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Quality of dried white salted noodles affected by microbial transglutaminase

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To examine the potential application of microbial transglutaminase (MTGase) in oriental noodle making, the effects of various MTGase addition levels on the rheological, textural and structural properties of noodles were investigated using good
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   Journal of the Science of Food and Agriculture J Sci Food Agric  85 :2587–2594 (2005)DOI: 10.1002/jsfa.2311 Quality of dried white salted noodles affectedby microbial transglutaminase Jianping Wu 1 , 2 ∗ and Harold Corke 2 1 Department of Human Nutritional Sciences, University of Manitoba, Winnipeg, Canada 2 Department of Botany, The University of Hong Kong, Pokfulam Road, Hong Kong, China Abstract: To examine the potential application of microbial transglutaminase (MTGase) in orientalnoodle making, the effects of various MTGase addition levels on the rheological, textural and structuralproperties of noodles were investigated using good quality (‘Red Bicycle’) and poor quality (‘Sandow’)wheat flours. Addition of MTGase at 5–20gkg − 1 levels, but not at 1gkg − 1 level, to the two different wheatflours decreased rapid visco-analyser (RVA) parameters of hot paste viscosity and final viscosity whileincreasing breakdown. For fresh white salted noodle dough sheets, the storage modulus ( G   ) and lossmodulus ( G   ) increased significantly at 1gkg − 1 MTGase addition for both types of flour, but there wasno clear trend with higher levels of MTGase. For dried white salted noodles, textural parameters (tensileforce, hardness and gumminess) generally increased, cooking loss was little affected and the yield of thecooked noodle was significantly decreased by MTGase. Color was slightly adversely affected. Scanningelectron microscopy (SEM) results indicated that physical properties of dry noodles were improvedthrough the formation of cross-links [ ε -( γ  -glutamyl)lysine] by MTGase. © 2005 Society of Chemical Industry Keywords:  microbial transglutaminase (MTGase); dried white salted noodles; rheological properties; texturalproperties; scanning electron microscopy (SEM) INTRODUCTION Transglutaminase (TGase, EC 2.3.2.13), is a trans-ferase, widely distributed in mammals, plants, fishand microorganisms, that catalyzes the acyl-transferreaction between the  γ  -carboxyamide groups of apeptide-bound glutaminyl residue in proteins as theacyl donors and a variety of primary amines and wateras the acyl acceptor, including the  ε -amino groupof lysine residues in certain proteins. 1 , 2 TGase canmodify proteins by means of amine incorporation,crosslinkinganddeamidation.TGasehasbeenappliedto catalysis of the cross-linking of a number of pro-teins, resulting in improvements in elasticity, watercapacity and other functional properties. 2–6 The pio-neering work of Motoki  et al  7 and Ando  et al  8 enabledlow-cost mass production of TGase from microor-ganisms by fermentation, opening up a wide arrayof potential food applications, such as in meat pro-cessing, fish and dairy products, tofu production,and wheat products. 2–6 , 9–11 Sakamoto et al  12 reportedthat microbial TGase (MTGase) could improve thestrength of fresh noodles. Other work indicated thatMTGase could improve the elasticity of dough, 13 or increase the strength of paste dough 6 and crumbstrength. 14 More recently,MTGase hasbeen exploredfurther as a potential enzyme for improving doughproperties and the quality of end products, 6 , 15–17 which are related to the formation of   ε -( γ  -Glu)Lyscross-links strengthening the dough network. 18–21 However, there has been limited application of TGasein oriental noodle making, and the effects of TGaseon different wheat flours have not been established.Noodles are one of the major foods consumed inEast Asian countries, and now can be found in mostgrocery stores all over the world. 