Textural Characteristics and Sensory Evaluation of Cooked Dry Chinese Noodles Based on Wheat-Sweet Potato Composite Flour

Abstract

Effects of sweet potato flour (SPF) addition on dry Chinese noodles prepared from five wheat flours with variable quality (weak to very strong) were investigated. Color values expressed as L*, a* and b* were markedly affected by the levels of SPF. SPF addition reduced the springiness, cohesiveness, and resilience of the cooked noodles, but exerted varied effects on hardness and adhesiveness. Total scores of noodle samples prepared from composite flours decreased significantly with exception of very strong or strong flour. However, the reduction of total scores in wheat-SPF noodles was mainly due to decreasing of color and taste scores.

Keywords:

• Dry Chinese noodle
• Wheat-sweet potato flour blend
• Textural analysis
• Sensory evaluation

INTRODUCTION

The sweet potato (Ipomoea batatas [L.], Lam), is an important crop in many parts of the world. It grows under many different ecological conditions, has a shorter growth period than most crops, and shows no marked seasonality.[1] At present, China is the biggest sweet potato producer and consumer in the world.[2]

Although it plays a vital role in food security in developing countries, in many districts, a marked drop in sweet potato production in the world is observed.[2] This attributed to many problems related to storage and transport of the fresh roots and its limitation in sweet potato products varieties.[3,4] Sweet potato can be processed into flour and has potential to become one of the sources of healthy food in the future.[5,6] There is now a renewed effort to broaden the food base in developing countries by creating new food products or improving traditional staple food products based on indigenous sweet potato. Sweet potato flour can be used as a substitute for wheat flour in many staple foods,such as bread, noodle, and cracks, and as an alternate market output for the farmers.[7,5,3]

Noodles are an integral part of the diet in most Asian countries. The main material for noodles production is wheat flour. In China, noodles are widely consumed and approximately 30–40% of Chinese wheat production is used to manufacture various kinds of wheat flour noodles, and most of the noodles are Dry Chinese noodle.[8,9] Researchers have tried to evaluate the characteristics of wheat-sweet potato composite flour in the production of several types of noodles. Chinese-style yellow alkaline noodles and Japanese-style white salted noodles could be prepared from composite flours containing a hard wheat flour plus 25% sweet potato flour (SPF), and sweet potato genotypes differing significantly in the color imparted to the composite flour noodles.[10] Sweet potato types (flour or puree) affected Hunter L, Hunter a/b ration and β-carotene concentration of the fresh composite flour noodles.[11]

China is a vast country and has complex ecological conditions. Many wheat varieties are commonly cultivated in China. To our knowledge, there is no systematic study so far on the influence of sweet potato flour on the instrumental texture and sensory characteristics of noodle products based on various wheat flours. In addition, sensory evaluation is necessary to ensure the acceptability of noodle supplemented with SPF, but there is no report about the effects of SPE on Chinese dry noodle quality. In this study, four representative and dominant wheat varieties with different quantity and quality of gluten cultivated in Northern of China and an American hard red winter wheat were selected as experimental materials, and the objective was to determine the instrumental textural properties and to evaluate the sensory properties of Dry Chinese noodle made from wheat-sweet potato flour blends.

MATERIALS AND METHODS

Materials

Four main wheat varieties (Yannong, Zimai, Weimai and Wennong) cultivated in Northern China were obtained from Sub-center of National Wheat Engineering Technology in Taian City, Shandong Province. American hard red winter wheat (HRWW) flour was supplied by Semi Global Flour Mills, Dongying City, Shandong Province. One sweet potato (Lushu 3) was obtained from Crop Institution of Shandong Academy of Agricultural Sciences. The samples of Chinese wheat and sweet potato were harvested in the 2005 season in the Farm of Plant Garden, Agronomy College, Shandong Agricultural University, Taian City, Shandong Province, China. All Chinese wheat grains were milled into straight flour in a Bühler Laboratory Mill (Bühler-Miag, Uzwil, Switzerland). The sweet potato roots were washed, peeled, sliced to 6 mm thickness, soaked in a 0.1% sodium metabisulfite, dried in a convection dryer at 50°C, and then ground into a flour which can pass through a 60–80 mesh screen (212 μm aperture).[12]

