Effect of Waxy Wheat Flour Blends on the Quality of Fresh and Stale Bread

Agricultural Sciences in China 2009, 8(4): 401-409April 2009© 2009, CAAS. All rights reserved. Published by Elsevier Ltd.Effect of Waxy Wheat Flour Blends on the Quality of Fresh and Stale Bread QIN Peng1, MA Chuan-xi3, WU Rong-lin2, KONG Zhi-you4 and ZHANG Bo-qiao21College of Agronomy and Biotechnology, Yunnan Agricultural University, Kunming 650201, P.R.China2Agricultural Research Institute of Lixiahe Region, Yangzhou 225007, P.R.China3College of Agronomy, Anhui Agricultural University, Hefei 230036, P.R.China4Department of Biology and Chemistry, Baoshan Teachers’ College, Baoshan 678000, P.R.ChinaAbstractStarch is the major component in the wheat kernel, which is mainly composed of amylose and amylopectin. The wheat without amylose in its endosperm was called “waxy wheat”. Waxy wheat can be used to adjust the amylose content and improve the wheat-based food quality by adding to non-waxy wheat flour. In order to investigate the effect of waxy wheat flour on the quality of fresh and stale bread, waxy wheat flour was added into the flour of Canadian Spring Wheat 2 at 0.0, 5.0, 10.0, 15.0, 20.0, 25.0, 30.0, and 35.0% to make breads. The physicochemical properties were adjusted to suitability by adding Yangmai 158 flour, and breads were evaluated for sensory quality, crumb firmness, loaf volume and weight loss over a period of 0, 2, 4, and 6 days. The result showed that the best total score of fresh bread was 82.9 by adding waxy flour at 7.0%, though no significant difference was found among blends with 0.0-15.0% of waxy flour. Breads with the addition of 22.0% waxy flour had lower firmness, and decreasing loss of weight. Waxy wheat flour blend at 15.0% was optimal in retarding staling without significant decreasing fresh bread quality in comparison to the control.Key words: waxy wheat, fresh bread, stale bread, qualityINTRODUCTIONAmylose is synthesized through the activity of the gran-ule-bound starch synthase (GBSS). In common wheat (Triticum aestivum L.), there are three structural genes encoding isoforms of GBSS locating on chromosomes 4A, 7A and 7D, respectively (Graybosch 1998). The presence of one or two GBSS null alleles results in the production of starch with reduced amylose content. Wheats with three GBSS null alleles produce essen-tially amylose-free, or waxy, starch (Graybosch 1998). The waxy wheat flour had high levels of water absorption, breakdown, SDS-sedimentation, damaged starch content, swelling power, peak viscosity, lower setback, pasting and peak temperature (Park et al. 2001;Kim et al. 2003; Sharma et al. 2002; Chakraborty et al. 2004; Guo 2002; Guo et al. 2003a, b; Morita et al. 2002b; Park and Baik 2004; Sasaki 2004). The flour formed an intermediate-strength dough that developed rapidly and was relatively susceptible to mixing. Analysis by differential scanning calorimetry and X-ray diffractometry showed waxy wheat starch had higher gelatinization temperatures, a greater degree of crystallization, and an absence of an amylose-lipid com-plex compared with nonwaxy wheat. Waxy wheat and corn starches showed greater refrigeration and freeze-thaw stabilities than nonwaxy starches as demonstrated by syneresis tests (Abdel-Aal et al. 2002). They were also similar in pasting properties, but waxy wheat starch required lower temperature and enthalpy to gelatinize (Abdel-Aal et al. 2002).Received 24 September, 2008 Accepted 19 December, 2008QIN Peng, Ph D, E-mail: qinpeng77@; Correspondence ZHANG Bo-qiao, E-mail: wheat@402QIN Peng et al.A research found that excessive addition of waxy hexaploid wheat flour to total wheat flour (>20%) re-sulted in poorer functional properties (sticky, lumpy, or less crispy