Relationship of dough thermomechanical properties with oil uptake,cooking and textural properties of instant fried noodles

Abstract

Instant noodles were prepared from fifteen diverse wheat cultivars varying widely in their flour quality and dough rheology. Dough thermomechanical parameters obtained by Mixolab and flour analytical properties were correlated with the quality of instant noodles including oil uptake, cooking quality and textural attributes. The Mixolab parameters dough development time and dough stability showed significant positive correlation with cooking time, cooked weight, overall acceptability, hardness, springiness, cohesiveness and chewiness of noodles, while negatively correlated with oil uptake and cooking loss, therefore, exhibiting a marked positive effect on quality of instant noodles. Lower protein breakdown represented by C2 torque was also positively related with overall acceptability, hardness, springiness, cohesiveness and chewiness of noodles. Stickiness/adhesiveness of noodles was revealed to be mainly conferred by falling number values (R²= 0.671) and damaged starch (R²= 0.523) content of wheat flour samples. Flour samples with lesser values of protein content, sodium dodecyl sulphate sedimentation volume, thermal stability of proteins, dough stability and dough development time were found to be linked with poor noodle quality. Medium strong flours performed better in noodle making, while weaker flours demonstrated poor noodle quality. Dough rheology of good noodle making flours was characterized with higher dough development time, dough stability, C2, C3, C4 as well as C5 values. Noodles with higher overall acceptability showed a more continuous and uniform protein starch matrix in comparison to the poor counterparts.

Keywords

Wheat flour dough rheology Mixolab instant noodle cooking quality oil uptake textural properties

Introduction

Although noodles are mainly consumed in China, Japan, Korea and Indonesia, instant noodles have been preferred worldwide with significant rise in consumption over past few years (WINA, 2011) due to their characteristics such as convenience, ease of production, widely acceptable taste, texture and affordable price. Instant noodles are made by subjecting the noodle strands cut from sheeted dough to steaming and frying process that gelatinizes the starch and quickly dehydrates the noodles. The resulting product develops porous spongy structure and has a distinctive ﬂavour (Rho et al., 1986; Wu et al., 1998). Inter-cultivar variation in protein characteristics and starch quality has been revealed to have significant effect on the oil uptake (Wu et al., 2006), cooking time and textural properties of instant noodles (Park and Baik, 2004a, 2004b). Empirical dough rheological characteristics have been studied widely by the researchers employing farinograph, extensograph, alveograph, rapid visco analyser and mixograph, etc. and have been effectively utilized to predict the quality of end product specifically bread, white salted noodles, dry noodles and alkaline noodles (Batey et al., 1997; Chen et al., 2011; Ohm et al., 2006; Tang et al., 1999; Khatkar et al., 1996; Xue et al., 2010). Mixolab is the only instrument that works upon actual dough properties while measuring simultaneously mixing, pasting, enzymatic as well as retrogradation properties. It has been used earlier by some researchers to study the effect of adding transglutaminase on oat dough thermomechanical characteristics (Han et al., 2013; Huang et al., 2010; Wang et al., 2011); effect of different flour extraction rate on dough rheology; assess the effect of hydrocolloids (Rosell et al., 2007), predict the quality of bread, cookies and cakes (Kahraman et al., 2008; Rosell et al., 2010; Ozturk et al., 2008) and characteristics of wheat dough and other cereal flours (Codina et al., 2012; Hadnadev et al., 2011). However, there are limited studies (Heo et al., 2013) done for instant noodle quality with little emphasis on the dough rheology. Therefore, correlation of mixolab parameters with the quality of instant noodles is important and it can be utilized to assess the instant noodle quality of wheat cultivars. The present study aimed to determine the inter-cultivar variation in dough thermomechanical properties of diverse wheat cultivars and understand their interrelationship with the oil uptake, cooking quality and textural attributes of instant-fried noodles.

Material and methods

Wheat cultivars and milling

Fifteen Indian wheat (Triticum aestivum) cultivars namely DBW 16, C 306, HS 490, HW 2004, PBW 343, PBW 443, PBW 550, WH 147, PBW 373, WH 283, WH 542, WH 711, WH 1021, WH 1025 and HI 977 were obtained from agricultural universities; IARI regional centres; DWR, Karnal and Central State Farm, Hisar, emphasizing on their diversity for preparation of instant noodles. All wheat samples were cleaned and stored in deep freezer (−18 ℃) until further use. Wheat grains were tempered to a moisture content of 15.5% at room temperature for 18 h and then milled in a Laboratory Mill (CD 1, Chopin, France) to obtain wheat flour of 60–65% extraction rate. The flour obtained was stored under refrigeration and thawed for 2 h prior to any analysis.

Analysis of wheat flour

The wheat flour samples were analysed for their moisture, ash and protein (N × 5.7) content according to standard AACC methods (2000). Damaged starch content was determined using SDmatic (Chopin, France). Sodium dodecyl sulphate (SDS) sedimentation volume of flour was examined by the method of Axford et al. (1979).