22 , 24 Dried noodlesare prepared from fresh noodles dehydrated to awater content of 125–145gkg − 1 either by naturaldrying or at controlled temperature and humidity. 23 The advantages of dried noodles are that they arelow-cost and easily cooked, and have a long shelf-life. 24 Dried white salted noodles have a simpleformulation (wheat flour, water and salt) and methodofpreparation. 25 The characteristicspreferred in driednoodles are a white appearance, free of blemishes,minimal disintegration during cooking, and a smoothsurface without mushiness. 25 , 26 The objectives of thisstudy were to examine the potential application of MTGase in dry noodle processing. MATERIALS AND METHODSMaterials Two types of commercial wheat flour with differentquality characteristics were purchased from Flour ∗ Correspondence to: Jianping Wu, Department of Human Nutritional Sciences, University of Manitoba, Winnipeg, MB, Canada R3T 2N2E-mail: wu2@cc.umanitoba.ca(  Received 12 November 2004; revised version received 11 March 2005; accepted 21 April 2005  )Published online 19 August 2005 © 2005 Society of Chemical Industry.  J Sci Food Agric  0022–5142/2005/$30.00  2587   J Wu, H Corke Manufacturers of Hong Kong (Kowloon, HongKong). ‘Sandow’ brand wheat flour is of poor qualityfor noodles, but is suited to biscuit or cake making.‘Red Bicycle’ brand wheat flour, made from US hardred winter (HRW) wheat, is used commercially fornoodle making in Hong Kong. All reagents wereanalytical grade, purchased from Sigma ChemicalCo. (St Louis, MO, USA). ‘Activa UltraDente’ is anMTGase preparation (enzyme activity, 24unitsg − 1 ),designed for the improvement of pasta and noodletexture, and was kindly provided by Ajinomoto Co.,Tokyo, Japan. General analysis Moisture, total ash, protein (N  ×  5 . 7), total starch,damaged starch and free lipids of wheat flour weremeasured using AACC 27 methods 44-15A, 08-01,46-11A, 76-13 (Total Starch Kit, Megazyme, Bray,Ireland),76-31(StarchDamageKit,Megazyme,Bray,Ireland) and 30-25 (Soxtec System HT6, Tecator,Hog¨an¨as, Sweden), respectively. The mixograph pro-cedure was carried out according to AACC 27 method54-40A using a 2g mixograph (National/TMCO,USA); sodium dodecyl sulfate (SDS) sedimentationwas performed according to Dick and Quick 28 with1g wheat flour (‘as-is’ moisture basis) in a custom-made rack fitted with a measuring scale (0–112mm)to read the SDS-sedimentation value (provided bythe University of California, Davis, CA, USA). Allmeasurements were carried out in triplicate. Wheat flour pasting properties A rapid visco-analyser model 3-D (RVA; NewportScientific Pty Ltd, Narrabeen, Australia) was usedto study the pasting behavior of wheat flours withMTGase addition. Wheat flour (3.5g, 140gkg − 1 m.b.) was mixed with 25g accuratelyweighed distilledwater or treatment solutions (MTGase was dissolvedin water to the level required), in a disposablealuminium RVA sample canister. The standardtemperature profile comprised the following steps:hold at 50 ◦ C for 2min, heat to 95 ◦ C over 6min,hold at 95 ◦ C for 4min, cool to 50 ◦ C over 4min, andhold at 50 ◦ C for 4min. All tests were performed atleast in duplicate. Noodle making The noodle formulation was: wheat flour 100 parts(140gkg − 1 m.b.), water 33 parts, salt (15gkg − 1 , onthe basis of ‘as is’ wheat flour weight). MTGase wasadded at levels of 1, 5, 10 and 20gkg − 1 respectively(on the basis of wheat flour weight, corresponding to24, 120, 240 and 480unitskg − 1 wheat flour), and wasdissolved completely before use. For each trial, 200gflour were mixed with 66g solution by hand for 5min;the crumbly dough was sheeted through the first rollgap four times and folded in half each time. Thenthis dough sheet was cut into four pieces and restedfor 15min in four different plastic bags. The doughpiece was