Flour Characteristics

Protein content (%N × 5.7) was determined by combustion nitrogen analysis (model FP-248 Lcco Dumas CAN analyzer) according to Association of Cereal Chemistry[13] approved method 46–30.[13] Gluten content and gluten index were determined using AACC approved Method 38–12.[13] Dough development time and dough stability time were determined by a farinograph (Brabender, Inc, Germany) according to the AACC approved method 54–21.[13] The gelatinization characteristics of flours were measured with a Rapid Visco Analyzer 4D (RVA) (Newport Scientific Pty Ltd., Australia) by the method of Collado et al.[12]

Preparation of Dry Chinese Noodle and Cooked Samples

Dry Chinese noodles (DCN) were prepared according to Chinese Standard Method SB/T 10137-93[14], using five wheat flours, or composite flours from respective wheat flour mixed with sweet potato flour (SPF) at 10, 20, or 30% levels. In the experimental samples, 300 g flour was used to produce the dough with a Mixer. An amount of water was calculated and added to yield dough with of 30-35% moisture, which produced optimum consistency for handling. Mixing was continued at speed of 61 r/min for 5 min, and at a speed of 126 r/min for 2 min. The dough was allowed to rest for 20 min at room temperature under a plastic wrap cover. The moist crumb aggregate mixture was fed between the rollers of a laboratory noodle machine with a gap setting of 2.00 mm. The resulting sheet was folded and underwent successive reduction passes of 3.50, 3.00, 2.50, 2.00, 1.50, and 1.00 mm. At the final set gapping of 1.00 mm, the sheets were cut by cutting rollers into strips with 2.00 mm wide, hung over glass rods and dried at 40°C and 70% of relative humidity for 10 h in a constant temperature and constant humidity test box. The noodle strips subsequently were dried at room temperature for 10 h. Finally, the strips were cut into 220-mm strips and packaged until use.

The cooked samples were also prepared according to Chinese Standard Method SB/T 10137-93.[14] Dry Chinese noodles (50 g) were cooked in 500 mL boiling water, using the optimum time for individual noodles until the opaque core of noodle disappeared when the noodle was squeezed between two glass plates. The cooked noodles were drained, rinsed for 1 min with distilled water (20°C).

Color Determination

The color of the noodle sheets (1.50 mm thick, prior to cutting into strips) was evaluated using colorimeter (Model Jc801, Color Techno System Corporation, Tokyo, Japan), and the CIE-Lab L*, a* and b* values were recorded as described by Baik et al.[15]. The L* value states the position on the white/black axis, the a* value the position on the red/green axis, and the b* value the position on the yellow/blue axis. Three measurements were taken at two different locations and the readings were averaged.

Instrumental Texture Profile Analysis (TPA) of Cooked Dry Chinese Noodles

Two replicates of cooked noodles were prepared; each time three sets of samples were evaluation by Texture Profile Analysis (TPA) using the TA-XT2 Texture (Stable Micro System, Haslemeres, England) within 5 min after cooking. Five strands of cooked noodles were placed parallel on a flat metal plate and compressed twice to 80% of the noodle height using a 3.175-mm thick metal blade.[15] According to method of Bourne,[16] hardness (height of the peak), and springiness (ratio between recovered height after first compression and the noodle height) of the noodle were determined from the force-time curve of the TPA. Adhesiveness is the negative area between the first and the second peak (The minus sign of original adhesiveness value means the values' direction in the TPA plot, and it was omitted and the absolute value was taken in results and discussion). Cohesiveness is the ratio between the area under the second peak and the area under the first peak. Resilience is the ratio between the area under the first compression curve to reach the peak and the area under the first compression curve after the peak.

Sensory Evaluation

Cooked noodles were evaluated for appearance (color, and external appearance), texture characteristics (smoothness, palate, elasticity, and stickiness) and taste by a panel of panelists. The ten trained panelists (five women and five men) consisting of graduate and undergraduate students from Food Science and Technology College, Shandong Agricultural University were familiar with noodles products and were trained individually in four sessions over a four-week period. They were informed about the purpose of this project and definitions of the seven sensory characteristics of Dry Chinese noodles. The quality attributes and use of the rating method were discussed from start to finish in the sessions. Sensory evaluation was done on the day in which noodles were prepared. Examination took place in tasting booths under normal white (for color evaluation) or red illumination. Final judgments were obtained by averaging the scores given by all panelists. The eating quality of cooked noodles was subjectively evaluated according to Chinese Standard Method SB/T10137-93 by panelists, and the cooked noodle parameters and the criteria used to determine noodle quality were shown in Table 1.

