Studying the Effects of Whole-Wheat Flour on the Rheological Properties and the Quality Attributes of Whole-Wheat Saltine

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Studying the effects of whole-wheat flour on the rheological properties and the quality attributes of whole-wheat saltine...

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LWT - Food Science and Technology 55 (2014) 43e50

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Studying the effects of whole-wheat ﬂour on the rheological properties and the quality attributes of whole-wheat saltine cracker using 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 China b Wheat Marketing Center, Inc., 1200 NW Naito Parkway, Suite 230, Portland, OR 97209, USA article info abstract

Article history: Quality attributes of soft wheat products are affected by physicochemical characteristics and rheological Received 2 May 2013 properties of wheat flour. Whole-wheat flour has a significant impact on baking qualities (stack height, Received in revised form stack weight, specific volume, and breaking strength) of whole-wheat saltine crackers due to its high 26 July 2013 water absorption capacity. SRC profiles, alveograph and rheometer parameters were determined to Accepted 30 July 2013 observe 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. Results Keywords: of SRC testing revealed that the water absorption of whole-wheat flour blends increased with the Rheological properties fl 0 00 fl Whole-wheat saltine cracker addition level of whole-wheat our. The rheological properties (G , G , P, L, W values) were in uenced fi fl Nuclear magnetic resonance (NMR) signi cantly by the presence of whole-wheat our. Results of NMR indicated that water migrated from Water migration gluten network into arabinoxylans matrix in whole-wheat dough system, resulting in inferior saltine Solvent retention capacity (SRC) cracker-baking qualities of whole-wheat flour, i.e., small breaking strength, stack height and specific volume. The stack height, specific volume, and breaking strength of end products showed significant correlations with the arabinoxylans, dough extensibility, and gluten index of whole-wheat flour. Ó 2013 Elsevier Ltd. All rights reserved.

1. Introduction wheat flour, especially the whole-wheat flour can significantly affect the rheological properties of cracker dough and end-product Crackers are an important product line within the large-scale quality. The formation of gluten in dough system was restrained by baking industry, and are a natural fit as portable and convenient whole-wheat flour of high-level water absorption capacity, which foods. Crackers can be divided into three broad categories: saltine was undesirable in the functionality of cracker flour (Slade, Levine, cracker (soda cracker), chemically leavened cracker, and enzyme Craig, & Arciszewski, 1994). Presumably, the arabinoxylans which cracker (Moore & Strouts, 2008). The quality of wheat products is are the main non-starch polysaccharides in wheat bran compete for determined by the rheological behaviours of dough. The pasting water with the dough main polymers, gluten and starch in whole- properties of starch gave useful prediction to the quality of soft wheat dough system, and interrupt the protein aggregation wheat products such as cookies, crackers and cakes (Serpil, Kevser, behaviour during heating (Rosell, Santos, & Collar, 2010). Bengihan, & Hamit, 2008). The volumes of bread and puff pastry At present, solvent retention capacity (SRC) and alveograph are were correlated with rheological properties of the dough (Sliwinski, the two traditional methods for estimating the potential perfor- Kolster, & van Vliet, 2004). Therefore, understanding the rheological mance of soft wheat flour. The SRC tests were developed to evaluate properties and machinability of dough system is essential for the quality of soft wheat flour in cookie and cracker products. In guiding the production of wheat products. However, whole-wheat general, alveograph is more appropriate for predicting the protein flour has a major impact on the rheological properties of dough functionality of soft wheat flours, while farinograph and mixograph and quality attributes of end products. The water absorption of are commonly used to evaluate hard wheat bread flours (Levine & Slade, 2004). Both the SRC and alveograph results are affected by fl * Corresponding author. Tel.: þ1 503 295 0823; fax: þ1 503 295 2735. the presence of wheat bran in ours. Since the alveograph mea- fi ** Corresponding author. Fax: þ86 51085867273. sures the xed-absorption dough, having bran involved will greatly E-mail addresses: [email protected], [email protected] (G.G. Hou). affect the amount of water available for gluten formation. Further,

