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Food Chemistry 223 (2017) 16–24
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Food Chemistry
journal homepage: www.elsevier .com/locate / foodchem
Microstructural, textural, and sensory properties of whole-wheat noodlemodified by enzymes and emulsifiers
http://dx.doi.org/10.1016/j.foodchem.2016.12.0210308-8146/� 2016 Elsevier Ltd. All rights reserved.
⇑ Corresponding author.E-mail addresses: [email protected] (M. Niu), [email protected] (G.G.
Hou), [email protected] (J. Kindelspire), [email protected](P. Krishnan), [email protected] (S. Zhao).
Meng Niu a,b, Gary G. Hou b,⇑, Julie Kindelspire c, Padmanaban Krishnan c, Siming Zhao a
aCollege of Food Science and Technology, Huazhong Agricultural University, 1 Shizishan Street, Wuhan 430070, Hubei Province, PR ChinabWheat Marketing Center, Inc., 1200 NW Naito Parkway, Suite 230, Portland, OR 97209, USAc South Dakota State University, 2380 Research Parkway, Room 113C, Brookings, SD 57007, USA
a r t i c l e i n f o
Article history:Received 23 July 2016Received in revised form 6 December 2016Accepted 9 December 2016Available online 10 December 2016
Keywords:Whole-wheat noodleMicrostructureTextureEnzymeEmulsifier
a b s t r a c t
With the utilization of enzymes including endoxylanase, glucose oxidase (GOX) and transglutaminase(TG), and emulsifiers comprising sodium stearoyl lactate (SSL) and soy lecithin, the microstructural,textural, and sensory properties of whole-wheat noodle (WWN) were modified. The development timeand stability of whole-wheat dough (WWD) were enhanced by TG due to the formation of a more com-pact gluten network, and by SSL resulting from the enhanced gluten strength. Microstructure graphs byscanning electron microscopy (SEM) verified that TG and SSL promoted the connectivity of gluten net-work and the coverage of starch granules in WWN. TG increased the hardness and elasticity of cookedWWN, while two emulsifiers increased the noodle cohesiveness. Additionally, TG and SSL improvedthe sensory properties of noodle such as bite, springiness, and mouth-feel. The results suggest that TGand SSL are effective ingredients in enhancing the gluten strength of WWD and improving the qualitiesof WWN.
� 2016 Elsevier Ltd. All rights reserved.
1. Introduction
Whole grains comprise intact, ground, cracked, or flaked cary-opses, in which all components (bran, germ, and endosperm) arepresent in the same relative proportions as in the intact grain.Thus, they contain all naturally occurring and essential substancesof the entire seed (Ye, Chacko, Chou, Kugizaki, & Liu, 2012). In theU.S., whole grains may include whole wheat, oats, brown rice, rye,corn, barley, millet, and sorghum. Whole-grain flour can beobtained by grinding the kernels into flour using several millingtechniques such as stone mill, hammer mill, and roller mill(Posner, 2009). Nowadays, consumers worldwide have shownincreasing interests in reducing disease risks andmanaging chronicdiseases by consuming health-promoting dietary ingredients.Whole-wheat flour (WWF), as one of the most important wholegrains, acts as a rich source of dietary fiber and phytochemicals(Hirawan, Ser, Arntfield, & Beta, 2010). Many epidemiological andclinical studies have shown that the long-term intake of whole-wheat products can provide many benefits for the patients suffer-ing from chronic diseases such as obesity, diabetes, and cancer
(Giacco, Della Pepa, Luongo, & Riccardi, 2011). However, theaddition of wheat bran not only causes rough surfaces and grittymouth-feel but also negatively affects the formation of gluten net-work in bran-contained products, leading to undesirable productquality. Much effort is being made to improve the quality charac-teristics of whole-wheat products. Liu et al. (2015) improved thesteamed bread making performance of WWF by different millingprocesses and found that the bran recombining grinding processprovided a larger height/diameter ratio and specific volume thanthe entire grain grinding process. Li, Hou, Chen, and Gehring(2013) enhanced the baking quality of whole-wheat saltine crack-er by including endoxylanase, vital wheat gluten, and gum Arabic,and reported that these ingredients increased the stack height andspecific volume of the crackers.
Noodles account for approximately 20–50% of the total wheatconsumed in Asia, and the popularity of noodles has expanded tomany countries outside of Asia (Hou, 2010). In view of this,introduction of Asian noodles made from WWF can be an effectiveway to promote the high-fiber food consumption and increase thehealth benefits for consumers around the world. Several studieshave been conducted to investigate the effects of bran on noodlequality and improve the textural and sensory properties ofwhole-wheat noodle (WWN). Jiang, Martin, Okot-Kotber, andSeib (2011) reported that dark wheat bran reduced the lightnessof noodle sheet. Song, Zhu, Pei, Ai, and Chen (2013) noted that
M. Niu et al. / Food Chemistry 223 (2017) 16–24 17
the presence of bran decreased the connectivity between starchgranules and gluten in noodle structure. Vijayakumar andBoopathy (2014) included tapioca flour and soy flour in noodle for-mula and improved the cooking qualities and sensory properties ofWWN. In our previous studies, the influences of wheat bran parti-cle size and grinding methods on the properties of WWF and itsnoodle qualities were investigated (Niu, Hou, Lee, & Chen, 2014a;Niu, Hou, Wang, & Chen, 2014b). The reduction of wheat bran orWWF particle sizes provided beneficial effects on the qualityimprovement of WWN. Alternatively, the use of special inorganicphosphate salts improved the color and textural properties ofWWN (Niu, Li, Wang, Chen, & Hou, 2014c). Despite some attemptshave been made to improve the color, texture, and sensory proper-ties of WWN, the use of functional ingredients that are commonlyused in baking industry has not been reported.
Commercial enzymes, such as transglutaminase (TG) and glu-cose oxidase (GOX), have been tested in refined noodle productsto improve their quality. Transglutaminase facilitates the forma-tion of the isopeptide bond, thereby leading to polymers of highmolecular weights. Bellido and Hatcher (2011) reported that TGcould polymerize the protein network and increase the stiffness,elasticity and firmness of yellow alkaline noodles. Choy, Hughes,and Small (2010) noted that the addition of TG into instant noodleformula enhanced the noodle hardness and improved the continu-ity of protein network. Gan, Wenhwei, Leemin, and Easa (2009)found that inclusion of TG yielded higher tensile strength andelasticity for noodles containing soy protein isolate. GOX causesthe oxidation of free sulfhydryl units in gluten proteins and pro-motes the formation of disulfide linkages. GOX has been reportedto improve the microstructure and storage quality of frozen noodlewhen used together with other ingredients (a-amylase and guargum) (Lv et al., 2014). Endoxylanase, another commercial enzyme,is capable of reducing the water holding capacity of araboxylans(AX) and redistributes water in flour-based products, but few stud-ies have reported its application in noodle product.
