Usage of enzymes in a novel baking process

Semin �zge Keskin, G�l�m Sumnu and Serpil Sahin

1 Introduction

Halogen lamp-microwave combination heating is a new tech-nology that combines the time-saving advantage of microwaveheating with the browning and crisping advantages of halogenlamp heating. Halogen lamp heating provides near-infraredradiation with low penetration depth. The radiation is focused atthe surface which can cause the surface temperature of breads toreach the required values for browning. There is no study onhalogen lamp-microwave combination baking in literature.The most evident problems seen in microwave-baked prod-

ucts are high moisture loss, firm texture, rapid staling, lack ofcolour and crust formation [1]. Additional product develop-ment is necessary in order to form microwave-baked productsthat have the same volume, texture and eating quality as thoseassociated with conventionally prepared ones. Conventionalformulations should be improved by using some additives suchas enzymes, gums or emulsifiers to solve the firmness problemin microwave baked breads. Halogen lamp baking combinedwith microwave baking may be an alternative to reduce theproblems in microwave-baked products. Although there arevarious studies about the investigation of the effects ofenzymes on quality of breads baked in conventional oven [2–4], there is not any information in the literature about theeffects of enzymes on quality of breads baked in either micro-wave or halogen lamp-microwave combination ovens. En-zymes are widely used as technological aids in several foodprocesses. In recent years, the baking industry has focused itsattention on the replacement of several chemical compoundsby enzymes [3]. Different enzymes are currently added to thebread-making process to improve dough handling, fresh breadquality and the shelf life.Amylases can be used to improve or control dough handling

properties and product quality. Amylases from fungal sourcesact on damaged starch reducing its ability to immobilize water,thus increasing dough mobility and resulting in improveddough handling [4]. The enhanced production of fermentablesugars increases yeast growth and thus the power to producecarbon dioxide. One suggested explanation of the positiveeffects of a-amylase in reducing staling is that the enzyme pro-duces low-molecular-weight branched-chain starch polymersas hydrolysis products, which interfere with amylopectinrecrystallization [4].

The positive effect of xylanase on bread volume is due tothe redistribution of water from the pentosan phase to the glu-ten phase [5]. The increase in the volume of the gluten fractionincreases its extensibility, which will result in better oven-spring. Xylanases are known to have an antistaling action dur-ing bread storage but their action is not clear. The improvingaction of xylanase might be primarily attributed to the hydroly-sis of the cell wall polysaccharides of the wheat grain. Themonosaccharides and oligosaccharides resulting from theenzyme action could affect the water balance and may interferewith protein-starch interaction during bread storage [3].Lipases can produce mono- and diglycerides from lipids,

which improve crumb softness of bread. Addition of specificlipases in combination with triglycerides also improves loafvolume, crumb softness and staling rate [2]. The generallyaccepted theory about the mechanism of antistaling action ofmonoglycerides is based on the ability of monoglycerides toform complexes with amylose and amylopectin. Additionally,the antifirming effect of emulsifiers was mainly attributed tothe weakened cohesion between the swollen starch granules,which are rich in amylopectin [6].Proteases help to break down the gluten protein so that the

dough is softer and more extensible. Proteases have beenshown to reduce the viscosity of dough with the cleavage ofpeptide bonds by releasing free water caused by the high waterbinding capacity of gluten [7]. During aging of the bread, amy-lopectin recrystallizes resulting in increased rigidity of thestarch granule and decreased flexibility of the gluten matrix[6]. As proteases modify gluten protein, these interactions areweakened and firming is decreased. Since proteases cause thecleavage of peptide bonds, they have the ability to give newamino groups as substrate to Maillard reactions, which contri-bute to the development of crust color and product flavor [8].The main objective of the study was to determine the effects

of different enzymes on the quality of breads baked in micro-wave and halogen lamp-microwave combination ovens. Thisstudy will also be an alternative to reduce the quality defectsof microwave baked products by using enzymes. In addition,the results obtained by microwave and combination bakingwill be compared to conventional baking which will giveinsights to the mechanisms of different baking methods.

