Dough rheology and bread quality of supplemented flours

Reologıa de la masa y calidad del pan de harinas suplementadas

Antonietta Baianoa,b* and Carmela Terraconea

aDepartment of Food Science, University of Foggia, via Napoli, 25–71100 Foggia, Italy; bIstituto per la Ricerca e le ApplicazioniBiotecnologiche per la Sicurezza e la Valorizzazione dei Prodotti Tipici e di Qualita, via Napoli, 25–71100 Foggia, Italy

(Received 3 March 2010; final version received 18 June 2010)

A commercial flour was alternatively supplemented with five enzymatic and two chemical additives. Two levels ofaddition were considered. The effects of additives on dough behavior and bread quality depended on the type ofpromoted biochemical reaction and, in some cases, were dose-dependent. Deformation energy (W) proved to be thebest single predictor of the specific volume (SV) (R ¼ 0.847) whereas the height/width ratio (HW) was betterpredicted by dough development time (DDT) (R ¼ 70.619). The application of response surface regressionfollowed by stepwise regression allowed to write two equations. The SV was greatly and positively affected by W,DDT, E (extensibility) and resistance to extensibility (R). Observed and predicted values were highlycorrelated (R ¼ 0.931). The model did not allow to generalize the positive dependence of the HW ratio of thecentral slice on W and softening, although predicted and observed values correlated together at middle strong level(R ¼ 0.704).

Keywords: bread specific volume; bread-making improvers; dough rheology; flour; height/width ratio; qualityprediction

Una harina comercial se suplemento con cinco aditivos enzimaticos y dos quımicos. Se consideraron dos niveles deadicion. Los efectos de aditivos en el comportamiento de masa y calidad de pan dependieron del tipo de reaccionbioquımica estimulada y, en algunos casos, fueron dosis dependientes. La energıa de deformacion (W) demostro serel mejor pronosticador de volumen especıfico (R ¼ 0,847), mientras el tiempo de desarrollo de masa (R ¼ 70,619)predijo mejor el ındice de altura/anchura. La aplicacion de regresion de superficie de respuesta seguida de unaregresion progresiva permitio escribir dos ecuaciones. El volumen especıfico fue mayor y positivamente afectado porW, tiempo de desarrollo de la masa, E (extensibilidad) y Resistencia a extensibilidad (R). Los valores observados ypronosticados resultaron altamente similares (R ¼ 0,931). El modelo no permitio la generalizacion de dependenciapositiva del ındice de altura/anchura de la rebanada central en W y suavidad, aunque los valores observados ypronosticados coincidieron en el nivel medio fuerte (R ¼ 0,704).

Palabras clave: volumen especıfico de pan; mejorante para la elaboracion pan; reologıa de la masa; harina; ındice dealtura/anchura; prediccion de calidad

Introduction

Bread is defined as a food made from flour or mealmixed with other dry and liquid ingredients, sometimescombined with a leavening agent, kneaded, shaped intoloaves and baked. Soft wheat flour is one of the mostlargely used flour in breadmaking as it is supplied withproteins such as prolamins and glutelins, respectivelyresponsible for viscosity-extensibility and elasticity ofthe dough matrix and of its ability to retain gasproduced during fermentation (Courtin & Delcour,2002).

The increasing mechanization of the baking in-dustry and the demand for a wide range of bread typeshave determined the necessity to modulate structureand viscoelastic properties of doughs. In order toimprove bread-making performance, chemical

compounds and enzymes are usually included in breadformulas (Dunnewing, van Vliet, & Orsel, 2002).These additions allow to pursue a variety of goalsincluding the obtainment of fermentable sugars, theimprovement of workability and loaf volume, theincrease of dough strength and the reduction ofretrogradation and crumb firmness. Additives for theproduction of bread of consistent quality with a longshelf life include emulsifiers, enzymes, reductants andantioxidants.

