Potential application of enzymes to improve quality of dry noodles by reducing water absorption of inferior-quality flour

Abstract

This study has investigated the characteristics of dry noodles made with Korean domestic wheat flours using enzyme treatment for reducing water absorption to improve noodle-making performance. The water solvent retention capacity (SRC) values of flour treated with α-amylase and xylanase significantly decreased with increasing enzyme concentrations up to 0.025% (flour weight basis), which confirmed the enzyme effect on reducing the water absorption capacity of damaged starches and arabinoxylans. Enzyme-treated cooked noodles showed changes in textural characteristics, depended on the enzyme type, water amount, and drying method. Applying α-amylase for reducing the water absorption capacity of flour could mitigate the issue of inferior dry-noodle-making performance. Sensory evaluation showed improved preference attributes of cooked noodles with α-amylase treatment. In conclusion, the α-amylase application could improve the quality of dry-noodle made of Korean domestic wheat flour by diminishing the undesirable effect of damaged starch in flour related to noodle quality.

Introduction

Wheat consumption as food in Korea is approximately 2 million tons per year (Korean Flour Millers Industrial Association, 2019). However, 99% of the total wheat usage is imported from the USA, Australia, and Canada because Korean domestic wheat production is limited to approximately 1% of the total wheat consumption. Numerous efforts have been made toward wheat breeding, cultivation, and utilization to increase Korean domestic wheat production and consumption. However, the quality of the flour milled from Korean domestic wheat has been perceived as inferior to that of the flour milled from imported wheat (Kang et al. 2008; Kim et al. 2015; Lee et al. 1997; Park et al. 1999; Park et al. 2003) because of the relatively high content of arabinoxylans and damaged starch. The flour quality varies greatly depending on the wheat variety, growing environment, and milling method, which substantially affects the major functional components in wheat flour, such as gluten protein, damaged starch, and arabinoxylans. These functional components are closely related to water absorption (Kweon et al. 2011b).

All-purpose wheat flour is commonly used for dry white-salted noodles in Korea (Korean Flour Millers Industrial Association 2019). Noodles are generally prepared using limited water; however, gluten development is essential for the processing and product quality. Besides, the high water absorption of flour due to high damaged starches and arabinoxylans is undesirable for making dry noodles because it results in a relatively long drying time. Therefore, flour with relatively low water absorption, damaged starches, and arabinoxylans would be preferred for high-quality dry noodles. Numerous studies on the fresh noodle-making performance of Korean domestic wheat flours have focused on wheat cultivars (Kang et al. 2008; Lee et al. 1997; Park et al. 1999). A few studies have been reported on dry noodles. Moon et al. (2019) evaluated dry-noodle-making performance using commercial Korean domestic wheat flours and the effect of drying conditions on the quality of dry noodles. Seo et al. (2020) compared the quality of commercial dry noodles made of Korean domestic wheat and imported wheat.

In the baking industry, enzymes are commonly used for improving the processability of poor-quality flour. Xylanase and α-amylase effectively reduce the high water uptake due to arabinoxylan and damaged starch in flour, respectively (Kweon et al. 2011a). The use of enzymes to decrease water absorption and improve the negative characteristics of flours used in noodle making is worth investigating. Changes in the properties of whole wheat noodles treated with various enzymes have been recently reported (Niu et al. 2017). Besides, the effect of transglutaminase, an enzyme that crosslinks proteins, has been studied primarily on various types of noodles such as instant fried noodles, dried white salted noodles, and Asian wheat noodles, including Chinese-style noodles (Bellido and Hatcher 2011; Choy et al. 2010; Wee and Henry 2019; Wu and Corke 2005). However, microbial transglutaminase used in processed foods could be a potential environmental cause of celiac disease (Lerner and Matthias 2015). No studies have investigated the application of enzymes for dry noodles, focusing on altering water absorption by reducing the impact of arabinoxylans and damaged starch.

In this study, the enzymes were applied to improve the dry-noodle quality of commercial Korean domestic flour, which has inferior quality. The effect of enzymes on reducing water absorption of flour and its dry noodle-making performance was investigated. The water retention capacity of flour treated with enzymes was measured using the solvent retention capacity (SRC) method. The dry noodle-making performance of the flour with the enzymes was assessed by analyzing the weight gain after cooking, the turbidity of the cooking water, and the textural properties of cooked noodles. Sensory evaluation of the cooked noodles was also performed.