Table 1 System for evaluation the quality of cooked Dry Chinese noodle

Parameters	Full score	Criterion
Color	10	Evaluation under white light. Desirable: Bright, white noodle surface, 8.5–10.0; Medium: 6-8.4; Undesirable: 1.0–6.0
External appearance	10	Smooth or deformed skin, the number, and size of specks or pinhole on noodle surface, evaluation under red light. Desirable: 8.5–10.0; Medium: 6–8.4; Undesirable: 1.0–6.0
Smoothness	5	Desirable: little resistance to the lips when drawn into mouth, 4.3–5; Medium: 3–4.3; Undesirable: 1–3
Palate	20	Firmness, the force required to cut through the noodle using front teeth. Desirable: medium firmness, 17–20; Medium: 12–17; undesirable: too hard or too soft firmness, 1–12
Elasticity	25	Elastic and cohesive when chewed; Desirable: 21–25; Medium: 15–21; Undesirable: 1–15
Stickiness	25	Desirable: not to stick to teeth when chewed, 21–25; Medium: 15–21; Undesirable: 10–15
Taste	5	Desirable: wheat flavor and aromatic taste when smelt and eaten, 4.3–5; Medium: 3–4.3; Undesirable: 1–3
Total score	100	Good quality, like much > 85; 85 > medium, acceptable > 70; poor quality, unacceptable < 70

Statistical Analysis

All statistical analyses were performed using SPSS 10.0 statistical software (SPSS Inc., Chicago, Illinois, USA). Significant difference was defined at P < 0.05 and calculated using Duncan's multiple test. At least two replications were made for flour characteristics analyses. Color and texture characteristics of noodles were determined in triplicate in replicate samples.

RESULTS AND DISCUSSION

Characteristics of Wheat Flours and Sweet Potato Flour

The results of wheat flours for various compositional, farinograph and pasting parameters are shown in Table 2. Among the four Chinese varieties,Yannong and Zimai are wheat varieties possessed strong dough properties (stability time ≥10 min, gluten index ≥38.0). The protein, wet gluten content, dry gluten content and gluten index of Zimai flour were higher than those of Yannong flour were, but the development time and stability time of Zimai were lower than those of Yannong were. Zimai showed the highest gluten index (72.13) followed by Yannong (gluten index 42.68). Weimai is a wheat variety that possessed medium dough properties. It contained the highest protein content (13.9%), wet gluten (38.86%), and dry gluten (12.1%). Wennong is a wheat variety that possessed weak dough properties and it showed the lowest gluten index (13.94), development time (2.7 min), and stability time (2.1 min). American hard red winter wheat (HRWW), as an extra strong flour, is mainly used in blending for bread production in China. Among all the experimental wheat flours, it showed the highest gluten index (94.9) and dry gluten content (13.4%), but its development time (6.84 min) and stability time (12.5 min) were not the highest.

Table 2 Characteristics of wheat flours and sweet potato flour

	Wheat flour					Sweet potato flour
Characteristics	Yannong	Zimai	Weimai	Wennong	HRWW	Lushu 3
Protein (%)	11.87	12.83	13.90	13.17	13.88	2.70
Wet gluten(%)	30.29	30.33	38.86	36.41	36.50	—
Gluten index	42.68	72.13	34.14	13.94	94.90	—
Dry gluten (%)	9.35	10.01	12.10	11.84	13.40	—
Development time (min)	9.00	6.00	3.70	2.70	6.84	—
Stability time (min)	14.7	12.0	3.5	2.1	12.5	—
Peak viscosity	188.75	219.58	189.00	248.67	183.20	181.08
Trough	137.50	149.58	132.42	178.00	127.10	102.75
Break down	51.25	70.00	56.58	70.67	56.10	78.33
Final viscosity	232.50	240.33	222.17	279.41	191.20	161.33
Set back	95.00	90.75	89.75	101.41	105.70	58.58

Among the five wheat flours, there were significant differences in the pasting characteristics of all experimental flours, including the peak viscosity, trough viscosity, “breakdown” value and final viscosity (P < 0.05). Yannong had the similar peak viscosity with Weimai and HRWW, and their peak viscosity values were significantly lower that those of Wennong and Zimai (P < 0.05). Yannong had the lowest “breakdown” value (51.25). The “breakdown” value of Zimai was similar to that of Wennong, and these were significantly higher than the other three wheat flours (P < 0.05). The RVA parameters values of Weimai were moderate and Wennong had the highest peak viscosity, trough viscosity and final viscosity among the five wheat flours. Selected characteristics of sweet potato “Lushu 3” flour were also presented in Table 2. Except for the “breakdown” value, the other RVA parameters including peak viscosity, trough viscosity, final viscosity and the “set back” value of SPF were much lower than those of all wheat flours. This might be attributed to the lower proportion of amylopectin in whole “Lushu 3” flour.