Emulsifiers allow to obtain stable dough beforebaking and prevent its collapse if subjected tovibrations, other mechanical strain or too long restingtime since the gas produced by the yeast during theproofing process is maintained inside the dough.DATEM (diacetyl tartaric esters of mono-glycerides)

*Corresponding author. Email: a.baiano@unifg.it

CyTA – Journal of FoodVol. 9, No. 3, November 2011, 180–186

ISSN 1947-6337 print/ISSN 1947-6345 online

� 2011 Taylor & Francis

DOI: 10.1080/19476337.2010.504885

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emulsifiers and lecithin can strengthen the wheat glutendue to its specific structure. They improve gas retentionand dough stability and provides for the requiredkneading and proofing tolerance and resistance againstmechanical shear. Emulsifiers also include monogly-cerides that are used for improving the crumb softness,the tenderness, and the fresh-keeping properties there-by preventing bread staling.

In recent years, the treatments with enzymes hasbeen preferred to the addition of chemical improvers asthey do not remain active in the final product and,therefore, do not have to appear on the label(Caballero, Gomez, & Rosell, 2007a).

Bread-making improvers can be classified in groupssuch as cross-linking enzymes and oxidants, polysac-charides and gluten degrading enzymes (Stojceska &Ainsworth, 2008). Gluten cross-linking enzymes im-prove the ability of dough to entrap gas and the breadcrumb texture and volume promoting the formation ofcovalent bonds between polypeptide chains (Gujral &Rosell, 2004) through mechanisms such as oxidativecoupling of thiols, cross-link of tyrosine residuesmediated by hydrogen peroxide and acyltransfersbetween aminoacid residues (Gerrard, 2002). Whenadded to a dough, oxidant enzymes such as hexoseoxidases induce the formation of disulphide bridgesbetween proteins and the gelation of pentosans,increasing dough strength and bread volume(Poulsen & Hostrup, 1998). Amylases, pentosanases,xylanases are hydrolytic enzymes able to changephysicochemical and structural properties of polysac-charides, making dough softer and viscous andincreasing the availability of fermentable sugars.a-amylase prolongs oven rise and results in anincreased loaf volume. Polysaccharides degradingenzymes are used also for their contribution to freshquality enhancement and staling prevention(Caballero, Gomez, & Rosell, 2007b). Gluten degrad-ing enzymes (protease) are sometimes used in bread-making formulation in order to avoid an excessiveincrease in dough tenacity due to the addition of glutencross-linking enzymes (Caballero et al., 2007a).

An increase in loaf volume and an improvement ofbread crumb structure can be pursued with theaddition of ascorbic acid that acts on the redox systemsof a wheat dough. In particular, the improver action ofthe ascorbic acid is due to its oxidation by gaseousoxygen to dehydroascorbic acid which determines therapid oxidation of glutathione present in flour thusminimizing the SH/SS interchange reactions of reducedglutathione with intermolecular SS bonds of glutenmolecules. These interchange reactions would depoly-merise gluten proteins and weaken the dough(Grosch & Wieser, 1999).

In the present study, the authors tested severalenzymatic and chemical bread-making improvers andevaluated their effects on dough rheology and breadquality of supplemented soft wheat flour.

Materials and methods

Raw materials

A commercial Italian soft wheat flour usually employedin bread-making was used. Its composition on wet basiswas: proteins 114.6 g kg71 (nitrogen to protein conver-sion factors 5.81), water 138.0 g kg71, ash 5.2 g kg71.

Enzymatic and chemical bread-making improverswere tested at two different levels of addition chosen onthe basis of preliminary tests and included in the rangesusually applied in bakery industry. The five commercialenzymes were: an a-amylase (5 and 15 mg kg71; 4150units g71; BakeZyme P 180 BG, DSM, The Nether-lands); a synergistic blend of xylanase and amylase (20and 100 mg kg71; 60 units g71; Fungamyl Super AX,Novozymes, Bagsvaerd, Denmark); a cellulase (80 and180 mg kg71; 3500 units g71; Celluclast, Novozymes,Bagsvaerd, Denmark); an hemicellulase (40 and 80 mgkg71; Panlyve HCB-5, Panlyven, France); a glucoseoxidase (15 and 40 mg kg71; 7500 units g71; M 300 B4,Millbo, Trecate, Italy).

The two commercial chemical improvers includedascorbic acid (60 and 120 mg kg71; E300, DSM, TheNetherlands) and a deactivated yeast rich in glu-tathione (10 and 30 g kg71; ERV HA41, DSM, TheNetherlands).