reduced to a final thickness of 1.6mm usingan Electric Pasta Making Machine (Mercato, Italy),by successive passes through four roll gaps withoutintermediate resting stages, sheeting five times foreach gap. The raw fresh noodle sheet was rested againfor 30min, and some of it was used for rheologicalmeasurements. Raw fresh noodles were produced bycutting the sheet into 25cm long, 2mm wide strips.The noodles were placed on a wire sieve to dry at25 ◦ C with air for 16h in an oven. After drying, thenoodles were stored in plastic bags for a week beforetesting. Rheological measurements A StressTech rheometer (Reologica Instruments AB,Lund, Sweden) was used for oscillatory tests (straincontrolled). The rheometer was equipped with 30mmdiameter parallel plates with a 1.6mm gap betweenthem, and the lower parallel plates were maintained at25 ◦ C for the frequency sweep oscillatory test. Freshnoodle sheets were cut into 30mm diameter circlesand placed between the plates. To prevent dryingof the edge of the sample, a thin layer of palm oilwas applied to cover the exposed dough surfaces.Before starting the measurement, the dough sheet wasrested for another 5min. Oscillatory measurementswere taken at 0.3% strain (a linear viscoelasticrange was found between 0.1 and 0.6%) over afrequency range of 0.5–70Hz. Storage or elasticmodulus ( G   ), loss or viscous modulus ( G   ), phasedegree ( ϕ , tan ϕ  =  G   / G   ) and complex viscosity ( η ∗ )were recorded using the instrument software. Allmeasurements were performed at least in duplicate. Determination of noodle color Dry noodles were ground to a powder using a blender(Kenwood, model KM250, UK), and sieved with a30-mesh sieve. Color was measured using a MinoltaCR-300 Chroma meter (Minolta, Tokyo, Japan) witha 13.5mm diameter viewing area. The values of   L ∗ and  b ∗ were the average of three measurements. Cooking properties Dry noodles (about 20g ‘as is’ m.b.) were cooked inboilingwater(400mL)for5.5minuntilthe whitecoredisappeared. They were cooled in water (20 ◦ C) for30s, rinsed with distilled water gently for about 2minthen drained for another 30s. All the water (about1000mL) was collected for cooking loss calculations.Excessive moisture was removed by lightly pattingthe strands between layers of paper towel for 1min.Cooked noodles were then weighed and their waterabsorption calculated as:Cooking yield  ( gkg − 1 )  =  weight of cookednoodles / weight of dry noodle  ( kgkg − 1 ) About 1000mL cooking water (including drained andfiltered water) was placed in a tared beaker ( W  1 ,g) evaporated using a hot-plate to about 50mL and 2588  J Sci Food Agric  85 :2587–2594 (2005)  Effect of transglutaminase of noodles then dried at 45 ◦ C to constant weight ( W  2 , g). Themoisture content of the dried noodle was determined( W  3 , g). The cooking loss was calculated as:Cooking loss = ( W  2  —  W  1 )/( 20—  W  3 ) kgkg − 1 All samples were analyzed in triplicate.  Analysis of textural properties Texture properties were analyzed with an SMSModel TA-XT2 i   texture analyzer (Stable MicroSystems,Godalming,UK),equippedwiththeTextureExpert software program (Version 5.16). All textureprofile analyses (TPA) were done at 25 ◦ C underambient relative humidity. Tensile strength analysisto assess elasticity and the breaking strength of cooked noodles, and TPA to measure noodle texturalproperties of hardness (HD) and gumminess (GU).were performed. For tensile strength analysis, theinstrument wasequipped with spaghetti/noodletensilegrips. The test speed was set at 1 . 0mms − 1 to avoidvibrations that would occur at high speeds. Thedistance between the parallel friction rollers was set at10cm.Noodlesweretestedindividuallybypositioningthrough slots and winding around parallel frictionrollers two or three times to reduce any slippage andtoanchorthesampleends.Fortextureprofileanalysis,the instrument was equipped with a cylindrical probe(38mm, probe model TA-4) and operated in thecompression mode. The probe speed was 1 . 