Dough thermomechanical properties assessed using Mixolab

Dough thermomechanical properties were studied using Mixolab (Chopin Technologies, France). Mixolab is capable of determining physical dough properties like mixing behaviour, dough strength and stability along with the pasting properties. It measures torque (Nm) produced by mixing dough between two kneading arms and provides comprehensive information about the protein and starch quality as well as enzymatic activity in a single test wherein actual dough is subjected to a dual mixing and temperature constraints. Chopin + protocol (inbuilt standard protocol in Mixolab software) employing a constant mixing speed of 80 r/min was used to assess the dough rheology. It allows (1) mixing of dough at constant temperature (30 ℃) for 8 min providing information about the mixing behavior of dough (2) gradual increase in dough temperature from 30 ℃ to 90 ℃ (8–23 min), which results in thermal weakening of dough due to continued mixing under increasing temperature initially and an increase in dough viscosity later on due to gelatinization of starch (3) a constant temperature of 90 ℃ for 7 min, which allows for the enzymatic action demonstrating reduction in dough viscosity in presence of enzymes (4) decrease in dough temperature from 90 ℃ to 50 ℃ over 10 min and then holding at 50 ℃ for 5 min, which raises dough torque owing to recrystallization of starch molecules i.e. retrogradation. During the above mentioned phases, five different torques i.e. C1, C2, C3, C4 and C5 are obtained, which are used to measure water absorption, protein weakening, starch gelatinization, stability of hot formed gel and starch retrogradation, respectively.

Preparation of instant noodles

Instant noodles were prepared using the standardized formulation and processing conditions. The formula ingredients including water (30.97%), alkaline salt (potassium carbonate and sodium carbonate, 1:1) (0.23%), guar gum (0.28%) and salt (1.54%) were used for preparation of noodles. Wheat flour 100 g (on 14% moisture basis) and water containing dissolved salts and guar gum were mixed thoroughly using mixer (Kitchen Aid) for 4 min. After mixing, the crumbly dough was formed into sheet using noodle machine (ATLAS, Marcato, Italy) by passing it through roll no. 1 four times and folding in half each time. The dough sheet formed (3.2 mm) was divided into two halves and rested for 10 min (25 ℃) in ziplock pouches. The dough sheet was then passed five times through roller unit attachment with the regulating knob set at position no. 2 (2.5 mm), 3 (2.0 mm), 4 (1.5 mm) and 5 (1.2 mm), respectively. After passing through the final roll, the dough sheet with final thickness of 1.2 mm was again rested for 30 min (25 ℃) in polybag to prevent moisture loss. After the final dough resting, dough sheet was cut through the cutter attachment. The resulting rectangular noodle strands (2 mm × 1.2 mm) were placed uniformly on a sieve and put into a preheated (100 ℃) steamer (Rice Cooker-Ultimate, UL-255) and steamed for 6.4 min. The steamed noodle strips were placed in a wire basket and immersed in oil (refined soyabean oil) at a temperature of 142 ℃ for 2 min in a deep fat fryer (Friendz-FZ 591). The fried noodle strips were allowed to cool for 15 min and excess oil was drained from the surface. The cooled samples were stored in ziplock pouches for further analysis.

Quality evaluation of instant noodles

Oil uptake

Oil uptake (%, o.d.b) was estimated according to approved AACC (2000) method using solvent extractor (SER148, Velp Scientifica, Usmate, Italy).

Cooking time, cooking loss and cooked weight

The optimum cooking time for noodles was determined according to the method of Oh et al. (1983). Fried instant noodle strands (10 g) were added to 500 mL of boiling water in a beaker. The noodles were cooked until the inner white core disappeared, which was checked by crushing cooked noodle strands between two glass plates. An aliquot of water left after cooking was evaporated in an oven at 105 ℃ for 4 h to determine cooking loss (%). The cooked weight was recorded as % increase in weight of noodles after cooking as specified by Wang et al. (2011).

Texture profile analysis

Texture profile analysis of cooked noodles was carried out using Texture Analyser (Stable Micro Systems TA-XT 2i, UK). The pre-test speed, test speed and post-test speed used were 2.0, 3.0 and 3.0 mm/sec, respectively; and the probe compression plate of 45 mm × 30 mm was used. Five noodle strands were placed completely flat and close to each other. Three replicates were taken for each sample completed within 15 min after cooking and the results have been presented as noodle hardness, springiness, adhesiveness, cohesiveness and chewiness.

Overall acceptability

Five panel members trained previously for assessing noodle characteristics were selected for conducting sensory analysis of instant noodles. Sensory analysis was done using composite scoring method in which scores were given to various quality characteristics of the product i.e. colour (15), shape and appearance (15), bite characteristics (15), chewiness (15), stickiness (15), taste (15) and cooked weight (10). The mean total score assigned out of 100 by panelists was used to assess the overall acceptability of the product.

Noodle microstructure

Microstructure of the good and poor instant noodles were analysed using scanning electron microscopy (SEMTRAC Mini, Nikkiso, Germany). The fried instant noodles strands were fractured to expose their inner structure and placed on to the stubs using double-sided sticky tape (Dexter et al., 1979). The exposed surface was coated with gold and then the inner surface was scanned at 5 kV potential and 100× magnification.

Statistical analysis

All determinations were made in triplicate. Data were analyzed using SPSS software version 16.0 (SPSS Inc.). Correlation among various parameters were derived using Pearson’s test (p < 0.05). The mean comparison was carried out using one-way ANOVA with Duncan’s multiple range test. The statistical significance was observed at p < 0.05. Multiple regression equations for noodle characteristics were derived using SPSS employing stepwise regression to retain the most significant variables influencing the quality parameter.