Dough preparation and bread-making procedure

Fifteen types of dough were produced: a control (C),made of 400 g of flour, 220.8 g of water (29 + 18C),8 g of sodium chloride and 4 g of active driedSaccharomyces cerevisiae; 14 formulations, each ofthem made with the same ingredients of the control(the dough water moisture was adjusted on the basis ofthe farinographic water absorption) and the furtheraddition of one of the seven bread-making improversat two different concentrations.

Doughs were produced at least in triplicate. Breadswere prepared according to the procedure described inthe AACC method 10–10B (2000). Dough was mixedin a spiral mixer (FA.M.A.G. srl, Messina, Italy) for15 min. At the end of mixing, the dough was placed ina proofing cabinet (JUNIORLEV, Castel MAC SpA,Treviso, Italy) for 60 min at 308C (80% moisture) forleavening; subsequently dough was flattened, foldedand replaced in the proofing cabinet. Then, it wasflattened again and shaped in loaves of 600 g andplaced in moulds for 45 min. Baking was carried out ina ventilated oven with steam injection at the beginningof baking (CIMAV-Verona, Italy) at 2208C for 30 min.Loaves were removed from the moulds and cooled for2 h at room temperature before analysis.

Analyses

The a-amylase activity was determined according tothe AACC Falling Number Method 56–81 method

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(1999) through a Falling Number apparatus (1500 s/n067182, Roma, Italy). The a-amylase activity isinversely correlated to the falling number thus a lowa-amylase activity corresponds to a high value of thisparameter.

Farinograph tests (water absorption, %; develop-ment time or DDT, min; softening index, BrabenderUnits or B.U.; stability, min) of doughs were per-formed through a Farinograph E (Brabender, Duis-burg, Germany) according to the AACC method 54–21(1995).

Alveograph tests were carried out in an AlveographNG (Villeneuve La Garenne Cedex, France) accordingto the AACC Method 54–30 (2000). The followingparameters were determined: tenacity (P, elasticity orresistance to extension), dough extensibility (L), thedeformation energy (W) and the curve configurationratio (P/L).

Concerning extensograph tests, flour strength (alsoknown as dough energy, expressed as cm2), maximumresistance to extensibility (R, expressed as Extenso-graphic Units, E.U.), extensibility (E, expressed as mm)and R/E ratio of doughs were tested using a Brabenderextensograph E (Duisburg, Germany) according to theAACC Method 54–10 (1995). After mixing in theFarinograph, each dough was divided into three pieces(150 g/piece) and proofed in a humidity chamber at308C. After 45, 90 and 135 min of proofing, one piecewas stretched until it breaks. The results were recordedon extensograms.

Quality analysis of fresh bread samples was carriedout by measuring, for each loaf, volume and the height/width ratio (HW) of the central slice. The loaf volumewas obtained by rapeseed displacement according tothe AACC Method 10–05 (2000).

Statistical analysis

Analyses were generally repeated at least three times.The averages and the standard deviations werecalculated using Excel software version 11.5.1 (Micro-soft, Redmond, USA). The Principal ComponentAnalysis (PCA), the analysis of variance (ANOVA)and the Duncan test (p 5 0.05) were performed usingthe software Winstat version 5.1 (Statsoft, Tulsa,USA). In order to determine the best single predictorsof the specific volume (SV) and the HW ratio, simplecorrelations analyses were performed between doughrheological parameters and bread quality indices andthe relative correlation coefficients (R), significancelevels (p) and standard errors (SE) were reported.Statistical methods were also employed to determine ifthe quality characteristics (SV and HW ratio) ofsupplemented breads could be predicted by the use ofan algorithm incorporating the dough rheologicalparameters. Models were calculated by means ofresponse surface regression at first to test accuracy ofprediction, and by means of stepwise regression to find

the best subgroup of tested variables with the highestmultiple determination coefficient (R2 adjusted). Bothstatistics were calculated on p 5 0.05 using the soft-ware Winstat version 5.1 (Statsoft, Tulsa, USA).