2 Materials and methods

2.1 Preparation of dough

Bread flour contains 32% wet gluten, 13.1% moisture and0.55% ash. The composition of the prepared dough was on

156 Nahrung/Food 48 (2004) No. 2, pp. 156–160 DOI: 10.1002/food.200300412 i 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

In this study, the effects of different enzymes (a-amylase, xylanase,lipase, protease) on quality of breads baked in different ovens (micro-wave, halogen lamp-microwave combination and conventional oven)were investigated. It was also aimed to reduce the quality problems ofbreads baked in microwave ovens with the usage of enzymes. As a con-trol, bread dough containing no enzyme was used. Specific volume,firmness and color of the breads were measured as quality parameters.

All of the enzymes were found to be effective in reducing the initialfirmness and increasing the specific volume of breads baked in micro-wave and halogen lamp-microwave combination ovens. However, inconventional baking, the effects of enzymes on crumb firmness wereseen mostly during storage. The color of protease enzyme added breadswere found to be significantly different from that of the no enzyme andthe other enzyme added breads in the case of all type of ovens.

Correspondence: Prof. G�l�m Sumnu, Middle East Technical Uni-versity, Food Eng. Dept., TR-06531 Ankara, TurkeyE-mail: gulum@metu.edu.trFax: +90-312-210 12 70

Keywords: Baking / Bread / Enzymes / Halogen lamp / Microwaves /

Enzymes in a novel baking process

i 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Nahrung/Food 48 (2004) No. 2, pp. 156–160 157

flour weight basis; 100% flour, 8% sugar, 6% milk powder,2% salt, 3% yeast, 8% margarine, 55% water. Four differenttypes of enzymes were used to compare their effects on qualityof breads baked in different ovens. These enzymes are practi-cally pure for industrial use, not analytical enzymes. Theseenzymes were fungal a-amylase (ORBAMIL ES 10X, activity:6500 U*/g), xylanase (ORBAZIM HC 1000, activity: 225U/g), lipase (ORBAZIM HC 120Y, activity: 32000 U/g) andprotease (ORBAPROTEASE P, activity: 35 U/g) and obtainedfrom ORBA Biyokimya (Istanbul, Turkey). a-Amylase wasadded to the flour as 5 g/100 kg flour, xylanase as 7.5 g/100 kgflour, lipase as 0.6 g/100 kg flour and protease as 60 g/100 kgflour. As a control, bread containing no enzyme was used.Dough was prepared by using the straight dough method. Firstof all, the dry ingredients were mixed. Yeast was dissolved inwater at 308C. Margarine was melted and added to the dryingredients in liquid phase together with the dissolved yeast.Water at 308C was added to the mixture. All the ingredientswere mixed by a mixer (Kitchen Aid, 5K45SS, USA) for3 min. After complete mixing of the dough, it was placed intothe incubator (N�ve EN 400, Turkey) at 308C and 85% relativehumidity for fermentation. The total duration of the fermenta-tion was 105 min. After the first 70 min, the dough was takenout of the incubator, punched and placed into the incubatoragain. A second punch took place after 35 min. The dough wasdivided into 50 g pieces after fermentation. Each piece wasshaped and placed into the incubator for the last time for20 min under the same incubation conditions.

2.2 Baking

Three different baking methods, microwave, halogen lamp-microwave combination and conventional baking, were used.For microwave and halogen lamp-microwave combination bak-ing, a halogen lamp-microwave combination oven (AdvantiumovenTM, General Electric Company, Louisville, KY, USA) wasused. Breads were microwave-baked for 0.75 min at 100%power operating only the microwave power of this oven. 70%halogen power – 30% microwave power for 3 min was used inhalogen lamp-microwave combination baking. The power ofmicrowave oven has been determined as 706 W by using IMPI2-liter test [9]. Only one bread was baked at a time. Conven-tional baking was performed in a commercial electrical oven(Arcelik ARMF 4 Plus). The prepared dough samples werebaked at 2008C for 13 min. The oven was preheated beforeplacing the dough samples into it. Four breads were baked at atime. After baking by different methods the breads were cooledat room temperature (20 l 28C) for 1 h. After cooling, thebreads were wrapped with stretch film and stored at 20 l 28Cfor 2 days.

