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Studyingtheeffectsofwhole-wheatflourontherheologicalpropertiesandthequalityattributesofwhole-wheatsaltine...

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Studying the effects of whole-wheat flour on the rheologicalproperties and the quality attributes of whole-wheat saltine crackerusing SRC, alveograph, rheometer, and NMR technique

Juan Li a,b, Gary G. Hou b,*, Zhengxing Chen a,**, Ai-Lan Chung b, Kathleen Gehring b

a School of Food Science and Technology, National Engineering Laboratory for Cereal Fermentation Technology, Jiangnan University, Wuxi,Jiangsu 214122, PR ChinabWheat Marketing Center, Inc., 1200 NW Naito Parkway, Suite 230, Portland, OR 97209, USA

a r t i c l e i n f o

Article history:Received 2 May 2013Received in revised form26 July 2013Accepted 30 July 2013

Keywords:Rheological propertiesWhole-wheat saltine crackerNuclear magnetic resonance (NMR)Water migrationSolvent retention capacity (SRC)

a b s t r a c t

Quality attributes of soft wheat products are affected by physicochemical characteristics and rheologicalproperties of wheat flour. Whole-wheat flour has a significant impact on baking qualities (stack height,stack weight, specific volume, and breaking strength) of whole-wheat saltine crackers due to its highwater absorption capacity. SRC profiles, alveograph and rheometer parameters were determined toobserve the effect of whole-wheat flour on whole-wheat cracker flour blends. NMR technique was uti-lized to demonstrate the water migration and competition in whole-wheat dough components. Resultsof SRC testing revealed that the water absorption of whole-wheat flour blends increased with theaddition level of whole-wheat flour. The rheological properties (G0 , G00, P, L, W values) were influencedsignificantly by the presence of whole-wheat flour. Results of NMR indicated that water migrated fromgluten network into arabinoxylans matrix in whole-wheat dough system, resulting in inferior saltinecracker-baking qualities of whole-wheat flour, i.e., small breaking strength, stack height and specificvolume. The stack height, specific volume, and breaking strength of end products showed significantcorrelations with the arabinoxylans, dough extensibility, and gluten index of whole-wheat flour.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Crackers are an important product line within the large-scalebaking industry, and are a natural fit as portable and convenientfoods. Crackers can be divided into three broad categories: saltinecracker (soda cracker), chemically leavened cracker, and enzymecracker (Moore & Strouts, 2008). The quality of wheat products isdetermined by the rheological behaviours of dough. The pastingproperties of starch gave useful prediction to the quality of softwheat products such as cookies, crackers and cakes (Serpil, Kevser,Bengihan, & Hamit, 2008). The volumes of bread and puff pastrywere correlatedwith rheological properties of the dough (Sliwinski,Kolster, & van Vliet, 2004). Therefore, understanding the rheologicalproperties and machinability of dough system is essential forguiding the production of wheat products. However, whole-wheatflour has a major impact on the rheological properties of doughand quality attributes of end products. The water absorption of

wheat flour, especially the whole-wheat flour can significantlyaffect the rheological properties of cracker dough and end-productquality. The formation of gluten in dough systemwas restrained bywhole-wheat flour of high-level water absorption capacity, whichwas undesirable in the functionality of cracker flour (Slade, Levine,Craig, & Arciszewski, 1994). Presumably, the arabinoxylans whichare themain non-starch polysaccharides inwheat bran compete forwater with the dough main polymers, gluten and starch in whole-wheat dough system, and interrupt the protein aggregationbehaviour during heating (Rosell, Santos, & Collar, 2010).

At present, solvent retention capacity (SRC) and alveograph arethe two traditional methods for estimating the potential perfor-mance of soft wheat flour. The SRC tests were developed to evaluatethe quality of soft wheat flour in cookie and cracker products. Ingeneral, alveograph is more appropriate for predicting the proteinfunctionality of soft wheat flours, while farinograph andmixographare commonly used to evaluate hard wheat bread flours (Levine &Slade, 2004). Both the SRC and alveograph results are affected bythe presence of wheat bran in flours. Since the alveograph mea-sures the fixed-absorption dough, having bran involved will greatlyaffect the amount of water available for gluten formation. Further,

* Corresponding author. Tel.: þ1 503 295 0823; fax: þ1 503 295 2735.** Corresponding author. Fax: þ86 51085867273.

E-mail addresses: ghou@wmcinc.org, houpdx@yahoo.com (G.G. Hou).

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bran particles can physically disrupt the gluten matrix, leading topremature bubble rupture (Li et al., 2012).

