lower than 500 µm. Research, Society and Development, v. 10, n. 4, e23610414086, 2021 (CC BY 4.

Instrumental color of flours and INs
Color measurements were performed as described by Pereira et al. (2019).

Experimental formulations
WF corresponds to the 100% refined wheat flour. 6 blends of WF with substitution of 5 or10 g/100g of beet, purple sweet potato and carrot flour were prepared in an HB 12 planetary mixer (Hypólito, Ferraz de Vasconcelos, BRA) for 5 minutes at speed 2.

Elaboration of instant noodles
The control instant noodle (INWF) (100 % WF)) was elaborated by mixing 500 g of flour or premix with 10 g of NaCl. The added water considered was calculated according to the water absorption (WA) from the farinographic analysis, as described by Vernaza et al. (2011).

Retained fat and fat loss contents after rehydration
The INs after rehydration were characterized for the retained fat according to method 30-25.01 (AACCI, 2010). Fat loss was measured by the difference between the fat adsorption and the retained fat after rehydration.

Cooking properties after rehydration
The INs were rehydrated in boiling water for 3 minutes and analyzed regarding the weight gain (WG) and solid loss (SL), according to the method 66-50.01 (AACCI, 2010).

In vitro glycemic index after rehydration
The in vitro glycemic index was performed only for the IN with higher partial WF replacement. The measurement was according to the method described by Leoro et al. (2010) were performed.

Antioxidant capacity after rehydration
The IN antioxidant capacity was carried out according the method ORAC (Oxygen Radical Absorbance Capacity) based on the methodology described by Dávalos et al. (2004) and the method ABTS (2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)) based on the methodology described by Re (1999). For the both methods were used hydrophilic and lipophilic extracts as described by Pertuzatti et al. (2014). Only for the IN with higher partial WF replacement were considered.

Statistical Analysis
The data obtained for the raw materials and for the IN were evaluated using analysis of variance (ANOVA) and comparing means (Tukey test), considering a 0.05 significance level. Table 1 shows the results of the proximate composition of the wheat flour (WF), beetroot (B), purple sweet potato (PSP) and carrot (C). The WF was found high in protein content and low in ash content, suggesting a good flour for noodles manufacturing and for the development gluten network, since there is no evidence of the outer layer from the wheat grain. C is a high fiber, sugar and protein content powder. Similar results were obtained by Gazalli et al. (2013) for dried carrot paste in oven at 50 °C. In the case of PSP, starch is the most predominant compound and the starch value is in agreement with those found by Ji et al. (2015) for different varieties of PSP. In addition, the powder is low in fat content and high in fiber content.

Chemical composition and instrumental color of raw materials
Fiber content for PSP was found lower in literature around 2.00 % (Ji et al., 2015), but the high content might be explained by the powder manufacturing by lyophilization where there is no heat process involved and can preserve the fiber structure with no breakage of polysaccharide-glycosidic linkage in dietary fiber polysaccharides (Lola, 2009). B exhibited a low content of fat and a high content in protein, fiber and sugar. Regarding the protein level, this value was higher than those reported by Costa et al. (2017) for waste beet powder at around 12.65 %. The high level of protein might be explained by the use of fertilizers which are rich in nitrogen. Fiber content was lower found by the same author, but it should be highlighted the use of waste materials i.e. peels and stalks which contain higher fiber content when compared to pulp. 1 Results are expressed as mean ± standard deviation; 1 values expressed in dry basis; 2 value of the difference (100-fat-ash-protein-total starch-total dietary fiber); 3 the conversion factor considered for wheat flour was 5.7 and 6.25 for the roots and tuber flours. Source: Authors (2021). The instrumental color of the flours is shown in the Table 2. The colors were characteristic to the pigments present in each sample. The WF showed a high luminosity due the blanching process after milling. For the other flours, the main pigment responsible for the color is the betalain in B, anthocyanin in PSP and β-carotene in C.

Farinograph
The effect on dough rheology properties of the partial WF replacement by 5 and 10 % of roots and tuber flours is presented in Table 3. The WF presented a high strength of the gluten network due to the high WA (≥58 %) and stability (≥15 min) (Schmiele et al., 2017). However, the WA is lower when compared to commercial IN (WA at 64.6%) and higher to the stability (stability at 12.5 min) (Hou, 2010).
It is important to understand the rheological properties to predict the final product quality. The water absorption (WA) of PSP composite flour at 10 % substitution was the highest. WA is the amount of water required which the gluten would have been completely developed. This effect is caused by the characteristic of amylose and amylopectin. (Shan et al., 2013) obtained similar results with the addition of PSP flour to the wheat flour with different levels of substitution. Regarding the C10 composite flour, which has a considerable amount of fiber when compared to the others, presents a high WA as well.
The presence of hydroxyl groups in the fiber structure increases the WA, which enable more water interaction through  From the data obtained, it is observed that WF replaced by roots and tuber flours showed a lower stability time as compared to the WF. It is expected due to the composition of the flours that can dilute gluten proteins and interfere in the gluten network development. The stability time is an important dough quality parameter. Lower is this parameter, the shorter is the dough mixture time without gluten network destruction. As well, the MTI was affected by the partial wheat flour replacement, indicating that the composite flour doughs have a lower tolerance to mechanical action over a prolonged mixing time (Leoro et al., 2010), specially the PSP composite flour.