0mms − 1 ,and compression distance was 75% of the noodlethickness.The maximumforcesetting was 7.0kg.Thepause between the first and second compression was2s. All the data were collected automatically by thesoftware. At least 12 individual noodle strands weretested for each sample. The maximum and minimumvalues were discarded. Scanning electron microscopy  Noodles were broken to expose the cross-sectionalsurface, and the surfaces were coated with gold– palladium (Au/Pd) with a sputter coater SCD 005(BAL-TEC, Germany) for about 240s. Samples werethen examined using a Steke Oscan 440 (LeicaCambridge Ltd, UK) under vacuum. For each groupsample at least eight images were examined. Statistical analysis All data were statistically analyzed using a computersoftware package (SAS, Version 6.12, Cary, NC,USA), using Duncan’s multiple range test (DMRT)to differentiate the means among different treatments( P   <  0 . 05). RESULTS AND DISCUSSION Analysis of wheat flours The results for various compositional, pasting andmixograph parameters (Table 1) show that RedBicycle flour has better quality characteristics for Table 1.  Proximate analysis of wheat flours Wheat flourCharacteristics Red Bicycle Sandow Composition (  gkg − 1  ) Ash a 5.0 7.2Damaged starch b 64.7 50.1 Total starch a 737 808Protein a 145 107Free lipids a 11.7 18.3 RVA pasting (RVU) c PV 254 220HPV 136 112Breakdown 118 108Setback 148 137Final viscosity 283 249SDS sedimentation (mm) 106 70.5 Mixograph data d Dough absorption  ( gkg − 1 )  654 596 TP (min) 4.02 3.56PW 16 11.5W8 9.65 3.9 a Calculated on a dry basis. b Calculated on an ‘as-is’ basis. c PV, peak viscosity; HPV, hot paste viscosity; RVU, rapid visco units.RVA values were the means of duplicates. d TP, time to peak; PW, maximum peak width; W8, width of curve aftermixing for 8min. All data were the means of triplicates. 0100806040200300240180120600 8 1612 204Time (min) Viscosity(RVU)    T  e  m  p  e  r  a   t  u  r  e   (             °    C   ) Temperature profilecontrol(+)120105 Figure 1.  Pasting characteristics of Red Bicycle flour as affected bymicroglutaminase. (  +  ) MTGase concentration  ( gkg − 1 ) . noodle making than Sandow flour, such as higherpeak viscosity and breakdown, SDS sedimentationvalue and mixograph parameters. 33 Effect of MTGase on pasting properties of wheatflour Addition of MTGase had the same effect on thepasting properties of Red Bicycle and Sandow flours,so the results for Red Bicycle flour are presentedfor illustration (Fig 1). Up to the stage of peakviscosity, nearly the same viscosity properties withand without MTGase addition were observed, whilehot paste viscosity was decreased significantly with  J Sci Food Agric  85 :2587–2594 (2005)  2589   J Wu, H Corke 5 and 10gkg − 1 additions [from 136 to 124 and 118rapidviscounits(RVU),respectively].Breakdownwassignificantly increased except with 1gkg − 1 addition,indicating that MTGase addition increased the abilityofwheatflourtowithstandtheheatingandshearstress.On cooling, re-association between starch molecules,especially amylose, causes viscosity to increase;however, MTGase addition significantly decreasedthe final viscosity, except at 1gkg − 1 addition, from283 RVU (without MTGase) to 246 RVU (5gkg − 1 addition) and 255 RVU (1gkg − 1 addition). Additionat 20gkg − 1 level had a similar influence on the pastingproperties as a 1gkg − 1 addition.Although the pasting properties of wheat flour aregenerally attributed to starch, changes in proteinstructure caused by factors such as cross-linkingcould also affect the pasting properties. It is likelythe creation of new cross-links in wheat glutenwith MTGase addition would disturb the internalstarch–protein interaction equilibrium, 29 where therupture of hydrated starch granules would physicallybe deterred because of entrapment of starch granulesby newly formed cross-linking networks among glutenmolecules, reflecting increased breakdown values.This would further interfere with the process of re-association of amylose during the cooling stage,causing a decrease in final viscosity in our study.Furthermore, the release of ammonia during theMTGase-catalyzed crosslinking reaction might alsobe related to the change in RVA pasting propertiesbecause of the alkali property of ammonia. 