Results and discussion

a-amylase activity and rheological properties of controland supplemented doughs

A certain a-amylase activity is desirable in flour sincethis enzyme is able to hydrolyze damaged raw starchacting upon interior portions of the starch moleculesand, thus, allowing the activity of the b-amylase. Thesehydrolysis reactions result in the production of maltosemolecules and other fermentable sugars that representa source of energy for yeasts involved in fermentation.Nevertheless, they are also responsible for severalchanges in dough properties including decrease of theabsorption capacity, slackening of dough consistencyand development of a stickier dough. The rate at whichthese changes occur is directly proportional to theamount of starch damage and a-amylase level of theflour. Bread flours with normal diastatic activity havefalling number values in the range from 220 to 250 s.Flours deficient in diastatic activity have values higherthan 400 s whereas over supplemented flours or flourmilled from sprout damaged wheat can show values upto 60 s.

The falling number values of the control and thesupplemented flours are reported in SupplementaryTable 1. Most of the samples showed a deficientdiastatic activity since their falling number valueswere included within the range 326–355 s. The excep-tions were represented by the a-amylase-supplementedflours, which showed mean values included in the rangeof the normal diastatic activity and significantly lowerthan those of the other samples (266 and 230 scorresponding to the addition of 5 and 15 mg kg71 ofthe enzyme, respectively). The addition of the blendxylanase–amylase did not determine reduction of thefalling number due to the counterbalancing effect of thefirst enzyme that is responsible for the hydrolysis of theb-xylan bounds, forming oligomers with diverse mole-cular mass, and responsible for the liberation of water,which becomes available to gluten (Bordei, 2005).According to literature (Satin, 1998; Defloor, De Geest,Schellekens, Martens, & Delcour, 1991; Khalil, Man-sour, & Dawoud, 2000), a high falling number iscorrelated with a high dough viscosity and, conse-quently, with a high bread firmness.

Among the farinograph parameters (SupplementaryTable 1), the water absorption percentage was posi-tively and significantly affected by the incorporation ofglucose oxidase into the flour but without differencesbetween the two levels of addition. Glucose oxidasecatalyses the oxidation of b-D-glucose to gluconic acidand hydrogen peroxide. The mechanism by which thisenzyme improves bread quality is still not completely

182 A. Baiano and C. Terracone

understood. Nevertheless, it has been found thathydrogen peroxide induces the oxidative gelation ofwater soluble pentosans (Gujral & Rosell, 2004) and agreater water sequestration (Bettge & Morris, 2007)that should explain the increase in water absorption.This hypothesis is coherent with the results obtained byVemulapalli, Miller, and Hoseney (1998) who observedthe drying effect exerted by glucose oxidase on dough,attributing it to the gel formation of water solublepentosans. Water absorption was negatively affected bythe supplementation with the powerful reducing agentglutathione since this tripeptide reduces the molecularweight of glutenin polymers by SH/SS interchangereactions (Joye, Lagrain, & Delcour, 2009) and conse-quently determines the water release. The addition ofa-amylase to flour significantly decreased dough devel-opment time (DDT) in accordance with the resultsreported previously (Hyun Kim, Maeda, & Morita,2006; Maeda, Hashimoto, Minoda, Tamagawa, &Morita, 2003). This tendency could be attributed toweakening of mixed doughs caused by the presence of alow molecular weight dextrins produced from damagedstarches by amylase hydrolysis. The DDT was alsodecreased by addition of cellulase due to the partialdegradation of cellulose to liberate oligosaccharidesand glucose. Reduction of DDT was detected on doughsupplemented with the highest level of xylanase–amylase blend and ascorbic acid or with the lowestlevel of glucose oxidase. Glutathione decreased DDTwhen added at the lowest level. On the contrary, DDTwas increased when glutathione was added at thehighest concentration. The reason of these oppositebehaviors should be found in the different redoxpotentials established into the dough systems depend-ing on the simultaneous presence and concentration ofsubstances that can possess oxidising or reducingproperties. All improvers tested increased the softeningindex, except for glucose oxidase. This oxidizing agentis not specific but acts on gluten thiols, glutathione or,also, ascorbic acid, resulting in prevention of doughsoftening through the transformation of thiol groupsinto disulphide bonds. The highest softening valueswere detected on dough supplemented with glutathione,cellulase, and xylanase–amylase blend at the highestlevels of addition. Glucose oxidase added at the highestconcentration was also the only additive able toincrease dough stability. The lowest stability timeswere measured on doughs supplemented with a-amylase, ascorbic acid and xylanase–amylase blend.Concerning ascorbic acid, this could seem an anom-alous result since the already explained effects of thisacid on SH/SS interchanges. Nevertheless, ascorbic acidfunctions as an oxidizing agent only in presence ofsufficient amounts of oxygen otherwise it cannot beconverted in dehydroascorbic acid and, in its reducedform, breaks gluten disulfide bonds (Hruskova &Novotna, 2003). The result obtained through additionof xylanase–amylase blend could be explained with the