NMR technique which is a useful tool to detect the macro-waterdistribution and migration among high-moisture samples non-invasively (Stapley, Hyde, Gladden, & Fryer, 1997) was successfullyapplied to examine the water migration between macromolecules(arabinoxylans and gluten network) in whole-wheat bread doughsystem (Li et al., 2012). Thus, the objectives of this study were: 1) toinvestigate the effect of whole-wheat flour on the rheologicalproperties of whole-wheat saltine cracker flour blends using therheometer, alveograph, and SRC testing; 2) to verify the mechanismof the impact of whole-wheat flour on the quality attributes ofwhole-wheat saltine cracker using the NMR technique; and 3) toestablish the relationship between the rheological properties ofwhole-wheat flour blends and end-product quality parameters.

2. Materials and methods

2.1. Materials

Soft white whole-wheat flour (SWWW; Ultragrain�) was kindlyprovided by ConAgra Flour Mills, Inc. (Omaha, NE, USA). Soft redwinter flour (SRW; Golden Shield, enriched and unbleached) andhard red winter flour (HRW; Harvest King winter wheat, enrichedand unbleached) were obtained from General Mills, Inc. (Minne-apolis, MN, USA). Baking soda (ARM & HAMMER Div. of Church &Dwigh, Co., Inc., Princeton, NJ, USA), yeast food (ADM Arkady Inc.,Olathe, KS, USA), salt (Morton Salt, Inc., Chicago, IL, USA), Criscovegetable shortening (trans-fat free) (J.M. Smucker Company, Orr-ville, OH, USA) and instant dry yeast (Lesaffre Yeast Corporation,Milwaukee, Wisconsin, USA) were purchased from a local super-market (Portland, Oregon, USA). The chemical reagents (ACS grade)used for conducting SRC tests were purchased from Nurnberg Sci-entific Company (Portland, OR, USA).

2.2. Whole-wheat saltine cracker flour blends preparation andanalysis

Whole-wheat saltine cracker flour samples were compositedfrom the blends of SWWW, SRW, and HRW flour (Table 1). HRWflour is suitable for making crackers (Slade et al., 1994) and meetsthe requirement of relatively high gluten strength for high-qualitycracker flour (Kweon, Slade, & Levine, 2011b). From our preliminarytrials (data not shown), the optimum addition range of HRW flourwas 10e20 g/100 g which was determined by the breaking strengthof end products (if HRW was �20 g/100 g, the end-product texturebecame harder and less crispy), so 15 g/100 g of HRW flour wasadded consistently in each group, except for the 100 g/100 gSWWW group. The addition levels of SWWW flour in flour blendswere 0 g/100 g (control flour blend), 25 g/100 g, 50 g/100 g, 75 g/100 g and 100 g/100 g, respectively.

Protein (AACCI 46-30.01), moisture (AACCI 44-15.02), ash(AACCI 08-01.01), starch damage (AACCI 76-33.01), wet gluten andgluten index (AACCI 38-12.02) of five different whole-wheat flour

blends were determined according to the AACC InternationalApproved Methods and results are shown in Table 2.

2.3. Whole-wheat saltine cracker preparation

2.3.1. FormulaIn the sponge, ingredients included flour (65 g/100 g), sour-

dough starter (4 g/100 g), instant dry yeast (0.3 g/100 g), yeast foods(0.03 g/100 g), and water (27 g/100 g, 29 g/100 g, 30 g/100 g, 32 g/100 g, and 34 g/100 g water was added into five whole-wheat flourblends, respectively). The sourdough starter was initially suppliedby the Oregon State University and was fed every day using oldstarter (50 g), HRW flour (100 g), and distilled water (50 g). Thestarter ingredients were mixed (Hobart A-200 mixer) at 1st speedfor 5 min until well blended, and the starter dough was placed in acontainer with a lid until it tripled in volume at room temperature.The dough ingredients included flour (35 g/100 g), shortening(14 g/100 g), salt (0.8 g/100 g), water (1 g/100 g), and baking soda(determined by the total titratable acidity of the sponge). All in-gredients were scaled on the basis of 500-g flour weight. Instantdry yeast, yeast foods, and salt were weighed and dispersed sepa-rately in the amount of water required in the formula before use.