Color of Chinese Noodle Sheet

Added SPF affected the L*, a* and b* values of noodle sheet (Fig. 1). The effects of SPF addition on L* value were dependent on variety and blend proportion. As the amount of SPF increased from 0 to 30% in wheat flours, lightness became significantly darker, indicated by decreasing L* values (Fig. 1a). The L* value usually reduced when non-wheat flours, such as sweet potato flour,[12,16] rye flour,[17] soy flour,[18] barley flour,[11] and garbanzo bean flour,[19] were incorporated into wheat flour to produce noodles. At the same SPF addition levels, wheat varieties had significant effects on L* values (P < 0.05). As more incorporation of SPF into respective wheat flour, the effects of SPF addition on the decline of L* value were lesser. Comparing to wheat control noodle sheet, at 10% of SPF addition, the L* value declined by the extents of 16.23, 14.23, 13.17, 12.10, and 7.63% for Yannong, Zimai, Weimai, Wennong, and HRWW, respectively, but comparing to wheat-10% SPF noodle sheet, at 30% of SPF addition, the L* value declined by the extents of 4.06%, 6.60%, 7.45%, 3.00%, and 4.87% for Yannong, Zimai, Weimai, Wennong and HRWW, respectively.

Figure 1 Variety dependent color changes in raw noodles sheets prepared by sweet potato flour with wheat flours. □ Yannong; ▪ Zimai; △ Weimai; ⋄ Wennong; • HRWW.

As the amount of SPF increased, there is significantly higher redness intensity in noodles, as indicated by increasing a* values (Fig. 1b). The changing trends of a* value in the respective wheat variety over SPF addition was similar. Increases in redness of noodle sheets by supplementation of non-wheat flour have also been reported by Collins and Pangloli,[18] Kruger et al.,[17] and Lee et al.[19] At higher incorporation of SPF, it is SPF, not wheat flour, has much influences on a* and b* value for wheat SPF blends. The a* value of HRWW showed significantly lower than those of other four Chinese wheat varieties, but at 30% of SPF addition, the gaps of a* values between the HRWW and the other Chinese wheat varieties became less.

The b* values of five wheat noodle sheets were significantly different (P < 0.05). At 10% of SPF addition, the b* values increased minimally (significantly for Yannong, Zimai and Wennong, but not significantly for Weimai) (Fig. 1c). The b* value of HRWW was much lower than those of the four Chinese wheat varieties. As SPF addition, the b* values of HRWW was sharply increased. The b* value of five wheat-30% SPF blends were significantly different (P < 0.05), but it seemed that the b* values of noodle sheets tend to be convergent or similar as SPF addition increase. Like a* value, it is SPF, not wheat flour, has much influences on b* value for wheat-SPF blends at higher SPF addition. The increase of b* value could be attributed to the direct influence of naturally occurring colored components in SPF such as flavonoids, which increase with higher SPF content in the admixture.[18] The interactions of non-wheat components with wheat components such as polyphenol oxidase (PPO) may result in yellow color in noodles.[10,11] The different responses to wheat varieties with the same SPF addition levels might be due to combined effects of both enzymatic (interactions between SPF components and wheat flours components) and non-enzymatic (SPF) browning.

Instrumental Texture Profile Analysis (TPA) of Cooked Noodles

The TPA parameters (hardness, adhesiveness, springiness, cohesiveness, and resilience) were affected by the wheat varieties or SPF addition levels (Table 3). In previous noodle experiments, Lee et al.[19] reported that TPA parameters of cooked noodles, including hardness, springiness, and cohesiveness, decreased significantly as garbanzo bean substitutions increased in wheat flour. The declines were thought to be due to a corresponding decrease in the amount of gluten in blends. The effects of gluten on TPA parameters in blends has also been documented that gluten addition into wheat flour significantly increased hardness, springiness, and cohesiveness.[20] The present results showed gluten is not the only factor influencing the hardness and adhesiveness values, but it is gluten that mainly affects the springiness, cohesiveness, and resilience values.