Sodium stearoyl lactylate (SSL), as a kind of anionic emulsifier,can cause gluten aggregation and increases dough strength by itsinteractions with gluten during mixing (Gomez, Ferrer, Anon, &Puppo, 2013). SSL was reported to enhance the structure develop-ment of instant fried noodle (Choy et al., 2010). Lecithin is a natu-rally occurring mixture of phosphatidyl choline with diverse fattyacid side chains such as stearic, oleic, and palmitic acids. It hasbeen used to modify the lipid digestion of instant noodles by pro-ducing small droplets (Hur, Lee, Lee, Bahk, & Kim, 2015). Ugarcic-Hardi, Jukic, Komlenic, Sabo, and Hardi (2007) included soy lecithinin noodle formula and found it could reduce noodle cooking loss.
These functional ingredients, commonly used in baking indus-try, have shown their effectiveness in improving the structure,cooking quality, and textural property of refined noodle productsexcept endoxylanase. But, none of them has been experimentedwith in WWN dough system. The aim of the study was to investi-gate the influences of enzymes (endoxylanase, GOX, and TG) andemulsifiers (SSL and soy lecithin) on the quality attributes ofWWN. This study was expected to demonstrate the interactionsbetween these ingredients and flour components in WWN, andprovide more effective methods and valuable guidance for furtherimprovement of WWN.
2. Materials and methods
2.1. Materials
Ultrafine hard white whole-wheat flour (WWF) was kindly pro-vided by Ardent Mills (Denver, Colorado, US). This special WWFwas produced by the steps of roller milling and separating wheat
kernels into refined and millfeed fractions, fine grinding of themillfeed fractions to mean particle size of small than 150 lm,and recombining the ground millfeeds with the refine flour. Themoisture, protein, and ash content of WWF were 11.20%, 12.67%(14% moisture basis, mb), and 1.52% (14% mb), respectively.Pentopan Mono BG (EC 3.2.1.8, 2500 U/g, lyophilized powder) isa purified (1, 4)-b-xylanase and was provided by NovozymeCompany (Franklinton, NC). Glucose oxidase (EC 1.1.3.4, 300 U/g,lyophilized powder) was purified from Aspergillus niger, transglu-taminase (EC 2.3.2.13, 100 U/g, lyophilized powder) was purifiedfrom guinea pig liver, and both enzymes were from Mühlenchemie(Ahrensburg, Germany). The enzyme unit, one U, is defined as theamount of enzyme that catalyzes the conversion of one micromoleof substrate per minute at a temperature of 25 �C and the optimalpH and substrate concentration that yield the maximal substrateconversion rate. Soy lecithin was manufactured by WillPowder(Miami Beach, Florida, US), and Sodium Stearoyl Lactate (SSL)was purchased from INRFood (Durham, North Carolina, US). Allingredients used in the study were food grade.
The usage levels of each ingredient were selected based on themanufacturers’ recommendations and our screening experiments.The addition levels for the three enzymes were 0.30, 0.75, and1.50 U per gram of WWF. The addition levels were 0.10%, 0.30%,and 0.50% (w/w, flour basis) for soy lecithin, and 0.25%, 0.50%,and 0.75% (w/w, flour basis) for SSL, respectively.
2.2. Starch pasting properties
The starch pasting properties ofWWF samples addedwith ingre-dients were determined with a Rapid Visco Analyzer (RVA, ModelSuper-3,Newport Scientific,Australia), using theAACC InternationalApproved Method 76-21 (American Association of Cereal Chemists,2010). A sample of 3.5 g WWF (14% mb), 25 mL of distilled water,and a defined addition level of each ingredient were mixed to forma slurry that was manually homogenized using a plastic paddle toavoid lump formation before the RVA test. The testswere conductedin a programmed heating and cooling cycle for 13 min. The parame-ters recorded were expressed in rapid visco units (RVU).
2.3. Dough mixing properties by Mixolab
The dough mixing properties of WWF were determined with aMixolab (Chopin Technologies, Villeneuve la Garenne, France). Aconstant dough weight (75 g) method was used. An exact amountof eachWWF sample with each ingredient was weighed and placedinto the mixer as specified by the Mixolab software. The settings ofthe heating and cooling circles were first maintained at 30 �C for8 min, increasing at 4 �C/min until the mixer temperature reached90 �C, decreasing at the same speed until the temperature reached50 �C after an 8-min holding period at 90 �C, and finally holding at50 �C for 6 min. The parameters obtained from the recorded curvewere water absorption (the percentage of water required for thedough to produce a torque of 1.1 ± 0.07 Nm), dough developmenttime (the time required to obtain C1), stability (the time duringwhich the torque produced is >C1-11%), peak torque (the maxi-mum torque produced during the heating stage), setback (the dif-ference between the torque after cooling at 50 �C and the torqueafter the holding time at 90 �C), and hot-gel stability (the ratio ofthe torque after the holding time at 90 �C and the maximum torqueduring the heating period). The measurements were performed intriplicate for each sample.
2.4. Preparation of noodles
The fresh raw noodles were prepared through mixing andsheeting on a pilot-scale noodle line, according to the procedure
18 M. Niu et al. / Food Chemistry 223 (2017) 16–24
described by Hou (2010). Each enzyme or emulsifier was pre-dissolved in half of the water, and salt was dissolved in the remain-ing water. The correct amount of solution was added to achieve aflour-water-salt weight ratio of 100:35:1.2. The final thickness ofthe noodle-dough sheet was calibrated to 1.20 ± 0.03 mm, andthe noodle sheet was slit into 2.5 mm-wide and 300 mm-longstrands with a #12 square-type slitter. The fresh raw noodles werestored in plastic bags at room temperature before analyses.