loss of dough tenacity and the production of a stickydough.

Concerning alveograph parameters (SupplementaryTable 2), supplementation with deactivated yeast cellsrich in glutathione caused significant decreases in bothdeformation energy (W) and tenacity (P) and significantincreases in extensibility (L) with respect to the control.The larger W and P changes occurred into samplesadded with glutathione at the highest concentration.These results were to be expected since glutathionebehaves as a reducing agent and is able to cause rupturesof disulfide cross-links by SH/SS interchanges (Grosch& Wieser, 1999), thus reducing the mean molecularweight of glutenins and inducing changes in the glutenstructure and in the balance between viscous and elasticproperties (G0 decreases more rapidly thanG00) (Berland& Launay, 1995). The addition of both an oxidativeenzyme, such as glucose oxidase and the ascorbic aciddetermined the opposite effect. The strengtheningaction of glucose oxidase (especially at the highestconcentration) was related to the hydrogen peroxideproduced during reaction that promoted the formationof disulphide linkages in gluten protein (Poulsen &Hostrup, 1998). The mechanism proposed for theimprover action of the ascorbic acid (L-threo-ascorbicacid, in particular) is based on the assumption that thedehydroascorbic acid formed inhibits the cleavage ofthe intermolecular SS bonds of gluten proteins thathappens in presence of reduced glutathione (Grosch &Wieser, 1999). The rate of L-threo-ascorbic acid oxida-tion in dough depends on the amount of oxygenkneaded into dough. The results reported in Supple-mentary Table 2 highlight that the amount of ascorbicacid added to the flour significantly influenced L and P/L parameters whereas no significant differences wereregistered for W and P between the two concentrationstested. The effects of polysaccharides degrading en-zymes on the alveograph parameters were lower thanthose of the additives that act on gluten surely due to thegreater influence of gluten network on dough rheology.The addition of cellulase, hemicellulase and thexylanase–amylase blend induced significant and con-sistent decreases in tenacity and P/L ratio. In fact, thepresence of polysaccharides deriving from outer layersof grain, pericarp and aleurone layer negativelyinfluences the gluten properties by changing the waterdistribution in the dough and also by having covalentinteractions with gluten. Such enzymes are able toimprove the rheological properties of dough bydegrading and solubilizing the polysaccharides thusallowing the water redistribution and the reduction ofthe interference of polysaccharide chains on the cellarchitecture (Baiano, Romaniello, Lamacchia, & LaNotte, 2009).

The extensograph data (Supplementary Table 3)are mainly useful in studying changes of flour strength,an important parameter correlated with bread quality.Maforimbo, Skurray, Uthayakumaran, and Wrigley

CyTA – Journal of Food 183

(2006) found that a decrease in resistance to extensi-bility explain the difficulties in breadmaking. Never-theless, the test still remains very empirical, althoughseveral efforts have been made (Bloksma, 1962) torelate the data obtained by this test to more funda-mental parameters. Glutathione significantly reducedflour energy and resistance to extensibility. Glucoseoxidase and ascorbic acid showed the opposite effect,increasing flour energy and resistance to extensibilityand reducing extensibility. Concerning flour strength,cellulase and hemicellulase showed dose-dependenteffects. The addition of the lower levels of cellulaseand hemicellulase left the flour strength almost un-changed. Cellulase at the higher level determined asignificant decrease in strength whereas the higher levelof hemicellulase caused its significant increase.