Results and discussion

Flour quality characteristics

Table 1 displays the analytical properties of wheat flours obtained from different wheat cultivars. The moisture and ash content ranged from 11.2 to 13.8% and 0.48 to 0.77%, respectively. Protein content was minimum i.e. 7.94% for cultivar PBW 373, whereas PBW 550 had the highest protein content of 14.36% among fifteen cultivars. Falling number indicates the enzymatic activity of wheat flour with higher values suggesting lower alpha-amylase activity. Falling number data suggested that the cultivar HS 490 had highest amylase activity, while the cultivar PBW 443 had negligible or very low amylase activity. Variation in SDS sedimentation volume reflects the differences in gluten ability to imbibe water and it largely depends on the quantity as well as quality of gluten proteins in wheat flour (Pinckney et al., 1957). The highest SDS volume i.e. 61 mL was recorded for the cultivar HI 977 and PBW 550, while the lowest value of 34 mL was obtained for the cultivar PBW 373. It can be examined from the Table 1 that wheat cultivars PBW 373 and HW 2004 had lower protein content and SDS volume exhibiting poor protein content and quality. On the other hand, cultivars HI 977, PBW 550, WH 283 and WH 147 had higher protein content along with SDS sedimentation volume demonstrating good protein content and quality. Damaged starch ranged from a minimum of 4.49% in cultivar HS 490 to maximum of 7.73% in cultivar HW 2004. The overall results suggested that the flour samples of different wheat cultivars vary considerably in terms of ash, protein, falling number, SDS sedimentation volume and damaged starch content.

Table 1.

Wheat flour characteristics of different wheat cultivars.*

Cultivar	Moisture (%)	Ash (%)	PC (%)	FN (s)	SDS SV (ml)	DaS (%)
C 306	12.6 c	0.73 h	12.68 fg	534 f	47 e	6.18 g
DBW 16	12.9 d	0.57 c	11.44 de	573 h	46 e	5.85 e
HI 977	13.1 e	0.65 e	12.48 f	509 e	61 j	6.47 h
HS 490	12.9 d	0.48 a	10.50 c	384 a	48 f	4.49 a
HW 2004	13.6 i	0.73 h	8.52 b	470 c	36 b	7.73 k
PBW 343	13.59 c	0.67 fg	13.37 h	514 e	49 f	6.75 i
PBW 373	13.8 j	0.62 d	7.94 a	476 c	34 a	5.56 c
PBW 443	11.2 a	0.77 i	13.89 i	674 k	50 g	7.10 j
PBW 550	13.4 gh	0.62 d	14.36 i	617 i	61 j	6.50 h
WH 1021	13.5 hi	0.57 c	11.88 cd	628 j	42 c	5.70 d
WH 1025	13.6 ij	0.73 h	10.97 c	515 e	48 f	6.46 h
WH 147	13.2 f	0.66 ef	13.07 gh	548 g	56 h	5.55 c
WH 283	13.3 fg	0.58 c	12.15 ef	477 c	60 i	5.96 f
WH 542	11.6 b	0.68 g	12.26 ef	500 d	45 d	6.45 h
WH 711	13.5 h	0.54 b	12.35 ef	448 b	43 c	5.15 b

PC: protein content; FN: falling number; SDS SV: SDS sedimentation volume; DaS: damaged starch

Mean values followed by different letters within a same column differ significantly (p > 0.05).

Dough thermomechanical properties

Dough thermomechanical characteristics for different wheat cultivars are presented in Table 2. During the first stage of mixing at constant temperature (30 ℃), Mixolab gives information regarding mixing behavior and dough strength demonstrated by the parameters dough development time (DDT) and dough stability (DS). Water absorption refers to the amount of water required to reach an optimum peak dough consistency of 1.11 ± 0.05 Nm torque at C1. The data obtained (Table 2) showed that the cultivar HS 490 required very less water i.e. 48.6%, while the cultivar C 306 required maximum water i.e. 62.8% to reach peak dough consistency C1. Significant differences were noticed in DDT and DS of flours. Cultivars with shorter DDT had lower DS, while those with longer DDT had higher dough strength. It can be observed that cultivars HS 490 and HW 2004 dough developed quickly while it took more than 7 min for the cultivars HI 977 and PBW 550. DS was also higher for cultivars HI 977 and PBW 550 along with DDT. However, minimum DS was obtained for cultivars WH 1021 and PBW 443.

Table 2.