2.5. Scanning electron microscopy (SEM)
The SEM study of the cross-section structure of raw noodle wascarried out as described by Niu et al. (2014c), using a scanningelectron microscope (Sigma VP, ZEISS International, Germany).The fresh noodles were soaked in glutaraldehyde solution (2.5%)for 2 h and rinsed with phosphate buffer (0.1 mol/L), followed bya secondary fixation in osmium tetroxide solution (1%) for 1.5 h.Then, the samples were eluted in graded ethanol series (30%,50%, 70%, 90%, and 100%) and isoamyl acetate was used to removethe ethanol. After being supercritical dried, dehydrated sampleswere mounted on an aluminum stub using a double-sided tapeand coated with 50 nm of gold, then observed at an acceleratingvoltage of 15 kV. The micrographs were taken at 600 �magnifica-tion. During preparation, the mounting solutions were kept uncon-taminated and the steps of sample sticking and coating wereperformed as quickly as possible to avoid possible contaminationfrom operating environment.
2.6. Color measurement
A Chroma meter (Konica Minolta CR-410, Japan) equipped withD50 illuminant was used to measure the color of raw noodle sheetsfollowing the methods of Hou (2010). An average of eight readingswas calculated for each measurement. Duplicate noodle prepara-tions were done on two different days. Noodle sheets were storedin sealed plastic bags at room temperature until the measurementswere taken.
2.7. Noodle cooking yield
The cooking yield was determined according to the methoddescribed by Hou (2010). A sample of 100 g raw noodle was cookedin boiling water for 5 min and rinsed in 26-27 �C water for 10 swith stirring. The noodles were then placed in a plastic strainer,and the excess water on the surface of the cooked noodles wasdrained by tapping the strainer forcefully 10 times (for about10 s) on the edge of a sink. The weight of the cooked noodle samplewas recorded, and the cooking yield was calculated as the massratio before and after cooking.
2.8. Textural properties
Textural profile analysis (TPA) of cooked noodle was deter-mined as described by Hou (2010), using a TA-XTPlus Texture Ana-lyzer (Texture Technology Corp., Scarsdale, NY). Cooked noodleswere prepared using the same procedures as noodle cooking yieldin Section 2.7. After the excess water on noodle surface wasremoved, the drained noodles were placed in a covered containerand three uniform long noodle strands were taken and cut to alength of 6.0 cm. Five short strands were randomly selected andplaced side by side on the base plate, and compressed with a TA-47W Pasta Blade (5-mm thickness flat blade) by using a 5 kg loadcell. The pre-test speed, test speed, and post-test speed were4 mm/s, 1 mm/s, and1 mm/s, respectively. The compression strainwas 70% of the noodle thickness, and the averages of at least eightanalyses were calculated. Four textural parameters, including
hardness, springiness, cohesiveness, and resilience, were recordedfrom the TPA.
2.9. Sensory evaluation
The sensory qualities of cooked noodle were determinedaccording to the method described by Fu and Malcolmson(2010), using a quantitative descriptive analysis (QDA). All pan-elists consume Asian noodles regularly. Before conducting formalsensory evaluation, panelists were given several training sessionson the attributes and procedures they must follow for assessingthe noodle products. During training, panelists received instruc-tions and samples varying in the intensities of the attributes beingevaluated. The training continued until panelists were in agree-ment with each other on their ratings, and they were able to repro-duce their judgments from one session to another. Eight trainedpanelists were included for the analyses and a ten-point hedonicscale was used. The sensory analyses included two steps. The firststep began immediately after the noodles were cooked, and thesecond step began when the noodles were soaked in a hot waterfor 5 min after cooking. The attributes evaluated were bite, springi-ness, mouth-feel, integrity, and total score. The control group waswithout added ingredient, and the score of each quality parameterwas set at 7.0. The test samples were scored against the controlsample.
2.10. Statistical analysis
All measurements were performed at least in triplicate. Statisti-cal analyses were carried out with SPSS 16.0 for Windows, usingone-way analyses of variance (ANOVA). P < 0.05 was consideredto be significant by using Duncan’s test.
3. Results and discussion
3.1. Starch pasting properties
Three enzymes showed little effect on the starch pasting prop-erties of WWF (data not shown), which might be due to the shortduration within the suitable temperature range (20–65 �C) of theenzymes in the standard RVA test cycle. Enzymes generally require45 to 60 min of incubation time to act on the wheat flour dough.The 13-min of RVA testing cycle only had 3 min within the suitabletemperature range of the enzymes, which were too short for theenzymes to show their effects on the starch gelatinization and ret-rogradation in WWF. Table 1 shows the starch pasting propertiesof WWF added with emulsifiers. Soy lecithin decreased the peakviscosity (PV) of WWF. Starch pasting involves post-pasting gran-ule swelling, granule disruption, carbohydrates leaching, formationof a three-dimensional network of leached molecules, and interac-tions between granule remnants and leached material. The starchviscosity reaches the peak value when starch granules swell tothe maximum volume, then followed by the granule disruptionand a reduction in viscosity. High swelling power is generallyrelated to high starch viscosity (Hirsch & Kokini, 2002). Soy lecithinis a group of phospholipids with HLB (hydrophilic-lipophilic bal-ance) value of smaller than 10, and are composed of phosphoricacid with choline, glycerol or other fatty acids. Amylose can beeasily associated with phospholipids to form amylose-lipid com-plexes, and the complexes restrict swelling of the starch granulesand reduce the pasting viscosity (Sasaki, Yasui, & Matsuki, 2000).Therefore, the reduced peak viscosity by soy lecithin was mainlyattributed to its interaction with amylose, which interrupted thegranule swelling during pasting.