2.3.2. Baking soda dosage determinationThe total titratable acidity (TTA) test was considered as an

indication of the fermentation process. To determine the bakingsoda dosage in the cracker dough formula and to control the finalproduct pH (in the range of 7e8), the TTA of cracker sponge wasdetermined after 18-h sponge fermentation. TTA was prepared bymixing 15 g sponge with 100 mL deionized water and stirred for30 s at 2nd speed using the Hamilton Beach commercial blender(model 908 Clamshell, Procter-Silex, Inc., USA) until the spongesample was completely dispersed. Then, the sponge slurry wastransferred into a 250 mL beaker with a stir bar inside and placedonto a magnetic stirrer (model PC-520, Coring Laboratory Stirrer,USA). 0.1 M/L NaOH solution was used to titrate (Brinkmann Dis-pensette, Germany) the sponge slurry until a final pH value of 6.6.The volume of NaOH solution used for titration was referred as theTTA value (Sutherland, 1989). The relationship between TTA andbaking soda dosage is shown in Table 3.

Table 1Flour blend composition of whole-wheat saltine crackers.

Amount ofSWWW (g/100 g)a

Sponge (65 g/100 g) Dough (35 g/100 g)

SWWW SRW HRW SWWW SRW

0 50 15 3525 25 25 15 3550 50 15 3575 50 15 25 10100 65 35

a SWWW: soft white whole-wheat; SRW: soft red winter; HRW: hard red winter.

Table 2Flour analysis.

Amount ofSWWW(g/100 g)a

Moisture(g/100 g)

Protein(g/100 g)b

Ash(g/100 g)b

Wet gluten(g/100 g)b

Glutenindex

Starchdamage(g/100 g)b

0 13.2 8.43 0.442 24.5 60.9 3.125 12.5 8.92 0.734 24.4 44.1 3.150 11.7 9.35 1.015 28.6 26.2 3.475 11.0 9.92 1.241 26.0 8.4 3.4100 10.3 9.77 1.522 22.2 6.6 3.4

a Abbreviations as in Table 1.b 14 g/100 g mb.

Table 3Total tritable acidity (TTA) of sponge and baking sodadosage in whole-wheat cracker dough.

TTA (mL) Baking soda (g)per 500 g flour

7e8 3.09e11 4.012e13 5.014e16 6.017e18 7.018e19 7.520e21 8.0

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2.3.3. Production proceduresThe sponge ingredients were mixed at 1st speed for 3 min and

2nd speed for another 2 min in a Hobart A-200 mixer equippedwith a McDuffy mixing bowl (National Manufacturing, Co. Lincoln,NE, USA). Then, the sponge was fermented at 28 �C and 85% RH in afermentation cabinet (National Manufacturing Co., Lincoln, NE,USA) for 18 h. After the 18-h fermentation, the remaining flour,water, shortening and dry ingredients (salt and baking soda) weremixed with the sponge and proofed for 2 h (when the dough pHwas 6e6.5) under the same conditions as the sponge. After thedough was proofed, 500 g dough was weighed and placed into aplastic container and shaped into a rectangular block(15 � 13.5 � 2.5 cm). The shaped dough block was formed into athin sheet using the SSO-615 Seewer Rondo Reversible LaminationMachine (Commercial Food Preparing Machine, Rondo Inc., USA) toreduce the thickness until the height, width, and length of thedough sheet were about 1.3e1.4 mm, 22.5 cm, and 40.0 cm,respectively. The detailed dough lamination settings were listed asfollows:

Set initial roll gap to 12mm/ 9mm/ 6mm/ foldedboth endsto the center, and then turned 90� / 12 mm / 10 mm /

8mm/6mm/4mm/ folded thedough into trifold/10mm/

8mm/ 6mm/ turned 90� / 4mm/ 3mm/ folded the doughinto trifold/ 10 mm/ 8 mm/ 6 mm/ turned 90� / 4 mm/

3mm/ 2mm/ 1.4mm/ adjusted roll gap to achieve afinal sheetthickness of 1.3e1.4 mm.

The dough sheet was then transferred onto a specially designedcutter-docker (Pizzinatto & Hoseney, 1980), and sprinkled with saltfollowed by using a rolling pin to roll on the dough sheet to suffi-ciently perforate it. The deck oven (PICCOLOI-3 Wachtel Company,Germany) and a specially designed rectangular-shaped baking rack(CB5 baking band) were preheated for 30 min at a 220 �C toptemperature and 215 �C bottom temperature. Loaded the dockedcracker dough sheet onto the baking rack and baked in the deckoven for 6e7 min (maximum bubbles appeared on the surface ofcrackers and their color became brown). After baking was com-plete, the cracker sheet was cooled at room temperature for 30 minand broken into individual pieces for analysis.