2.3 Bread analysis

The bread-specific volume was determined by the rape seeddisplacement method [10]. Firmness of breads was measuredusing a universal testing machine (Lloyd Instruments LR 30K,UK). Breads were compressed for 25% at a speed of 55 mm/min. Bread samples were prepared according to the method ofAACC [10]. Firmness measurements were done on fresh (aftercooling of breads for 1 h) and stale (after 2 days storage) breadsamples. The crust color of the bread samples was measuredusing a Minolta color reader (CR-10, Japan) using the Hunter

L*, a*, and b* color scale. Triplicate readings were carried outat room temperature from different positions of bread crust,and mean value was recorded. Total color change (DE) wascalculated from the following equation in which dough wasused as the reference point, whose L*, a*, b* value wasdenoted by L0, a0 and b0.

DE = [(L* – L0)2 + (a* – a0)2 + (b* – b0)2]1/2

2.4 Statistical analysis

Analysis of variance (ANOVA) was performed to determinesignificant differences between different enzyme types (p f

0.05). Variable means were compared by Duncan’s MultipleRange test. At least three replications were done for eachexperimental condition.

3 Results and discussion

All of the enzymes were found to be significantly effectiveto obtain breads with higher specific volumes in microwaveoven as compared to no enzyme added breads (Fig. 1). Theeffects of a-amylase and protease in increasing the specificvolume of microwave baked breads were significantly differentfrom other enzymes. The positive effect of a-amylase on thespecific volume of breads was due to its influence on starch.Immediately after dough preparation, the yeast starts to fer-ment the available sugars into alcohols and carbon dioxide,which causes rising of the dough. Protease addition helps tobreak down the gluten protein so that the dough is more exten-sible. The increased extensibility of gluten film retains the gasthat is evolved in the system better for flour containing astrong gluten [8]. Therefore, breads treated with protease hadhigher volumes. Addition of lipase to the bread doughincreased the volume of breads significantly as compared to noenzyme added breads due to the effect of mono- and diglycer-ides produced by lipase on the volume. Emulsifiers like mono-and diglycerides, were shown to increase the volume of micro-wave-baked breads [11]. Xylanase-added breads had highervolumes compared to no enzyme added breads. The positiveeffect of xylanase on the bread volume may be due to theredistribution of water from the pentosan phase to the glutenphase. The increase in the volume of the gluten fractionbecause of water transfer increases its extensibility, which

* Units are a part of the terminology specifically used by the producerof enzymes.

Figure 1. Effects of enzymes on the specific volume of breads bakedin microwave oven. Bars with different letters (a, b, c) are significantlydifferent (p f 0.05).

Keskin et al.

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results in better ovenspring [5]. The deleterious effects ofstrong overdosage of endoxylanases on loaf volume are notrepresentative of the effects obtained when endoxylanases areused at optimum concentration [12]. Pentosanase activity pro-duces a softer dough if side activities are minimized and thedough will not be sticky and remain machinable [8].In halogen lamp-microwave combination baking similar to

the microwave treatment, protease and a-amylase were foundto be significantly different from the other enzymes in affect-ing the specific volume of breads (Fig. 2). In conventionaloven, protease was found to be the most effective enzymeamong the others (Fig. 3).All of the enzymes were found to be significantly effective

on firmness of breads baked in microwave oven meaning thatbreads treated with any types of the enzymes were softer thanthat of the control breads (Fig. 4). The firmness problem of themicrowave baked bread interior is usually associated with glu-ten-microwave interactions [13]. Microwave heating couldhave alligned gluten proteins by strong hydrogen bonds whichcould have created firmness during cooling [14]. Moreover,more amylose leached during microwave baking as comparedto conventional baking were shown to increase the firmness ofmicrowave baked products [15]. As a-amylases are starch-hydrolysing enzymes, degradation of starch will result in the