Table 3 Texture profile analysis of cooked Dry Chinese noodles from five wheat flours and their respective blends with sweet potato flour.*

	SPF addition	Yannong	Zimai	Weimai	Wennong	HRWW
Hardness (N)	0%	2.51c	3.03b	3.44a	2.17a	4.41a
	10%	2.43c	3.22b	3.67a	2.87b	4.14a
	20%	3.86a	3.44a	3.67a	2.74b	3.18b
	30%	2.75b	3.43a	2.14b	3.17c	2.68c
Adhesiveness** (N·Sec)	0%	0.088c	0.056b	0.127a	0.073c	0.118a
	10%	0.081c	0.060b	0.132a	0.113b	0.094b
	20%	0.142a	0.069b	0.143a	0.108b	0.100b
	30%	0.117b	0.117a	0.094b	0.147a	0.101b
Springiness	0%	0.93 a	0.95 a	0.83 a	0.90 a	0.94a
	10%	0.91 a	0.89b	0.78 ab	0.80 b	0.93a
	20%	0.79 b	0.90b	0.72 b	0.71 b	0.89b
	30%	0.77 b	0.85 c	0.75 b	0.74 b	0.81c
Cohesiveness	0%	0.68a	0.66a	0.62a	0.63b	0.70a
	10%	0.60b	0.67a	0.53b	0.61a	0.68a
	20%	0.51c	0.65a	0.50b	0.58a	0.61b
	30%	0.51c	0.61b	0.48c	0.51b	0.54c
Resilience	0%	0.313a	0.313a	0.250a	0.262a	0.358a
	10%	0.278b	0.319a	0.203b	0.248a	0.304b
	20%	0.197c	0.304a	0.179b	0.207b	0.277c
	30%	0.212c	0.272b	0.201b	0.203b	0.272c
*Mean values in the same column in each parameter with different letters are significantly different (P < 0.05). **For adhesiveness values, the minus signs were all omitted.

Hardness and adhesiveness

The hardness values of cooked noodles made from wheat flours ranged from 2.17 N for Wennong to 4.41 N for HRWW. As the amount of SPF increased, cooked noodle hardness values increased for Zimai and Wennong, but decreased for Weimai and HRWW. In noodles prepared from Yannong flour and its corresponding composite flours, the hardness value at 20% SPF addition reached the highest, and it was significantly higher than those of other noodles (P < 0.05). The adhesiveness values of cooked noodles made from wheat flours were ranged from 0.056 N·Sec for Zimai to 0.127 N·Sec for Weimai. As the amount of SPF increased, adhesiveness increased for Zimai and Wennong, but decreased for HRWW and Weimai. 20% addition SPF to Yannong, the adhesiveness was significantly higher than those of the control wheat flour or its blends (P < 0.05).

These erratic results indicated that not only gluten strength affects the hardness or adhesiveness values of cooked noodles. The starch properties might also play an important role in the hardness or adhesiveness values. It has been reported that the instrumental hardness of fish sausage was correlated strongly with the sensory hardness and both attributes increased in magnitude with higher starch additions to the preparation.[21] The noodle hardness were affected by final viscosity and set back,[22,23] amylopectin content,[23] and retrogradation rate.[24] Although it has been reported that addition of gluten decreased significantly adhesiveness values of noodle,[20] Lee et al.[19] reported that there were no significantly differences as percentage of garbanzo bean substitutions increased from 0 to 30%, and Chen et al.[25] reported the adhesiveness of Chinese fresh noodle from wheat flours had significant correlations to amylose content. It might be significant to know which factor or ingredient lead to the different changing patterns of the hardness or adhesiveness values with SPF addition.

Springiness, cohesiveness and resilience

The values of springiness, cohesiveness and resilience of noodle samples prepared from wheat flours ranged from 0.83 (Weimai) to 0.95 (Zimai), 0.62 (Weimai) to 0.70 (HRWW), 0.250 (Weimai) to 0.358 (HRWW), respectively. These values of blend noodles decreased significantly with SPF addition from 10 to 30% although the decline extents and patterns were not the same among the respective wheat flours. These declines might probably be contributed to the gluten net changing in blend flours. The declines of springiness and cohesiveness in blend samples were consistent with the results of wheat-garbanzo bean blend noodles.[19] Resilience is the description of the rubbery state (recovery of their energy) of noodles, which is influenced by the overall gluten protein network. Other flour characteristics might also influence the value. The resilience of Japanese wheat noodles was significantly correlated to final viscosity and set back of wheat flours.[22]

