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Author:Selinheimo, Emilia
Title:Effect of laccase and xylanase on the structure formation of wheat flour and gluten doughs
Lakkaasin ja ksylanaasin vaikutus vehnäjauho- ja gluteenitaikinan rakenteen muodostumiseen
Publication type:Master's thesis
Publication year:2004
Pages:vi + 100      Language:   eng
Department/School:Kemian tekniikan osasto
Main subject:Bioprosessitekniikka   (Kem-70)
Supervisor:Leisola, Matti
Instructor:Autio, Karin ; Kruus, Kristiina
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark TKK  4910   | Archive
Abstract (eng): In the literature survey, properties of wheat flour and dough as well as the structure formation of wheat bread were discussed, with special emphasis on rheology.
Also the theory and a few measurement methods of the rheology were shortly introduced.
Considering the influence of enzymes on bread making, a structure formation by an oxidative mechanism was discussed.
The enzymes that were viewed more precisely on their effect on the structure formation of wheat bread included lipoxygenase, glucose oxidase, peroxidase, laccase and transglutaminase.

In the experimental part of the study, the effect of Aspergillus oryzae and Bacillus subtilis xylanases and Trametes hirsuta and Melanocarpus albomyces laccases, separately and together, on the structure of wheat flour dough and gluten dough were examined.
The experiments of added free ferulic acid (FA) were done to clarify the role of FA in dough structure formation.

The rheological experiments were performed with Kieffer dough and gluten extensibility rig, when the dough extensibility Ex and the resistance to stretching Rmax, were determined.

In a rheology point of view, laccases increased the maximum resistance Rmax of dough and decreased the dough extensibility Ex at Rmax, whereas xylanases decreased the Rmax of dough and increased the Ex at Rmax in flour and gluten doughs.
Considering the protein-AX fraction, hardening by laccases and softening by xylanases were weaker in gluten doughs, which was presumably due to the lower AX content in gluten.
Like xylanases, the added free FA softened the flour dough structure, as well.

As a function of dough resting time, the structure of laccase treated doughs was observed to soften.
The softening effect was strengthened as a function of laccase activity.
The reason for the softening phenomenon was probably the laccase-mediated depolymerisation of cross-linked arabinoxylan network, resulting from mobile FA radicals.

Combined laccase and xylanase experiments led to doughs of higher Rmax, with no remarkable change in Ex.
The effect of laccase seemed to be predominant, especially at low xylanase dosages, but when xylanase was added to flour dough at high concentration, the hardening effect of laccase on dough was decreased.
Presumably, when the AX fraction was hydrolyzed effectively by xylanase, laccase was not able to create a strong AX network.
Similar decrease in laccase mediated hardening in doughs was not seen, when performing the combined laccase and xylanase test with gluten, which was presumably due to low AX content of gluten.

The results indicated the critical role of feruloylated arabinoxylan fraction in laccase-catalysed structure formation both in flour and gluten, although in gluten doughs, protein fraction might have also been affected.
Abstract (fin): Työn kirjallisuusosassa tarkasteltiin vehnäjauhon ominaisuuksia sekä vehnätaikinan ja -leivän rakenteenmuodostusta.
Kaikkia aihealueita, kuten jauhokomponenttien ominaisuuksia, leivonnan teoriaa ja entsyymejä, käsiteltiin pääasiassa reologiselta näkökannalta.
Lisaksi sivuttiin lyhyesti reologian teoriaa ja reologisia mittausmenetelmiä.
Leivonnassa käytettävien entsyymien osalta keskityttiin lähinnä oksidatiivisella mekanismilla toimiviin ristisilloittaviin entsyymeihin.
Lipoksygenaasi-, glukoosi oksidaasi-, peroksidaasi-, lakkaasi- ja transglutaminaasientsyymejä, sekä erityisesti niiden vaikutusta leivän rakenteenmuodostumiseen tarkasteltiin entsyymeistä yksityiskohtaisimmin.

Työn kokeellisessa osassa tutkittiin Aspergillus oryzae ja Bacillus subtius -ksylanaasien sekä Trametes hirsuta ja Melanocarpus albomyces -lakkaasien vaikutusta, yhdessä ja erikseen, vehnäjauho- ja gluteenitaikinan rakenteeseen.
Lisäksi vapaan ferulahapon vaikutusta taikinassa pyrittiin selvittämään.
Taikinoiden reologiset mittaukset suoritettiin "Kieffer Dough and Gluten Extensibility Rig" -mittauslaitteistolla, jolloin taikinoiden venyvyys Ex ja venytysvastus Rmax, pystyttiin määrittämään.

Reologisten mittausten perusteella havaittiin, että lakkaasit lisäsivät ja ksylanaasit vähensivät taikinan venytysvastusta Rmax, kun taas taikinan venyvyys Ex väheni lakkaasien vaikutuksesta ja lisääntyi ksylanaasien vaikutuksesta.
Vapaan ferulahapon havaittiin ksylanaasien tavoin pehmentävän jauhotaikinan rakennetta.
Tarkastellessa taikinoiden proteiini- ja arabinoksylaani (AX) -osuuksia todettiin, että taikinan kovettuminen lakkaasien vaikutuksesta ja pehmeneminen ksylanaasien vaikutuksesta oli heikompaa gIuteenitaikinoissa, mikä johtui todennäköisesti gluteenin pienemmästä AX-pitoisuudesta.

Lakkaasilla käsiteltyjen taikinoiden havaittiin pehmenevän ajan funktiona.
Pehmeneminen johtunee lakkaasin vaikutuksesta rakentuneen AX-verkon depolymeroitumisesta, mikä johtui todennäköisesti lakkaasin muodostamien vapaiden F A-radikaalien reaktioista AX-fraktiossa.
Lakkaasin ja ksylanaasin yhteisvaikutuksen osalta havaittiin lakkaasin oleva dominoivana pienemmillä aktiivisuuksilla, mutta korkeammilla ksylanaasiaktiivisuuksilla lakkaasin taikinaa kovettava vaikutus heikkeni.
Oletettavasti ksylanaasin pilkkoessa tehokkaasti AX-fraktiota lakkaasi ei kyennyt muodostamaan vahvaa AX-verkkorakennetta.
Gluteenitaikinoissa vastaavaa heikentymistä ei havaittu, mikä johtui todennäköisesti gluteenitaikinan pienestä AX-pitoisuudesta.
Johtopäätöksenä voidaan todeta, että lakkaasin pääasiallisena substraattina toimii AX-fraktio, vaikkakin gluteenitaikinoissa epäiltiin lakkaasin vaikuttaneen myös proteiineihin.
ED:2004-09-10
INSSI record number: 26240
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