textures) in almost every end use prod-uct (Hayakawa et al. 2004). However, incorporation of <20% waxy hexaploid wheat flour produced con-siderable improvement in shelf-life characteristics (Hayakawa et al. 2004).Some studies on noodles with waxy flour blends were achieved previously. Adding 40% waxy wheat flour should improve the dry white Chinese noodle quality (Qin et al. 2008), and adding 20-30% waxy flour into wild type flour improved the quality of the white salted noodles, and the optimal amylose content was 21-24% (Guo 2002). White salted noodles pro-duced from blends of regular and waxy wheat flours became softer as the proportion of waxy wheat flour increased, even when protein content of flour blends increased, and amylose content of starch correlated positively with hardness and negatively with cohesive-ness of cooked white salted noodles (Park et al. 2004; Baik et al. 2003). Noodles prepared from waxy wheat flours exhibited the shortest cooking time, signifying the influence of starch amylose content on cooking time of noodles (Park et al. 2004), and had a higher compressive force than nonwaxy noodles when the strain was >80%, indicating the waxy wheat noodles were soft but difficult to completely cut through (Sasaki et al. 2004). In eight near-isogenic wheat lines with different Wx protein-deficiency, the white salted noodle from the flours of single-null types, which lack either the Wx-B1 or Wx-D1 proteins, and double-null types, which lack the Wx-A1 and Wx-D1 proteins, especially the latter, had desirable textures (Ishida et al. 2003), and wheat with lower amylose content compared to wild-type wheat, was suitable for producing yellow alkaline noodles with acceptable texture, especially when considering the elasticity and smoothness (Yuko et al. 2006). In addition, some studies showed that it should be ideal for restaurant (on-site) tortilla production or circumstances where tortillas were consumed shortly (within a day) after production when adding 10-20% waxy flour into wild-type flours. The optimal flour amylose content for hot-press wheat tortilla products was 24-26% (Guo et al. 2003a). When the waxy flour proportions were below 25%, the firmness of Chinese steamed bread stored at -18°C for 3 days gradually decreased with the increase of waxy flour (Qin et al. 2007). Staling of baked goods is ascribed to the action of starch which results in losses for bakers and consumers. Bread staling was characterized by toughening of the crust, firming of the crumb, losing of moisture and flavor, and a corresponding loss in product freshness (Bhattacharya et al. 2002). As to the two types of starch, amylose was considered to be primarily respon-sible for gel structure and crystallinity, and amylopec-tin for long-term rheological and structural changes of starch gels. So amylose was considered to be the pri-mary factor of staling for baked products. Normal wheat starch contains 20-30% amylose and the rest is amylopectin, and waxy wheat starch contains a little or no amylose and therefore it has specific effects on ge-latinization and retrogradation. Due to its slow retro-gradation rate, waxy wheat was preferred for refrigrerated and frozen food products (Graybosch et al. 1998).The consumption of bread is steady and increasing in China, but few studies were fulfilled on bread quality with waxy wheat flour blends. Breadcrumbs became softer with increasing of waxy-wheat flour substitution, and 40% waxy-wheat flour made larger loaves and improved the glutinous texture, such as the chewing property or adhesiveness of breadcrumbs, compared with normal flour alone. Waxy wheat flour retarded the staling of breadcrumbs during storage and acceler-ated the refreshing of breadcrumb softness and