It is interesting to clarify the physico-chemical mechanism of TPA's parameters, but TPA's influence factors are seldom documented in literatures. In view of the complexity of wheat and SPF components and the interactions thereof, it is impossible to determine the exact relationship between the flours components and TPA parameters using the present experimental studies. Gill et al.[26] have reported the impact of starch properties on noodle making properties of Indian wheat flours. They separated starches and investigated for morphological, thermal, rheological, and retrogradation properties. As it is difficult to select suitable material with similar flour characteristics, suitable methods (individual component separation or dough recombination) should be taken to get the ends.

Sensory Evaluation of Cooked Noodles

The descriptive panel utilized seven attributes, two appearance attributes (color, and external appearance), four texture attributes (smoothness, palate, elasticity and stickiness), and taste, to describe the differences in the sensory characteristics of the cooked noodle samples prepared from the five wheat flour and their wheat-SPF blends. The sensory properties of cooked noodles are shown in Table 4. ANOVA suggested that the five wheat flour noodles were significantly different in their overall sensory characteristics as measured by the seven attributes and all sensory scores were significantly affected by SPF addition levels.

Table 4 Sensory scores of Dry Chinese noodle prepared from wheat flours mixed with sweet potato flour.*

Wheat flour	SPF levels	Col*, **	Ext	Smo	Pal	Ela	Sti	Tas	Tot 1	Tot 2
Yannong	0%	8.12a	7.9a	3.98a	15.7c	22.2a	17.8bc	4.15a	79.85	67.58
	10%	4.90b	7.9a	3.67ab	16.7bc	19.4b	18.4b	2.60b	73.57	66.07
	20%	5.34b	7.5a	3.23c	18.2a	19.9b	18.8b	2.05b	75.02	67.63
	30%	2.98c	7.0a	3.41bc	17.8ab	13.7c	22.7a	2.05b	69.64	64.61
Zimai	0%	7.52a	7.7ab	2.89b	13.2b	20.7a	16.9b	4.60a	73.51	61.39
	10%	5.04b	8.3a	3.27b	12.8b	18.9a	21.8a	3.00ab	73.11	65.07
	20%	5.06b	7.0b	3.82a	16.6a	19.2a	21.6a	2.10b	75.38	68.22
	30%	2.12c	7.2ab	3.98a	17.8a	17.8c	22.3a	2.45b	73.65	69.08
Weimai	0%	9.02a	8.9a	4.27a	19.3a	19.8a	17.6b	4.35a	83.24	69.87
	10%	6.42b	7.3ab	4.04a	18.7a	13.4b	19.7a	2.25b	71.81	63.14
	20%	4.92c	7.4b	3.93a	18.4a	14.2b	20.6a	2.10b	71.55	64.53
	30%	4.94c	7.1b	4.00a	15.3b	12.8b	19.6a	2.55b	66.29	58.80
Wennong	0%	7.82a	8.4a	4.42a	12.3a	14.5a	21.3ab	3.80a	72.54	60.92
	10%	5.78b	7.4ab	4.20ab	9.45b	11.8bc	18.7bc	2.40b	59.73	51.55
	20%	5.48b	7.8a	4.23ab	13.4a	13.2ab	19.5b	2.65b	66.27	58.14
	30%	4.66c	6.9b	3.96b	13.1a	10.5c	22.3a	2.60b	64.02	56.76
	0%	8.04a	7.4a	3.23b	10.72c	20.7b	17.8b	3.40a	71.29	59.85
HRWW	10%	5.78b	7.5a	3.92a	17.40ab	21.5ab	18.7b	2.35b	77.15	69.02
	20%	3.14c	7.2a	4.21a	16.70b	22.3a	21.3a	2.40b	77.25	71.71
	30%	2.84d	6.7a	3.85a	19.10a	18.2c	20.7ab	2.30b	73.69	68.55
*Mean values in the same column in each wheat varieties with different letters are significantly different (P < 0.05). **Col = color; Ext = external appearance; Smo = smoothness; Ela = elasticity; Pal = palate; Sti = stickiness; Tas = taste; Tot 1 = total score; Tot 2 = total score not including color and taste scores.

