Effect of Extruded Corn Pericarp Dietary Fiber on Dough Rheology and Dumpling Wrapper Quality

Abstract

Finely ground extruded corn pericarp dietary fiber (ECPDF) was incorporated in wheat flour at 2%, 5%, 8%, 10% and 12% levels and the effects of ECPDF on dough rheology, raw and cooked dumpling wrapper quality were investigated in this paper. Results showed that water absorption, extensibility and ratio number had significant correlation with ECPDF replacement level; the optimal cooking time and cooking loss rate of dumpling wrapper decreased with adding EPCDF from 0%–12%; all textural parameters of raw dumpling wrappers were significantly correlated with ECPDF addition; springiness, cohesiveness and resilience of cooking samples had significant correlation with ECPDF. The highest substitution level was considered as 10% ECPDF in the range of our studies.

Introduction

The lack of dietary fiber consumption is associated with the risk of coronary heart disease, diabetes, obesity, and some forms of cancer (Mann and Cummings, 2009). Dietary fiber can also influence some functional properties of foods, such as water holding capacity, oil holding capacity, emulsification, and/or gel formation. Fiber-rich by-products with high dietary fiber and bioactive compound contents possess several beneficial nutritive and protective effects (Drizikova et al., 2005; Parmar and Kar, 2007; Sturtzel et al., 2010). Corn pericarp is a by-product of starch production and an important source of dietary fiber in cereals (Watson, 2003), which is discarded or used as animal feed (Yu, 2005). The arteriosclerosis index of rats fed with corn pericarp dietary fiber was lower than those fed with wheat bran and red beans (Dong et al., 2000).

Dumplings are a kind of traditional food in China that is preferred by all kinds of consumer groups. Cooked fresh-made dumplings have better mouth-feel and flavor than the cooked frozen type, which are consumed widely. The wrapper's handling properties and filling characteristics heavily determine the quality of both raw and frozen dumplings (Zhang et al., 2011). The dumpling wrapper mainly made from wheat flour. Flour characteristics are important factors affecting the quality of dumplings (Lou and Yang, 2004). Compared with bread and noodles, dumplings are rarely studied. Research on the relationship between the quality characteristics of flour and dumpling wrapper quality have not been thoroughly investigated (Wang and Liang, 2003), especially when using flour blends enriched with dietary fiber for dumpling wrapper making.

The objective of this paper was to investigate the influence of dietary fiber prepared from corn pericarp by extrusion for the partial substitution of wheat flour on the rheological properties of wheat dough and study the quality of dumpling wrapper prepared from the blend flours.

Materials and Methods

Materials and reagents    Corn pericarp was obtained from the Zhongxing Corn Processing Plant in Henan Province, P.R. China. Wheat flour (Zhengzhou Jinyuan Flour Industry Co., Ltd., Henan Province, P.R. China) was purchased from the local supermarket (protein content 10.78%). All other chemical reagents were analytical grade.

Corn pericarp dietary fiber (CPDF) was prepared in the laboratory. Corn pericarp was passed through 40 mesh and dispersed in 80°C distilled water at a 25:1 liquid-to-solid ratio (L/S, mL/g) in a glass beaker. After soaking at 80°C for 1 hour with continuous agitation, the beaker was placed in the chamber of an ultrasonic apparatus (Kunshan Ultrasonic Instrument Co., Ltd., Jiangsu Province, P. R. China, 40 KHz, maximum sonic power 200 W ) and treated at 50°C for 80 min at an ultrasonic power of 180 W. After precipitating with dehydrated ethanol, the mixture was washed with dehydrated ethanol and acetone, filtered, and dried. The dried corn pericarp dietary fiber was ground to 80-mesh and stored in desiccators prior to extrusion (Total dietary fiber content 87.3%).