30 , 31 Inconsideration of the effect of MTGase preparationfiller (maltodextrin) on viscosity, Bel´en  et al  32 foundthat the RVA pasting viscosity of corn starch wassignificantlydecreasedonlywithincreasingsubstitutedmaltodextrin levels from 50 to 100gkg − 1 . However,a significant decrease in final viscosity was observedeven at the dose of 5gkg − 1 enzyme preparation. Themaltodextrin level in our study was significantly lowerthan the amount in the work of Bel´en  et al  ; 32 thereforeits effect on viscosity might not be obvious at lowconcentration. Effects of MTGase on rheological properties offresh prepared noodles Protein is the main contributor to the rheologicalproperties of fresh noodles; therefore, cross-linkingof gluten proteins with MTGase addition certainlyaffects these properties (Fig 2). Drastic increases forbothstoragemodulus( G   )andlossmodulus( G   )wereobserved even at the level of 1gkg − 1 , but the effectdecreased (although it was higher than the control)with higher levels of enzyme. An obvious decrease wasfound at 10gkg − 1 addition for Red Bicycle noodlesand5gkg − 1 additionforSandownoodles.Itshouldbenoted that these levelsactually correspond to the pointatwhichnoodle’sstructurewassignificantlyimproved.The reason for this is not apparent. The added doses(in the range 240–480unitskg − 1 of wheat flour) inour study were lower than or comparable to previousstudies, such as 3000unitskg − 1 of gluten in the workof Larre  et al  , 18 168000unitskg − 1 (or 8ppm; 1ppm is21unitsg − 1 flour) of wheat flour in the work of Tsengand Lai, 17 and 133 . 7unitskg − 1 of wheat flour in thework of Bauer  et al  . 20 50100150200250300350Red Bicycle50100150200250Red Bicycle501001502002500 10 20 30 40 50 7060Frequency (Hz)Sando501001502002503003500 10 20 30 40 50 7060Frequency (Hz)Sando       G    ′        (      K      P     a      )      G    ′        (      K      P     a      )      G    ′   ′        (      K      P     a      )      G    ′   ′        (      K      P     a      ) Figure 2.  Variation of storage modulus (  G   ) and loss modulus (  G   ) with frequency for sheeted dough treated with microglutaminase at variouslevels for two wheat flours [MTGase concentration(gkg − 1  ): (multi) 0; (solid triangle) 1; (open triangle) 5; (open circle) 10; (solid circle) 20]. 2590  J Sci Food Agric  85 :2587–2594 (2005)  Effect of transglutaminase of noodles Larre  et al  18 reported that, with gluten treated byMTGase, both  G   and  G   increased with increasingMTGase levels, which was slightly different from ourresults. They demonstrated that the improvement inviscoelastic properties in gluten was accompaniedby the formation of polymers through isopeptidicbonds catalyzed by MTGase, especially among thosehigh molecular weight glutenin subunits (HMW-GS). 18 On the other hand, the effect of increasingMTGase levels in our study may be related to thelimited content of lysine in gluten (gluten containshigh amounts of glutamine), 40 which would restrictthe cross-linking reaction at high MTGase dose.Therefore, rheological properties might be affectedby the existing threshold number of connections forcross-links in the gluten network. 18 The rheologicalproperties are also probably affected by competing forwater with maltodextrin. Maltodextrin, the filler inthe enzyme preparation, was reported to have highwater absorption ability. 