Table 1RVA starch pasting properties of whole-wheat flour (WWF) added with ingredients.a,b
Sample Peak viscosity Trough Breakdown Final viscosity Setback Peak time (min)
Control 127.25 ± 1.02c 73.50 ± 0.81c 53.75 ± 0.56c 155.25 ± 1.56cd 85.75 ± 0.82b 5.60 ± 0.03a
Soy L-0.10% 118.58 ± 1.25b 69.17 ± 0.78ab 49.42 ± 0.64b 151.42 ± 1.33bc 82.25 ± 0.78ab 5.53 ± 0.03a
Soy L-0.30% 115.92 ± 1.32ab 68.83 ± 0.97a 49.58 ± 0.53b 148.58 ± 1.45ab 79.25 ± 0.95a 5.53 ± 0.03a
Soy L-0.50% 113.25 ± 0.98a 66.33 ± 1.02a 44.42 ± 0.73a 145.33 ± 1.38a 79.50 ± 0.84a 5.47 ± 0.06a
SSL-0.25% 128.58 ± 1.30c 71.83 ± 1.05bc 52.75 ± 0.83c 157.58 ± 1.53d 90.75 ± 0.92c 5.93 ± 0.03b
SSL-0.50% 130.67 ± 1.23cd 74.08 ± 0.93c 52.58 ± 0.60c 177.42 ± 1.35e 103.33 ± 0.72d 6.07 ± 0.00c
SSL-0.75% 134.17 ± 1.21d 87.50 ± 0.72d 46.67 ± 0.72a 227.08 ± 1.51f 139.58 ± 0.83e 6.20 ± 0.03d
Means with different small letter superscripts in the same column are significantly different at P < 0.05.a Control: WWF without enzymes or emulsifiers; Soy L-0.10%, 0.30%, and 0.50%: WWF with additional 0.10%, 0.30%, and 0.50% of soy lecithin, respectively; SSL-0.25%,
0.50%, and 0.75%: WWF with additional 0.25%, 0.50%, and 0.75% of SSL, respectively. All additional levels were on a flour basis.b Results are presented as means ± standard deviations (n = 3).
M. Niu et al. / Food Chemistry 223 (2017) 16–24 19
Contrary to soy lecithin, SSL increased the PV of WWF, and therewas an upward trend with the increased addition level. Similarresults were observed by Ali and Hasnain (2013a), who noted thatSSL increased the PV of oxidized white sorghum starch. However,Azizi and Rao (2005) reported that the PV and trough of wheatstarch were reduced when SSL was added; only FV was increased.The discrepancies in these studies could be caused by the differ-ences in starch concentration, chemical structure, and composi-tions in the tested samples (Ali & Hasnain, 2013b; VanSteertegem, Pareyt, Brijs, & Delcour, 2013). As a hydrophilic surfac-tant, SSL tends to mechanically cover starch granules due to theinteractions with water molecules and restricts the entry of waterinto the granules, thereby prolonging the arrival of PV during theheating period (Eliasson, Larsson, & Miezis, 1981). But, this cover-ing layer is unstable under heat; once the coverage is disrupted byheating, SSL can facilitate the water absorption by its polar endsextending outside the single helical amylose chains (Ali &Hasnain, 2013a). Thus, at high temperature (90–95 �C), SSL helpsincrease the swelling of starch granules and promote the develop-ment of starch viscosity.
During the breakdown process, starch molecules disintegrateand further amylose exudation takes place. The setback valuerepresents the degree of retrogradation in starch. Soy lecithindecreased the breakdown value and setback value of WWF,which was mainly due to its interaction with amylose thatreduced the amylose leaching and recrystallization. SSL reducedthe breakdown value, but increased the peak time and setbackvalue. As mentioned above, SSL tends to cover starch granulesand restricts the entry of water into the granules, therebyincreasing the peak time. It is interesting to note that SSL is gen-erally used in bread baking to retard staling during storage; theincreased setback value observed here seems to contradict itstypical function. Nevertheless, many previous studies alsoshowed that SSL increased the setback value of sorghum starch,wheat starch, and wheat flour in RVA profiles (Ali & Hasnain,2013a; Van Steertegem et al., 2013). According to VanSteertegem et al. (2013), SSL induced a viscosity increase uponcooling and increased the setback value because of its complex-ation with amylose, leading to increased amylose aggregation.The mechanism by which SSL retards bread staling is attributedto its capacity of forming complexes with amylose and amy-lopectin. Upon cooling, these complexes do not participate inthe crystal formation and texture firming, and the staling processis thus inhibited. Therefore, it can be seen that the increased set-back value by SSL in apparent viscosity profiles is not contradic-tory to its function in retarding staling; instead, both of them areassociated with the cross-linking ability of SSL. The report ofCollar (2003) confirms this explanation that suitable viscositytrends for retarding bread staling include delayed pasting tem-perature, high viscosities, and high setback values in starch past-ing profiles.
3.2. Mixolab parameters
The dough mixing properties of WWF and starch pasting prop-erties of WWD measured by Mixolab represent the behaviors ofprotein and starch when subjected to both mechanical stress andtemperature changes. In a typical Mixolab curve, the early stage(0–23 min) demonstrates the properties of gluten, and the latterstage (24–45 min) displays the characteristics of starch (Huanget al., 2010). Compared to the starch pasting properties measuredby the RVA test in flour-water slurry, the latter stage of the Mixolabtest exhibits the starch pasting properties in a dough system.Therefore, the results from these twomethods show different traitsof starch pasting and may not be directly compared with. Table 2shows the Mixolab parameters of WWF with addition of enzymesor emulsifiers. Each ingredient showed slightly but significantly(p < 0.05) higher water absorption than the control group, exceptfor SSL; endoxylanase exhibited the highest water absorptionvalue. Endoxylanases transform water-insoluble AX into solubleforms by cleaving the glycosidic bonds; more exposure of hydro-philic groups in AX promotes bindings with water and increaseswater absorption. Soy lecithin showed a small increase in waterabsorption, mainly because of water-binding activity of its hydro-philic ends. As SSL binds with starch molecules, coverage is formedon starch granules; it interrupts the water entering into the gran-ules and reduces the water absorption at low temperature (30 �C).Both TG and SSL increased the development and stability times ofWWD, confirming their ability to enhance gluten strength. Inanother study, Choy et al. (2010) also reported that TG and SSLstrengthened the structure of dough prepared for instant fried noo-dle. TG can modify the rheological behavior of dough by promotingthe formation of a more compact gluten matrix and conferring agreater degree of orientation to the gluten network (Autio et al.,2005). SSL interacts with hydrophobic regions of the gluten pro-teins by its lipophilic groups and forms hydrogen bonds with theamino groups of glutamine, thus promoting the aggregation of pro-teins and yielding stronger dough (Gomez et al., 2013). Anenhancement to gluten strength by these two ingredients isresponsible for the increases in the development time and stabilityof WWD.