Materials and methods

Materials

Three Korean domestic wheat flours A, B, and C were used. One commercial all-purpose flour was used to make control noodle for sensory evaluation. α-Αmylase (Fungamyl 2500 SG, Novozymes, Bagsvaerd, Denmark), xylanase A (Biobake 10XP, Kerry Group, Cork, Ireland), and xylanase B (Shearzyme, Novozymes) were used. All other reagents were of analytical grade.

Analysis of flour quality using solvent retention capacity (SRC) and water SRC of flours treated with enzymes

According to Method 56–11.02 (AACC, 2010), SRC test was performed to evaluate quality of Korean domestic wheat flour and all-purpose flour. Five grams of flour were added to each of the four pre-weighed 50 mL conical tubes. Four solutions were prepared: distilled water, 5% (w/w) lactic acid, 5% (w/w) sodium carbonate, and 50% (w/w) sucrose solution. Each solution (25 g) was added to each tube containing flour. The tubes containing the flour sample and solution were shaken at 5 min intervals for 20 min to disperse and hydrate the flour sufficiently and, subsequently, centrifuged at 1000 × g for 15 min in a centrifuge (LaboGene 1248, Gyrozen Inc., Daejeon, Korea). The supernatant in the tube was discarded after centrifugation, and the pellet and tube were weighed. The % SRC values were calculated according to the following equation (Lerner and Matthias 2015):

$$\%\text{Solvent}\text{Retention}\text{Capacity}=\left[\frac{\text{Gel weight}}{\text{Flour weight}}-1\right]\times \left[\frac{86}{100-\text{Flour moisture}}\right]\times 100$$

Change in water absorption by the Korean domestic wheat flour with enzyme treatment was evaluated by SRC values of the flour samples in water containing each enzyme at 0.025, 0.050, and 0.100% (based on flour weight in gram).

Preparation of dry noodle made of flour treated with enzymes

According to the method described by Guo et al. (2003), noodle making was conducted with slight modifications. For dry-noodle making of Korean domestic wheat flour with enzyme treatment, flour A was selected as representing inferior quality. Flour sample (100 g) and 2 g of salt (NaCl) were mixed with 27 or 30 g of distilled water (based on the water SRC value of the flour) or enzyme solution (0.025% of the flour weight in grams) for 15 min using a micro pin mixer (100 g, National Manufacturing Inc., Lincoln, NE, USA). The mixed dough was placed in a plastic bag and rested for 10 min in a resting chamber (Phantom M301 Combi, Samjung, Gyeonggi, Korea) at 35 °C and 85% relative humidity. The dough was continuously sheeted to 3.0, 2.0, and 1.5 mm thickness and cut into noodles using a noodle maker (SN-88, Samwoo Industrial Co., Daegu, Korea). The fresh noodles were dried using a dryer (SelfCookingCenter WE 61, Rational AG, Landsberg am Lech, Germany) according to two drying conditions. Drying condition A was at 30 °C with air blow for 16 h. Drying condition B consisted of 5 step-by-steps controlled temperature and humidity: step 1, 30 °C, RH 75%, 0.5 h; step 2, 40 °C, RH 50%, 1.5 h; step 3, 40 °C, RH 50%, 1.5 h; step 4, 60 °C, RH 25%, 5.5 h; step 5, 30 °C, RH 25%, 2.0 h.

Quality analysis of cooked noodle made of flour treated with enzymes

A noodle sample (15 g) was placed in 500 mL of boiling distilled water and cooked for 15 min. To measure the weight gain of the cooked noodles, the dry noodles were weighed before cooking, and the cooked noodles were weighed before rinsing. The weight gain was calculated as the difference between the weight of the dry and cooked noodles.

The turbidity of the cooking water drained after noodle cooking was measured using a spectrophotometer (X-ma 6100PC, Human Corporation, Seoul, Korea) at a wavelength of 675 nm.