2.4. End-product evaluation

Stack height, stack weight, specific volume, texture analysis,color, moisture and pH of the end products were determined. Thestack height and stack weight were measured using seven samplepieces. The stack height was measured by a vernier caliper (Mitu-toyo Manufacturing Co., Ltd., Japan), measuring once and turningthe crackers 90� and measuring again to obtain the average value.The cracker specific volume was determined with the BVM-L 370TexVol (TexVol Instruments Inc., Viken, Sweden) by dividing thevolume by weight. The breaking strength of the cracker wasmeasured by the TA-XTPlus Texture Analyzer (Texture TechnologiesCorp., Scarsdale, NY, USA) using the three point bending fixture(model TA-92). This adjustable three point bend/snap fixture wasplaced onto the TA-90 platform. An individual cracker was placedover the two legs (4.5 cm apart) and a metal knife blade (model TA-43R, 3-mm thick with rounded end) was centered over the middleof the cracker and moved downward during testing until thecracker broke. The pretest speed, test speed, and post-test speedwere 2.0 mm/s, 3.0 mm/s and 10.0 mm/s, respectively. The testdistance was 35.0 mm and contact force was 5 g. The peak forcedisplayed in the texture graph was the force required to break thecracker and was recorded as the breaking force of the cracker. Thecolor (L, a*, b*) values of the crackers were determined by the CR-410 Chroma Meter (Konica Minolta Sensing, Inc., Japan). All mea-surements were conducted at least three times.

2.5. SRC testing

Solvent retention capacity (SRC) tests including water SRC (W-SRC), lactic acid SRC (LA-SRC), sodium carbonate SRC (SC-SRC), andsucrose SRC (Suc-SRC) of flour blends of varying SWWW were ac-cording to the AACC International Approved Method 56-11.02.

2.6. Rheological measurements

2.6.1. Alveograph analysisAlveograph parameters were determined by the Alveo-

Consistograph (Chopin, Villeneuve-La-Garenne, France) accordingto the AACC International Approved Method 54-30.02. Doughtenacity (P), extensibility (L) and deformation energy (W) weredetermined.

2.6.2. Rheometer determinationThe rheological properties (storage modulus, G0; loss modulus,

G00) of whole-wheat flour blends were determined using an AR1000Rheometer (TA Instruments, New Castle, USA). The testing probewas a standard steel parallel plate (20 mm diameter, 1 mm-gapdistance). Each sample was determined in triplicates under thefrequency sweep test (frequency: 0.1e100 Hz; temperature: 28 �C).

2.7. NMR

Water migration between the arabinoxylans (AX) matrix andgluten network in whole-wheat cracker dough system wasobserved using the NMR systemwhich is represented by spin�spinrelaxation time (T2). The relaxation measurements were performedon a Niumag Desktop Pulsed NMR Analyzer (Shanghai NiumagElectronics Technology Co. Ltd., China). The detailed parametersand procedures of measurements were described in our previousstudy (Li et al., 2012).

2.8. Statistical analysis

Statistical analyses were conducted with the SPSS software 17(SPSS Institute, Chicago, USA). Pearson’s correlation coefficientsbetween quality of end products and SRC and alveograph param-eters were also calculated.

3. Results and discussion

3.1. Effect of whole-wheat flour on end-product baking quality

Quality characteristics of end products were affected bydifferent composition levels of whole-wheat flour (Table 4). Thestack weight, stack height, specific volume and breaking strength ofcrackers decreased as the addition level of SWWW flour increased.The moisture content and pH of the end products were in thecommercial range of 2e4 g/100 g and 7e8, respectively.

Carbon dioxide gas generation reduced the dough density anddry matter was lost during dough fermentation (Faridi & Johnson,1977). With the increasing level of whole-wheat flour, more vola-tile gas and acids were produced resulting in decreased stack heightand stack weight of crackers. The higher amount of whole-wheatflour tended to produce an uneven and less puffiness internaltexture. It was noticed that the gluten index values of flour blendsreduced dramatically from 60.9 to 6.6 with the increase of whole-wheat flour (Table 2). Therefore, crackers with higher level ofSWWW flour were more fragile (less breaking force) and hadsmaller specific volume. The AX in whole-wheat flour are a majorcomponent of cell wall polysaccharide and are present in the aleu-rone and bran layers of thewheat kernels (Courtin & Delcour, 2002).

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AX are a highly water-absorbing component, which exert a negativeeffect on the quality of crackers, especially on the volume of crackers(Kweon, Slade, & Levine, 2011a). The high water-absorbing com-ponents restrained the hydration of the gluten proteins fromforming the proper network needed for gas retention. The crackerdough was too tight to allow for puffing during baking, resulting inreduction of the stack height and specific volume of end products(Carey et al., 2002). The generation of discontinuous protein filmdecreased the breaking strength and reduced the bubbling of thewhole-wheat crackers during baking. Thus, the development of thegluten network during doughmachining was a decisive factor to thesuperior baking quality of whole-wheat flour blends. As expected,the color of the end products gradually became browner and darkerwith the increased ratio of whole-wheat flour (Fig. 1).