44 J. Li et al. / LWT - Food Science and Technology 55 (2014) 43e50 bran particles can physically disrupt the gluten matrix, leading to Table 2 premature bubble rupture (Li et al., 2012). Flour analysis. NMR technique which is a useful tool to detect the macro-water Amount of Moisture Protein Ash Wet gluten Gluten Starch distribution and migration among high-moisture samples non- SWWW (g/100 g) (g/100 g)b (g/100 g)b (g/100 g)b index damage a b invasively (Stapley, Hyde, Gladden, & Fryer, 1997) was successfully (g/100 g) (g/100 g) applied to examine the water migration between macromolecules 0 13.2 8.43 0.442 24.5 60.9 3.1 (arabinoxylans and gluten network) in whole-wheat bread dough 25 12.5 8.92 0.734 24.4 44.1 3.1 system (Li et al., 2012). Thus, the objectives of this study were: 1) to 50 11.7 9.35 1.015 28.6 26.2 3.4 75 11.0 9.92 1.241 26.0 8.4 3.4 fl investigate the effect of whole-wheat our on the rheological 100 10.3 9.77 1.522 22.2 6.6 3.4 properties of whole-wheat saltine cracker flour blends using the a Abbreviations as in Table 1. rheometer, alveograph, and SRC testing; 2) to verify the mechanism b 14 g/100 g mb. of the impact of whole-wheat flour on the quality attributes of whole-wheat saltine cracker using the NMR technique; and 3) to blends were determined according to the AACC International establish the relationship between the rheological properties of Approved Methods and results are shown in Table 2. whole-wheat flour blends and end-product quality parameters.

2.3. Whole-wheat saltine cracker preparation 2. Materials and methods

2.3.1. Formula 2.1. Materials In the sponge, ingredients included flour (65 g/100 g), sour- Ò dough starter (4 g/100 g), instant dry yeast (0.3 g/100 g), yeast foods Soft white whole-wheat flour (SWWW; Ultragrain ) was kindly (0.03 g/100 g), and water (27 g/100 g, 29 g/100 g, 30 g/100 g, 32 g/ provided by ConAgra Flour Mills, Inc. (Omaha, NE, USA). Soft red 100 g, and 34 g/100 g water was added into five whole-wheat flour winter flour (SRW; Golden Shield, enriched and unbleached) and blends, respectively). The sourdough starter was initially supplied hard red winter flour (HRW; Harvest King winter wheat, enriched by the Oregon State University and was fed every day using old and unbleached) were obtained from General Mills, Inc. (Minne- starter (50 g), HRW flour (100 g), and distilled water (50 g). The apolis, MN, USA). Baking soda (ARM & HAMMER Div. of Church & starter ingredients were mixed (Hobart A-200 mixer) at 1st speed Dwigh, Co., Inc., Princeton, NJ, USA), yeast food (ADM Arkady Inc., for 5 min until well blended, and the starter dough was placed in a Olathe, KS, USA), salt (Morton Salt, Inc., Chicago, IL, USA), Crisco container with a lid until it tripled in volume at room temperature. vegetable shortening (trans-fat free) (J.M. Smucker Company, Orr- The dough ingredients included flour (35 g/100 g), shortening ville, OH, USA) and instant dry yeast (Lesaffre Yeast Corporation, (14 g/100 g), salt (0.8 g/100 g), water (1 g/100 g), and baking soda Milwaukee, Wisconsin, USA) were purchased from a local super- (determined by the total titratable acidity of the sponge). All in- market (Portland, Oregon, USA). The chemical reagents (ACS grade) gredients were scaled on the basis of 500-g flour weight. Instant used for conducting SRC tests were purchased from Nurnberg Sci- dry yeast, yeast foods, and salt were weighed and dispersed sepa- entific Company (Portland, OR, USA). rately in the amount of water required in the formula before use. 2.2. Whole-wheat saltine cracker flour blends preparation and 2.3.2. Baking soda dosage determination analysis The total titratable acidity (TTA) test was considered as an indication of the fermentation process. To determine the baking Whole-wheat saltine cracker flour samples were composited soda dosage in the cracker dough formula and to control the final from the blends of SWWW, SRW, and HRW flour (Table 1). HRW product pH (in the range of 7e8), the TTA of cracker sponge was flour is suitable for making crackers (Slade et al., 1994) and meets determined after 18-h sponge fermentation. TTA was prepared by the requirement of relatively high gluten strength for high-quality mixing 15 g sponge with 100 mL deionized water and stirred for cracker flour (Kweon, Slade, & Levine, 2011b). From our preliminary 30 s at 2nd speed using the Hamilton Beach commercial blender trials (data not shown), the optimum addition range of HRW flour (model 908 Clamshell, Procter-Silex, Inc., USA) until the sponge was 10e20 g/100 g which was determined by the breaking strength sample was completely dispersed. Then, the sponge slurry was of end products (if HRW was 20 g/100 g, the end-product texture transferred into a 250 mL beaker with a stir bar inside and placed became harder and less crispy), so 15 g/100 g of HRW flour was onto a magnetic stirrer (model PC-520, Coring Laboratory Stirrer, added consistently in each group, except for the 100 g/100 g USA). 0.1 M/L NaOH solution was used to titrate (Brinkmann Dis- SWWW group. The addition levels of SWWW flour in flour blends pensette, Germany) the sponge slurry until a final pH value of 6.6. were 0 g/100 g (control flour blend), 25 g/100 g, 50 g/100 g, 75 g/ The volume of NaOH solution used for titration was referred as the 100 g and 100 g/100 g, respectively. TTA value (Sutherland, 1989). The relationship between TTA and Protein (AACCI 46-30.01), moisture (AACCI 44-15.02), ash baking soda dosage is shown in Table 3. (AACCI 08-01.01), starch damage (AACCI 76-33.01), wet gluten and gluten index (AACCI 38-12.02) of five different whole-wheat flour Table 3 Total tritable acidity (TTA) of sponge and baking soda Table 1 dosage in whole-wheat cracker dough. Flour blend composition of whole-wheat saltine crackers. TTA (mL) Baking soda (g) Amount of Sponge (65 g/100 g) Dough (35 g/100 g) per 500 g flour SWWW (g/100 g)a SWWW SRW HRW SWWW SRW 7e8 3.0 05015359e11 4.0 25 25 25 15 35 12e13 5.0 50 50 15 35 14e16 6.0 75 50 15 25 10 17e18 7.0 100 65 35 18e19 7.5 20e21 8.0 a SWWW: soft white whole-wheat; SRW: soft red winter; HRW: hard red winter. Author's personal copy