Thermomechanical characterization of wheat flour using Mixolab.*

Cultivar	WA	DDT	DS	C1T	C2T	C3T	C4T	C5T
C 306	62.8 m	2.88 d	4.07 c	1.12 cd	0.49 g	1.80 ef	2.25 i	2.69 c
DBW 16	53.7 c	3.18 f	5.82 i	1.12 de	0.44 ef	1.95 j	2.24 i	3.81 k
HI 977	55.7 f	7.47 n	10.68 o	1.10 bc	0.59 i	1.91 ij	1.98 h	2.86 d
HS 490	48.6 a	1.85 a	4.17 e	1.14 f	0.32 a	2.40 m	1.66 d	4.07 l
HW 2004	59.7 k	1.98 b	4.10 d	1.09 b	0.53 h	1.81 f	1.92 g	2.32 a
PBW 343	55.2 e	4.29 j	8.22 l	1.09 b	0.49 g	1.69 a	2.20 h	3.52 i
PBW 373	52.9 b	3.25 h	4.60 g	1.13 ef	0.42 d	1.86 h	1.67 d	3.58 j
PBW 443	57.6 h	2.95 e	3.93 b	1.12 cd	0.45 f	1.72 b	1.54 b	2.30 a
PBW 550	61.5 l	7.30 m	9.47 n	1.07 a	0.53 h	1.78 c	1.76 f	2.53 b
WH 1021	57.7 i	2.65 c	3.42 a	1.07 a	0.38 b	1.84 g	1.61 c	3.03 g
WH 1025	57.2 h	3.21 g	4.20 f	1.10 bc	0.43 de	1.98 k	1.79 f	2.91 f
WH 147	54.1 d	7.24 l	8.53 m	1.11 cd	0.52 h	2.14 l	1.38 a	3.21 g
WH 283	58.9 j	2.95 e	6.35 k	1.10 bc	0.50 g	1.93 jk	1.79 f	2.90 ef
WH 542	56.5 g	5.22 k	6.05 j	1.11 cd	0.45 f	1.90 i	1.79 f	3.42 h
WH 711	57.6 h	4.02 i	5.43 h	1.10 bc	0.40 c	1.78 d	1.70 e	2.89 e

WA: water absorption; DDT: dough development time; DS: dough stability; C1T: torque at C1; C2T: torque at C2; C3T: torque at C3; C4T: torque at C4; C5T: torque at C5.

Mean values followed by different letters within a same column differ significantly (p > 0.05).

C2 represents the minimum torque attained when the dough undergoes mixing as well as heating. It signifies the quality and stability of wheat protein network to thermal weakening with lower values showing poor gluten quality. Thermal stability of proteins is an important parameter which demonstrates gluten quality and strength (Kovacs et al., 2004). Again it was observed that the cultivars HS 490 and WH 1021 had a lower C2 torque demonstrating greater weakening in proteins. On the other hand, the cultivar HI 977 depicted maximum C2 torque with minimal degradation or weakening in protein network which may also be attributed to its higher DS.

The swelling and rupture of starch granules undergoing gelatinization masks the protein weakening and results in a rapid increase in the dough viscosity. The maximum torque acquired (C3) reflects the quality of starch in wheat flour. It may be observed that C3 torque was the highest for the cultivar HS 490, whereas it was the least for cultivar PBW 373.

C4 torque represents the torque exhibited by dough while mixing under a constant elevated temperature (90 ℃). A lower torque indicates lower stability of hot-formed gel. Thus, a steeper decrease in torque from C3 to C4 represents higher enzymatic activity in flour. The cultivars C 306, HI 977, HW 2004 and PBW 343 showed an increase in C4 torque specifying the lack of enzyme alpha amylase in flour obtained from these cultivars.

The dough in the final stages of Mixolab run is subjected to a decrease in temperature from 90 ℃ to 50 ℃ and further holding it at 50 ℃ which allows for the recrystallization and rearrangement of starch molecules. The peak/maximum torque imparted by the dough to mixing arms is termed as C5 torque which develops due to an increase in dough consistency as a result of retrogradation in dough. Maximum retrogradation was depicted by the cultivar HS 490 as it attained maximum C5 torque, while minimum was noticed in the case of cultivar HW 2004.

Mixolab parameters implied a significant variation among the flour samples in terms of dough strength, gluten quality and starch properties. On the basis of rheological parameters obtained using Mixolab, the flour samples of cultivars HI 977 and PBW 550 exhibited the rheological characteristics of ‘extra strong’ flour with longer DDT i.e. above 7 min, greater DS and lower breakdown/weakening. On the contrary, the cultivars HW 2004, HS 490, WH 1021 could be characterized ‘weak’ as indicated by their shorter DDT, lower DS and more degradation in protein network (C2). Additionally, the flour samples of cultivars WH 283, WH 147, WH 542 and DBW 16 may be regarded as medium strong. Lowest peak viscosity was depicted by cultivars PBW 343 and PBW 443. Cultivar PBW 443, HW 2004, PBW 550 also showed minimum retrogradation, while cultivar HS 490, DBW 16 and C 306 were characterized by maximum retrogradation. Considering the starch properties, the highest C3 and C5 was seen for cultivar HS 490, which had minimum falling number, DDT, damaged starch and protein breakdown along with a lower protein content and SDS sedimentation volume suggesting major difference in starch properties among the cultivars.