Bread quality of control and supplemented doughs

All additives influenced significantly (p 5 0.05) thebread SV (Supplementary Figure 1). The addition ofdeactivated yeast rich in glutathione produced con-siderable decrease of SV due to the dough weakeningand the coalescence of small gas cells in larger cellsduring proofing. The other additives allowed to obtainloaves having higher SV than the unsupplementedones. The greatest volume was measured on breadloaves from flour supplemented with 180 mg kg71 ofcellulase. As the consequence of the hydrolytic actionof this and other polysaccharide degrading enzymes,some free sugars such pentoses and hexoses can bereleased and fermented by the microorganisms (Marti-nez-Anaya, Devesa, Andreu, Escriva, & Collar, 1999).

HW ratio is included among parameters necessaryfor the evaluation of the baking product quality. In factit is an index of the proofing behavior (the better isproofing, the higher is this ratio) and, consequently, ofthe loaf shape. The HW ratio (Supplementary Table 4)was increased by addition of cellulase and ascorbic acidindependently on concentration. Concerning the otherimprovers, the effect was dose-dependent. In fact, theaddition of the lowest amount of a-amylase and of thehighest amounts of xylanase–amylase blend and hemi-cellulase caused increases of HW ratio. Instead, the HWratio was decreased by addition of xylanase–amylaseblend at the lowest concentration and by the highestamount of deactivated yeast rich in glutathione.

Relationship between rheological properties and breadquality parameters of control and supplemented doughs

The PCA was applied to dough rheological parameters(Supplementary Figure 2) in order to provide knowl-edge about the existence of relationships amongproperties and to reach a preliminary definition ofgroups of parameters that can characterize anddiscriminate between dough samples. The first twoprincipal components (PC1 and PC2) accounted for

75.55% of the variance (58.44 and 17.06%, respec-tively). High relationships were shown within each ofthe following three groups of rheological parameters:alveograph W, P, P/L, farinograph water absorption,and extensograph flour strength, R, R/E; a-amylaseactivity and farinograph DDT and stability; alveo-graph L, farinograph softening index, and extenso-graph E. On the basis of their rheological properties, itwas possible to discriminate the following groups ofsamples: one group including doughs supplemented withascorbic acid 60 and 120 mg kg71 (clearly characterizedby the highest values of P, P/L, R and R/E); one groupincluding doughs supplemented with a-amylase 5 and15 mg kg71; another group made of control and doughssupplemented with hemicellulase 40 mg kg71, xylanase–amylase blend 20 mg kg71, hemicellulase 80 mg kg71.The other supplemented doughs were clearly separatedon the plane of the principal components 1 and 2.Doughs supplemented with cellulase 180 mg kg71 werecharacterized by the highest values of softening, L and E.On the basis of these results, the effects of the addition ofa-amylase or ascorbic acid on the whole set of therheological parameters were independent on theirconcentration whereas the other improvers showeddose-dependent effects.

Because the dough characteristics are known toinfluence the quality of bakery products, it wasreasonable to expect that these rheological parameterswould be correlated with measurable characteristics ofthe final product.

First of all, simple correlations between doughrheological parameters and quality characteristics ofsupplemented breads were tested and the results arepresented in Supplementary Table 5. According to thesedata, various alveograph, farinograph and extenso-graph parameters influenced the SV of supplementedbreads. The alveograph parameters W, P and P/L werefound to be positively and significantly correlated to theSV whereas no significant correlations were foundbetween L and the SV. According to previous works(Shogren, Finney, Bolte, & Hoseney, 1963; Shogren,Finney, Hoseney, & Bolte, 1963), L is an importantpredictor of loaf volume in bread from USA wheatflours since additional extensibility is required tomoderate their high elasticity (P) and prevent the crumbchewiness. Instead, W is the best single predictor inbread from European flours (Faridi & Rasper, 1987)since the latter have lower P values and, thus, a betterbalance between elasticity and extensibility. Accordingto Junqueira, Rocha, Moreira, and Castro (2007),wheat flour strength has a great effect also on volumeof French breads and increases in volume are oftenpositively correlated to flour strength and tenacity(Gomez, Oliete, Caballero, Ronda, & Blanco, 2008;Jai Pal Singh Sidhu & Bawa, 2002). In fact, flourstrength is a measure of the gluten quality whereastenacity is a predictor of the ability of the dough toretain gas. Among farinograph indices, the water