The cooked noodles were lightly rinsed in tap water for approximately 30 s, gently shaken on a sieve to remove the water, and analyzed within 5 min. The textural properties of the cooked noodles were analyzed according to Baik et al. (1994). Five cooked noodle strands (6 cm length) were placed in parallel on a texture analyzer (CT3, Brookfield, Middleboro, MA, USA) and compressed twice. An Asian noodle rig (TA 7) with a minor adjustment for the texture analyzer was used as a probe. The test mode was Texture Profile Analysis (TPA), and its parameters were as follows: pre-test speed, 2 mm/s; test speed, 1 mm/s; post-test speed, 1 mm/s; and deformation, 70%. The firmness, resilience, springiness, cohesiveness, and chewiness of the noodles were recorded.

Sensory evaluation of the cooked noodles

The sensory evaluation of the cooked noodles was conducted with approval from the Institutional Review Board of Pusan National University (Approval Number: PNU IRB/2019_02_HR). Thirty panelists were enrolled through voluntary participation and aged 19–65; healthy; non-pregnant; and not allergic to any food, especially wheat flour. They exhibited no difficulty ingesting and swallowing food. They evaluated the four cooked noodle samples, including the control, which was the noodles prepared with the control noodle flour (a commercial all-purpose flour). The control, a representative noodle, was used as a criterion for evaluating the quality improvement of dry noodles made of Korean domestic wheat flour by enzyme treatment. The other three noodle samples were prepared with Korean domestic flour: two dry noodles treated with α-amylase and xylanase A at 0.025% and one prepared without enzymes. The rheological property of fresh noodles made with flour treated with enzymes was determined to confirm the effect of enzymes. Before drying fresh noodles made with flour treated with enzymes to make dry noodle, the force (F) as resistance and distance (D) as extensibility of the fresh noodles were measured using a texture analyzer (CT3, Brookfield, Middleboro, MA, USA), and the conditions for the measurement were: test mode, tension; pretest speed, 2 mm/s; test speed, 3.3 mm/s; probe, Kieffer rig (TA-KF); target value, 20 mm. The average F and D, and F/D values were calculated from the ten measurements.

After boiling the dry noodles, each panelist received five strands of each cooked noodle in a white paper dish (50 × 50 × 20 mm) coded with random 3-digit numbers to evaluate their attributes using a 9-point scale. The attributes were intensity (brightness, firmness, chewiness), preference (appearance, color, firmness, chewiness), and overall preference. To avoid sensory fatigue, the panelists used drinking water before evaluating each sample.

Statistical analysis

All tests were performed in duplicate, and the data were evaluated using ANOVA and Tukey’s HSD test for mean comparison between samples (SPSS version22.0, Armonk, NY, USA). Pearson’s correlation test was used for analyzing the relationships between the measured parameters. A significant difference was considered at p < 0.05, unless otherwise specified.

Results and discussion

Flour quality measured by SRC

The moisture content of flour samples is shown in Table 1 and ranged from 11.7 to 13.7%. Regardless of wheat origin, different millers added different amounts of water in the wheat tempering process, resulting in the different moisture contents of flour samples. Thus, wheat flour moisture is generally affected by tempering conditions of wheat (Kweon et al. 2009).

Table 1.

Moisture content, ash content, and SRC values of the flour samples

Flour	Moisture content (%)	Ash content (%)	SRC (%)				GPI3
			Water	Lactic acid	Sodium carbonate	Sucrose
A1	12.3 ± 0.0b2	0.65 ± 0.00c	65.7 ± 0.0b	100.2 ± 0.3c	89.5 ± 0.3c	110.2 ± 0.1c	0.50 ± 0.00a
B	11.7 ± 0.0a	0.75 ± 0.01d	65.3 ± 0.0b	92.3 ± 0.1b	78.7 ± 0.0b	104.3 ± 0.3b	0.50 ± 0.00ab
C	13.7 ± 0.0c	0.48 ± 0.00b	62.8 ± 0.2a	87.4 ± 0.2a	77.7 ± 0.3a	94.4 ± 0.4a	0.51 ± 0.00b
AP	12.4 ± 0.0b	0.37 ± 0.00a	67.7 ± 0.0c	122.9 ± 0.2d	91.6 ± 0.1d	113.0 ± 0.1d	0.60 ± 0.00c