Extrusion processing    A DS32 double screw extruder (Jinan Saixin Machinery Co., Ltd., Shangdong Province, P.R. China) was used to puff up the corn pericarp dietary fiber. CPDF of 80-mesh size and 50% moisture content was conveyed into the extruder with a single-screw feeder, which was operated at a feed rate of 25 kg h⁻¹ to 30 kg h⁻¹. The extruder was operated at a screw speed of 120 rpm. The temperature was set at 150°C. After extrusion, the samples were dried, ground to 80-mesh, and stored in plastic bags.

Farinograph and extensograph tests of Dough    Dough specimens were prepared from blends containing 0% (control), 2%, 5%, 8%, 10%, and 12% (w/w) extruded corn pericarp dietary fiber (ECPDF) flours by substituting wheat flour. The effect of ECPDF on the mixing profile of the dough was investigated using farinograph-E (Brabender, Duisburg, Germany) (ISO5530-1-1997). The dough extensibility was studied using extensograph-E (Brabender, Duisburg, Germany) (ISO5530-2-1997).

Farinograph indices were determined, including the water absorption of a blend, development time of dough, stability of dough, the degree of softening of dough, and farinograph quality number.

The indices, such as extensibility, resistance to extension at constant deformation (50 mm), ratio number, and energy were determined through extension tests. Farinograph and extensograph indices were determined in four replications.

Evaluation of dumpling wrapper quality

(1) Preparation of raw dumpling wrapper

Dumpling dough was prepared by mixing flour with water to achieve 40% water absorption using a dough mixer (Guangzhou Panyu Lifeng Food Machinery Factory, Guangdong Province, P.R. China) for 10 min. After mixing, the dough was kept in a proofer (Guangzhou Baiyun District Meitian Kitchen Appliances Factory, Guangdong Province, P.R. China) at 30°C and 85% relative humidity for 30 min. The dough was passed through a roller (DMT-5, Longkou Fuxing Machine Factory, Shangdong Province, P.R. China) 8 – 14 times, gradually reducing the roller gap to produce dough sheets. The resulting dough sheets were 1 mm thick. The final sheets were cut into round pieces with a round stainless steel cutter (55 mm in diameter) to produce the dumpling wrappers.

(2) Determination of optimum cooking time

The optimum cooking time for each sample was evaluated by observing the time of disappearance of white core of wrappers (every 30 s after 3 min cooking) according to AACC Method 66 – 50 (American Association of Cereal Chemists, 2000). The cooked wrapper was cut along the diameter direction with a knife and placed on a transparent glass slide.

(3) Determination of cooking loss and cooking yield

The dumpling wrapper (55 mm in diameter) was cooked in 500 mL boiling distilled water at the optimal cooking time. Cooking water was collected in stainless steel pots pre-dried to a constant weight. The stainless steel pots were placed into an air oven at 105°C and evaporated to dryness. The residue was weighed and the cooking loss was reported as a percentage of the starting material (calculated by dry basis).

At the same time, the dumpling wrapper samples were removed from the cooking water and drained for 2 min, and the weight was evaluated. The cooking yield was expressed as the mass ratio after and before cooking.

(4) Texture properties of dumpling wrapper

Texture profile analysis (TPA) and shear test of the uncooked and cooked dumpling wrappers were detected using a TA-XT Plus texture analyzer (Stable Micro Systems Ltd., Surrey, UK) according to the method described by Yilmaz et al. (2012). The samples were cooked in the same procedure as mentioned above. The cooked wrappers were drained of surface water and kept in distilled water for 30 s before analysis. Fresh dumpling wrappers were analyzed directly.

TA-XT Plus settings for the TPA were: Mode, TPA; Pre-test speed, 1.0 mm/s; Test speed, 0.8 mm/s; Post-test speed, 0.8 mm/s; Strain, 70%; Time, 1 s; Trigger type, 5.0 g; and Probe, P/35 aluminum cylindrical probe. The values for hardness, chewiness, adhesiveness, springiness, resilience, and cohesiveness were determined for each sample.