gluti-nous texture after reheating (Morita et al. 2002a). A 20% waxy wheat flour blend was optimal in retarding staling while producing bread quality compared with the control. It was further established that bread made with 20% waxy flour gave lower firmness values after 5 days of storage in comparison to bread made with 3% shortening. These results suggest that 20% waxy wheat flour could substitute for use of shortening to achieve desirable crumb softness and to retard staling upon storage (Bhattacharya et al. 2002). Consequently, partial substitution of waxy-wheat flour for normal flour was considered favorable for baking. The breads made from waxy wheat flour blends were poor in texture, dark in color, and with low quality score. However, the higher water content can be achieved after waxyEffect of Waxy Wheat Flour Blends on the Quality of Fresh and Stale Bread403flour blending, which results in a softer crumb and a slower rate of bread firming, these results suggest waxy flour could improve shelf life of bread (Liu et al. 2004). Waxy wheat flour bread was significantly softer than commercial white flour bread during storage, and the qualities of breads were also improved using partial waxy wheat flour substitution (10, 30, or 50%) for commercial white flour (Pham et al. 2007). In addition, incorporation of waxy flour with 10% proportion showed the lower firmness after storing 7 days at 4°C (Lee et al. 2001). Previous studies did not consider physicochemical changes during flours blend, so the waxy wheat flour blends were unfitted for breadmaking ultimately. For example, stability time of waxy wheat blends was too short to make bread (less than 5 min). In the present study, waxy wheat flour was added to Canadian Spring Wheat 2 at different levels, and Yangmai 158 was blended to adjust the identical physicochemical properties, and these composites were used for baking bread and evaluating. Our aim was to show the function of waxy wheat flour blends for fresh and stale bread quality with-out decreasing flour physicochemical properties. MATERIALS AND METHODSWheat samplesA hard red spring (HRS) wheat cultivar, Canadian Spring Wheat 2, was used as a base flour to experimental line of waxy wheat, and another HRS wheat cultivar, Yangmai 158, was blended to adjust the identical physicochemical properties in the main. Waxy wheat flour was added at levels of 0.0, 5.0, 10.0, 15.0, 20.0, 25.0, 30.0, and 35.0%, and these composites were used for baking bread. Ca-nadian Spring Wheat 2 was selected for its high protein content, high development and stability time that waxy wheat line could not achieve (Table 1). Canadian Spring Wheat 2, Yangmai 158 and waxy wheat were milled with Buhler (Buller Wuxi Machinery Manufacturing Co., Ltd., Wuxi, China). In contrast with blends of waxy wheat flour, Jinxiang, a first-rate commercial flour in breadbaking made in Hong Kong was used in this experiment.Analysis of flour characteristicsThe moisture and protein content, Zeleny sedimentation, and wheat gluten of the flours were determined using Approved Method 44-15A, 46-13, 56-60, and 38-12A (AACC 2000), respectively. Amylose and total starch contents were measured according to Approved Method 61-03 and 76-13 of AACC (AACC 2000), respectively. Damaged starch content was determined according to AACC Approved Method 76-30A (AACC 2000). Rheological properties of the flour doughs were de-termined with the Brabender farinograph and extensograph (BRABENDER GmbH & Co. KG, Detmold, Germany) according to AACC Approved Method 54-21 and 54-10 (AACC 2000), respectively. Starch paste viscosity was measured using the mi-cro-visco-amylograph of Brabender 803201, (BRABENDER GmbH & Co. KG, Detmold, Germany). Flour (15 g, 14% mb) was