Effects of SPF on Appearance and Smoothness Scores of Cooked Noodles

Normally, clear and bright noodles with free of any darkening or discoloration are favored by traditional dry Chinese noodle consumers[27]. Color, external appearances, and smoothness scores were significantly affected by SPF addition levels.

Color

SPF addition significantly reduced color scores of cooked noodles. At 10% SPF addition, the noodles displayed the yellowish and it was not preferred by most panelists. Probably because of different evaluation standards or consumer's preferences, the results were not consistent with the research of Pangloli et al.[11], who reported that use of SPF produced noodles with uniform color, and all blend samples with 10% SPF received scores indicating “like moderately” to “like very much”. At 30% SPF addition, the noodle displayed blackish and the color attribute could be thought “undesirable very much” with low scores. Color scores of cooked wheat SPF blends noodles should be cultivar dependent, as indicated that the scores were significantly different among cultivars at the same SPF addition. Color evaluation scores were affected by glossiness, whiteness and brightness in cooked dry Chinese noodles,[28] and this resulted in that color scores were not only influenced by L* or a* values, and they were not correlated significantly (P > 0.05).

External appearance and Smoothness

External appearance and Smoothness are seldom used simultaneously to evaluate noodle quality out of China. They are efficient criteria to differentiate Chinese noodles prepared from wheat flours. [9,29,30] In this study, the two parameters were used to evaluate the effects of SPF addition on wheat-SPF noodle. As SPF addition increased, the sensory scores of external appearance decreased significantly. The decline patterns of the five wheat SPF cooked noodles with addition were similar. At 30% level of addition, there was no significant difference among the five wheat cultivars (P > 0.05). Hatcher et al.^[23] have reported that adding barley flour to wheat flour can decrease the appearances scores of noodle. Although Inglett et al.[31] have reported that adding rice flour to wheat flour had no effects on the Asian noodles appearance scores, this might be the results of an hydrocolloid, Nutrim, added in the samples in the mean time. The decrease in appearances scores might result from the differences of particle size and ingredients between the wheat flours and adding flours. On the other hand, as SPF addition increased, the sensory scores of smoothness decreased significantly for Wennong and Weimai, but increased significantly for Zimia, HRWW and Yannong. Smoothness is related with the stickiness or hardness more closely. Although Wei et al.[32] could combine two criteria as one to evaluate the wheat-clover leaf-powder noodle quality, our study showed it was better to use external appearance and smoothness separately to evaluate noodle quality, because there is not complete correlation between them.

Effects of SPF on Palate, Elasticity and Stickiness Scores of Cooked Noodle

Palate

Palate scores were significant difference among all wheat samples. Except Weimai, the addition of SPF increased the palate evaluation score of noodle in respective wheat varieties. Palate is a traits related with hardness (firmness) of noodle. Khouryieh et al.[33] reported that sensory scores, firmness, of noodle containing Bripro (whey protein isolate) or soy flour was comparable with the instrumental textural analysis (hardness in TPA profile). It was not the observed in this study. For example, as SPF addition, the hardness of Zimai decreased, but the palate scores increased. This was because too hard or too soft of noodle quality was not desirable for Dry Chinese noodles. Contrary to Chinese consumers, Korean consumers prefer cooked noodles with soft texture, and there was a significant negative correlation between Korean consumer preferences and hardness.[34]

Elasticity

With SPF addition the elastic evaluation score of blend noodle decreased significantly in respective wheat varieties. This was consistent with the results of previous reports. Lei et al.[35] have reported that elasticity was significantly related with TPA's springiness, and Tang et al.[20] also reported that adding gluten into soft wheat flour could improve the elasticity of noodle. The elasticity decrease in wheat-SPF noodle might result from the dilution of gluten in noodle dough.

Stickiness

SPF addition significantly affected stickiness scores of cooked noodles. Low stickiness of noodle is desirable for Dry Chinese noodle consumers, the lower stickiness of noodles, the higher stickiness scores. Collins et al.[18] have reported that the 10% SPF had no effects on stickiness evaluation of the noodles; this was consistent with the results of Yannong and Zimai. At 30% addition of SPF, the stickiness evaluation score of noodles increased significantly. In spaghetti, sensory stickiness is related to the amount of amylose leached from the gelatinized starch granules,[36] and it is not strongly affected by protein content.[37]

