Quality and sensory properties of instant fried noodles made with soybean and carrot pomace flour

Wheat flour commonly used in making noodles is rich in starch but poor in protein and fiber. Wheat flour substituted with soybean and carrot pomace flours were used to produce instant fried noodles. Soybean is high in protein while carrot pomace is rich in dietary fiber. The aim of this study was to evaluate the effect of substituting wheat flour with soybean and carrot pomace flour on the physicochemical, cooking and sensory properties of instant fried noodles. Four flour blends in ratios of 100:0:0, 80:15:5, 70:20:10, 60:25:15 wheat, soybean and carrot pomace flour respectively were prepared. The results indicated a significant difference (P<0.05) in protein and crude fiber content of the noodles made from the flour blends. The cooking loss and water absorption increased with increase in the amount of substituted soybean and carrot pomace flour. There was no significant difference in the tensile strength among noodles. However, breaking length of the noodles decreased with increase in replacement of soybean and carrot pomace flour. The noodles decreased in brightness with increased carrot pomace substitution. Noodles made from 80% wheat flour, 15% soybean flour and 5% carrot pomace were the most preferred by the sensory panelist. Incorporation of soybean flour and carrot pomace flour improved the nutritional quality and sensory attributes of the instant fried noodles.


INTRODUCTION
Consumption of noodles has increased worldwide because of their convenience, palatability, shelf stability and affordability. Noodles are pasta products mainly made from flour, water, salt. The properties of the flour, type of salt and the manufacturing process leads to a wide array of noodles types (Fu, 2008;Gulia et al., 2014). Noodles are mainly made by a process of mixing raw materials, dough sheeting, compounding, sheeting / rolling and cutting. Noodle strands coming out of cutting rolls are further processed to produce different types of noodles (Fu, 2008;Gulia et al., 2014;Adejuwon et al., 2020). Two types of noodles are generally known, white salted noodles made from flour, sodium chloride and water, and yellow alkaline noodles made from flour, alkaline salts (sodium tripolyphosphate and sodium carbonate) and water (Asenstorfer et al., 2006;Siah and Quail, 2018).
Wheat flour used in making noodles is rich in starch but *Corresponding author. Email: irene.orina@jkuat.ac.ke.
Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License low in protein (essential amino acids especially lysine), dietary fiber and vitamins which are lost during wheat flour refinement (Dewettinck et al., 2008). Previous studies have tried solving this problem by substituting wheat flour with various foods rich in protein and fiber. These includes substituting wheat flour with potato flour (Kang et al., 2017), soy flour (Rani et al., 2019), seeweed flour (Kumoro et al., 2016), lentil (Rathod and Annapure, 2017), ground linseed (Zhu and Li, 2019), apple pomace (Xu et al., 2020), carrot puree (Prerana and Anupama, 2020), finger millet (Hymavathi et al., 2019) and oyster mushrooms (Arora et al., 2018). Limited studies have incorporated soybean flour together with carrot pomace in the noodles. Soybean flour provides extra protein while carrot pomace provides fiber and beta carotene to the wheat flour noodles. Soybeans are excellent sources of protein (35-40%), rich in calcium, iron, phosphorous and vitamins (Udachan et al., 2018). Noodles made mainly from wheat flour are rich in carbohydrates but are deficient in terms of protein quality and amino acid (Udachan et al., 2018). Incorporation of soybean flour seeks to improve the protein quality of noodles. Several studies have successfully incorporated soy flour in noodles (Pakhare et al., 2016;Jalgaonkar et al., 2018;Huh et al., 2019;Rani et al., 2019Rani et al., , 2020Violalita et al., 2020). Pakhare et al. (2016) reported a significant increase in protein content of noodles supplemented with defatted soy bean flour. Cooking loss and cooking time of the noodles also increased significantly.
Carrot has gained increased attention over the years due to its richness in antioxidants and beta carotene (provitamin A) (Sharma et al., 2012). Carrot pomace is the by-product of carrot juice extraction unit. During carrot juice production, 30-50% of the carrot remains as pomace, and up to 50% of the carotene is lost with the pomace (Sharma et al., 2012). The pomace is mainly disposed as feed or manure, however, it contains a good residual amount of all the vitamins, minerals and dietary fiber (Surbhi et al., 2018). Incorporation of carrot pomace in food will decrease its environmental load problem. Various attempts have been made at utilizing carrot pomace in foods such as cookies (Ahmad et al., 2016;Sahni and Shere, 2017), cake (Majzoobi et al., 2016;Semwal et al., 2016), sausage  and pasta (Jalgaonkar et al., 2018).
The aim of this study was to evaluate the effect of incorporating different proportions of soybean flour and carrot pomace flour on nutritional composition, physical properties and sensory characteristics of instant fried noodles.