3.2. Effect of whole-wheat flour on SRC profiles of whole-wheatflour blends

The gluten performance index (GPI) is defined as GPI ¼ Lacticacid SRC/(Sodium carbonate SRC þ Sucrose SRC) and considered as

a better predictor of overall performance of cracker flour than theLA-SRC value alone (Kweon et al., 2011b). The SRC values and GPI ofcracker flours are shown in Fig. 2. The SRC values of control flourblend (0 g/100 g SWWW)which was a blend of 85 g/100 g SRWand15 g/100 g HRW were: W-SRC ¼ 55.3 g/100 g, LA-SRC ¼ 95.5 g/100 g, SC-SRC ¼ 72.3 g/100 g, and Suc-SRC ¼ 104.1 g/100 g. Typicalstandard SRC values for soft wheat sponge-and-dough cracker (e.g.,saltine crackers) flour were reported as: W-SRC � 57 g/100 g, LA-SRC � 100 g/100 g, SC-SRC � 72 g/100 g, and Suc-SRC � 96 g/100 g(Kweon et al., 2011b). The four SRC values of the control flour blendwere similar to the typical standard except for the slight differencesin LA-SRC and Suc-SRC, which may be due to the addition of 15 g/100 g HRW flour. If there was more HRW, the LA-SRC would begreater, probably over 100 g/100 g. The reduction in LA-SRCcompared to the target range was probably due to the SRW, butthe increase in Suc-SRC was probably due to the HRW. The SRCvalues and GPI (0.54) of the control flour blend suggested that it

Fig. 1. The color values (L, a* and b*) of the crackers made from five different additionlevels of soft white whole-wheat (SWWW) flours. L: lightness; a*: redness-greenness;b*: blueness-yellowness.

Fig. 2. Effects of soft white whole-wheat (SWWW) flour on the solvent retentioncapacity (SRC) values of whole-wheat flour blends. SRC: solvent retention capacity; W-SRC: water SRC; LA-SRC: lactic acid SRC; SC-SRC: sodium carbonate SRC; Suc-SRC:sucrose SRC; GPI (Gluten Performance Index) ¼ Lactic Acid SRC/(SodiumCarbonate þ Sucrose) SRC.

Table 4End-product quality evaluation.a

Amount of SWWW(g/100 g)b

Stack weightc,d (g) Stack heightd (mm) Specific volume (mL/g) Breaking strength (g) Moisture (g/100 g) pH

0 27.2 � 0.2a 34.8 � 0.4a 1.27 � 0.06a 1236.3 � 70.1a 3.1 7.725 27.0 � 0.2a 32.7 � 0.3b 1.25 � 0.02a 1052.7 � 82.6b 3.1 7.650 26.5 � 0.3b 29.8 � 0.4c 1.14 � 0.04b 829.8 � 25.6c 3.9 7.175 25.1 � 0.3c 28.9 � 0.3c 1.02 � 0.03c 732.0 � 23.0c 3.7 7.4100 24.9 � 0.4d 26.8 � 0.6d 1.00 � 0.02c 700.6 � 16.6c 3.6 7.3

a Data were the mean value � S.D. Values in the same column followed by the same letters are not significantly different (P < 0.05). Standard deviation was at least threereplicate experiments.

b Abbreviations as in Table 1.c Dry basis.d Stack of 7 crackers.

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was within a marginal range of soda cracker flour with sufficientgluten strength and good cracker-baking performance. The GPI ofother cracker flour blends containing various amounts of SWWWwere much lower than that of the control flour blend, indicatingweaker gluten strength and less puffing during baking. As thepercentage of SWWW flour increased in the flour blend, both theSRC values and GPI changed gradually, in proportion to the amountof SWWW added.

LA-SRC reflects protein content, glutenin characteristics andgeneral gluten functionality; SC-SRC is associated with the level ofdamaged starch; Suc-SRC is related to the pentosan (also known asarabinoxylans) content; and W-SRC is affected by all of those flourconstituents (AACCI Methods 56-11.02). Damaged starch is smallparticles of starch broken away from the main starch granules inwheat during milling, and has a strong water retention capacity(Mulla, Bharadwaj, Annapure, & Singhal, 2010). When starchgranules are damaged, cleavage of the smaller granule will facilitatehydration and swelling during dough preparation (Tester, 1997).The damaged starch of whole-wheat flour blends were at low levels(between 3.1 and 3.4 g/100 g) and increased slightly with theincreased level of whole-wheat flour due to the low-level damagedstarch (3.1 g/100 g) of Ultragrain soft white flour used in the study.Results showed that the W-SRC, SC-SRC, and Suc-SRC valuesincreased with the amount of whole-wheat flour due to the in-crease of high water absorbent components such as damagedstarch and arabinoxylans in flours.