TG at 1.50 U/g reduced the setback value of WWD, whereas SSLincreased it. Starch retrogradation occurs during cooling and stor-age. The amylose portion of the starch crystallizes within hours,while amylopectin crystallization contributes to the long-termstaling during the storage (Nunes, Moore, Ryan, & Arendt, 2009).The results indicated that TG inhibited the amylose recrystalliza-tion in WWD, which were directly related to its interactions withstarch molecules and interception on the connections betweenamylose chains. However, this phenomenon was not observed inthe RVA test, probably due to different systems (flour-water slurryfor the RVA test vs. dough for Mixolab). As mentioned in Sec-tion 3.1, SSL can complex with amylose and increase the viscosity
Table 2Mixolab parameters of whole-wheat flour (WWF) added with ingredients.a,b
Sample Water absorption (%) Development time (min) Stability (min) Peak torque (Nm) Setback value (Nm) Hot-gel stability (Nm)
Control 61.5 ± 0.0b 5.60 ± 0.08a 9.94 ± 0.17a 1.70 ± 0.03ab 0.85 ± 0.02b 0.88 ± 0.02a
+Endoxylanase 63.8 ± 0.1e 5.65 ± 0.12a 10.18 ± 0.16a 1.73 ± 0.04ab 0.86 ± 0.01b 0.90 ± 0.01a
+TG 62.0 ± 0.0c 5.90 ± 0.10b 10.80 ± 0.19b 1.81 ± 0.02b 0.72 ± 0.03a 0.95 ± 0.01b
+GOX 62.5 ± 0.0d 5.63 ± 0.09a 10.18 ± 0.18a 1.73 ± 0.03ab 0.86 ± 0.02b 0.90 ± 0.02a
+Soy L 62.3 ± 0.2cd 5.73 ± 0.08ab 10.14 ± 0.15a 1.68 ± 0.05a 0.87 ± 0.02b 0.92 ± 0.01ab
+SSL 60.4 ± 0.1a 6.21 ± 0.10c 10.86 ± 0.19b 1.70 ± 0.04a 0.92 ± 0.01c 0.98 ± 0.02b
Means with different small letter superscripts in the same column are significantly different at P < 0.05.a Control: WWF without enzymes or emulsifiers; + Endoxylanase: WWF with additional 1.50 U of endoxylanase; + TG: WWF with additional 1.50 U of TG; + GOX: WWF
with additional 1.50 U of GOX; + Soy L: WWF with additional 0.50% of soy lecithin (w/w, based on WWF); + SSL: WWF with additional 0.75% of SSL (w/w, based on WWF).b Results are presented as means ± standard deviations (n = 3).
20 M. Niu et al. / Food Chemistry 223 (2017) 16–24
during gelatinization. In the Mixolab test, the increase of starchviscosity in WWD induces the enhancement of WWD torque.Although SSL binds with starch molecules and inhibits the crystalformation, the increase in WWD torque occurred upon coolingand therefore indicated increased setback value. In addition, bothTG and SSL increased hot-gel stability of WWD, probably due tothe interactions with amylose that retarded the amylose exudationafter starch granules physically disrupted. Unlike TG and SSL, otheringredients showed no significant effect on Mixolab parameters(Table 2). Previous studies have reported the strengthening effectof lecithin on wheat dough (Selmair & Koehler, 2009). Lecithincan interact with proteins by its fatty acid chains, and therebyreduce protein solubility and promote the protein aggregation.Soy lecithin exhibited little impact on the WWD strength probablydue to the low usage or the dilution of gluten proteins in WWDsystem. Although endoxylanases promoted the water absorptionof WWD, they did not exert significant influence on gluten forma-tion. It was likely that the water was still held by AX rather thantransferred into gluten due to low dosage of endoxylanases used,thereby making little contribution to gluten development.
3.3. SEM images
As displayed in Fig. 1, the control group showed a more openand porous structure compared with the groups added with ingre-dients, except for the GOX group. Starch granules can be easilyidentified and are not completely covered by gluten matrix in thecontrol group. As for the three enzymes, TG showed the thickestand most compact gluten structure of WWN, which was mostlikely associated with enhanced dough strength and mixing stabil-ity caused by TG, as indicated in Section 3.2. Bellido and Hatcher(2011) also reported the reinforcing properties of TG in the thick-ness of protein layer and starch granules coverage of refined yellowalkaline noodle. However, an even more disaggregated structurecompared to the control group was observed with an inclusion ofGOX. This observation was contrary to its typical function in bak-ing. Previous studies have demonstrated that GOX increases thecontent of gluten macromolecule polymers and reinforces thestrength of wheat dough (Steffolani, Ribotta, Perez, & Leon,2010), but our results (Fig. 1C) showed GOX disrupted the interac-tion between the protein and starch in WWN. The adverse effect ofGOX on the structure of WWN needs further investigation. Inap-propriate addition levels and/or interference of wheat bran parti-cles in our whole-wheat noodle dough system are speculated forcausing this discrepancy in results.
Both soy lecithin and SSL increased the thickness of the proteinlayer and the coverage of starch granules in WWN. Compared tosoy lecithin, the SSL group exhibited a larger degree of connectivityin the gluten network of WWN, which was in agreement with theMixolab dough mixing properties (Table 2). Due to the amphiphilicproperties, SSL propels the aggregation of gluten proteins andbinds with starch granules, thereby promoting proteins-starch
interactions in noodle dough. These interactions facilitate thedevelopment of a gluten-starch-lipid complex and generate a morecompact structure (Mettler & Seibel, 1993). Choy et al. (2010) alsoreported a more continuous matrix with the addition of 0.5% SSL ininstant noodle formula, but SSL exhibited a more connectivity ofgluten network than TG, which was discrepant with the presentstudy. The discrepancy in observed results was probably causedby the different cross-linking abilities of SSL and TG within thetwo different noodle formulations (instant noodle made fromrefined flour vs. white raw noodle made from WWF). In overall,TG and SSL showed more favorable impacts on the structural char-acteristics of WWN.
3.4. Noodle color and cooking yield
As shown in Table 3, endoxylanase at 1.50 U/g decreased theL⁄24hvalue, and increased the values of a⁄24h, b⁄24h, and DL⁄ in WWN.On the contrary, TG and GOX increased the value of L⁄24h at 0.75and 1.50 U/g, respectively, and the DL⁄ value was reduced by TGand SSL. These results demonstrated that TG and GOX enhancedthe color quality of WWN, and discoloration was inhibited by TGand SSL. Noodle discoloration is generally associated with polyphe-nol oxidases (PPO), phenolic substrates, and the surrounding envi-ronment parameters such as pH and ionic strength (Asenstorfer,Appelbee, & Mares, 2009). TG and SSL had minor changes on thepH and ionic strength of WWD (data not shown), thus the reduceddiscoloration (smaller DL⁄) might result from the fact that TG andSSL interacted with phenolic substances and reduced the contactbetween PPO and its substrates. Furthermore, soy lecithin exhibitedno significant impact on the L⁄24h value, but increased the value ofa⁄24h and reduced the DL⁄ value at level of 0.50%. In summary, TG,SSL, and soy lecithin interfered with the color browning of WWN.GOX showed little effect on the DL⁄ value but increased the L⁄24h-value, therefore also improving the color quality of WWN.