184 A. Baiano and C. Terracone

absorption was positively correlated to the SVs sinceevaporation of water absorbed in dough at kneadingstage supports bread volume increase (Svec & Hrusko-va, 2009) whereas a negative correlation was foundbetween the DDT and the SV. Both the extensographflour strength and R were positively correlated to theSV, accordance with the finding of Nash et al. (2007).Among the rheological properties studied, W waspositive correlated to the HW ratio of loaves whereasthe DDT showed a good but negative correlation to it.Concerning the DDT, these results were opposite tothose obtained by Uhlen et al. (2004) that found a highbut positive correlation of this index to both the volume(R ¼ 0.89) and HW ratio of the loaf (R ¼ 0.90) ofhearth bread. Nevertheless, Uhlen et al. (2004) used abaking system different from that applied in the presentresearch and this thing could explain the different resultsobtained by the two groups of researchers. On the basisof correlation coefficient, probability level and standarderror, the best single predictor of the SVwas representedby the alveograph parameter W whereas the HW ratiowas better predicted by the DDT. DDT was negativelycorrelated to the HW ratio. It could be supposed thatthe longer was the DDT (the time necessary to reach theoptimal consistency of 500 B.U.), the lower was theelasticity and cohesiveness of dough, thus giving rise toless leavened loaves. The farinograph softening indexand stability were not suitable to predict neither the SVsnor the HW ratio since those indices are greatly affectedby the presence of large molecules able to bind water.

For prediction of bread SV and HW ratio, theapplication of response surface regression followed bystepwise regression allowed to write the following twofinal equations:

(1) SV ¼ 21.26945 þ 0.816476Wþ 0.003436 E2

þ 0.06898 6 R 6 DDT, with a rate of exp-lained variability R2

adjusted ¼ 0.830.(2) HW ¼ 0.520903 þ 0.000009 6 W 6 softening,

with a rate of explained variability R2adjusted ¼

0.457.

According to the high R2adjusted value, the SV of

supplemented breads was greatly affected by alveo-graph W, farinograph DDT and extensograph E and Rparameters. Observed and predicted values were highlycorrelated (R ¼ 0.931) regardless the high standarderror (14.209). On the basis of the low R2

adjusted value,the model did not allow to generalize the dependenceof HW ratio on the selected rheological properties,although predicted and observed values correlatedtogether at middle strong level and with a low standarderror (R ¼ 0.704, SE 0.034).

Conclusions

The addition of bread-making improvers can be usedin order to modify dough rheological behavior and

bread quality characteristics. Parameters correlated todough strength and elasticity were increased by glucoseoxidase and ascorbic acid. With the exception of glucoseoxidase, all the additives increased softening index anddecrease stability. The negative effect of ascorbic acid onfarinograph softening index and stability was notobserved neither on alveogram nor on extensographparameters. This absence of correlation between farino-graph softening and alveograph or extensograph strengthindices could be explained by the statement that the firstdescribe the dough behavior during kneading whereas thelatter are a measure of the behavior of a dough submittedto a stress like the proofing is.

Bread SV and HW ratio was significantly affectedby individual enzyme addition. The addition ofdeactivated yeast rich in glutathione decreased SV of16–22% whereas the other additives allowed toobtained loaves with higher SV than control. Thebest performances were obtained through addition of180 mg kg71 of cellulase that allowed to increase thebread SV of about 21% and the HW ratio of 16% withrespect to the unsupplemented formulation. On thecontrary, the addition of deactivated yeast rich inglutathione gave the worst results.

Some dough rheological properties can be used aspredictors of bread quality characteristics and thisability could be used to modify dough formulationsdepending on the characteristics desired in bread finalproducts. In particular, the alveograph parameter Wand the farinograph DDT were proved to be the bestsingle predictor of SV and HW ratio, respectively,whereas the application of response surface regressionfollowed by stepwise regression allowed to establishthat the SV of supplemented breads was positivelyaffected by W, DDT, E and R whereas the HW ratiopositively depended on W and softening.

Supplementary material

The supplementary material for this article is availableonline at http://dx.doi.org/10.1080/19476337.2010.504885

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