LA-SRC had no linear correlation with the W-SRC, SC-SRC andSuc-SRC values, and the LA-SRC and GPI values did not correlatewith the composition level of SWWW flour. However, the W-SRCincreased with the amount of SWWW flour in the flour blend. TheSRC values (W-SRC ¼ 66.2 g/100 g, LA-SRC ¼ 74.9 g/100 g, SC-SRC ¼ 84.2 g/100 g and Suc-SRC ¼ 112.3 g/100 g) of 100 g/100 gSWWW cracker flour were significantly different from those of thetypical standard flour as reported. The SRC values of 100 g/100 gwhole-wheat flour exhibited higher water absorption, weak glutenstrength (lower level of LA-SRC value), and higher levels ofdamaged starch and arabinoxylans than other flour blends withless SWWW flour. The GPI of 100 g/100 g whole-wheat flour wasvery low (GPI¼ 0.38), indicating much inferior baking performancethan the flour blends of lower content of whole-wheat flour.

Generally speaking, for commercial cracker production, high-quality saltine cracker flour requires relatively high glutenstrength, within the class of soft wheat, and low water absorptioncapacity (Kweon et al., 2011b). Thus, flours with higher LA-SRC,lower water SRC, SC-SRC, and Suc-SRC values were preferred forsuperior quality of commercial crackers for puffing and bubbling(Slade et al., 1994). Also the GPI was shown to have a better cor-relation with the cracker-baking performance. Cracker flour with aGPI <0.52 produced unacceptable performance and excessiveblistering during baking (Kweon et al., 2011b).

3.3. Effect of whole-wheat flour on alveograph parameters ofwhole-wheat flour blends

The alveograph parameters (Fig. 3) showed that the P-value andP/L ratio had positive correlations with the percentage of SWWWflour; however the L and W values had a negative correlation withthe amount of SWWW flour.

The “gold standard” of alveograph parameters for ideal-qualityrefined white cracker flour is P ¼ 35 � 5, L ¼ 100 � 10, andW ¼ 90 � 15. If P-value is too low (<30) or too high (>40), the flourwould be too soft to form proper blistering on crackers or too hardfor crackers to spread enough, respectively. W-value should not betoo low (<75) or too high (>105). If the gluten strength is tooweak,gas cells coalesce and gas is released prematurely; if gluten is too

strong the cracker dough will be too elastic to resist puffing duringbaking. If L-value is less than 90, the implication is that the dough islack of extensibility and bubble breakage will occur during baking(Slade et al., 1994). The destructive and cleaving effects of wheatbrans with large-sized particles and native enzymes on the internalgluten network result in less extensibility of gluten matrix (Li et al.,2012). Although the alveograph values of control flour blend had aslight difference from the “gold standard”, the control flour blendhad lower P and P/L values, higher W and L values which werepreferred for a better cracker-baking quality. Nevertheless, thealveograph parameters of 100 g/100 g SWWW flour showed verydifferent results from the “gold standard”.

The higher level of P-value (63mm)was caused by the high levelof water-absorbing components (arabinoxylans and damagedstarch) in the whole-wheat flour and the dough was too firm toexpand. Preston, Kilborn, and Dexter (1987) reported that thestarch damage was positively correlated with P, L, W, and P/L ofCanadian hard red spring wheat doughs. The lower level of L-value(21mm) andW-value (54mm)was due to theweak gluten strengthof the whole-wheat flour. Moreover, the P/L ratio (3.00) of 100 g/100 g whole-wheat flour was much higher than that of the controlflour blend (P/L ¼ 0.32), which indicated that there was a lack ofbalance between elasticity and extensibility for the whole-wheatcracker dough to retain gas for expansion during fermentationand baking as measured by the alveograph.

3.4. Effect of whole-wheat flour on rheometer parameters of whole-wheat flour blends

The increased level of whole-wheat flour had a destructive ef-fect on the formation of gluten network. Development of gluten incracker dough during mixing and sheeting was a critical factor of

Fig. 3. Effects of soft white whole-wheat (SWWW) flour on the alveograph values ofwhole-wheat flour blends. P: dough tenacity; L: dough extensibility; W: doughdeformation energy.