dispersed in 100 mL of wa-ter and heated in the micro-visico-amylograph bowl from 30 to 93°C at a rate of 5.5°C min-1, with consistent stir-ring by rotating the bowl at 250 r/min. The paste was held for 1 min at 93°C and cooled to 50°C at a rate of 5.5°C min-1, and held for 1 min at 50°C.Breadbaking proceduresAll samples were mixed to optimum development until a thin membrane was formed and could be seen when stretched. The water added to form optimum dough was according to water absorption of flour obtained on the farinograph. The baking formula (flour basis) was flour (14% mb) 100.0 g, sugar 6.0 g, salt 1.5 g, short-ening 3.0 g, vacuum-packed yeast 1.6 g, defatted milk powder 4.0 g. A three-step punching procedure was adopted using 55-25-10 min of fermentation. All doughs were proofed at 30°C for 55 min at 85% rh before baking.Table 1 Proportions of three wheat flours in blends (14% mb)Genotype Proportion in wheat flour blends (%)Waxy wheat0.0 5.010.015.020.025.030.035.0 Canadian Spring Wheat 241.344.447.550.753.856.960.163.2 Yangmai 15858.750.642.534.326.218.19.9 1.8404QIN Peng et al.Dough pieces were baked at 225°C for 15 min. Fresh bread loaves were tested for cooling 60 min, and stale bread loaves were tested 2, 4 and 6 days after baking.Bread quality evaluationsThe volume of each loaf was measured by rapeseed displacement 60 min after bread was removed from oven. Crust, shape, crumb color, crumb smoothness,crumb texture, crumb elasticity, and taste were scored by five experts in baking, with the best scores of 5, 5,5, 10, 25, 10, and 5, respectively. The best score of loaf volume was 35 (>860 mL). For the staling study,the loaves were placed in Ziploc bags, stored at room temperature (20-22°C), and evaluated for firmness and the losses of weight and loaf volume after 0, 2, 4 and 6days. The central slices from each loaf were used to determine firmness with a stable micro systems tex-ture analyzer (TA. XT. Plus, Stable Micro Systems Ltd.,Surrey, England) according to Approved Method 74-09 (AACC 2000). The losses of bread weight and loaf volume during storage were measured by a balance (0.01 g) and a rapeseed displacement.Statistical analysesAll experiments were performed in 2 times for each sample. Analysis of variance, correlation, stepwise regression, regression equation and fitted curve were performed using the Statistical Analysis System 9.0(SAS 9.0). Significance was defined at P <0.05.RESULTSPhysicochemical properties floursThe physicochemical properties of three basic wheatsamples used in present experiment were showed in Table 2. Canadian Spring Wheat 2 was selected for its high gluten and protein content, and mixing properties.Waxy wheat flour possess of weak dough mixing prop-erties as indicated by low dough stability to produce bread though its high protein and gluten contents. Only Canadian Spring Wheat 2 blended waxy wheat flour with 0.0-35.0% proportions were too strong to make bread, so Yangmai 158 was used for its mid-stability adjusting blends to appropriate level.Wheat flour blends properties were showed in Table 3. Water absorptions, developments and peak tempera-tures were not different significantly in all waxy flour blends. Stabilities, wet gluten contents, gluten indexes,and protein contents of waxy flour blends were 8.85-17.35 min, 32.90-7.06% (14% mb), 80.82-88.75%,3.06-27.82, 17.10-27.64%, and 12.87-13.74%,respectively. The damaged starch and amylose con-tents (% of starch) were decreased dramatically with the increasing of waxy flours in blends. Farinograph and extensograph data showed that all of these flour blend doughs were strong enough to bread baking, and thus the differences in bread making should most at-tribute to the effect of waxy flour. Jinxiang