J. Li et al. / LWT - Food Science and Technology 55 (2014) 43e50 45

2.3.3. Production procedures 2.5. SRC testing The sponge ingredients were mixed at 1st speed for 3 min and 2nd speed for another 2 min in a Hobart A-200 mixer equipped Solvent retention capacity (SRC) tests including water SRC (W- with a McDuffy mixing bowl (National Manufacturing, Co. Lincoln, SRC), lactic acid SRC (LA-SRC), sodium carbonate SRC (SC-SRC), and NE, USA). Then, the sponge was fermented at 28 C and 85% RH in a sucrose SRC (Suc-SRC) of flour blends of varying SWWW were ac- fermentation cabinet (National Manufacturing Co., Lincoln, NE, cording to the AACC International Approved Method 56-11.02. USA) for 18 h. After the 18-h fermentation, the remaining flour, water, shortening and dry ingredients (salt and baking soda) were 2.6. Rheological measurements mixed with the sponge and proofed for 2 h (when the dough pH was 6e6.5) under the same conditions as the sponge. After the 2.6.1. Alveograph analysis dough was proofed, 500 g dough was weighed and placed into a Alveograph parameters were determined by the Alveo- plastic container and shaped into a rectangular block Consistograph (Chopin, Villeneuve-La-Garenne, France) according (15 13.5 2.5 cm). The shaped dough block was formed into a to the AACC International Approved Method 54-30.02. Dough thin sheet using the SSO-615 Seewer Rondo Reversible Lamination tenacity (P), extensibility (L) and deformation energy (W)were Machine (Commercial Food Preparing Machine, Rondo Inc., USA) to determined. reduce the thickness until the height, width, and length of the dough sheet were about 1.3e1.4 mm, 22.5 cm, and 40.0 cm, 2.6.2. Rheometer determination respectively. The detailed dough lamination settings were listed as The rheological properties (storage modulus, G0; loss modulus, follows: G00) of whole-wheat flour blends were determined using an AR1000 Set initial roll gap to 12 mm / 9mm/ 6mm/ folded both ends Rheometer (TA Instruments, New Castle, USA). The testing probe to the center, and then turned 90 / 12 mm / 10 mm / was a standard steel parallel plate (20 mm diameter, 1 mm-gap 8mm/ 6mm/ 4mm/ folded the dough into trifold / 10 mm / distance). Each sample was determined in triplicates under the 8mm/ 6mm/ turned 90 / 4mm/ 3mm/ folded the dough frequency sweep test (frequency: 0.1e100 Hz; temperature: 28 C). into trifold / 10 mm / 8mm/ 6mm/ turned 90 / 4mm/ 3mm/ 2mm/ 1.4 mm / adjusted roll gap to achieve a final sheet 2.7. NMR thickness of 1.3e1.4 mm. The dough sheet was then transferred onto a specially designed Water migration between the arabinoxylans (AX) matrix and cutter-docker (Pizzinatto & Hoseney, 1980), and sprinkled with salt gluten network in whole-wheat cracker dough system was followed by using a rolling pin to roll on the dough sheet to suffi- observed using the NMR system which is represented by spinspin ciently perforate it. The deck oven (PICCOLOI-3 Wachtel Company, relaxation time (T2). The relaxation measurements were performed Germany) and a specially designed rectangular-shaped baking rack on a Niumag Desktop Pulsed NMR Analyzer (Shanghai Niumag (CB5 baking band) were preheated for 30 min at a 220 C top Electronics Technology Co. Ltd., China). The detailed parameters temperature and 215 C bottom temperature. Loaded the docked and procedures of measurements were described in our previous cracker dough sheet onto the