Cooking yield is commonly regarded as one of the most impor-tant indicators that represent the cooking performance of noodlesby both consumers and industry. High cooking yield is generallyconsidered as desired quality. Noodle cooking yield is mainlydetermined by starch gelatinization and swelling of gluten net-work (Majzoobi, Ostovan, & Farahnaky, 2011). Of all ingredientstested, only SSL showed significant (p < 0.05) effect on the cookingyield of WWN at levels of 0.50% and 0.75%. SSL reduced the cookingyield as the addition level was increased. In general, the increase instarch pasting viscosity results in increased cooking yield, mostlydue to higher swelling power. In the present study, SSL increasedthe starch pasting viscosities of WWF, but the noodle cooking yieldwas reduced. It was speculated that due to the protection from thephysical structure, the coverage on starch granules formed by SSLwas probably more difficult to disrupt under heating in WWN,compared to that in flour-water slurry (RVA test), and the morestable covering layer restricted the WWN swelling during cooking.Previous studies have reported that SSL induces a low entry of
Fig. 1. The microstructure of whole-wheat noodles (WWN) added with ingredients. A, Control (WWN without enzymes or emulsifiers); B, WWN with additional 1.50 U/g ofendoxylanase in formula; C, WWN with additional 1.50 U/g of GOX in formula; D, WWN with additional 1.50 U/g of TG in formula; E, WWN with additional 0.50% of soylecithin in formula; F, WWN with additional 0.75% of SSL in formula. All additional levels were on a flour basis. SSG, small starch granule; LSG, large starch granule; WSG,wrapped starch granule; NSG, non-wrapped starch granule; WB, wheat bran; PM, protein matrix.
M. Niu et al. / Food Chemistry 223 (2017) 16–24 21
water into the starch granules by covering the starch granules (Ali& Hasnain, 2013b; Eliasson et al., 1981). As indicated by ourresults, SSL revealed the emulsifying property in WWN by yieldingreduced cooking yields. Moreover, the result was also supported bythe Mixolab results (Table 2), in which SSL reduced water absorp-tion primarily because of its interference with the water enteringinto starch granules. Ugarcic-Hardi et al. (2007) reported that soylecithin increased the water uptake of refined noodle during cook-ing. However, the water-binding activity of soy lecithin was prob-ably interfered by WWF, and therefore little increase in cookingyield was observed in the present study.
3.5. Textural properties
Table 4 shows the textural properties of cooked WWN addedwith ingredients. Both TG and soy lecithin increased the hardnessvalue of cooked WWN. It has been reported previously that thefirmness of yellow alkaline noodles increased with TG supplemen-tation (Bellido & Hatcher, 2011). Choy et al. (2010) also reportedthat TG addition increased the hardness of instant noodle by 65%and 58%, respectively, at two different water addition levels (35%
and 40%). In the present study, TG enhanced the hardness ofcooked WWN only by 8%, 13%, and 17%, respectively, at three addi-tion levels. The discrepancy in noodle hardness increase betweenthese two studies was probably due to different noodle strand size,formulation, and/or the interference of wheat bran. Lecithin caninteract with gluten proteins and increase dough strength, andthe enhanced noodle hardness results from its dough strengthen-ing property. However, soy lecithin demonstrated little strength-ening effect on WWD as indicated by Mixolab results (Table 2).The varying influences of soy lecithin on WWD and WWN mightbe related to different moisture contents in the two systems. Incontrast with TG and soy lecithin, SSL significantly (p < 0.05)reduced the hardness of WWN at the addition level of 0.75%. Asdiscussed in Section of 3.2, SSL enhanced the gluten strength inWWD by promoting the aggregation of gluten proteins and form-ing a strong protein network. The higher gluten strength usuallyyields harder noodle texture. Meanwhile, SSL also significantly(p < 0.05) increased starch peak viscosity at 0.75% addition level(Table 1), and higher starch peak viscosity generally caused softernoodle texture (Wang, Hou, Hsu, & Zhou, 2011). Therefore, it can beconcluded that the net effect on noodle hardness by SSL is
Table 3Color and cooking yield of whole-wheat noodle (WWN) added with ingredientsa,b,c
Sample L⁄24h a⁄24h b⁄24h DL⁄ Cooking yield (%)
Control 59.25 ± 0.27cd 5.54 ± 0.09b 18.08 ± 0.15ab 12.69 ± 0.16de 193.0 ± 1.5bc