The dumpling sheets for the shear test (60 mm × 30 mm) were first cooked at the optimal cooking time and then kept in distilled water for 30 s. The surface water was drained and the maximum shearing force was determined. The TA-XT Plus settings for the shear test were: Mode, Measure Force in Compression; Pre-test speed, 1.0 mm/s; Test speed, 0.8 mm/s; Post-test speed, 10.0 mm/s; Strain, 90%; Trigger type, 5.0 g; and Probe, a light knife blade (A/LKB).

(5) Statistical analysis

Analysis of variance (ANOVA) was performed using SPSS for windows (version 17.0, U.S.A.). Duncan's test was used to determine the significance of differences among means. Confidence levels were set at 95% ( p < 0.05).

Results and Discussion

Farinograph characteristics and extensographic properties of dough    The results of the dough properties as influenced by ECPDF enrichment are shown in Fig. 1. Water absorption increased from 62.6% to 72.9% with the increase of the ECPDF proportion in the blend from 0% to 12%, respectively. Dough development time increased with the increase of ECPDF proportion from 2% to 10% but decreased at 12% ECPDF. The dough sample containing 8% ECPDF exhibited higher stability.

Fig. 1.

Effect of addition of ECPDF on farinograph parameters

Effect of addition of ECPDF on water absorption of blend flour (a), development time of dough (c), stability of dough (c), degree of softening of dough (b) and farinograph quality number (FQN) (d)

The degree of dough softening decreased with the increase of the ECPDF proportion in flour blends from 0% to 8% but increased as the ECPDF proportion increased from 8% to 12%. The farinograph quality number steadily increased with ECPDF proportion from 0% to 8% but decreased from 8% to 12%. The characteristics of strong flours include a long development time, high stability with a small degree of softening, and high farinograph quality number (Mohammed et al., 2012). Therefore, it seems adding ECPDF to flour improved the farinograph features with the degree of improvement depending on ECPDF proportion.

The effects of various ECPDF proportions on the extensographic characteristics in the maximum resistance to extension and extensibility after 45, 90, and 135 min proving times are shown in Fig 2. The resistance to extension and ratio number increased with increasing ECPDF proportion in blend flour, whereas the value of extensibility and energy decreased, which is in agreement with the results of the study on the behavior of dough enriched with carob fiber (Mis et al., 2012). The increase in proving time also caused a reduction of dough extensibility. The extension of proving time from 90 min to 135 min significantly increased dough resistance to extension.

Fig. 2.

Effect of addition of ECPDF on extensograph parameters.

Effect of addition of ECPDF on energy (a), resistance to extension at constant deformation (50 mm) (b), extensibility (c) and the ratio number measured by extensograph at different proving times (d).

Correlations between addition levels of ECPDF and rheological parameters were shown in Table 1. Water absorption is the farinograph parameter best correlated with ECPDF proportion, which is in agreement with the observations of Wang et al. (2002).

Table 1. Correlations between addition levels of ECPDF and rheological parameters

Rheological parameters	Proving time (min)	ECPDF
Farinograph parameters
Water absorption		0.971**
Development time		0.367
Stability		0.491
Degree of softening		−0.045
Farinograph quality number		0.537
Extensograph parameters
Energy (cm2)	45	−0.540
	90	−0.456
	135	−0.586
Resistance to extension (EU)	45	0.414
	90	0.692
	135	0.841*
Extensibility (mm)	45	−0.953**
	90	−0.944**
	135	0.986**
Ratio number	45	0.885*
	90	0.868*
	135	0.964**

^**. Correlation is significant at the 0.01 level.

^*. Correlation is significant at the 0.05 level.

This was likely caused by the high soluble dietary fiber content (14.7%) in ECPDF, which allows more water interactions through hydrogen bonding (Rosell et al., 2001). Extensibility and the ratio number were negatively significantly correlated with ECPDF proportion.