baking rack and baked in the deck study (Li et al., 2012). oven for 6e7 min (maximum bubbles appeared on the surface of crackers and their color became brown). After baking was com- 2.8. Statistical analysis plete, the cracker sheet was cooled at room temperature for 30 min and broken into individual pieces for analysis. Statistical analyses were conducted with the SPSS software 17 (SPSS Institute, Chicago, USA). Pearson’s correlation coefficients 2.4. End-product evaluation between quality of end products and SRC and alveograph parameters were also calculated. Stack height, stack weight, specific volume, texture analysis, color, moisture and pH of the end products were determined. The 3. Results and discussion stack height and stack weight were measured using seven sample pieces. The stack height was measured by a vernier caliper (Mitu- 3.1. Effect of whole-wheat flour on end-product baking quality toyo Manufacturing Co., Ltd., Japan), measuring once and turning the crackers 90 and measuring again to obtain the average value. Quality characteristics of end products were affected by The cracker specific volume was determined with the BVM-L 370 different composition levels of whole-wheat flour (Table 4). The TexVol (TexVol Instruments Inc., Viken, Sweden) by dividing the stack weight, stack height, specific volume and breaking strength of volume by weight. The breaking strength of the cracker was crackers decreased as the addition level of SWWW flour increased. measured by the TA-XTPlus Texture Analyzer (Texture Technologies The moisture content and pH of the end products were in the Corp., Scarsdale, NY, USA) using the three point bending fixture commercial range of 2e4 g/100 g and 7e8, respectively. (model TA-92). This adjustable three point bend/snap fixture was Carbon dioxide gas generation reduced the dough density and placed onto the TA-90 platform. An individual cracker was placed dry matter was lost during dough fermentation (Faridi & Johnson, over the two legs (4.5 cm apart) and a metal knife blade (model TA- 1977). With the increasing level of whole-wheat flour, more vola- 43R, 3-mm thick with rounded end) was centered over the middle tile gas and acids were produced resulting in decreased stack height of the cracker and moved downward during testing until the and stack weight of crackers. The higher amount of whole-wheat cracker broke. The pretest speed, test speed, and post-test speed flour tended to produce an uneven and less puffiness internal were 2.0 mm/s, 3.0 mm/s and 10.0 mm/s, respectively. The test texture. It was noticed that the gluten index values of flour blends distance was 35.0 mm and contact force was 5 g. The peak force reduced dramatically from 60.9 to 6.6 with the increase of whole- displayed in the texture graph was the force required to break the wheat flour (Table 2). Therefore, crackers with higher level of cracker and was recorded as the breaking force of the cracker. The SWWW flour were more fragile (less breaking force) and had color (L, a*, b*) values of the crackers were determined by the CR- smaller specific volume. The AX in whole-wheat flour are a major 410 Chroma Meter (Konica Minolta Sensing, Inc., Japan). All mea- component of cell wall polysaccharide and are present in the aleu- surements were conducted at least three times. rone and bran layers of the wheat kernels (Courtin & Delcour, 2002). Author's personal copy