¹A, B, C: Korean domestic flours; AP: all-purpose flour

²Results are expressed as mean ± SD. Values with the same letter within the same column are not significantly different (p < 0.05) according to Tukey’s HSD test

³GPI: gluten performance index = SRC Lactic acid/(SRC Sodium carbonate + SRC Sucrose)

The ash content of flour samples is shown in Table 1, and ranged from 0.37 to 0.75%. Korean domestic wheat flour A, B, and C exhibited significantly higher ash content than all-purpose flour as control (p < 0.05), indicated undesirable flour properties for making noodles. The desired ash content of flour for white-salted noodles is 0.37–0.40%. High ash content can indicate high extraction and high level of bran particles, contributing to an increased level of polyphenol oxidase activity resulting in darker noodle color (Moon et al. 2018). Zhang et al. (2005) also reported a negative relationship of ash content of flour with the brightness. Therefore, concerning ash content, Korean domestic wheat flour quality would be inferior to all-purpose flour.

The SRC values of flour samples are also shown in Table 1. SRC values of Korean domestic wheat flour A, B, and C in all solvents were significantly lower than those of the all-purpose flour (p < 0.05). However, among Korean flour samples, SRC values of flour A in all solvents were significantly higher than those of flour B and C (p < 0.05), indicating relatively high contribution to water absorption, gluten, damaged starch, and arabinoxylans (Kweon et al. 2011b). Additionally, the lactic acid SRC values of Korean domestic wheat flour samples were much lower than that of all-purpose flour. Lactic acid SRC indicated gluten strength, and all-purpose flour is expected greater gluten strength than Korean domestic wheat flour.

The SRC values of flour showed higher sodium carbonate and sucrose SRC values, indicating the high exaggerated swelling of damaged starch and arabinoxylans, respectively (Kweon et al. 2011b). Because of the high water absorption resulting from these components, the flour could be considered inferior quality for making noodles, requiring sufficient gluten development by adding ingredients or modifying processing. Dry noodles are formulated with low and limited water; however, gluten development is required for desirable sheeting, cutting, drying, cooking, and texture. Moreover, the calculated gluten performance index (GPI) [GPI = lactic acid SRC/(sodium carbonate SRC + sucrose SRC)] values of the Korean domestic wheat flour A, B, and C were 0.50–51, compared to all-purpose flour (0.60), which indicated significantly weaker gluten strength (Kweon et al. 2011a). Thus, although overall SRC results exhibited the inferior quality of all Korean domestic wheat flour samples to all-purpose flour, Korean domestic flour A appeared the lowest quality.

Water SRC of flours treated with enzymes

The water SRC results of Korean domestic wheat flours with enzyme treatment are shown in Fig. 1. All three flours were treated with α-amylase and xylanase A and xylanase B at three concentrations (0.025, 0.050, and 0.100% of the flour weight in grams). The water SRC values of the flour samples decreased significantly with increasing enzyme concentration. The water SRC values of the flours decreased sharply up to 0.025% with α-amylase and xylanase B and 0.050% with xylanase A; further increase in enzyme concentration slowed down the decrease. Xylanase A was more effective than α-amylase and xylanase B in decreasing water SRC values, suggesting the hydrolysis of water-accessible arabinoxylans that caused relatively high water absorption of flour (Kweon et al. 2011a) by xylanase A. Also the result suggested different reaction mechanisms or activities of the two xylanases. The absorption, hygroscopicity, and water-holding capacity of the water-soluble hemicelluloses of flour are substantially destroyed by reducing the linear or backbone degree of polymerization of these polymers and reducing their network-forming ability using pentosanase (similar to xylanase A) (Slade et al. 1994). Duyvejonck et al. (2011) reported that the water SRC values of European commercial wheat flours decreased upon treatment with fungal (Aspergillus aculeatus) xylanase. Among three flour samples, flour A showed a different trend in decreasing water SRC values compared to flour B and C. Decreasing water SRC of flour A by xylanase was more significant than flour B and C due to high arabinoxylan contribution based on high sucrose SRC value.

Fig. 1.