Effects of SPF on Noodle Taste

The taste is the combination flavor and odor in cooked Dry Chinese noodles.[38] Sweet potato flour significantly reduced taste score; the decline patterns were different for individual wheat flour and their SPF additions. Ten percent SPF addition to wheat flour was enough to significantly reduce taste scores of the cooked noodles. This is due to the SPF strong sweet. In case of blends prepared from Yannong or Zimai with SPFs, taste scores decreased significantly as SPF addition increased from 10 to 30%, but the magnitude of decrease was much lower than those as SPF addition increased from 0 to 10%. As SPF addition increased from 10 to 30%, there were no significant differences in taste scores for Weimai, Wennong and HRWW. There were no significant differences observed among blend samples at 30% SPF addition (P > 0.05). These might be contributed to the panelists' preference in evaluating the blend samples. Although stringent training is expected to improve the taste evaluation in judging the noodle quality, it seemed that once SPF addition exceeding 10%, and the taste attribute could be thought “undesirable very much.”

Total Scores and Acceptability of SPF Noodles

Total scores of cooked Dry Chinese noodle from wheat flours varied from 83.0 (Weimai,) to 70.7 (HRWW), and they were all considered to be acceptable to consumers (Table 4). To avoid reducing noodle quality as adding SPF, some strong wheat flours (such as HRWW and Zimai) should be selected in Dry Chinese noodle manufacturing. He et al.[29] reported that Chinese noodles prepared from most wheat varieties (about 81.5 or 69.8% in two different locations) cultivated in Northern China were acceptable. SPF addition increased the total scores of cooked noodles prepared from HRWW, decreased from Yannong, Wennong and Weimai, and had slight effects for Zimai. Except Wennong-SPF and Weimai-30% SPF blends, all wheat-SPF blend noodles were considered to be acceptable. This results indicated that the gluten strength have great effects on the sensory quality of cooked Dry Chinese noodle prepared from wheat-SPF composite flours.

The reductions of sensory scores of wheat-SPF noodles were mainly due to the decreasing of color and taste scores. The sensory scores not including color and taste scores indicated that SPF additions had positive effects for HRWW, Yannong and Zimai, and had little effects on Weimai (Table 4). That is to say, more wheat flours could be selectable for Dry Chinese noodle considering certain food markets that are more open and skewed toward less conventional Dry Chinese noodle. It has been reported that alfalfa noodles, deviating significantly from the common white color,[39] and hearth bread containing sweet potato flour, having the sweet flavor,[40] offer highly desirable texture and nutritional values, and therefore were well established in the respective marketplaces in China. After necessary sensory evaluation, SPF noodle blended with wheat flour with some strong or medium strong flours might be used in dry noodle products. However, the sensory standards system to evaluate blend noodles should be different from that of Dry Chinese noodles and need to be developed for special consumers in future experiments.

CONCLUSIONS

The effects of sweet potato flour addition on L*, a*, and b* values were variety dependent and their amount in the noodle. As the amount of SPF increased in wheat flours, lightness became significantly darker, and there is significantly higher redness intensity in noodles. As SPF addition increased, hardness, and adhesiveness values displayed different changing trends, increased or decreased, but the springiness, cohesiveness, and resilience values of blend noodles decreased significantly in respective wheat flours. The TPA results indicated that not only gluten strength affects the hardness or adhesiveness values of cooked noodles. Other components, such as starch, might also play an important role in the two values. It is mainly gluten strength that affects the springiness, cohesiveness, and resilience values. All sensory scores were significantly affected by SPF addition levels and wheat varieties. The gluten strength greatly affected the sensory quality of cooked Dry Chinese noodle prepared from wheat-SPF composite flours. Some strong flours (such as HRWW and Zimai) should be selected in Dry Chinese noodle prepared from composite flours. SPF noodle blended with some strong or medium strong wheat flours could be used in dry noodle products for special consumers who have different preferences for color or taste. In general, the use of SPF in partial replacement of wheat flour could significantly affect cooked Chinese noodles textural and sensory quality; the effects of SPF on noodle quality were variety- and SPF addition level- depended. Individual wheat flour characteristics testing and sensory evaluation are necessary for wheat-SPF noodles during Dry Chinese noodle manufacturing. This offers opportunities to efficiently use SPF in the manufacture of Dry Chinese noodles.

ACKNOWLEDGMENTS

The authors are grateful for the cooperation and kind help received during the project. National Natural Science Foundation of China (30671270), and Program for Growing Superior Grain Cultivators in Shandong Province (2005) provided financial support for this research.