46 J. Li et al. / LWT - Food Science and Technology 55 (2014) 43e50

Table 4 End-product quality evaluation.a

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

0 27.2 0.2a 34.8 0.4a 1.27 0.06a 1236.3 70.1a 3.1 7.7 25 27.0 0.2a 32.7 0.3b 1.25 0.02a 1052.7 82.6b 3.1 7.6 50 26.5 0.3b 29.8 0.4c 1.14 0.04b 829.8 25.6c 3.9 7.1 75 25.1 0.3c 28.9 0.3c 1.02 0.03c 732.0 23.0c 3.7 7.4 100 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 three replicate experiments. b Abbreviations as in Table 1. c Dry basis. d Stack of 7 crackers.

AX are a highly water-absorbing component, which exert a negative a better predictor of overall performance of cracker flour than the effect on the quality of crackers, especially on the volume of crackers LA-SRC value alone (Kweon et al., 2011b). The SRC values and GPI of (Kweon, Slade, & Levine, 2011a). The high water-absorbing com- cracker flours are shown in Fig. 2. The SRC values of control flour ponents restrained the hydration of the gluten proteins from blend (0 g/100 g SWWW) which was a blend of 85 g/100 g SRW and forming the proper network needed for gas retention. The cracker 15 g/100 g HRW were: W-SRC ¼ 55.3 g/100 g, LA-SRC ¼ 95.5 g/ dough was too tight to allow for puffing during baking, resulting in 100 g, SC-SRC ¼ 72.3 g/100 g, and Suc-SRC ¼ 104.1 g/100 g. Typical reduction of the stack height and specific volume of end products standard SRC values for soft wheat sponge-and-dough cracker (e.g., (Carey et al., 2002). The generation of discontinuous protein film saltine crackers) flour were reported as: W-SRC 57 g/100 g, LA- decreased the breaking strength and reduced the bubbling of the SRC 100 g/100 g, SC-SRC 72 g/100 g, and Suc-SRC 96 g/100 g whole-wheat crackers during baking. Thus, the development of the (Kweon et al., 2011b). The four SRC values of the control flour blend gluten network during dough machining was a decisive factor to the were similar to the typical standard except for the slight differences superior baking quality of whole-wheat flour blends. As expected, in LA-SRC and Suc-SRC, which may be due to the addition of 15 g/ the color of the end products gradually became browner and darker 100 g HRW flour. If there was more HRW, the LA-SRC would be with the increased ratio of whole-wheat flour (Fig. 1). greater, probably over 100 g/100 g. The reduction in LA-SRC compared to the target range was probably due to the SRW, but 3.2. Effect of whole-wheat flour on SRC profiles of whole-wheat the increase in Suc-SRC was probably due to the HRW. The SRC fl flour blends values and GPI (0.54) of the control our blend suggested that it

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

Fig. 2. Effects of soft white whole-wheat (SWWW) flour on the solvent retention capacity (SRC) values of whole-wheat flour blends. SRC: solvent retention capacity; W- Fig. 1. The color values (L, a* and b*) of the crackers made from five different addition SRC: water SRC; LA-SRC: lactic acid SRC; SC-SRC: sodium carbonate SRC; Suc-SRC: levels of soft white whole-wheat (SWWW) flours. L: lightness; a*: redness-greenness; sucrose SRC; GPI (Gluten Performance Index) ¼ Lactic Acid SRC/(Sodium b*: blueness-yellowness. Carbonate þ Sucrose) SRC. Author's personal copy