Wheat and soybean flour
Commercial wheat flour was obtained from a local supermarket, defatted soy flour was obtained from Soy Africa Company, Kenya.

Preparation of carrot pomace flour
Fresh carrots were purchased from a local market in Juja, Kenya. Pomace flour was obtained according to a method described by Gull et al. (2015). The carrots were washed in running tap water to remove extraneous material followed by juice extraction. Carrot pomace was collected, spread on aluminum foils and oven dried at 60°C for 4 h. The dried pomace was ground and packed in air tight container for further use.

Formulation of composite flour
Wheat flour, soybean flour and carrot pomace flour were mixed at different proportions as shown in Table 1.

Noodle production
The noodles were processed at Jomo Kenyatta University of Agriculture and Technology (JKUAT) Nissin Foods Limited. Recipe for making noodles was provided by JKUAT Nissin Foods. One kilogram of each flour blends (as shown in Table 1) were mixed separately with water (360 ml/kg), table salt (16 g/kg), sodium bicarbonate (2 g/kg) and sodium tri polyphosphate (2 g/kg) in a rotary mixer. A thick sheet of dough formed which was allowed to rest for 20 min in a plastic bag. The dough was then passed through extension rollers to reduce thickness. The thin sheet of dough produced was passed through a shredder. The shredded dough was then cut at 10 cm spacing, steamed for 20 min and deep fried at 140°C in palm oil for 30 s. The instant fried noodles were then cooled at room temperature and packed in airtight bags.

Proximate analysis
Proximate analysis of instant fried noodles prepared from the different flour blends were determined using standard methods of AOAC (2010). Proximate analysis was done in triplicate to obtain a mean value for each nutrient.

Total carotenoid content
This was determined using AOAC (2010) method. About 2 g of each sample was weighed, transferred into a mortar and a 10 ml of acetone added. A pinch of acid washed sand was added and the sample was thoroughly ground using pestle until it produced no more color. The acetone extract was transferred into a 25 ml volumetric flask and topped up with acetone. The extract was transferred into a separating column and 25 ml of petroleum ether was added. The separating column was shaken vigorously then allowed to stand. The mixture separated into two, and acetone which is at the bottom was released from the column. Distilled water was added to wash off the acetone, this was done severally to completely wash off the acetone. After extraction, the total carotenoid content was determined using UV-Vis spectrophotometer (PD 3000UV APEL Co.) at 450 nm. Beta carotene standard curve was used to calculate the total carotenoid content. Results were presented as mg/100 g.

Mineral content analysis
Mineral content (calcium (Ca), magnesium (Mg), zinc (Zn) and phosphorous (P)) of the noodles were determined using atomic Table 1. Quantity of wheat, soybean and carrot pomace flour blends prepared. Control  100  0  0  Sample A  80  15  5  Sample B  70  20  10  Sample C  60  25  15 absorption spectroscopy (AAS) (model 210 VPG) according to AOAC (2010) method. Absorbance was recorded and standard curves of each individual element were plotted. Results were expressed as mg/100 g sample.

Cooking time
This was determined by noticing the time of disappearance of the core of the noodle strand during cooking (every 30 s) by squeezing the noodles between two transparent glasses slides (Prerana and Anupama, 2020).

Cooking loss
This is the amount of solid substance lost into the cooking water and was determined according to the method described by Ritthiruangdej et al. (2011). Ten grams of the sample noodles was placed in 300 ml of boiling distilled water in a 500 ml beaker and cooked to optimum time. The cooking water was collected (thoroughly agitating the total cooking water before sampling) after draining the noodles. The cooking water was placed in aluminum vessel then placed in an oven at 105°C and evaporated to dryness. The residue was weighed and reported as percentage of the uncooked noodles.

Water absorption
Three grams of the sample noodles were boiled in 200 ml of water until completely cooked (when center of the noodles becoming transparent). The cooked noodles were washed with distilled water then drained for 5 min and weighed immediately. Water absorption was reported as percent increase in the weight of cooked noodles compared to the uncooked noodles weight (Takahashi et al., 2005).

Color analysis
The color of uncooked noodles samples were measured using a Hunter Lab color analyzer. In the Hunter's lab colorimeter, the color of a sample is denoted by the three dimensions, L*, a* and b*. The L* value is a measurement of brightness (100 for perfect white to 0 for black, as the eye would evaluate it), a* value represents the redgreen coordinates (negative is green while positive is red), b* value is the blue to yellow coordinates (negative is blue while positive is yellow). The L*, a* and b* readings of the noodles were obtained directly from the instrument.