Interrelationships among flour and dough thermomechanical characteristics

Correlations among flour quality characteristics and dough thermomechanical characteristics have been depicted in Table 3. Flour protein content was positively correlated with dough strength properties including DDT (R²= 0.529), DS (R²= 0.485) and also contributed to greater water absorption. Total mineral content in flour represented as ash content appeared to improve water absorption (R²= 0.494) as well as gluten strength (R²= 0.469) while significantly decreased (R²= -0.601) the retrogradation. SDS volume reflecting the quality of gluten proteins (especially glutenins) was found to be highly associated with DDT (R²= 0.639), DS (R²= 0.725) and C2 torque (R²= 0.502) along with protein content (R²= 0.706). The glutenins build large polymers and have been known to be crucial in determining the mixing requirement and dough resistance as stated by MacRitchie and Lafiandra (1997). Falling number was weakly correlated with water absorption, ash content and protein content while negatively associated with C1 and C3 torque. Damage starch content of flour was also positively correlated with water absorption (R²= 0.571), gluten quality (R²= 0.620) and C4 torque while negatively linked with starch peak viscosity (C3) and retrogradation (C5). Flour hydration capacity has been reported to be especially linked to damaged starch content (Berton et al., 2002; Rahman et al., 2000). Starch damage during milling is a function of grain hardness. Starch granules in hard wheat are fractured more during milling due to strong adhesion between the starch granules and the protein matrix in comparison to soft grains. This leads to greater water absorption on addition of water to the ﬂour (Rahman et al., 2000). Among the flour samples, the cultivar HS 490 with the lowest damaged starch absorbed the least water during dough preparation.

Table 3.

Correlations among flour quality parameters and dough thermomechanical characteristics

WA	DDT	DS	C1T	C2T	C3T	C4T	C5T	Ash	PC	SDSV	FN	DaS
WA	1
DDT	ns	1
DS	ns	0.897**	1
C1T	−0.585**	ns	ns	1
C2T	0.482**	0.611**	0.696**	−0.338*	1
C3T	−0.683**	ns	ns	0.504**	−0.366*	1
C4T	ns	ns	ns	ns	ns	−0.332*	1
C5T	−0.829**	ns	ns	0.505**	−0.510**	0.584**	ns	1
Ash	0.494**	ns	ns	ns	0.469**	−0.475**	0.332*	−0.601**	1
PC	0.342*	0.529**	0.485**	−0.356*	ns	ns	ns	ns	ns	1
SDSV	ns	0.639**	0.725**	ns	0.502**	ns	ns	ns	ns	0.706**	1
FN	0.325*	ns	ns	−0.311*	ns	−0.430**	ns	−0.306*	0.305*	0.486**	ns	1
DaS	0.571**	ns	ns	−0.390**	0.620**	−0.639**	0.384**	−0.660**	0.810**	ns	ns	0.419**	1

Correlation is significant at 0.05 level.

Correlation is significant at 0.01 level.

A significant positive correlation (R²= 0.897) was obtained for DDT and DS highlighting that cultivars which take longer time to mix also have a greater DS as was noticed in cultivars HI 977 and PBW 550. A negative correlation (R²= −0.585) was observed between water absorption and C1 torque, which is obvious because higher water in dough decreases dough consistency thereby reducing the torque. Protein quality indicated by C2 was observed to have a significant positive correlation with water absorption (R²= 0.482), DDT (R²= 0.611) as well as DS (R²= 0.696) as these parameters also relate to dough strength. Negative correlations were observed for C3 torque with water absorption (R²= −0.674) and C2 (R²= −0.366) stating that higher gluten index or protein quality is associated with lower starch paste viscosity. This may be accredited to the competition among gluten and starch components in a limited water system thus reducing the starch paste viscosity. It can also be concluded from Table 3 that greater water absorption reduced retrogradation in dough and the higher C1 and C3 contributed to higher C5 torque as well. On the other hand, lesser protein weakening in dough also favored lower retrogradation during cooling phase.

Instant noodle quality

Differences in the quality of instant noodles prepared from different wheat cultivars in terms of oil uptake, cooking quality, overall acceptability and textural properties have been summarized in Table 4. Correlations among different flour quality characteristics, dough rheology and noodle quality have been summarized in Table 5.

Table 4.

Oil uptake, cooking quality and textural properties of instant-fried noodles prepared from different wheat flours*

Cultivar	Cooking quality				Textural properties
Cultivar	OU	CT	CW	CL	OA	HD	SP	CO	AD	CH
C 306	21.75 g	2.45 b	200.7 c	17.72 g	69 e	39.82 f	1.32 h	1.22 i	−0.32 i	64.13 i
DBW 16	17.97 c	3.30 e	201.9 c	14.88 b	87 k	40.26 g	1.27 e	1.21 h	−0.15 c	61.87 h
HI 977	19.61 e	3.32 e	210.1 d	14.30 b	81 i	44.4 k	1.41 k	1.24j	−0.31 gh	77.58 m
HS 490	20.30 f	3.00 c	195.3 b	15.15 c	63 b	42.58 j	1.26 e	1.12 a	−0.29 g	60.09 g
HW 2004	22.66 h	2.30 a	191.7 a	17.13f	65 c	35.69 d	1.32 h	1.20 g	−0.16 c	56.53 e
PBW 343	17.29 c	4.30 g	221.2 g	17.69 g	79 h	41.11 i	1.15 b	1.18 e	−0.15 c	55.79 e
PBW 373	21.56 g	2.45 b	200.9 c	16.34 e	74 f	34.62 c	1.30 g	1.15 b	−0.30 g	51.76 c
PBW 443	16.96 b	4.10 f	224.2 g	16.13 e	67 d	43.49 k	1.19 c	1.16 c	−0.07 a	60.03 g
PBW 550	15.42 a	4.00 f	229.3 h	15.75 d	76 g	44.04 l	1.38 j	1.22 i	−0.17 d	74.15 l
WH 1021	18.09 cd	3.00 c	220.3 f	15.60 d	55 a	32.57 a	1.11 a	1.20 g	−0.12 b	43.38 a
WH 1025	17.35 c	3.15 d	213.2 e	15.50 d	77 g	33.02 b	1.28 f	1.17 d	−0.22 f	49.45 b
WH 147	15.53 a	4.00 f	218.0 f	13.21 a	83 j	41.59 h	1.37 g	1.18 e	−0.22 f	67.23 k
WH 283	18.55 d	3.00 c	209.1 d	15.55 c	81 i	39.89 f	1.38 j	1.19f	−0.29 g	65.51j
WH 542	18.31 d	3.30 e	208.1 d	16.25 e	86 k	36.86 e	1.35 i	1.15 b	−0.19 e	57.23 f
WH 711	17.52 c	2.45 b	211.5 d	17.27 f	78 h	35.52 d	1.23 d	1.20 g	−0.31gh	52.43 d