Extensograph
The extensograph properties of the WF and its composite doughs are shown in the Table 4. Through this analysis, it is possible to evaluate the dough stretch resistance and elasticity. The results show that the WF and its composite doughs increased the resistance to extension over the rest time. Comparing the extensographic parameters after 135 min, it is observed that the WF dough had the lowest value for resistance to extension whereas the WF composite dough with 10 % of root flours present the highest value for this parameter. On the other hand, the wheat WF the highest value for extensibility. This suggests that the addiction of the root flours weakened the extensographic properties of the dough probably due to the decrease of wheat gluten content that is interfered by the other compounds from the root flours (starch, fiber). In general, the WF composite dough had great resistance to extension and lower extensibility, resulting in stiffer and denser doughs.

Viscoamylographic properties
The values for the viscoamylographic properties of the WF and its blends are shown in the Table 5. The mean value of PV ranged from 2387.33 to 1162.33 cP, corresponding to the WF and PSP10, respectively. Peak viscosity corresponds to the starch capability to swell freely before their breakdown. The results show that WF had the highest value for this parameter because of the high starch content in wheat flour. It is also observed that the higher the level of partial substitution, the lower is the peak viscosity. PSP10 had the lowest value probably due to the high fiber and protein contents.
Retrogradation or setback viscosity is related to the reordering of starch molecules. The lower setback values, the lower is the rate of syneresis and retro gradation. Setback values differs significantly between the samples, especially for the samples of high level of partial wheat replacement. This indicates that the addition of 10 % of roots can improve the dough quality as it decreases the setback value compared to control (WF).  Table 6 shows the moisture, fat absorption and fat loss contents found in the instant noodles production. During the deep-frying process at temperature of 135-160°, the product surface water vaporizes quickly creating a porous spongy structure. The evaporated water will be replaced by the frying oil forming small channels that will support the further rehydration. The instant noodle moisture varied from 2.60 % to 8.95 %. According to (Kumobura, 1998), the final moisture product should be less than 10 % in order to provide microbiological stability.

Moisture, fat absorption and retained fat in IN during process
Regarding the fat absorption, the samples obtained values between 22.00 % and 26.06 %. Commercial noodles present a fat content ranged from 16-24 % (Wu et al., 2006). In this study, the majority of samples is in this range, except INB10. This effect is probably caused by moisture of the sample and due to the heterogeneous structure formed during the process that may retain a higher fat content.  Table 7 shows the results of instrumental color for the deep-fried IN. Luminosity (L*) was affected by the addition of root and tuber flours in the WF and there significantly difference between the samples. It is observed that the value for L* decreased with the high partial replacement of the WF. The darkness of the noodles is explained by the presence of their pigments that contributes to the color improvement. In the case of IN that contain C, the darkness might be explained by the oxidation of carotenoids that is affected by the heat.

Cooking properties and fat loss in IN after rehydration
The cooking properties (weigh gain and soluble solid loss) of the deep-fried instant noodles are shown in Table 6.
Cooking characteristics of noodles are very important for the consumer market and it will also influence the technological quality of the final product. High level of solid loss is an undesirable characteristic and indicates that the pasta has a low cooking tolerance. Weight gain indicates the ability of the starch-protein structure to absolve water during cooking.
Weight gain ranged from 127.10 to 154.16 %, corresponding to samples that contain beetroot. This result is likely due to the high fiber and protein contents in beetroot flour. Similar effect on water absorption were reported by Sipos et al.
Solid loss corresponds to loss of starch and other solids from the product during the cooking. It was observed that solid loss increased with the increasing level of root flours replacement in wheat flour. According to Hoseney (1998), cooking loss for a good quality pasta should be lower than 12 %. In the case of beetroot product, the high solid loss may due to the high sugar content in this sample and also to the soluble dietary fiber content.
Regarding the fat loss during the rehydration, the majority of the samples presented a higher value when compared to the INWF, representing greater nutritional viability, since IN has a significant amount of residual fat and its consumption causes a great concern for health.  (Brand-Miller et al., 2003). In addition, diets with low glycemic indexes have beneficial effects for the weight control and for the immunity system.   (mainly cyanidin or peonidin) were identified in purple sweet potato (Kano et al., 2005) with different solubility and a high stability which probably explain the better performance obtained in INPSP10 in the antioxidant capacity. In the case of INC10, besides the improvement in β-carotene bioaccessibility and bioavaiability due to the thermal process, there is a loss of antioxidant capacity because of the isomeration of the molecules (Knockaert et al., 2012).

Conclusion
The wheat flour replacement through 5 and 10 % of root and tuber flours showed promise results. The use of B, C and PSP had great results regarding the technological properties i.e, cooking properties and instrumental texture. Moreover, the final product with higher WF replacement (10 %) provide a product with interesting nutritional properties: high antioxidant capacity and low glycemic index. Therefore, they can provide to consumers wellness and wellbeing. It is important to highlight, that the use of roots and tubers can offer different sensory experience for the consumers, especially in terms of color and taste.