Water SRC values of Korean domestic flours A, B, and C treated with α-amylase, xylanase A and xylanase B at different concentrations

Quality of dry and cooked noodle prepared with enzyme treatment

The moisture content of the dry noodles ranged from 13.6 to 14.6% for the noodles dried under drying condition A (static drying at 30 °C with air blowing for 16 h) and 14.3 to 14.8% for the noodles dried under drying condition B (combi and dry mode-stepwise drying for 11 h) (Table 2). The drying times of the two drying methods are different to reach a similar final moisture content of dry noodles, indicating different drying rates. Drying method B exhibited considerably faster moisture loss during drying than drying method A. Enzyme treatment except for α-amylase did not significantly influence the rate of moisture loss during drying. The moisture content of the noodles prepared with α-amylase treatment and less water dried under drying condition A only showed somewhat low moisture content, compared with all other noodles. Moon et al. (2019) reported a significant increase in the drying rate upon increasing the drying temperature or applying air circulation or ventilation and two times higher drying rate for stepwise drying than for the 30 °C drying with air circulation.

Table 2.

Quality characteristics of cooked noodles with enzyme treatment and water amounts dried under different drying conditions

Drying condition	Enzyme	Water	Moisture content of dry noodle (%)	Textural parameters of cooked noodle
				Firmness	Resilience	Cohesiveness	Springiness	Chewiness
				(N)		(Ratio)	(Ratio)	(N)
Drying condition A2	None	30	14.6 ± 0.1bcd1	28.2 ± 0.8f	0.19 ± 0.02 cd	0.42 ± 0.01c	0.84 ± 0.04 cd	9.9 ± 0.7d
	α-Amylase	30	14.5 ± 0.1bcd	23.9 ± 0.8e	0.24 ± 0.02e	0.46 ± 0.01e	0.80 ± 0.04bcd	8.7 ± 0.8c
		27	13.6 ± 0.1a	27.4 ± 0.5f	0.19 ± 0.02 cd	0.44 ± 0.02cde	0.86 ± 0.02d	10.3 ± 0.7d
	Xylanase A	30	14.4 ± 0.2b	18.6 ± 0.9c	0.20 ± 0.02d	0.46 ± 0.02de	0.79 ± 0.06abc	6.7 ± 0.7b
		27	14.3 ± 0.1b	22.3 ± 0.7de	0.17 ± 0.01bc	0.38 ± 0.02b	0.78 ± 0.04abc	6.6 ± 0.7b
Drying condition B	None	30	14.4 ± 0.1bc	27.5 ± 1.5f	0.15 ± 0.02b	0.43 ± 0.02 cd	0.82 ± 0.03 cd	9.7 ± 1.1 cd
	α-Amylase	30	14.8 ± 0.1 cd	17.5 ± 1.7c	0.18 ± 0.01bcd	0.46 ± 0.01e	0.78 ± 0.03abc	6.3 ± 0.7b
		27	14.8 ± 0.1d	20.5 ± 0.9d	0.18 ± 0.02bcd	0.45 ± 0.02cde	0.78 ± 0.03abc	7.2 ± 0.5b
	Xylanase A	30	14.3 ± 0.2b	13.6 ± 1.1a	0.12 ± 0.01a	0.36 ± 0.01ab	0.74 ± 0.04ab	3.7 ± 0.5a
		27	14.4 ± 0.1bc	15.6 ± 1.1b	0.11 ± 0.00a	0.35 ± 0.01a	0.73 ± 0.03a	4.0 ± 0.2a

¹Results are expressed as the mean ± SD. Values with the same letter within the same column are not significantly different (p < 0.05) according to Tukey’s HSD test

²Drying condition A: 30 °C with air blow for 16 h; Drying condition B: 5 step-by-steps controlled temperature and humidity—step 1, 30 °C, RH 75%, 0.5 h; step 2, 40 °C, RH 50%, 1.5 h; step 3, 40 °C, RH 50%, 1.5 h; step 4, 60 °C, RH 25%, 5.5 h; step 5, 30 °C, RH 25%, 2.0 h