J. Li et al. / LWT - Food Science and Technology 55 (2014) 43e50 47 was within a marginal range of soda cracker flour with sufficient gluten strength and good cracker-baking performance. The GPI of other cracker flour blends containing various amounts of SWWW were much lower than that of the control flour blend, indicating weaker gluten strength and less puffing during baking. As the percentage of SWWW flour increased in the flour blend, both the SRC values and GPI changed gradually, in proportion to the amount of SWWW added. LA-SRC reflects protein content, glutenin characteristics and general gluten functionality; SC-SRC is associated with the level of damaged starch; Suc-SRC is related to the pentosan (also known as arabinoxylans) content; and W-SRC is affected by all of those flour constituents (AACCI Methods 56-11.02). Damaged starch is small particles of starch broken away from the main starch granules in wheat during milling, and has a strong water retention capacity (Mulla, Bharadwaj, Annapure, & Singhal, 2010). When starch granules are damaged, cleavage of the smaller granule will facilitate hydration 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 the increased level of whole-wheat flour due to the low-level damaged starch (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 values increased with the amount of whole-wheat flour due to the increase of high water absorbent components such as damaged starch and arabinoxylans in flours. LA-SRC had no linear correlation with the W-SRC, SC-SRC and Suc-SRC values, and the LA-SRC and GPI values did not correlate with the composition level of SWWW flour. However, the W-SRC Fig. 3. Effects of soft white whole-wheat (SWWW) flour on the alveograph values of increased with the amount of SWWW flour in the flour blend. The whole-wheat flour blends. P: dough tenacity; L: dough extensibility; W: dough SRC values (W-SRC ¼ 66.2 g/100 g, LA-SRC ¼ 74.9 g/100 g, SC- deformation energy. SRC ¼ 84.2 g/100 g and Suc-SRC ¼ 112.3 g/100 g) of 100 g/100 g SWWW cracker flour were significantly different from those of the strong the cracker dough will be too elastic to resist puffing during typical standard flour as reported. The SRC values of 100 g/100 g baking. If L-value is less than 90, the implication is that the dough is whole-wheat flour exhibited higher water absorption, weak gluten lack of extensibility and bubble breakage will occur during baking strength (lower level of LA-SRC value), and higher levels of (Slade et al., 1994). The destructive and cleaving effects of wheat damaged starch and arabinoxylans than other flour blends with brans with large-sized particles and native enzymes on the internal less SWWW flour. The GPI of 100 g/100 g whole-wheat flour was gluten network result in less extensibility of gluten matrix (Li et al., very low (GPI ¼ 0.38), indicating much inferior baking performance 2012). Although the alveograph values of control flour blend had a than the flour blends of lower content of whole-wheat flour. slight difference from the “gold standard”, the control flour blend Generally speaking, for commercial cracker production, high- had lower P and P/L values, higher W and L values which were quality saltine cracker flour requires relatively high gluten preferred for a better cracker-baking quality. Nevertheless, the strength, within the class of soft wheat, and low water absorption alveograph parameters of 100 g/100 g SWWW flour showed very capacity (Kweon et al., 2011b). Thus, flours with higher LA-SRC, different results from the “gold standard”. lower water SRC, SC-SRC, and Suc-SRC values were preferred for The higher level of P-value (63 mm) was caused by the high level superior quality of commercial crackers for puffing and bubbling of water-absorbing components (arabinoxylans and damaged (Slade et al., 1994). Also the GPI was shown to have a better cor- starch) in the whole-wheat flour and the dough was too firm to relation with the cracker-baking performance. Cracker flour with a expand. Preston, Kilborn, and Dexter (1987) reported that the GPI <0.52 produced unacceptable performance and excessive starch damage was positively correlated with P, L, W, and P/L of blistering during baking (Kweon et al., 2011b). Canadian hard red spring wheat doughs. The lower level of L-value (21 mm) and W-value (54 mm) was due to the weak gluten strength 3.3. Effect of whole-wheat flour on alveograph parameters of of the whole-wheat flour. Moreover, the P/L ratio (3.00) of 100 g/ whole-wheat flour blends 100 g whole-wheat flour was much higher than that of the control flour blend (P/L ¼ 0.32), which indicated that there was a lack of The alveograph parameters (Fig. 3) showed that the P-value and balance between elasticity and extensibility for the whole-wheat P/L ratio had positive correlations with the percentage of SWWW cracker dough to retain gas for expansion during fermentation flour; however the L and W values had a negative correlation with and baking as measured by the alveograph. the amount of SWWW flour. The “gold standard” of alveograph parameters for ideal-quality refined white cracker flour is P ¼ 35 5, L ¼ 100 10, and 3.4. Effect of whole-wheat flour on rheometer parameters of whole- W ¼ 90 15. If P-value is too low (<30) or too high (>40), the flour wheat flour blends would be too soft to form proper blistering on crackers or too hard for crackers to spread enough, respectively. W-value should not be The increased level of whole-wheat flour had a destructive ef- too low (<75) or too high (>105). If the gluten strength is too weak, fect on the formation of gluten network. Development of gluten in gas cells coalesce and gas is released prematurely; if gluten is too cracker dough during mixing and sheeting was a critical factor of Author's personal copy