Noodle texture analysis
Texture analysis of cooked noodles was measured using a Texture Analyzer (TA-XT2i) under optimal test conditions. Measurements were carried out at room temperature exactly ten minutes after cooking according to the method described by Lu et al. (2009). Instrument was set at break mode: test speed 1 mm/s. Two texture parameters were obtained tensile strength (maximum force; N) and breaking length (distance at maximum force).

Sensory evaluation
All noodles samples were cooked to the optimum cooking time and served to 20 untrained panelist. Samples were coded with threedigit random numbers and served in random order. Parameters evaluated were aroma, taste, color, texture and overall acceptability using a 9 point hedonic scale, where 9 = like extremely and 1 = dislike extremely (Gunathilake and Abeyrathne, 2008).

Statistical analysis
The means and standard deviations were determined for all the nutritional, textural, cooking and sensory qualities studied. The significant differences of mean values were assessed with one-way analysis of variance (ANOVA) followed by Duncan's test using SPSS software (Version 17.0 Inc.). Significant differences were determined at P<0.05.

Proximate analysis
Chemical composition of instant fried noodles with supplemented soybean flour and carrot pomace flour are shown in Table 2. Moisture content of the noodles decreased with increased supplementation with the control having the highest moisture content of 4.861%.
Cooking loss = Weight of remainig solid content after oven drying Weight of fresh noodles × 100 Water absortpion = (Weight of cooked noodles − Weight of uncooked noodles) Weight of uncooked noodles × 100 of the noodle strands to evaporate (Gulia et al., 2014;Adejuwon et al., 2020). Moisture content is critical in controlling microbial growth and hence determining the shelf life of the noodles. Carbohydrate content of the noodles decreased with substitution of wheat flour. Sample C with 25% soybean flour and 15% carrot pomace flour had the lowest carbohydrate content of 71.911%. Ash content increased with replacement of wheat flour, noodles containing 60% wheat flour (Sample C) had the highest ash content (2.352%) while the control had the lowest (0.592%). Ash content gives an indication of the availability of minerals in a given food sample. The increase in ash content is attributed to the added soybean and carrot pomace flour. The percentage protein content of the instant noodles ranged from 8.314 to 16.46%. Sample C had the highest protein content while the control had the lowest. This is attributed to the increase in the proportion of soybean flour added which is rich in protein (Medic et al., 2014). This increase in protein is in agreement with previous studies (Collins and Pangloli, 1997;Adegunwa et al., 2012;Omeire et al., 2014;Rani et al., 2019).
There was a decrease in fat content with substitution of wheat flour, Sample C had the lowest content and was significantly different from other samples. The decrease could be due to increase in the proportion of soy flour (defatted) in the flour blend. Collins and Pangloli (1997) reported a decrease in fat content of noodles with addition of defatted soybean flour, however, other studies observed an increment in fat content (Adegunwa et al., 2012;Omeire et al., 2014). The increase in the amount of carrot pomace substituted could have also led to decrease in the amount of oil absorbed by the noodles. In a previous study, preharvest-dropped apple powder (PDAP) appeared to be very effective in lowering oil absorption of instant fried noodles (Kim et al., 2013).
The highest fiber content was found in Sample C (2.403%) and the lowest value was in the control sample (0.913%). The increase in fiber content is due to increase in carrot pomace in the blended flour. Similar trends on increase in fiber content were also reported in biscuits with added carrot pomace (Baljeet et al., 2014;Parveen et al., 2017). Dietary fiber plays an important role in prevention of constipation, regulation of blood sugar, protection against heart diseases and prevention of certain forms of cancers (Rajpurohit, 2018).
Carrots is a rich source of carotenoids and beta carotene, they are precursor of vitamin A and act as free-radical scavengers (Sharma et al., 2012;Surbhi et al., 2018). Carotenoids have been linked with the enhancement of immune system and decreased risk of degenerative diseases such as cancer, cardiovascular disease, age related macular degeneration and cataract formation (Faullks and Southon, 2001;Sharma et al., 2012). There was an increase in the total carotenoids content with increased carrot pomace supplementation as shown in Table 2.
Increase in total carotenoid content with replacement of wheat flour with carrot puree in noodles was also reported by Prerana and Anupama (2020). Since carotenoids are affected by heat (Rodriguez-Amaya and Kimura, 2004), this analysis was done immediately after production of the noodles. There was a significant difference in total carotenoid content of the noodles prepared from the flour blends, with Sample C having the highest amount.