34 Therefore, the presence of the filler could affect gluten network developmentand MTGase-catalyzed cross-link reaction, 20 andthe formation of hydrogen bonds between starchand protein. 35 However, a recent report showedthat a 25gkg − 1 substitution for wheat flour usingdextrin (with a dextrose equivalent of 3–40) did notsignificantly affect viscoelastic properties of dough. 36 This amount is higher than the maltodextrin amountin our tested levels. Similarly, Defloor and Delcour 37 also reported that addition of maltodextrins upto 36gkg − 1 did not significantly change doughrheology. Although there was no direct evidenceto suggest that an MTGase-catalyzed secondaryreaction might predominate and affect the doughproperties at high concentration of MTGase, thepossible secondary reaction of deamidation couldalso affect the rheological properties at high MTGaseconcentration. 38 Effects of MTGase on the noodle texture Tensile strength analysis was used to assess elasticityand breaking strength of cooked noodles; it wasfound that tensile force increased significantly for RedBicycle noodles at 1gkg − 1 with a maximum valuefound at 5gkg − 1 level (Table 2). Increasing levelswould tend to decrease the value compared with the5gkg − 1 level. A similar phenomenon was observedfor Sandow noodles, but tensile force increased withincreasing MTGase level up to 20gkg − 1 . Our resultsare in good agreement with the work of Sakamoto et al  12 who reported that the breaking strength of boiled Chinese noodles increased correspondinglywith MTGase concentrationBoth hardness and gumminess increased withincreasing MTGase for both noodles (Table 2), whichwas related to the cross-linking function of MTGase.TheseresultsindicatedthatMTGasecouldactdirectlyon the proteins in wheat flour, and improve firmnessand elasticity by reinforcing the network structure. Table 2.  Effect of added microbial transglutaminase on the texturalproperties of white dry salted noodles a  Texture profile analysisMTGase Tensileaddition  ( gkg − 1 )  force (g) Hardness (N) Gumminess (N) Sandow  0 8.9d 23.7d 11.2e1 9.6cd 25.4bcd 13.4cd5 10.9c 25.7bcd 14.3bcd10 11.0c 27.2abc 13.8bcd20 13.0a 27.8abc 15.3abc Red Bicycle 0 11.2bc 25.2cd 13.0de1 12.7ab 27.5abc 15.8ab5 14.3a 28.3ab 16.6a10 13.4a 29.4a 17.2a20 14.2a 29.1a 16.9a a Means within the column followed by common letters are notsignificantly different at  P  <  0 . 05. Table 3.  Effect of added microbial transglutaminase on colorproperties of dry white salted noodles a MTGAse addition  ( gkg − 1 )  L b ∗ Sandow  0 92.8c 7.0d1 92.9c 7.6b5 92.3d 8.1a10 93.1b 7.6b20 93.2ab 7.5bc Red Bicycle 0 93.2ab 6.2e1 92.9c 6.7d5 92.8c 6.7d10 92.8c 7.2c20 93.4a 6.9d a Means within the column followed by common letters are notsignificantly different at  P  <  0 . 05. Effects of MTGase on noodle color Color and appearance are the initial quality charac-teristics observed by the consumer. Brightness andan absence of undesirable discoloration (specks) areessential for perception of high quality of dry noodles. L ∗ wassignificantlydecreasedupto10gkg − 1 addition,not at 20gkg − 1 addition, for Red Bicycle noodles.A significant decrease was observed only at 5gkg − 1 MTGase addition for Sandow noodles, while at 10and 20gkg − 1 addition,  L ∗ was increased (Table 3).The value of   b ∗ increased significantly with the addi-tion of MTGase even at the lowest level  ( 1gkg − 1 ) for both noodles (Table 3), but decreased at 10 and20gkg − 1 levels for Sandow noodles (still higher thanthe control). This deterioration in color appearancewas not visually detectable as the change in  L ∗ or  b ∗ was less than 2 units. The ammonia released duringthe formation of crosslinks might contribute to thedeterioration in noodle color 30 as the slightly alka-line ammonia would tend to detach flavones from theflour and thus impart a yellower color. 39 In addition,  J Sci Food Agric  85 :2587–2594 (2005)  2591
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