48 J. Li et al. / LWT - Food Science and Technology 55 (2014) 43e50 affecting the cracker quality (Kweon et al., 2011a). In the frequency G0 (which was correlated with the protein content) did not result sweep test, the G0 (storage modulus) of whole-wheat dough in strong elasticity of dough and full formation of gluten network, reduced with the addition level of SWWW flour, which indicated which may be caused by the high water absorption of wheat bran in that the elasticity of whole-wheat cracker dough was restrained. whole-wheat dough system. Thus, the preferable baking quality of The high water absorbent-capacity of wheat bran competes for whole-wheat products cannot be demonstrated by the high-level water with the gluten network and starch granule in whole-wheat G0-value. dough system, which inhibited sufficient water absorption and The rheological properties of flours have been reported to formation of gluten network (Rosell et al., 2010). The AX is the main depend on starch granular structure, amylose to amylopectin ratio, component of wheat bran, and it shows the ability of sequestrating and the presence of phosphate esters (Singh & Singh, 2001). The water and restricting the formation of gluten network in whole- presence of large starch granules in wheat flour is likely responsible wheat bread dough (Li et al., 2012). However, the G0-value for high G0 and G00 values (Kaur, Singh, & Sodhi, 2002). However, the increased again as the SWWW flour content exceeded 50 g/100 g; starch content and its granular size were diluted and sheared by the the flour blend with 75 g/100 g SWWW had the highest G0 (Fig. 4a), increased level of wheat bran in whole-wheat flour (Li et al., 2012). which may be related to the highest protein content of this blend Therefore, the result of G00 of cracker dough reduced with the (Table 2). This result indicated that the G0 was more affected by the increasing SWWW flour content (Fig. 4b) may be caused by the protein content of flour blend than by the shearing action of wheat smaller granular size and shape of the native starches in the system. bran in the frequency sweep test. G0 represents the dynamic elas- In addition, the reduced G00-value of whole-wheat dough indicated ticity and G00 represents the dynamic viscous property. As shown in that the G00 was less to do with the flour protein content and more Fig. 4, the G0 values were larger than the G00 values, indicating that to do with the bran content in the frequency sweep test. High G00- the dough was more elastic than viscous. However, the high-level value may be beneficial to the quality of whole-wheat products.

3.5. Water competition and migration

To demonstrate the water migration and competitive water sequestration between the AX matrix and gluten network in whole-wheat cracker ﬂour system, the T2 relaxation time of whole- wheat ﬂour blends were determined by NMR. T2 relaxation time typical curve of wheat dough (Fig. 5) includes three peaks: T21 (01 ms), T22 (1100 ms), and T23 (1001000 ms), which represent, tightly, less tightly, and weakly bound water, respectively (Lu & Seetharaman, 2013). X-axis in T2 relaxation time curve represents the water activity of food material. A shorter T2 relaxation time indicates a lower degree of water freedom. Y-axis in T2 relaxation time curve represents the signal amplitude of protons. Peak area of T2 curve represents the relative content of hydrogen protons (moisture content) absorbed by hydrophilic components. The peak T21 in T2 relaxation time curve represented the water absorbed by the AX matrix and starch. The AX has a strong binding capacity for water due to its polysaccharide structure (Izydorczyk & Biliaderis, 1995). The peak T22 represented the water absorbed by the gluten network. The gluten has a high-amount water absorption 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)25g/ Fig. 5. T2 relaxation time distribution of whole-wheat cracker flour blends with five 100 g SWWW; (:) 50 g/100 g SWWW; (;) 75 g/100 g SWWW; (A) 100 g/100 g different levels of soft white whole-wheat (SWWW) flour: d Control: 0 g/100 g; : SWWW. 25 g/100 g; : 50 g/100 g; : 75 g/100 g; : 100 g/100 g. Author's personal copy