The weight gain of the dry noodles after cooking is shown in Fig. 3. For the dry noodles made without enzyme addition, their weight gain following cooking was 122% for the noodles dried under drying condition A and 120% for those dried under drying condition B, indicating no significant difference between the results of the two drying methods. For the dry noodles prepared with enzyme addition, the weight gain following cooking for the noodles treated with xylanase A and dried under drying condition B was noticeably high (159.7–179.9%) compared to that dried under drying condition A (123.6–137.1%) (Fig. 2). Thus, enzyme treatment increased weight gain following the cooking of the noodles. During drying under drying condition B, the enzyme reaction might be considerably faster than that under drying condition A because the higher humidity and drying temperature associated with the former provides favorable conditions. Slade et al. (1994) described the potential depolymerization reaction of xylanase on water-soluble hemicellulose hydrolyzed to 17 degrees of polymerization, which ultimately lost its ability to form a network. As a result, the noodles treated with xylanase A could quickly swell during cooking and gain weight.

Fig. 3.

Rheological property of fresh noodles treated with different enzymes and water amounts by Kieffer Rig. The same letters above the bars indicate no significant differences (p < 0.05) according to Tukey’s HSD test

Fig. 2.

Weight gain during cooking of the dry noodles (a) and turbidity of the cooking water (b) with different enzymes (α-amylase and xylanase A) and water amounts dried under different drying conditions. The same letters above the bars indicate no significant differences (p < 0.05) according to Tukey’s HSD test

Figure 2 presents the turbidity of the cooking water of the dry noodles after cooking. For the dry noodles made without enzyme addition, the turbidity of the cooking water was 0.49 ΔA hr-1 g flour-1 for the noodles dried under drying condition A, and 0.55 ΔA hr-1 g flour-1 for those under drying condition B, which also showed a slight difference by the drying method. For the dry noodles made with enzyme addition, the turbidity of the cooking water for the noodles added with xylanase A and dried under drying condition B was noticeably high at 0.91–0.99 ΔA hr-1 g flour-1, compared with that under drying condition A at 0.61–0.65 ΔA hr-1 g flour-1 (Fig. 3) (p < 0.05). When noodles were produced without a reduction in the added water amount, the effect of xylanase A on the turbidity of cooking water was considerably more significant, resulting in greater weight gain during cooking for the noodles dried under both drying conditions. Moon et al. (2018) reported a significant positive correlation between weight gain and turbidity for dry noodles prepared with different commercial Korean domestic wheat flours.

Increased turbidity indicated increased cooking loss during the cooking of noodles. The more significant cooking loss could result from weaker protein network formation (Baik and Lee, 2003). After boiling the noodles prepared with xylanase, the higher turbidity of the cooking water indicated a higher amount of solid materials leached out during boiling because of the xylanase-induced breakdown of the arabinoxylan network.

Table 2 presents the textural properties of cooked noodles. The firmness and chewiness of the cooked noodles prepared with Korean domestic wheat flour without enzyme treatment were 28.2 N and 9.9 N, respectively, for the noodles dried under drying condition A, and 27.5 N and 9.7 N, respectively, for those dried under drying condition B. Thus, for both flours, the textural properties of the cooked noodles dried under the two conditions were not significantly different. However, noodles prepared with Korean domestic wheat flour were firmer and less resilient than those prepared with the flour with enzyme treatment.

Compared with the noodles prepared without enzyme treatment, the noodles prepared with α-amylase treatment exhibited lower firmness and chewiness for the cooked noodles and significantly greater resilience under both drying conditions. The firmness and chewiness of the cooked noodles decreased to a considerably greater extent under drying condition B than under drying condition A. Drying condition B, which involved a higher temperature and higher humidity, would enable a considerably faster enzyme reaction than drying condition A, which involved lower temperature without humidity control. Generally, the rates of enzyme reactions roughly double with a temperature increase of 10 °C (Laidler and Peterman 1979). The firmness and chewiness of the cooked noodles with xylanase treatment were 13.6–22.0 N and 3.7–6.7 N, respectively, for the noodles dried under both conditions; compared to these values, the firmness and chewiness with α-amylase treatment were significantly lower for the noodles dried under drying condition B but not for those dried under drying condition A (p < 0.05). The cooked noodles prepared with less water (27 g/100 g flour) and enzyme treatment showed a firmer texture than those prepared without reduced water or enzyme treatment (30 g/100 g flour). As explained earlier, in the reaction of xylanase during dough development (Slade et al. 1994), the noodle texture could be softened by more significant swelling during cooking due to loss of the ability to form a network via potential depolymerization of water-soluble hemicellulose.