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affecting the cracker quality (Kweon et al., 2011a). In the frequencysweep test, the G0 (storage modulus) of whole-wheat doughreduced with the addition level of SWWW flour, which indicatedthat the elasticity of whole-wheat cracker dough was restrained.The high water absorbent-capacity of wheat bran competes forwater with the gluten network and starch granule in whole-wheatdough system, which inhibited sufficient water absorption andformation of gluten network (Rosell et al., 2010). The AX is the maincomponent of wheat bran, and it shows the ability of sequestratingwater and restricting the formation of gluten network in whole-wheat bread dough (Li et al., 2012). However, the G0-valueincreased again as the SWWW flour content exceeded 50 g/100 g;the flour blend with 75 g/100 g SWWWhad the highest G0 (Fig. 4a),which may be related to the highest protein content of this blend(Table 2). This result indicated that the G0 was more affected by theprotein content of flour blend than by the shearing action of wheatbran in the frequency sweep test. G0 represents the dynamic elas-ticity and G00 represents the dynamic viscous property. As shown inFig. 4, the G0 values were larger than the G00 values, indicating thatthe dough was more elastic than viscous. However, the high-level

G0 (which was correlated with the protein content) did not resultin strong elasticity of dough and full formation of gluten network,whichmay be caused by the highwater absorption of wheat bran inwhole-wheat dough system. Thus, the preferable baking quality ofwhole-wheat products cannot be demonstrated by the high-levelG0-value.

The rheological properties of flours have been reported todepend on starch granular structure, amylose to amylopectin ratio,and the presence of phosphate esters (Singh & Singh, 2001). Thepresence of large starch granules inwheat flour is likely responsiblefor high G0 and G00 values (Kaur, Singh, & Sodhi, 2002). However, thestarch content and its granular sizewere diluted and sheared by theincreased level of wheat bran in whole-wheat flour (Li et al., 2012).Therefore, the result of G00 of cracker dough reduced with theincreasing SWWW flour content (Fig. 4b) may be caused by thesmaller granular size and shape of the native starches in the system.In addition, the reduced G00-value of whole-wheat dough indicatedthat the G00 was less to do with the flour protein content and moreto do with the bran content in the frequency sweep test. High G00-value may be beneficial to the quality of whole-wheat products.

3.5. Water competition and migration

To demonstrate the water migration and competitive watersequestration between the AX matrix and gluten network inwhole-wheat cracker flour system, the T2 relaxation time of whole-wheat flour blends were determined by NMR. T2 relaxation timetypical curve of wheat dough (Fig. 5) includes three peaks: T21(0�1ms), T22 (1�100ms), and T23 (100�1000ms), which represent,tightly, less tightly, and weakly bound water, respectively(Lu & Seetharaman, 2013). X-axis in T2 relaxation time curve rep-resents the water activity of food material. A shorter T2 relaxationtime indicates a lower degree of water freedom. Y-axis in T2relaxation time curve represents the signal amplitude of protons.Peak area of T2 curve represents the relative content of hydrogenprotons (moisture content) absorbed by hydrophilic components.The peak T21 in T2 relaxation time curve represented the waterabsorbed by the AX matrix and starch. The AX has a strong bindingcapacity for water due to its polysaccharide structure (Izydorczyk &Biliaderis, 1995). The peak T22 represented the water absorbed bythe gluten network. The gluten has a high-amount water absorp-tion capacity caused by its porous framework (Li et al., 2012). The

Fig. 4. Effects of soft white whole-wheat (SWWW) flour on the rheological properties(a. G0: storage modulus; b. G00: loss modulus) in the frequency sweep test of whole-wheat cracker dough blended with (-) 0 g/100 g SWWW flour (SWWW); (C) 25 g/100 g SWWW; (:) 50 g/100 g SWWW; (;) 75 g/100 g SWWW; (A) 100 g/100 gSWWW.

Fig. 5. T2 relaxation time distribution of whole-wheat cracker flour blends with fivedifferent levels of soft white whole-wheat (SWWW) flour: d Control: 0 g/100 g; :25 g/100 g; : 50 g/100 g; : 75 g/100 g; : 100 g/100 g.