OU: oil uptake (% o.d.b), CT: cooking time (min), CW: cooked weight (g/100 g), CL: cooking loss (%), OA: overall acceptability score; HD: hardness (N); SP: springiness; CO: cohesiveness; AD: adhesiveness (N/s) and CH: chewiness (N).

Mean values followed by different letters within a same column differ significantly (p > 0.05).

Table 5.

Correlations of flour characteristics and dough thermomechanical properties with the oil uptake, cooking quality and textural properties of instant fried noodles

OU	CT	CW	CL	OA	HD	SP	CO	AD	CH
WA	ns	ns	ns	0.440**	ns	ns	ns	0.605**	ns	ns
DDT	−0.540**	0.526**	0.486**	−0.458**	0.549**	0.464**	0.522**	0.381**	ns	0.656**
DS	−0.438**	0.549**	0.383**	−0.390**	0.601**	0.612**	0.509**	0.430**	ns	0.752**
C1T	0.342*	ns	−0.499**	ns	ns	ns	ns	−0.505**	−0.372*	ns
C2T	ns	ns	ns	ns	0.393**	0.427**	0.602**	0.630**	ns	0.689**
C3T	ns	ns	−0.368*	−0.632**	ns	ns	ns	−0.457**	−0.344*	ns
C4T	0.345*	ns	ns	0.442*	ns	ns	ns	0.433**	ns	ns
C5T	ns	ns	ns	ns	ns	ns	ns	−0.477**	ns	ns
Ash	ns	ns	ns	ns	ns	ns	ns	ns	0.331*	ns
PC	−0.734**	0.709**	0.699**	ns	ns	0.567**	ns	0.329*	ns	0.446**
SDSV	−0.561**	0.596**	0.468**	−0.521**	0.379*	0.727**	0.465**	0.330*	ns	0.780**
FN	−0.488**	0.504**	0.545**	ns	ns	ns	ns	ns	0.713**	ns
DaS	ns	ns	ns	0.316*	ns	ns	ns	ns	0.523**	ns

WA: water absorption; DDT: dough development time; DS: dough stability; C1T: torque at C1; C2T: torque at C2; C3T: torque at C3; C4T: torque at C4; C5T: torque at C5; PC: protein content; FN: falling number; SDSV: SDS sedimentation volume; DaS: damaged starch; OU: oil uptake; CT: cooking time; CW: cooked weight; CL: cooking loss; OA: overall acceptability score; HD: hardness; SP: springiness; CO: cohesiveness; AD: adhesiveness; CH: chewiness; ns: not significant.

Correlation is significant at 0.05 level.

Correlation is significant at 0.01 level.

Oil uptake

Oil uptake in noodles varied from 15.5 to 22.7%. Noodles prepared from wheat cultivars HW 2004, C 306 and PBW 373 demonstrated higher oil uptake, while cultivars PBW 550 and WH 147 showed lower oil uptake. Protein content (R²= −0.734) and SDS sedimentation volume (R²= −0.561) were significantly negatively associated with noodle oil uptake. High protein content and SDS sedimentation volume of flour favors the development of a strong and firm noodle structure, which restricts absorption of oil during frying (Park and Baik, 2004a). In addition, flours with lower protein content exhibited formation of coarser globules in noodles during steaming, which allows for greater penetration of oil while frying (Moss et al., 1987). Mixolab parameters DDT and DS were negatively correlated with oil content of noodles. However, flour protein content was observed to be an important determinant of oil content, which explained for 54.9% variability in it (Table 6).

Table 6.

Equations derived to predict instant noodle quality using flour characteristics and mixolab parameters by stepwise regression

Quality criteria	Equation derived	R ²
Oil uptake	29.27–0.901PC	0.549
Cooking time	4.231 + 0.335PC–0.136WA + 0.447DaS	0.860
Cooked weight	154.10 + 4.745PC	0.606
Cooking loss	34.46–6.50C3T–0.009FN–0.22DS	0.816
Overall acceptability	60.188 + 2.45DS	0.371
Hardness	22.064 + 0.351SDSV	0.525
Springiness	0.272 + 1.058C2T + 0.277C3T	0.642
Adhesiveness	−0.620 + 0.001FN	0.505
Cohesiveness	1.044 + 0.307C2T	0.435
Chewiness	–187.31 + 0.653SDSV + 69.68C2T + 165.91C1T	0.843

WA: water absorption; DS: dough stability; C1T: torque at C1; C2T: torque at C2; C3T: torque at C3; PC: protein content; FN: falling number; SDSV: SDS sedimentation volume; DaS: damaged starch.