Cooking properties of dumpling wrapper    Dumpling quality is determined by the characteristics of both wrapper and filling. Thus, wrapper properties play an important role in dumpling quality. The cooking process is an important procedure in dumpling preparation. Although the cooking properties of dumpling wrapper were rarely investigated, some studies on the cooking characteristics of noodles, related to the determination of the acceptability of noodles by consumers, have been conducted (Güler et al., 2002; Tudorică et al., 2002). Thus, based on the detection method of noodle cooking properties, the quality of dumpling wrapper cooking was evaluated in terms of optimal cooking time, cooking yield, and cooking loss.

The cooking properties of the dumpling wrappers are shown in Table 2. Compared with control (without ECPDF) , the addition of ECPDF slightly decreased the optimal cooking time and cooking loss of dumpling wrapper, but without any significant changes. However, cooking yield significantly increased with the increase of ECPDF proportion from 0% to 12%, perhaps due to the highly hydrophilic properties of ECPDF.

Table 2. Cooking properties of dumpling wrapper

ECPDF % (w/w)	Optimal cooking time min	Cooking loss %	Cooking yield %
0	3.50 ± 0.29b	4.99 ± 0.13b	102.95 ± 0.21a
2	3.10 ± 0.14a	2.10 ± 0.00a	108.05 ± 0.00b
5	3.00 ± 0.07a	3.52 ± 0.00a	115.50 ± 0.02c
8	3.10 ± 0.14a	3.20 ± 0.00a	118.75 ± 0.04d
10	3.00 ± 0.07a	3.14 ± 0.00a	120.95 ± 4.51e
12	3.00 ± 0.31a	2.58 ± 0.00a	121.25 ± 0.09e

Values with the same superscripts in a column did not differ signifcantly (p< 0.05).

Mean ± standard deviation of three replicates.

Texture properties of cooked dumpling wrappers    Texture is one of the major quality attributes that determine sensory quality (Varela et al., 2008). Textural profile analysis (TPA) is one of the accepted instrumental methods of detecting the sensory texture attributes. Textural attributes of the raw and cooked dumpling wrappers were measured and summarized in Table 3 and Table 4.

Table 3. TPA parameters of raw dumpling wrapper

Texture profiles	ECPDF % (w/w)
	0	2	5	8	10	12
Hardness (kN)	2.3 ± 1.0c	25.0 ± 0.8b	25.0 ± 1.4b	27.6 ± 1.5a	28.0 ± 0.7a	29.0 ± 1.6a
Adhesiveness (kN s)	−0.01 ± 0.02a	−0.69 ± 0.30bc	−0.28 ± 0.42ab	−1.03 ± 0.03c	−3.48 ± 0.17d	−3.40 ± 0.20d
Springiness (s)	0.65 ± 0.10b	0.97 ± 0.00a	0.87 ± 0.08a	0.97 ± 0.00a	0.87 ± 0.00a	0.88 ± 0.01a
Cohesiveness	0.77 ± 0.19b	0.94 ± 0.01a	0.94 ± 0.01a	0.96 ± 0.02a	0.96 ± 0.02a	0.92 ± 0.02a
Chewiness (kN s)	1.13 ± 0.52c	23.00 ± 0.67ab	20.69 ± 3.07b	25.90 ± 1.61a	23.47 ± 0.70ab	23.39 ± 1.09ab
Resilience	0.73 ± 0.07b	0.95 ± 0.01a	0.93 ± 0.00a	0.95 ± 0.00a	0.95 ± 0.00a	0.89 ± 0.03a

Values with the same superscripts in a line did not differ signifcantly (p < 0.05). Mean ± standard deviation of three replicates.