Endoxylanase-0.30 U/g 58.68 ± 0.21bc 5.76 ± 0.07bc 18.45 ± 0.12ab 12.92 ± 0.18de 191.1 ± 1.8ab
Endoxylanase-0.75 U/g 58.20 ± 0.25b 5.91 ± 0.08bc 18.53 ± 0.13bc 13.24 ± 0.20ef 191.9 ± 2.0ab
Endoxylanase-1.50 U/g 57.09 ± 0.27a 6.23 ± 0.10c 18.98 ± 0.19c 13.55 ± 0.14f 195.9 ± 1.5c
TG-0.30 U/g 60.10 ± 0.20de 5.40 ± 0.12ab 17.95 ± 0.15ab 11.94 ± 0.15d 193.0 ± 1.7bc
TG-0.75 U/g 60.92 ± 0.22ef 5.32 ± 0.13ab 17.82 ± 0.14ab 10.78 ± 0.20ab 190.6 ± 2.0ab
TG-1.50 U/g 61.83 ± 0.30f 5.21 ± 0.10ab 17.79 ± 0.19ab 10.03 ± 0.19a 190.9 ± 1.8ab
GOX-0.30 U/g 60.81 ± 0.27e 5.25 ± 0.15ab 17.81 ± 0.20ab 12.56 ± 0.16de 189.2 ± 1.6ab
GOX-0.75 U/g 61.25 ± 0.21ef 5.20 ± 0.11ab 17.70 ± 0.15ab 12.49 ± 0.15de 192.0 ± 1.8b
GOX-1.50 U/g 61.73 ± 0.31ef 5.11 ± 0.09a 17.63 ± 0.19a 12.32 ± 0.18d 191.3 ± 2.0ab
Soy L-0.10% 58.87 ± 0.23bc 5.82 ± 0.08bc 18.60 ± 0.17bc 11.70 ± 0.16cd 191.1 ± 1.5ab
Soy L-0.30% 58.77 ± 0.31bc 5.92 ± 0.09bc 18.69 ± 0.18bc 11.41 ± 0.15bc 190.3 ± 1.6ab
Soy L-0.50% 59.24 ± 0.27cd 6.00 ± 0.10c 18.75 ± 0.19bc 11.38 ± 0.14bc 189.0 ± 1.8ab
SSL-0.25% 59.69 ± 0.30d 5.29 ± 0.12ab 18.04 ± 0.13ab 11.73 ± 0.18cd 190.3 ± 2.0ab
SSL-0.50% 59.84 ± 0.25d 5.30 ± 0.11ab 17.99 ± 0.12ab 11.44 ± 0.19bc 188.0 ± 1.9a
SSL-0.75% 60.56 ± 0.29de 5.25 ± 0.10ab 18.02 ± 0.14ab 11.32 ± 0.20bc 188.2 ± 1.6a
Means with different small letter superscripts in the same column are significantly different at P < 0.05.a L⁄24h: lightness; a⁄24h: redness – greenness; b⁄24h: yellowness – blueness; DL⁄: L⁄0h – L⁄24h. The L⁄24h, a⁄24h, and b⁄24h values listed in the table were measured at 24 h after
preparation.b Endpxylanase-0.30, 0.75, and 1.50 U/g: WWN with additional 0.30, 0.75, and 1.50 U of endoxylanases per gram of WWF in formula, respectively; TG-0.30, 0.75, and
1.50 U/g: WWN with additional 0.30, 0.75, and 1.50 U of TG per gram of WWF in formula, respectively; GOX-0.30, 0.75, and 1.50 U/g: WWN with additional 0.30, 0.75, and1.50 U of GOX per gram of WWF in formula, respectively; Soy L-0.10%, 0.30%, and 0.50%:WWNwith additional 0.10%, 0.30%, and 0.50% of soy lecithin (w/w, based onWWF) informula, respectively; SSL-0.25%, 0.50%, and 0.75%: WWN with additional 0.25%, 0.50%, and 0.75% of SSL (w/w, based on WWF) in formula, respectively.
c Results are presented as means ± standard deviations (n = 12 for color measurement; n = 3 for cooking yield analysis).
Table 4Textural properties of cooked whole-wheat noodle (WWN) added with ingredientsa,b
Sample Hardness (g) Springiness Cohesiveness Resilience
Control 1635.1 ± 16.3b 0.951 ± 0.010a 0.496 ± 0.005b 0.210 ± 0.004b
Endoxylanase-0.30U/g 1636.3 ± 19.0b 0.950 ± 0.012a 0.495 ± 0.006b 0.211 ± 0.005b
Endoxylanase-0.75U/g 1646.2 ± 16.4bc 0.955 ± 0.010ab 0.506 ± 0.005bc 0.215 ± 0.004bc
Endoxylanase-1.50U/g 1631.4 ± 20.5b 0.952 ± 0.011a 0.513 ± 0.007bc 0.218 ± 0.005bc
TG-0.30U/g 1773.9 ± 17.5de 0.971 ± 0.015ab 0.501 ± 0.005bc 0.221 ± 0.006bc
TG-0.75U/g 1854.6 ± 18.9ef 0.983 ± 0.011ab 0.505 ± 0.006bc 0.224 ± 0.004bc
TG-1.50U/g 1917.6 ± 14.5f 0.994 ± 0.010b 0.516 ± 0.006bc 0.230 ± 0.003c
GOX-0.30U/g 1644.6 ± 19.9bc 0.952 ± 0.012a 0.484 ± 0.008ab 0.190 ± 0.004ab
GOX-0.75U/g 1658.2 ± 20.1bc 0.959 ± 0.013ab 0.472 ± 0.005ab 0.193 ± 0.003ab
GOX-1.50U/g 1678.4 ± 17.7bc 0.957 ± 0.012ab 0.460 ± 0.006a 0.185 ± 0.005a
Soy L-0.10% 1677.5 ± 19.2bc 0.946 ± 0.013a 0.502 ± 0.008bc 0.212 ± 0.006b
Soy L-0.30% 1692.3 ± 16.3cd 0.957 ± 0.011ab 0.510 ± 0.007bc 0.216 ± 0.005bc
Soy L-0.50% 1708.7 ± 14.9cd 0.970 ± 0.010ab 0.517 ± 0.006c 0.220 ± 0.004bc
SSL-0.25% 1659.2 ± 18.8bc 0.953 ± 0.012a 0.505 ± 0.005bc 0.215 ± 0.005bc
SSL-0.50% 1605.6 ± 16.8ab 0.962 ± 0.014ab 0.508 ± 0.007bc 0.219 ± 0.004bc
SSL-0.75% 1555.0 ± 15.6a 0.969 ± 0.013ab 0.527 ± 0.006c 0.227 ± 0.005c
Means with different small letter superscripts in the same column are significantly different at P < 0.05.a Endpxylanase-0.30, 0.75, and 1.50 U/g: WWN with additional 0.30, 0.75, and 1.50 U of endoxylanases per gram of WWF in formula, respectively; TG-0.30, 0.75, and
1.50 U/g: WWN with additional 0.30, 0.75, and 1.50 U of TG per gram of WWF in formula, respectively; GOX-0.30, 0.75, and 1.50 U/g: WWN with additional 0.30, 0.75, and1.50 U of GOX per gram of WWF in formula, respectively; Soy L-0.10%, 0.30%, and 0.50%:WWNwith additional 0.10%, 0.30%, and 0.50% of soy lecithin (w/w, based onWWF) informula, respectively; SSL-0.25%, 0.50%, and 0.75%: WWN with additional 0.25%, 0.50%, and 0.75% of SSL (w/w, based on WWF) in formula, respectively.
b Results are presented as means ± standard deviations (n = 8).