Noodles prepared with the addition of α-amylase exhibited increased resilience due to decreased firmness and increased recovery, compared with those prepared without enzyme addition; however, reduction in water amount produced no change in the resilience of these noodles. The resilience of the noodles was significantly lower with the addition of xylanase than without enzyme treatment.

Overall, the effect of the enzyme on the quality of dry noodles was more apparent in drying methods involving humidity and temperature control, such as drying under drying condition B, than in drying methods without humidity control as drying under drying condition A. Noodles prepared with the addition of enzymes showed significant changes in the textural characteristics of cooked noodles. The extent of the changes depended on the enzyme type, water amount, and drying method. A disadvantage of dry noodles was that they required longer cooking time than other types of noodles because the drying process reduces the size of the air cells in the noodles, which results in a long time for water penetration and absorption (Fu 2008). Therefore, there is potential for shortening the cooking time for dry noodles prepared with α-amylase treatment for achieving targeted firmness and resilience of cooked noodles.

Sensory characteristics of cooked noodles

The rheological property of fresh noodles before drying to confirm the enzyme reaction is presented in Fig. 3. The rheological properties of fresh noodles made of Korean domestic wheat flour A with two enzymes (α-amylase and xylanase A) and water reduction demonstrated a noticeable effect upon the enzyme addition. In particular, compared with the flour without the addition of enzymes, the flour with the addition of xylanase A and 10% water reduction showed a similar force (F), distance (D), and F/D values, indicating a softening effect by the enzyme. Li et al. (2013) studied the effect of endoxylanase on the alveograph of soft, white, whole-wheat flour and observed a decreased dough tenacity and increased extensibility. However, following water reduction and both enzyme treatments, the fresh noodles exhibited a similar or slightly higher force and F/D ratio than the fresh noodles prepared with Korean domestic wheat flour or control all-purpose flour without enzyme treatment. The effect of xylanase A on the rheological property of fresh noodles prepared with reduced water was much more significant than α-amylase. Noodle made with a reduced amount of water and α-amylase could successfully develop the dough without weakening the quality, which was close to that with control all-purpose flour. The water-holding capacity of damaged starch and arabinoxylans is likely reduced by α-amylase and xylanase A, and more water is available to develop the dough.

The results of the sensory evaluation are shown in Fig. 4. The intensity of color was significantly lower for the control noodles than for the noodles prepared using the Korean domestic wheat flour, which resulted in a higher preference for the former (p < 0.05). The noodles with Korean domestic wheat flour, regardless of enzyme treatment, were significantly dark-colored, indicating high polyphenol oxidase activity (Moon et al. 2018). The color evaluation in the study is consistent with previous studies on the increased preference for noodles with a brighter color. For improving the color of noodles with Korean domestic wheat flour, lipase or lipoxygenase can be applied in future studies (Si and Drost-Lustenberger 2002; Cato et al. 2006). The firmness of the noodles with the Korean domestic wheat flour was significantly greater without enzyme treatment but significantly lower with enzyme treatment than those with the control flour. Without enzyme treatment, the chewiness of the noodles with the Korean domestic wheat flour was similar to that with the control flour; however, enzyme treatment significantly lowered the chewiness for the former. Xylanase reduced the firmness and chewiness to a considerably greater extent than α-amylase. The results of the sensory evaluation appeared similar to that with the instrumental analysis of textural properties.

Fig. 4.

Intensity (a) and preference (b) attributes of cooked noodles with α-amylase and xylanase A treatments, determined by sensory evaluation

The noodles with the control flour exhibited similar or higher preference concerning the appearance, color, firmness, chewiness, and overall preference than those with the Korean domestic wheat flour. Among the noodle samples with the Korean domestic wheat flour, α-amylase-treated noodles showed a higher preference than xylanase-treated noodles and non-enzyme-treated noodles. However, xylanase-treated noodles exhibited a similar preference to non-enzyme-treated noodles. Therefore, the inferior quality of Korean domestic wheat flour for noodle-making could be improved using α-amylase treatment, resulting in a significant increase in textural and overall preference (p < 0.05).

Declarations

Conflict of interest

The authors declare no conflict of interest.