J. Li et al. / LWT - Food Science and Technology 55 (2014) 43e50 49

Table 5 significant correlation with the whole-wheat cracker quality pa- fl T2 relaxation time distribution of whole-wheat our blend with different percent- rameters and therefore, was ineffective in predicting the protein ages of soft white whole-wheat flour. functionality in whole-wheat products (Bettge, Morris, DeMacon, & Amount of Peak ratiob Kidwell, 2002). If such a prediction is desired, SDS-Sedimentation SWWW (g/100 g)a fl T21 T22 T23 may work better on whole-wheat our for functional protein prediction. P-value may not be a good indicator of dough strength in 0 0.0446 0.0011 0.9355 0.0031 0.0199 0.0002 25 0.0458 0.0016 0.9344 0.0028 0.0198 0.0001 the whole-wheat dough system since the dough was measured at a 50 0.0621 0.0013 0.9180 0.0025 0.0199 0.0001 constant 50 g/100 g water absorption; the addition of SWWW 75 0.0751 0.0015 0.9049 0.0030 0.0200 0.0002 made the dough drier and artificially increased P-value. Also, this 100 0.0844 0.0018 0.8954 0.0027 0.0202 0.0002 was partly due to the competitive water absorption by wheat bran a Abbreviations as in Table 1. and the physical disruption to the gluten matrix, as discussed b Percentage of each peak area in total areas (T21, T22, and T23). earlier in the Introduction. Both alveograph L and W values were positively correlated with the quality parameters of the end product, suggesting that the alveograph may be a useful tool to predict results (Table 5) show that the peak area ratio of T21 (Area T21/Area the end-use quality of whole-wheat cracker flour blends. The [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, gluten index also showed significant positive correlations with the 50 g/100 g, 75 g/100 g, 100 g/100 g). A negative correlation quality attributes of whole-wheat cracker. Whole-wheat flour blends of higher gluten index values yielded greater stack height, (r ¼0.998; P < 0.05) was found between the peak area ratio of T22 specific volume, and breaking strength of the end products. Thus, (Area T22/Area [T21 þ T22 þ T23]) and the addition level of SWWW the gluten index may also be useful in predicting the performance flour. The peak area ratio of T23 did not change significantly. These results indicated that the water migrated from the gluten network of whole-wheat cracker flour and end-product quality. into the AX matrix in whole-wheat cracker dough system, and inhibited the water absorption of gluten to form the network 4. Conclusions structure to maintain its gas-retention ability. Thus, the bubbles and puffy internal structure of whole-wheat crackers were The rheological behaviours of whole-wheat flour blends were 0 restrained due to the weak gas-retention capacity of whole-wheat greatly affected by the addition level of SWWW flour. The G -value dough, resulting in inferior baking quality of end products. Mean- appeared to be affected more by the protein content than by the while, the peak T21 shifted to the left, suggesting that the water shearing action of wheat bran in whole-wheat dough system, and 00 holding capacity of AX was enhanced with the increased level of G -value was more affected by the bran content. High water ab- whole-wheat flour. sorption capacity of whole-wheat flour had a detrimental effect on the quality attributes (especially oven spring) of whole-wheat 3.6. Correlation analysis saltine crackers. The competition for water by AX from gluten matrix in whole-wheat dough system restricted the proper for- In this research, the W-SRC was significantly correlated with mation of gluten network, which reduced its gas-retention capa- alveograph values. W-SRC had a positive correlation with the P- bility. Alveograph parameters, SRC values, and gluten index value (r ¼ 0.98, P < 0.01) and was negatively correlated with the L- appeared to be useful tools to predict the saltine cracker-baking value (r ¼0.99, P < 0.01) and the W-value (r ¼0.99, P < 0.01). performance of the whole-wheat flour and end-product quality. 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, Acknowledgement P < 0.01) and Suc-SRC values (r ¼ 0.98, P < 0.01); both L and W values had a significant negative correlation with SC-SRC and Suc- We acknowledge the Shanghai Niumag Electronics Technology SRC values. The P/L ratio was positively correlated with SC-SRC Co., Ltd. (Shanghai, China) for technical assistance. (r ¼ 0.93, P < 0.05) and Suc-SRC (r ¼ 0.92, P < 0.05). LA-SRC and GPI were independent of all alveograph parameters. 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