decrease in the amount of available starch for amylose leach-ing. This causes a reduction in firmness [16]. For this reason,a-amylase was found to be effective to reduce the firmness ofmicrowave-baked breads. Proteases are capable of breakingdown the gluten protein. Therefore, in the presence of protease,less gluten might be available to interact with microwaves andthe breads became less firm. Microwave breads formulatedwith low gluten flour were found to be softer [11]. Lipaseenzyme reduced the firmness of microwave-baked breads sincelipases produce mono- and diglycerides which have the abilityto form complexes with amylose. Microwave breads contain-ing xylanase enzyme were found to be softer than the onescontaining no enzymes which might be related to waterreleased by xylanase. The extra water can affect gelatinizationand formation of amylose-lipid complex [17].Like microwave baking, all of the enzymes were found to be

effective in reducing the firmness of breads during halogenlamp-microwave combination baking (Fig. 5). The enzymeeffects on quality of breads baked in halogen lamp-microwavecombination oven were similar to that of microwave heating.This shows that microwave heating mechanism was moredominant than halogen lamp heating mechanism in halogenlamp-microwave combination oven. In contrast to novel bakingprocesses, in conventional oven none of the enzymes were

Figure 2. Effects of enzymes on the specific volume of breads bakedin halogen lamp-microwave combination oven. Bars with different let-ters (a, b, c) are significantly different (p f 0.05).

Figure 3. Effects of enzymes on the specific volume of breads bakedin conventional oven. Bars with different letters (a, b, c) are signifi-cantly different (p f 0.05).

Figure 4. Effects of enzymes on the firmness of breads baked inmicrowave oven. Bars with different letters (a, b, c) are significantlydifferent (p f 0.05).

Figure 5. Effects of enzymes on the firmness of breads baked inhalogen lamp-microwave combination oven. Bars with different letters(a, b, c) are significantly different (p f 0.05).

Enzymes in a novel baking process

i 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Nahrung/Food 48 (2004) No. 2, pp. 156–160 159

found to be significantly effective in reducing the initial firm-ness of breads (Fig. 6). Enzymes are generally known to reducethe staling rate while having only a minor effect on initial firm-ness of conventionally baked breads [2].The DE values of breads baked in microwave oven were

close to zero (between 2–3) meaning that a similar color withthe dough was obtained. It is well-known that the shortprocessing time and low temperatures common to microwaveprocessing usually do not promote the Maillard reaction whichis responsible for the production of many flavor and colorcompounds [18]. Protease added breads were found to havesignificantly different DE values (5.2) from the others meaningthat these breads were darker in color. The crust color of pro-tease added samples were significantly darker from that of the

others in halogen lamp-microwave combination baking also(Fig. 7). Proteases were known to produce new amino acids orpeptides required for Maillard reaction [8]. Similarly, the DEvalue of conventionally baked breads treated with protease wasfound to be significantly different from that of the no enzymeadded breads and breads with the other enzymes (Fig. 8).Crumb firmness was highest after 2 days of storage when

halogen lamp-microwave combination baking was used(Table 1). This may be related to the high moisture loss duringhalogen lamp-microwave combination baking. Enzyme addi-tion was found to be very much effective in reduction of firm-ness of breads baked in both microwave and halogen lamp-microwave combination ovens during storage, too (Table 1).The positive effect of a-amylase was due to its ability to pro-duce dextrins as hydrolysis products, which might interferewith amylopectin recrystallization. Amylopectin retrogradationis considered as the main cause of crumb firming during stor-age [17]. Xylanases were found to be significantly effective onstaling of breads due to their ability of affecting the water inthe system. The monosaccharides and oligosaccharides result-ing from the xylanase action could affect the water balanceand may interfere with protein-starch interaction responsiblefrom crumb-firming during bread storage [3]. The effective-ness of lipase on the firmness of microwave baked breads dur-ing storage can be explained by the production of mono- anddiglycerides by lipase. Monoglycerides produced from lipaseretard the firming process by forming complexes with amyloseor amylopectin. During staling, as the crumb loses kineticenergy, interactions between starch and gluten increase innumber and strength which contribute to bread firming [19].Gluten is the continuous phase and remnants of starch granulesare the discontinuous phase. Since refreshing of bread restores

Figure 6. Effects of enzymes on the firmness of breads baked inconventional oven. Bars with different letters (a, b, c) are significantlydifferent (p f 0.05).