was excel-lent in physicochemical properties in breadbaking.Bread qualityBread quality scores were displayed in Table 4. With the increasing of waxy flour proportions, crumb smoothness and crumb elasticity were decreased dramatically, whereas no significant differences were detected in crust, crumb color, taste, and shape.Blends with 10.0 and 35.0% waxy wheat flour pos-sessed the largest loaf volumes, and those with 25.0and 30.0% waxy wheat flour showed the least.Crumb structure with 5.0% waxy wheat flour was higher than other proportions. As to total scores,Table 2 Physicochemical properties of three basic wheat flours (14% mb)Water Tolerance Flour Wet Gluten ProteinAmylose Starch Damaged Genotypeabsorption index quality gluten index contentcontent content starch (%) (BU)number content (%)(%)(%)(%, starch)(%)content (%)Waxy wheat line 64.7 a 5.0 b 4.9 c 39.0 a 90.0 c 36.0 b 34.9 b 54.8 c 12.8 b -0.15 b 64.44 c 19.35 b Yangmai 15858.2 c 4.8 b 12.8 b 18.0 b 151.5 b 30.2 c 29.5 c 74.4 b 10.9 c 27.74 a 72.56 a 19.35 b Canadian Spring Wheat 262.5 b11.7 a25.4 a12.0 c323.5 a41.5 a35.8 a94.3 a14.3 a28.14 a68.26 b29.04 aValues followed by different letters in the same column indicate significant difference (P <0.05). The same as below.Development (min)Sedimentation(mL)Stability (min)Effect of Waxy Wheat Flour Blends on the Quality of Fresh and Stale Bread 405there was no significant difference among blends with 0.0-15.0% waxy wheat flour. These results showed that adding waxy wheat flour at appropriate level should not affect the bread total scores, though it decreased the crumb smoothness, crumb texture, and crumb elasticity. Scores of bread made from Jinxiang flour was excellent compared with waxy wheat flour blends, mostly determined by its greater loaf volume.Correlations of bread scores and physico-chemical propertiesCorrelations of bread scores and physicochemical properties were showed in Table 5. Breakdown and setback positively correlated with bread crust,crumb smoothness, crumb elasticity, and totalscores. The increasing of water absorption resulted in the decreasing of loaf volume, but dough devel-opment was positively correlated with loaf volume,shape, crumb elasticity and total scores. Crumb color was affected by dough stability, tolerance in-dex and farinograph quality number. Gluten index was more important than wet gluten to bread scores.With the increasing of gluten index, the scores of loaf volume, shape, crumb smoothness, crumb texture, and crumb elasticity scores were increased.The gluten index was highly positively correlated with total score, so it should mostly determine the bread qualities.Amylose content positively affected on the bread crust, crumb smoothness, crumb texture, crumb elas-ticity and total scores. Since amylose content was de-creased when excessive waxy wheat flour was addedTable 3 Physicochemical properties of waxy flour blends (14% mb)Water absorptionDevelopmentStability Tolerance Flour quality Wet gluten Gluten indexProtein (%)(min)(min)index number content (%)(%)content (%)0.0% waxy 63.70 a 8.10 b 10.2 bcd 23.0 c 145.5 b 32.9 f 88.75 bc 12.9 f 5.0% waxy 64.55 a 7.85 b 9.6 cd 26.0 b 137.0 b 34.8 e 87.50 abc 12.9 de 10.0% waxy 62.85 b 7.60 b 16.8 b 15.5 de 231.5 a 34.8 e 88.79 ab 13.1 d 15.0% waxy 64.55 a 7.10 b 8.9 d 29.0 a 125.0 b 35.4 d 86.42 bc 13.2 cd 20.0% waxy 64.70 a 8.20 b 17.4 ab 13.0 ef 237.0 a 35.5 d 85.21 cd 13.4 c 25.0% waxy 64.50 a 7.70 b 16.7 b 12.5 ef 237.0 a 36.2 c 83.29 de 13.5 bc 30.0% waxy 64.50 a 7.50 b 12.9 c 16.5 d 197.5 a 37.1 b 81.94 ef 13.6 b 35.0% Waxy 64.70 a 7.05 b 11.4 c 18.0 d 188.5 a 36.7 b 80.82 f 13.7 b Jinxiang 64.55 a 9.95 a 17.9 a 12.5 ef225.0 a38.5 a89.91 a 14.8 a Damaged starch Amylose Starch PeakPeakBreakdown Setback