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results (Table 5) show that the peak area ratio of T21 (Area T21/Area[T21 þ T22 þ T23]) had a positive correlation (r ¼ 0.994; P < 0.05)with the increased level of SWWW flour (0 g/100 g, 25 g/100 g,50 g/100 g, 75 g/100 g, 100 g/100 g). A negative correlation(r¼�0.998; P< 0.05) was found between the peak area ratio of T22(Area T22/Area [T21 þ T22 þ T23]) and the addition level of SWWWflour. The peak area ratio of T23 did not change significantly. Theseresults indicated that the water migrated from the gluten networkinto the AX matrix in whole-wheat cracker dough system, andinhibited the water absorption of gluten to form the networkstructure to maintain its gas-retention ability. Thus, the bubblesand puffy internal structure of whole-wheat crackers wererestrained due to the weak gas-retention capacity of whole-wheatdough, resulting in inferior baking quality of end products. Mean-while, the peak T21 shifted to the left, suggesting that the waterholding capacity of AX was enhanced with the increased level ofwhole-wheat flour.

3.6. Correlation analysis

In this research, the W-SRC was significantly correlated withalveograph values. W-SRC had a positive correlation with the P-value (r ¼ 0.98, P < 0.01) and was negatively correlated with the L-value (r ¼ �0.99, P < 0.01) and the W-value (r ¼ �0.99, P < 0.01).The P/L ratio was positively correlated with the W-SRC (r ¼ 0.92,P < 0.05). P-value was positively correlated with SC-SRC (r ¼ 0.99,P < 0.01) and Suc-SRC values (r ¼ 0.98, P < 0.01); both L and Wvalues had a significant negative correlation with SC-SRC and Suc-SRC values. The P/L ratio was positively correlated with SC-SRC(r ¼ 0.93, P < 0.05) and Suc-SRC (r ¼ 0.92, P < 0.05). LA-SRC andGPI were independent of all alveograph parameters.

The correlations among the end-product quality parameters,SRC and alveograph values were also observed (Table 6). The end-product quality parameters were significantly correlated with theSC-SRC, Suc-SRC and W-SRC. LA-SRC values did not show

significant correlation with the whole-wheat cracker quality pa-rameters and therefore, was ineffective in predicting the proteinfunctionality inwhole-wheat products (Bettge, Morris, DeMacon, &Kidwell, 2002). If such a prediction is desired, SDS-Sedimentationmay work better on whole-wheat flour for functional protein pre-diction. P-value may not be a good indicator of dough strength inthe whole-wheat dough system since the dough was measured at aconstant 50 g/100 g water absorption; the addition of SWWWmade the dough drier and artificially increased P-value. Also, thiswas partly due to the competitive water absorption by wheat branand the physical disruption to the gluten matrix, as discussedearlier in the Introduction. Both alveograph L and W values werepositively correlated with the quality parameters of the end prod-uct, suggesting that the alveograph may be a useful tool to predictthe end-use quality of whole-wheat cracker flour blends. Thegluten index also showed significant positive correlations with thequality attributes of whole-wheat cracker. Whole-wheat flourblends of higher gluten index values yielded greater stack height,specific volume, and breaking strength of the end products. Thus,the gluten index may also be useful in predicting the performanceof whole-wheat cracker flour and end-product quality.

4. Conclusions

The rheological behaviours of whole-wheat flour blends weregreatly affected by the addition level of SWWW flour. The G0-valueappeared to be affected more by the protein content than by theshearing action of wheat bran in whole-wheat dough system, andG00-value was more affected by the bran content. High water ab-sorption capacity of whole-wheat flour had a detrimental effect onthe quality attributes (especially oven spring) of whole-wheatsaltine crackers. The competition for water by AX from glutenmatrix in whole-wheat dough system restricted the proper for-mation of gluten network, which reduced its gas-retention capa-bility. Alveograph parameters, SRC values, and gluten indexappeared to be useful tools to predict the saltine cracker-bakingperformance of the whole-wheat flour and end-product quality.

Acknowledgement

We acknowledge the Shanghai Niumag Electronics TechnologyCo., Ltd. (Shanghai, China) for technical assistance.

References

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Table 5T2 relaxation time distribution of whole-wheat flour blend with different percent-ages of soft white whole-wheat flour.

Amount ofSWWW (g/100 g)a

Peak ratiob

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0 0.0446 � 0.0011 0.9355 � 0.0031 0.0199 � 0.000225 0.0458 � 0.0016 0.9344 � 0.0028 0.0198 � 0.000150 0.0621 � 0.0013 0.9180 � 0.0025 0.0199 � 0.000175 0.0751 � 0.0015 0.9049 � 0.0030 0.0200 � 0.0002100 0.0844 � 0.0018 0.8954 � 0.0027 0.0202 � 0.0002

a Abbreviations as in Table 1.b Percentage of each peak area in total areas (T21, T22, and T23).

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**Correlation is significant at the 0.01 level (P < 0.01).*Correlation is significant at the 0.05 level (P < 0.05); ns, not significance.

a Abbreviations as in Figs. 4 and 5.

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