Figure 7. Effects of enzymes on DE value of breads baked in halogenlamp-microwave combination oven. Bars with different letters (a, b, c)are significantly different (p f 0.05).

Table 1. Effects of enzymes on firmness of breads (N) baked by different methods after 2 days of storage

Baking method Noenzyme

Amylase Xylanase Lipase Protease

Conventional 3.79a 3.64ba 3.09b 3.24ba 3.10bMicrowave 7.25a 6.12b 5.82b 5.67b 5.59bHalogen lamp-microwave combination 7.67a 6.62c 7.27b 6.64c 6.09d

Firmness values with different letters (a, b, c, d) are significantly different within a row (p f 0.05).

Figure 8. Effects of enzymes on DE value of breads baked in con-ventional oven. Bars with different letters (a, b, c) are significantly dif-ferent (p f 0.05).

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160 Nahrung/Food 48 (2004) No. 2, pp. 156–160 i 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

freshness, cross-links between gluten and starch that contributeto bread firming must be relatively weak possibly hydrogenbonds. As gluten was modified by protease action, interactionsbetween starch and gluten were weakened which caused areduction in firmness during storage.Table 2 shows the percentage of reduction in firmness of

breads baked in different ovens as compared to no enzymeadded breads. In conventional baking, enzymes were found tobe effective in reducing firmness mostly during storage.Unlike conventional baking, in microwave baking all of theenzymes were effective on initial crumb firmness. Such aresult was obtained because of the difference in heatingmechanisms of conventional and microwave baking. Additionof enzymes solved most of these problems related to micro-wave heating and showed a positive effect on the firmness ofbreads baked in microwave oven. The initial firmness problemof the bread interior due to the high amount of amylose mighthave been reduced by addition of a-amylase and lipaseenzymes. The firmness problem due to the gluten-microwaveinteraction and microwave induced gluten changes might bereduced by the usage of proteases which broke down the glutenprotein resulting in softer breads. It was suggested that xyla-nases could have a specific action on the rate of gluten forma-tion and the quality of the gluten [20]. This may explain thereported beneficial effect of xylanases on crumb firmness ofbreads baked in microwave oven. Since microwave heatingwas more dominant in affecting firmness than halogen lampheating, the effects of enzymes on reducing the firmness ofbreads during halogen lamp-microwave combination bakingwere found to be similar to that in microwave baking.

4 Concluding remarks

In microwave and halogen lamp-microwave combinationbaking, all of the enzymes were effective in reducing initialcrumb firmness and firmness during storage. However, in con-ventional baking, enzymes reduced the firmness of breadsmostly during storage. The enzymes were also responsible forthe increase of the specific volume of breads baked in micro-wave and halogen lamp-microwave combination ovens.Enzymes can be recommended to be used in breads baked inboth microwave and halogen lamp-microwave combinationbaking in order to reduce firmness of these products.

General Electrics Company is greatly acknowledged for dona-tion of the halogen lamp-microwave combination oven(AdvantiumTM oven). ORBA Biyokimya (Istanbul, Turkey) sup-plied all of the enzymes. This research was supported by Mid-dle East Technical University (BAP-2003-07-02-00-69).

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Received September 29, 2003Accepted November 25, 2003

Table 2. Percentage reduction in firmness of breads baked in different ovens

Baking method Time of analysis Amylase Xylanase Lipase Protease

Conventional Just after baking 0 0 0 11.94After 2 days storage 3.96 18.47 14.51 18.21

Microwave Just after baking 33.33 29.17 17.71 23.96After 2 days storage 15.59 19.72 21.79 22.90

Halogen lamp-microwave combination Just after baking 49.84 47.87 41.97 61.31After 2 days storage 13.69 5.22 13.43 20.60