Cooking quality

Cooking quality in this study was assessed in terms of cooking time, weight gain after cooking and cooking loss. Cooked weight and cooking loss of instant noodles ranged from 191.70 to 229.26 g/100 g and 13.21 to 17.29%, respectively. Noodles prepared from PBW 550, PBW 443 and WH 147 required longer cooking time, while the noodles prepared from the cultivars HW 2004 and C 306 noodles cooked quickly. Higher protein content and SDS sedimentation volume increased cooking time as well as cooked weight of noodles. SDS sedimentation volume also decreased cooking loss in noodles. Cooking time was well predicted (R²= 0.860) by taking into account protein content, water absorption and damaged starch content of flour (Table 6). On the other hand, cooking loss was dependent on the starch properties i.e. C3 and damaged starch of flour along with falling number. Damage starch contributed to a slightly higher cooking loss in noodles. Mixolab parameters DDT and DS were negatively correlated with cooking loss, while positively linked with cooked weight of noodles. Dough paste peak viscosity (C3) was also negatively associated with cooking loss and cooked weight of noodles. Flour protein content alone was responsible for 60.6% variation in cooked weight of noodles (Table 6). The experimental results clearly demonstrated that wheat cultivars with stronger dough characteristics were more suitable for instant noodle preparation as they had lower oil uptake as well as cooking loss both of which are important for consumer as well as manufacturers. However, the cooking time of noodles prepared from stronger cultivars such as PBW 550 was significantly higher i.e. 4.00 min in comparison to the noodle prepared with weaker cultivars like HW 2004, which took only 2.30 min for optimal cooking. This may be attributed to the fact that a strong and firm network of protein and starch (Figure 2), which is responsible for reduced oil uptake, also resists the faster hydration of noodles while cooking. Although lower cooking time is preferred for faster and easy cooking of noodles, which is exhibited by the weaker flour. It is pertinent to mention here that the noodles with lower cooking time tend to have poor textural stability in hot water in turn becoming undesirably softer, and soggy with higher cooking loss, which makes them unsuitable for consumption. Thus, wheat cultivars having stronger dough properties yield noodles with desirable firm and elastic noodle texture, which keeps the noodle strands firm and discrete during and after cooking.

Textural properties

Cooked noodle hardness, springiness, adhesiveness, cohesiveness and chewiness significantly varied from 32.57 to 44.4 N, 1.11 to 1.41, −0.07 to −0.32 N/s, 1.12 to 1.24 and 43.38 to 77.58 N, respectively. Textural hardness/firmness for cooked noodles was maximum for the cultivars HI 977 and PBW 550, whereas WH 1021 exhibited soft noodle texture. Springiness which is a measure of noodle elasticity was also higher for HI 977 and lowest for WH 1021. Stickiness/adhesiveness in noodles is an undesirable parameter for noodle quality. Noodle stickiness/adhesiveness is defined as the work required to separate the probe from noodle surface and represented by the negative area obtained between the first and the second peak. Most sticky noodles were obtained from cultivar C 306, while less sticky noodles were obtained from WH 1021. Falling number and damaged starch were revealed to be the critical parameters responsible for noodle adhesiveness/stickiness (Table 5). Chewiness of cooked noodles was higher for HI 977 and PBW 550, while least for WH 1021, WH 1025 and PBW 373. The textural attributes were more related to protein quality measured in terms of SDS sedimentation volume and C2. Higher gluten index or lower protein breakdown represented by C2 torque was positively linked with hardness, springiness, cohesiveness and chewiness of noodles. Kovacs et al. (2004) investigated that the thermal stability of gluten proteins indicates gluten strength, which maintain noodle texture during cooking by delaying hydration and preventing excessive disintegration of starch granules. Higher water absorption was found to improve the cohesiveness in noodles, but it also increased the cooking loss slightly. DS and DDT were positively correlated with hardness, springiness, cohesiveness and chewiness of noodles. On the other hand, starch paste viscosity (C3) was negatively correlated with cohesiveness and adhesiveness of noodles. In addition to C3, greater C5 torque was found to be responsible for reduced cohesiveness in noodles illustrating that the noodle cohesiveness was more related to protein content and quality along with water absorption, which might contribute to a strong network formation.

Overall acceptability

Overall acceptability score ranged from 55 to 87. The individual scores assigned to quality parameters considered for determining overall acceptability have been elaborated in Table 7. It may be noted that good noodles were prepared from cultivars DBW 16, WH 147, WH 542 and WH 283, whereas noodles prepared from cultivars HS 490, C 306, WH 1021, HW 2004 were of poor quality, which is also evident by their oil uptake, cooking quality and textural properties. The cultivars HS 490, HW 2004, WH 1021 and C 306 needed shorter cooking time and were associated with lower noodle hardness, higher oil uptake, lower cooked weight, chewiness and overall acceptability score. Flour samples from cultivars PBW 550 and HI 977 characterized as extra strong by the Mixolab produced noodles with maximum hardness and springiness. These were not considered as best noodle making cultivars and slightly lower acceptability score was assigned to them in comparison to cultivars DBW 16, WH 542 and WH 147. This is due to the reason that the noodles prepared were extra firm and chewy, which again become a bit undesirable. Also, during preparation of noodles from these extra strong cultivars, the sheet as well as noodles showed recoiling. Therefore, overall results revealed that medium strong flour with good protein content and quality are more desirable as compared to the extra strong or weaker flour.