content (%)content (%)content (%)temperature (°C)viscosity (BU)(BU)(BU)0.0% waxy 27.8 a 27.6 a 69.97 b 90.10 a 410.5 a 64.5 abc 191.0 a 5.0% waxy 25.0 a 26.1 a 69.88 b 90.20 a 383.5 b 66.0 a 184.5 a 10.0% waxy 20.0 b 24.7 bc 70.04 b 90.15 a 351.5 c 54.0 bcd 180.5 ab 15.0% waxy 15.5 c 23.2 c 69.95 b 90.00 a 332.0 d 49.5 cd 181.0 ab 20.0% waxy 12.5 d 21.7 d 69.87 b 89.75 a 313.0 e 48.0 d 170.0 ab 25.0% waxy 10.3 e 20.1 d 69.78 b 90.95 a 287.0f 56.5 bcd 152.5 bc 30.0% waxy 9.3e 18.5ef 69.44 b 90.60 a 280.5f 55.5 bcd 152.0 bc 35.0% waxy 3.1f 17.1f 69.60 b 91.30 a 258.5 g 32.5 e 138.0 c Jinxiang20.9 b23.9 bc77.87 a91.35 a359.0 c54.5 bcd167.5 abSamples Samples Table 4 Bread properties and evaluation of eating quality from blended wheat flour with waxy wheat flourBread scoresV olume Crust color Appearance Crumb color Smoothness Crumb textureCrumb elasticityTaste Total score 0.0% waxy 782.5 c 29 bc 4.5 a 3.75 a 4.00 a 8.00 a 21.5 b 8.00 ab 4.25 a 83.0 b 5.0% waxy 752.5 d 28 c 4.5 a 4.00 a 3.75 a 7.25 b 23.0 a 7.75 b 4.25 a 82.5 b 10.0% waxy 807.5 b 30 b 4.0 a 4.00 a 4.25 a 7.25 b 22.0 b 7.50 b 4.00 a 83.0 b 15.0% waxy 787.5 c 30 b 4.0 a 3.75 a 4.00 a 7.50 b 21.0 b 5.75 c 4.00 a 80.0 bc 20.0% waxy 780.0 c 30 b 4.0 a 4.00 a 4.25 a 6.50 c 20.0 c 4.00 d 4.25 a 77.0 c 25.0% waxy 757.5 d 28 c 4.0 a 3.75 a 4.00 a 6.50 c 21.0 b 3.75 de 4.50 a 75.5 c 30.0% waxy 762.5 d 28 c 4.0 a 3.75 a 4.00 a 3.75 d 19.5 c 3.25 e 4.25 a 70.5 d 35.0% waxy 797.5 bc 30 a 4.0 a 3.75 a 4.00 a 3.00 e 19.0 c 3.00 e 4.25 a 71.0 d Jinxiang857.5 a35 a4.0 a4.25 a4.25 a8.25 a23.0 a8.75 a4.50 a92.0 aLoaf volume(mL)Samples406QIN Peng et al.to non-waxy ones, bread qualities were decreased ultimately.Resistance, extensibility, maximum resistance, ra-tio number and maximum ratio number of the second and the third times tested during fermentation were more important for bread qualities, all of them posi-tive correlated to the bread total scores, except for the extensibility. Moreover, starch, damage starch,and protein contents positively affected the bread scores.Regression analysis of fresh bread total score and waxy wheat flour proportion in blendsThe effect of waxy wheat flour blends physicochemi-cal properties on total bread score was investigated by regression analysis. Fresh bread total score (Y ) and waxy wheat flour proportion (X ) were fitted for cubic curve (Fig.1), and the regression equation was Y =80.24+82.81X -713.42X 2+1139.39X 3 (R 2=0.98,P =0.001).According to the regression equation, when waxy wheat flour proportion was 7.0% in flour blends, the best score was obtained with 82.9. It indicated that adding lower proportion of waxy wheat flour into non-waxy ones increased bread quality.The stepwise regression analysis suggested that there existed the closest correlation between gluten in-dex (X 1) and energy (90 min) (X 2) values with fresh bread total score, and Y =-55.88+1.38X 1+0.13X 2(R 2=0.99, P =0.000) (Table 6), it indicated that glu-Table 5 Correlation coefficients of bread scores and waxy flour blends propertiesSensory scores of breadV olume Crust color Appearance Crumb color Smoothness Crumb textureCrumb elasticityTaste Total score Development 0.65*0.120.79**0.380.530.620.66*0.540.74*Stability0.60-0.390.560.76**0.250.330.160.420.43Tolerance index-0.530.36-0.370.65*0.03-0.130.01-0.51-0.23Flour quality number 0.47-0.460.380.70*0.000.11-0.060.400.19Gluten index 0.68*0.420.65*0.430.89**0.89**0.92**-0.070.97**Protein content0.80**-0.440.560.530.020.180.090.550.38Damaged starch content -0.080.590.31-0.160.66*0.590.75*-0.090.51Amylose content 0.240.72*0.400.040.88**0.81**0.91**-0.190.77**Starch content 0.94**-0.010.73*0.550.510.64*0.580.410.81**Whiteness -0.25-0.70*-0.22-0.05-0.76*-0.69*-0.69*0.31-0.65*Peak viscosity -0.130.590.27-0.210.600.510.70*-0.120.44Breakdown 0.270.72*0.350.000.64*0.72*0.74*-0.110.66*Setback0.220.63*0.310.090.85**0.72*0.80**-0.390.70*Energy (45 min)0.65*-0.050.67*0.320.410.63*0.610.460.68*Maximum resistance (45 min)0.480.040.64*0.280.500.580.64*0.500.65*Resistance (90 min)0.52-0.050.570.250.610.550.630.260.67*Extensibility (90 min)-0.50-0.01-0.47-0.27-0.68*-0.59-0.69*-0.13-0.70*Maximum resistance (90 min)0.490.040.500.180.73*0.66*0.71*0.070.73*Ratio number (90 min)0.55-0.080.590.280.560.530.610.290.66*Maximum ratio number (90 min)0.55-0.040.540.250.64*0.590.66*0.180.70*Resistance (135 min)0.65*0.030.72*0.400.530.600.66*0.490.73*Extensibility (135min)-0.52-0.02-0.66*-0.32-0.57-0.60-0.66*-0.46-0.69*Maximum resistance (135 min)0.68*0.300.68*0.440.74*0.78**0.85**0.360.89**Ratio (135 min)0.63-0.080.71*0.380.440.510.570.510.65*Maximum ratio (135 min)0.65*0.010.72*0.400.530.600.66*0.490.73**and ** indicate significance at 0.05 and 0.01 probability levels, respectively.Physicochemical characteristicsTable 6 Stepwise regression analysis of bread scores and wheat flour blends physicochemical propertiesDependent variable Independent variableRegression equationR 2F P Total score (Y 1)Y 1=-55.88-1.38X 1+0.13X 20.988282.340.000Crust color (Y 2)Y 2=5.91+0.74X 3+0.19X 4-0.36X 5-0.01X 6+0.001X 71.00017781.850.000Smoothness (Y 3)Y 3=469.15-5.02X 80.79528.220.002Crumb texture (Y 4)Y 4=70.79-3.76X 90.70517.750.006Crumb elasticity (Y 5)Y 5=-28.99+0.48X 10+0.65X 110.95983.480.000Taste (Y 6)Y 6=2.12-1.31X 120.63513.170.011Gluten index (X 1), Energy (90 min) (X 2)Yellowness (b) (X 3), peak temperature (X 4)starch content (X 5), time to breakdown (X 6)peak viscosity (X 7)Whiteness (L) (X 8)Protein content (X 9)Amylose content (X 10), sedimentation (X 11)Redness (a) (X 12)Effect of Waxy Wheat Flour Blends on the Quality of Fresh and Stale Bread 407ten index and energy (90 min) mostly affected quality of bread.Influence of waxy flour blend on staling bread was showed in Table 6. The effect of addition of waxy flour on bread firmness was not significantly different among all samples baked 1 h later. The crumb firm-ness was increased during storing. Wheat flour blends with 0.0, 5.0, and 35.0% waxy flour possessed the highest firmness after storing for 6 days, but there was no significant difference among blends with 10.0-30.0%waxy wheat flour and Jinxiang. The loss of loaf vol-ume with 35.0% waxy wheat flour was the highest,whereas that with 25.0 and 30.0% was the lowest. No significant difference was found in the loss of loaf vol-ume during storing when waxy wheat flour was less than 20.0%.Firmnesses of bread made from waxy wheat flour with different proportions storing for 6 d were showed in Fig.2. Firmness of bread (Y ) and waxy wheat flour proportion (X ) were fitted for cubic curve, and the re-gression equation was Y =6.67-14.78X -23.07X 2+171.52X 3 (R 2=0.86,P =0.03). According to the re-gression equation, when waxy wheat flour proportion was 22.0% in blends, the lowest firmness was obtained with 4.13 g.Weight loss of bread with different waxy wheat flour proportion were fit for a linear equation (Fig.3)(Y =3.66-2.37X ,R 2=0.55,P =0.04). Weight loss of bread was decreased with increasing of waxy wheat flour proportion in blends. These results indicated that adding of 22.0% waxy wheat flour in blends shouldretard the bread shelf life at the furthest.Fig. 1 Regression analysis of bread total score and waxy wheat flour proportion in blends.Fig.2 Regression analysis of bread firmness and proportion ofwaxy wheat flour during storing.Fig. 3 Regression analysis of weight loss and proportion of waxy wheat flour during storing.DISCUSSIONSome previous studies paid a lot attention to the effect of waxy wheat flour proportion