Mineral concentration
Carrots are good sources of calcium and phosphorous (Surbhi et al., 2018) while soybeans are a good source of magnesium and zinc (Reddy and Duke, 2015). Substitution of wheat flour with carrot pomace and soybean flour led to an increase in the mineral concentration of dry instant noodles (Table 3). Sample C had the highest  amount of zinc but was not significantly different from Sample B. Phosphorous content of Sample A and B was not significantly different. Prerana and Anupama (2020) also reported an increase in mineral content of noodles substituted with carrot puree.

Cooking qualities
Cooking time refers to the time in minutes required to gelatinize the starch core of noodles (Prerana and Anupama, 2020). The cooking time increase with replacement of wheat flour as shown in Table 4 (Table 4). Cooking loss is an important factor denoting cooking quality of noodles. Structural stability of noodles during cooking process is determined by cooking loss. High cooking loss is undesirable because it represents high solubility of starch, resulting in turbid cooking water, low cooking tolerance and sticky texture (Wandee et al., 2014). There was significant difference (P< 0.05) in the water absorption of all the noodles made. Water absorption increased with substitution of wheat flour. Sample C had the highest percent water absorption (135%) while the control had the lowest value of 125%. The increase in water absorption is attributed to the high protein content of soybean flour (Rani et al., 2019) and high fiber content in the carrot pomace flour.

Color characteristics of noodles
Color is an important quality trait in noodles. Noodles should be bright in color and slow in discoloration with time after processing (Fu, 2008). Red or dull grey colored noodles are undesirable to most consumers. Factors influencing the color of a product are alkaline formulations used during processing, flour refinement and enzymatic browning associated with polyphenol oxidase (Asenstorfer et al., 2006). Figure 1 shows noodles made from the different composite flour and control.
Color evaluation showed variation in the lightness value among the noodle samples as shown by the L * values ( Table 5). Lightness of the noodles decreased with replacement of wheat with soybean and carrot pomace flour. The redness (a*) values increased with supplementation with Sample C having the highest value   but was not significantly different from sample B. The yellowness (b*) values also increase with the control being significantly different from the rest of the noodle samples.

Texture analysis
Textural characteristics of noodles are among the important consideration in determining their quality. The quality of the noodles is primarily defined by texture and appearance (Ross, 2006). The textile profile of the noodles prepared from the composite flour is shown in Table 6. The tensile strength and breaking length decreased with substitution of the wheat flour. The control had the highest tensile strength and was significantly different from the noodles prepared from the composite flours. This decrease in tensile strength is ascribed to addition of non-gluten flours which weakens the gluten strength of the dough hence the overall structure of the noodles (Kovacs et al., 2004). Gluten make up 80% of the total protein in wheat flour. Gluten is responsible for dough extensibility and strength, replacing wheat flour impairs the gluten matrix hence leading to the weakening of the noodle texture (Kovacs et al., 2004). Similar trend was reported by other studies who substituted wheat flour with Tilapia bone flour (Sirichokworrakit, 2014) and unripe banana flour (Ritthiruangdej et al., 2011).

Sensory analysis
Sensory parameters of cooked noodles evaluated (taste, aroma, color, texture and overall acceptability) are shown in Table 7. Sample A with 80% wheat flour, 15% soybean flour and 5% carrot pomace was the most preferred by the panelist. Sample C scored the lowest score in taste (5.833), texture (5.363) and overall acceptability (6.051). The control scored the lowest in color. Sensory characteristics like smell, taste, appearance influence food acceptability more than the nutritive value. They play a significant role in the selection of a food item.

Conclusion
Instant fried noodles were prepared by substituting wheat flour with soybean (15, 20 and 25%) and carrot pomace flour (5, 10 and 15%) in an effort to improve their protein and dietary fiber content. Addition of soybean and carrot pomace flour in the noodles increased their protein, crude ash, crude fiber and total carotenoid content. Cooking time, cooking loss and water absorption of the prepared noodles increased with replacement of wheat flour. Lightness of the noodles decreased with replacement of wheat with soybean and carrot pomace flour. The control (100% wheat flour) had the highest tensile strength and was significantly different from the noodles prepared from the composite flours. Sensory analysis showed that noodles prepared from substitution of wheat with 15% soybean flour and 5% carrot pomace flour had the highest rating in taste, color, aroma, texture and overall acceptability. Soybean and carrot pomace flour can be used to formulate nutritious noodles with acceptable sensory properties.