Table 7.

Score assigned to different quality attributes of noodles.*

Wheat cultivar	Colour (15)	Shape and appearance (15)	Bite characteristics (15)	Chewiness (15)	Stickiness (15)	Taste (15)	Cooked weight (10)
C 306	8 c	11 c	13 e	13 f	6 b	13 e	5 b
DBW 16	13 f	15 g	15 f	15 h	10 e	12 d	7 c
HI 977	12 e	14 f	13 e	14 g	8 d	12 d	8 e
HS 490	6 a	13 e	8 a	13f	5 a	10 b	7 c
HW 2004	7 b	10 b	11 c	11 d	10 e	12 d	4 a
PBW 343	12 e	14 f	15 f	8 b	10 e	11 c	9 f
PBW 373	12 e	14 f	12 d	10 c	8 d	10 b	8 e
PBW 443	7 b	11 c	10 b	7 a	14 h	10 b	8 e
PBW 550	11 d	10 b	13 e	12 e	10 e	12 d	8 e
WH 1021	6 a	8 a	8 a	8 b	10 e	8 a	7 d
WH 1025	11 d	12 d	13 e	10 c	11 f	12 d	8 e
WH 147	13 f	14 f	13 e	11 d	12 g	12 d	8 e
WH 283	13 f	14 f	15 f	13 f	7 c	13 e	6 c
WH 542	13 f	14 f	15 f	13 f	10 e	14 f	7 d
WH 711	12 e	14 f	12 d	12 e	8 d	12 d	8 e

Overall acceptability score (OA) of noodles mentioned in Table 4 was calculated by adding the different quality attribute scores mentioned here.

Mean values followed by different letters within a same column differ significantly (p > 0.05).

Thermomechanical and microstructural basis of variation in good and poor noodle making cultivars

Insights into the dough thermomechanical properties of good (DBW 16, WH 542) and poor (HW 2004, WH 1021) noodle making cultivars (Figure 1) showed that there were marked differences in their protein and starch quality properties. It is evident from the graph that HW 2004 and WH 1021 had lower DS, C3 and C5 torque when compared to good noodle cultivars. Although, HW 2004 had a higher C2 torque indicating lesser protein weakening, it exhibited the lowest C3, C4 and C5 torque signifying that only gluten stability is not enough for a cultivar to perform better in noodle making; dough strength and good starch quality are required as well. DBW 16 and WH 542 both had a good protein quality as well as starch properties in contrast to WH 1021 and HW 2004, therefore, contributing to good noodle quality. It may further be noted that though there were insignificant differences in the protein, ash and damaged starch content of WH 1021 and DBW 16, the quality of proteins and starch were mainly responsible for the wide variation in their noodle quality, which has been manifested by their dough rheology. C5 torque varied much for good and poor noodle making cultivars with higher torque associated with good noodles. In case of bread, cake and chapatti, retrogradation has been reported to degrade the quality of the product, but here, pronounced gelling was not found to be associated with poor noodle quality. This may be attributed to the fact that instant noodles are generally consumed and analyzed as soon as they are prepared. Moreover, the final dough viscosity after cooling reflects the interactions between amylose and amylopectin in the formation of gel structure. Generally, higher amylose contents in flour increases final gel strength, which may be responsible for maintaining the good noodle quality. The undesirable properties of noodles with lower amylose content have been reported by Park and Baik (2004b) using reconstituted flours. It was also noticed that the paste viscosity (C3) was higher in good noodle cultivars. Additionally, the C3 peak was obtained a bit earlier in poor noodle cultivars in contrast with good cultivars. Furthermore, the microstructure analysis of instant noodles prepared from cultivars DBW 16 and HW 2004 confirmed a more continuous protein and starch network in noodles prepared from cultivar DBW 16. In contrast, noodle prepared from the cultivar HW 2004 had more extensive open areas suggesting a discontinuous protein starch network (Figure 2), which may be held responsible for the major quality difference between the noodles prepared from these cultivars.

Conclusion

Mixolab parameters implied a significant variation among the flour samples in terms of dough strength, gluten quality and starch properties. Flour samples of wheat cultivars HW 2004, HS 490 and WH 1021, characterized as weak by the Mixolab, were found to be unsuitable for noodle preparation. The desirable noodle texture of cooked noodles, which include a relatively firm and elastic bite, was dependent on protein quality reflected by higher values of DDT, DS and thermal stability of gluten proteins. Higher protein content and SDS sedimentation volume significantly decreased noodle oil uptake, increased cooking time, cooked weight and also improved the noodle textural attributes. The quality aspects studied here are crucial for selecting the suitable flour for instant noodle production. Characterization of protein and starch properties may further clarify the intercultivar differences, which make the flour perform better for instant noodle preparation.

Footnotes

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

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