in bread quality, but ignored the final physiochemical properties of waxy wheat flour blends, so the result might not show the408QIN Peng et al.true effect of waxy wheat flour on fresh and stale qual-ity of bread, and the conclusion drew from their stud-ies may be iffy. In the present study, physicochemical properties of waxy wheat flour blends were adjusted to the identical level for breadbaking, so the result could better show the effect of waxy wheat flour on the qual-ity of fresh and stale bread.The high water absorption, protein content and weak rheological properties were obtained in waxy wheat flour. Adding waxy wheat flour to Canadian Spring Wheat 2, and the final physiochemical properties were adjusted to approximate levels with Yangmai 158 for breadmaking.Adding waxy wheat flour with appropriate propor-tions (such as within 15.0% in this study) should not decrease the total score of fresh bread, though crumb texture, crumb smoothness and crumb elasticity de-creased slightly. However, superfluous waxy flour re-sulted the increasing of amylopectin content, its con-sistency decreases during heating course, the structure stability of waxy wheat flour blends bread reduce, and this resulted in the decreased bread crumb texture, crumb elasticity and taste. Instead, adding 7.0% waxy wheat flour had the potential of increasing fresh bread quality for increasing the bread loaf volume. Incorporation of waxy flour resulted in the signifi-cant decrease of crumb firmness during storing. Blends with 25.0-30.0% waxy wheat flour were most effec-tive in reducing the increase of the crumb firmness and weight loss of bread, though the fresh bread qualities were decreased compared with the control with 0.0% waxy wheat flour. The blends with 22.0% waxy wheat flour effectively retarded the shelf life of bread for the lowest firmness and the lower weight loss after 6 days’storing. Because the addition of 0.0-15.0% waxy wheat flour to non-waxy ones did not decrease the fresh bread total scores significantly, and decreased the firmness and weight losses effectively, appropriate proportions of waxy wheat such as 15.0% of waxy wheat flour blend was optimal in retarding staling without decreas-ing bread qualities compared with the control. These results suggested that adding the waxy flour with ap-propriate proportions could increase the shelf life with-out decreasing the quality of fresh bread, and it was possible to partly use waxy flour in bread baking in the future.AcknowledgementsThis work was supported by the National High Tech-nology Research and Development Program of China (863 Program, 2001AA241033 and 2006AA100102) and Yunnan Provincial Education Department Scientific Research Program, China (08Y0166). We wish to thank Prof. Zhang Boqiao, Dr. Gao Derong, Zhang Yong, Lu Guofeng, Wu Hongya, Lu Chengbin, from Lixiahe Re-gion Agricultural Research Institute of Jiangsu Province, China, and Prof. Tian Jichun, from Shandong Agricul-tural University, China, for their assistance in conduct-ing the experiment.ReferencesAbdel-Aal E S M, Hucl P, Chibbar R N, Han H L, Demeke T.2002. Physicochemical and structural characteristics of flours and starches from waxy and nonwaxy wheats. Cereal Chemistry,79, 458-464.American Association of Cereal Chemists (AACC). 2000. AACC International Approved Methods. 10th ed.Baik B K, Lee M R. 2003. Effects of starch amylose content of wheat on textural properties of white salted noodles. Cereal Chemistry,80, 304-309.Baik B K, Park C S, Paszczynska B, Konzak C F. 2003.Characteristics of noodles and bread prepared from doublenull partial waxy wheat. Cereal Chemistry,80, 627-633. Bhattacharya M, Erazo C S V, Doehlert D C. 2002. 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