Table 4. TPA parameters of cooked dumpling wrapper

Texture profiles	ECPDF % (w/w)
	0	2	5	8	10	12
Hardness (kN)	6.0 ± 0.2c	20.6 ± 0.4a	20.0 ± 2.3ab	17.7 ± 4.7ab	16.6 ± 2.0ab	15.3 ± 2.2b
Adhesiveness (kN s)	−0.16 ± 0.02a	−6.30 ± 0.29c	−5.00 ± 1.89c	−2.78 ± 0.41b	−2.69 ± 0.54b	−2.82 ± 1.20b
Springiness (s)	0.60 ± 0.44b	0.83 ± 0.02ab	0.87 ± 0.04a	0.92 ± 0.02a	0.93 ± 0.02a	0.93 ± 0.02a
Cohesiveness	0.89 ± 0.00a	0.81 ± 0.02ab	0.81 ± 0.01ab	0.82 ± 0.08ab	0.75 ± 0.02b	0.77 ± 0.03b
Chewiness (kN s)	4.65 ± 0.64b	14.03 ± 0.68a	14.20 ± 1.04a	13.50 ± 4.82a	11.61 ± 1.70a	10.93 ± 1.41a
Resilience	0.57 ± 0.02a	0.58 ± 0.00a	0.54 ± 0.08a	0.51 ± 0.25a	0.42 ± 0.03a	0.41 ± 0.04a
Maximum shear force (N)	19.64 ± 1.68b	30.29 ± 7.84a	30.78 ± 1.49a	33.85 ± 2.65a	23.88 ± 2.27b	22.12 ± 2.04b

Values with the same superscripts in a line did not differ significantly (p < 0.05). Mean ± standard deviation of three replicates.

The hardness, absolute value of adhesiveness, springiness, cohesiveness and chewiness of raw and cooked dumpling wrappers with ECPDF were all higher than the control. No significant differences were observed in springiness, cohesiveness, and resilience among raw samples with ECPDF and in springiness, chewiness, resilience among cooked samples with ECPDF. The results suggested that ECPDF enrichment didn't compromise drastically the wrapper texture. Different ECPDF percentages ranging from 2% to 12% did not affect the springiness and resilience of raw and cooked dumpling wrappers.

Correlations between addition of ECPDF and the texture profiles of raw and cooked dumpling wrapper were summarized in Table 5. The results illustrated that all textural parameters of raw dumpling wrappers were significantly correlated with ECPDF addition ( p < 0.05), whereas only the springiness, cohesiveness, and resilience of cooked samples were significantly correlated with ECPDF (p < 0.05). The cooking process altered the texture properties of dumpling wrappers and increased the springiness and cohesiveness of dumpling wrappers

Table 5. Correlations between addition of ECPDF and the texture profiles of raw and cooked dumpling wrapper

	Texture profiles of dumpling wrapper
	Hardness	Adhesiveness	Springiness	Cohesiveness	Chewiness	Resilience
ECPDF	0.780a**	−0.881a**	0.459a*	0.457a*	0.719a**	0.541a*
	0.265b	0.053b	0.520b**	−0.637b**	0.264b	−0.481b*

^a: The texture profiles of raw dumpling wrapper;

^b: The texture profiles of cooked dumpling wrapper.

^**. Correlation is significant at the 0.01 level (1-tailed).

^*. Correlation is significant at the 0.05 level (1-tailed). Mean ± standard deviation of three replicates.

Conclusions

Adding ECPDF brought health benefits to dumpling wrappers while didn't compromise significantly the texture properties of the product. Water absorption was the farinograph parameters best correlated with the addition levels of ECPDF. Extensibility had negatively significant correlation with ECPDF replacement percentage. The optimal cooking time and cooking loss of dumpling wrapper decreased and water absorption capacity increased with adding EPCDF from 0% – 12%. All textural parameters of raw dumpling wrappers were significantly correlated with ECPDF addition; and that the parameters of cooking samples which still had significant correlation with ECPDF were springiness, cohesiveness and resilience. The highest substitution level was considered as 10% ECPDF.

Ackowledgements    We gratefully acknowledge the financial support received by the Natural Science Research Project 2011A550003 of the Education Department of Henan Province, China, by Chinese National Natural Science Foundation (Grant No. 31201294), by Key Programs for Science and Technology Development of Henan Province (Grant No.102102210123), by Special Fund for Grain -scientific Research in the Public Interest (Grant No. 201313011).

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