22 M. Niu et al. / Food Chemistry 223 (2017) 16–24
determined by the balance of improved gluten strength andincreased peak viscosity, and the results clearly showed that athigh addition level (0.75%), SSL contributed more to improved peakviscosity, thus making noodle texture significantly (p < 0.05) softer(Table 4).
Soy lecithin and SSL increased the cohesiveness value of cookednoodles at levels of 0.50% and 0.75%, respectively. Meanwhile, SSLenhanced the resilience of WWN at 0.75%. It was directly related tothe enhancement of gluten strength by SSL. Additionally, SSL cancomplex with starch granules by binding amylose and therebyincrease protein-starch interactions, which also contributes tothe increased cohesiveness and resilience values (Mettler &Seibel, 1993; Ward, Gao, De, Gilbert, & Fitzgerald, 2006). Soylecithin increased the cohesiveness but showed no change on theresilience of WWN, demonstrating a lower dough strengtheningeffect than SSL. The increased dough strength and stability bySSL, as reported in Section 3.2 could support this result. Besides
covering on starch granules and reducing water uptake duringcooking (Table 3), SSL probably causes more reduction in therepulsing charges on the protein surface by binding more tightlywith proteins, thus allowing more protein aggregation comparedto soy lecithin. With regard to enzymes, GOX decreased the cohe-siveness and resilience values of WWN, indicating the reducedintegrity and elasticity of cookedWWN. On the contrary, TG signif-icantly (p < 0.05) increased the springiness and resilience of WWNat 1.50 U/g, which was probably due to the formation of a morecompact gluten network (Fig. 1). Additionally, endoxylanaseshowed no significant influence on the textural attributes of WWN.
3.6. Sensory evaluation
Table 5 illustrated the sensory properties of cooked WWNadded with ingredients. Noodle sensory attributes such as bite,springiness, and integrity are highly associated with the structural
Table 5Sensory qualities of cooked whole-wheat noodle (WWN) added with ingredientsa,.b
Sample Bite Springiness Mouthfeel Bite (after 5 min) Springiness (after 5 min) Mouthfeel (after 5 min) Integrity Total Score
Control 7.0 ± 0.0b 7.0 ± 0.0b 7.0 ± 0.0a 7.0 ± 0.0NS 7.0 ± 0.0NS 7.0 ± 0.0a 7.0 ± 0.0b 7.0 ± 0.0a
+Endoxylanase 6.9 ± 0.3b 7.0 ± 0.3b 7.1 ± 0.4ab 6.8 ± 0.3 6.9 ± 0.4 7.1 ± 0.3ab 6.8 ± 0.4ab 6.9 ± 0.3a
+TG 7.9 ± 0.3c 8.1 ± 0.3c 7.4 ± 0.3ab 7.4 ± 0.4 7.3 ± 0.2 8.0 ± 0.3b 7.9 ± 0.2c 7.5 ± 0.3ab
+GOX 6.1 ± 0.2a 6.0 ± 0.3a 6.7 ± 0.2a 6.8 ± 0.4 6.8 ± 0.3 6.6 ± 0.2a 6.0 ± 0.3a 6.5 ± 0.2a
+Soy L 6.9 ± 0.3b 7.1 ± 0.4b 7.0 ± 0.3a 6.9 ± 0.4 7.0 ± 0.4 7.1 ± 0.4ab 7.1 ± 0.3bc 7.0 ± 0.4a
+SSL 7.9 ± 0.3c 7.9 ± 0.4b 7.9 ± 0.2b 7.3 ± 0.3 7.2 ± 0.3 7.3 ± 0.4ab 7.4 ± 0.3bc 7.9 ± 0.2b
Means with different small letter superscripts in the same column are significantly different at P < 0.05.NS indicates that values in the same column are not significantly different.
a Control: WWNwithout enzymes or emulsifiers; + Endoxylanase: WWNwith additional 1.50 U of endoxylanase per gram of WWF in formula; + TG: WWNwith additional1.50 U of TG per gram of WWF in formula; + GOX: WWN with additional 1.50 U of GOX per gram of WWF in formula; + Soy L: WWN with additional 0.50% of soy lecithin (w/w, based on WWF) in formula; + SSL: WWN with additional 0.75% of SSL (w/w, based on WWF) in formula.
b Results are presented as means ± standard deviations (n = 8).
M. Niu et al. / Food Chemistry 223 (2017) 16–24 23
and textural properties of cooked noodle. Endoxylanases had noeffect on the sensory properties of WWN, whereas the GOX groupshowed the lower scores on the properties of bite, springiness, andintegrity, indicating a detrimental effect on the sensory quality ofWWN. The results were consistent with the noodle microstructureas examined by SEM in Section 3.3, and textural properties in Sec-tion 3.5, which indicated that endoxylanases showed little effecton noodle structure and texture, and GOX disrupted noodle struc-ture and reduced cohesiveness and resilience values of WWN.Although soy lecithin showed some enhancements on themicrostructure and texture of WWN, it did not show significantimpact on the sensory attributes observed. Sensory evaluationmay not be sensitive enough to detect differences in microstruc-ture and texture as analyzed by SEM and TPA.
SSL increased the bite, mouth-feel, and total scores of WWN asevaluated by the panelists, and TG exhibited pronounced improve-ments in the scores of bite, springiness, mouth-feel (after 5 min),and integrity. The improvements on the noodle sensory propertiesby SSL and TG were directly related to the changes on the doughmixing properties and noodle texture that SSL and TG hadmodified.
4. Conclusions
TG and SSL were found more effective in modifying the qualitycharacteristics of WWN. SEM analysis showed that TG and SSLenhanced the interaction between the protein matrix and starchgranules in WWN. Texture profile analysis indicated that TGincreased the hardness, springiness, and resilience of cookedWWN, and SSL improved the noodle cohesiveness. Additionally,sensory evaluation confirmed that TG and SSL significantly(p < 0.05) improved sensory eating properties of cooked WWN.These results demonstrated that some of common baking ingredi-ents could be used to improve the quality characteristics of WWNin combination with other options as reported.
Conflict of interest
All authors have seen and agree with the contents of the manu-script, and there is no conflict of interest to report.
Funding
This work was partially supported by National Natural ScienceFoundation of China (Grant No. 31501520), and FundamentalResearch Funds for the Central Universities (Grant No.2662015QC029; 2662014BQ056)
Acknowledgement
We are grateful to Electron Microscopy and NanofabricationCenter of Portland State University for performing scanning elec-tron microscopy analysis.
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