Arabinoxylan as partial flour replacer: The effect on bread properties and economics of bread making

Koegelenberg, Danika (2016-03)

Thesis (MEng)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: Wheat bran, used for animal feed, is a good candidate for production of higher value products such as arabinoxylan (AX). Extracted AX holds potential as a partial flour replacer in the bread making industry. The aim of this study was to maximise flour removal while using the minimum AX addition possible while maintaining physical bread properties. The extraction of AX from wheat bran was accomplished using alkaline conditions. The purity of AX extracted at lab scale (275 ml) was 44.3% at the optimum extraction conditions (0.5 M NaOH, 240 min, 80°C). Large scale extraction (27 l) resulted in an extract with 49.3% purity, with addition of purification steps including ultrafiltration, anion exchange chromatography and ethanol precipitation. The two extracts obtained on small scale (E1) and large scale (E2) both had high average molecular weights (620 000 and 470 000 Da, respectively) and arabinose to xylose (A/X) ratios of 0.7 and 0.6. With inclusion of the additional purification steps at large scale, the whiteness index of the final extract was increased from 33 to 93. For the application purpose, the lighter extract colour will have a less prominent effect on bread colour and is therefore advantageous. The high water binding capacity of AX allows for increased dough water absorption resulting in an altered final bread weight and volume. However, at optimal AX addition and flour removal levels, these product properties can be maintained. This was achieved with inclusion of 0.8% crude AX extract and 2.5% flour removal, while increasing water absorption by nearly 2%. The only physical difference between the AX containing loaves and the control was in colour, due to the darker colour of the extract. However, a discolouration step included in the extraction of E2 resulted in a significantly lighter final product compared to loaves containing E1. Comparison of E1 and E2 to highly pure AX resulted in similar final product properties indicating that the extracts’ performance was not affected by the purity. Furthermore, inclusion of an oxidative enzyme, laccase, resulted in a softer final product as determined using a texture analyser. AX production cost was estimated at R110/ kg resulting in higher production costs for AX containing loaves compared to commercial white bread. In order to maintain profit margins the selling price of AX containing loaves have to be increased by 9.6%. In conclusion, crude AX extracted from the animal feed co-product, wheat bran, is a feasible candidate for application in the bread making process as a partial flour replacer.

AFRIKAANSE OPSOMMING: Graan semels, wat gebruik word vir dierevoer, is ‘n goeie kandidaat vir die produksie van hoër waarde produkte soos arabinoxylan (AX). Geëkstraeerde AX het die potensiaal om as gedeeltelike meel vervanger toegepas te word in die brood maak bedryf. Die doel van die studie was om meel verwydering te maksimeer en terselfdetyd die minimum hoeveelheid AX toe te voeg om sodoende die fisiese eienskappe van brood te behou. Die ekstraksie van AX uit graan semels was uitgevoer onder alkaliese kondisies. Die suiwerheid van die AX geëkstraeer op laboratorium skaal (275 ml) was 44.3% by die optimum ekstraksie kondisies (0.5 M NaOH, 240 min, 80°C). Grootskaalse ekstraksie (27 l) het gelei tot ‘n ekstrak met 49.3% suiwerheid, deur middel van addisionele suiweringstappe insluitend, ultrafiltrasie, anioon uitruil kroomatografie en etanol presipitasie. Die twee ekstrakte wat verkry is vanaf klein skaal (E1) en groot skaal (E2) het beide hoë gemiddelde molekulêre massas (620 000 and 470 000 Da, onderskeidelik) en arabinose tot xylose (A/X) verhoudings van 0.7 en 0.6. Met die toevoeging van addisionele suiweringstappe op groot skaal, het die witheid indeks van die finale ekstrak toegeneem vanaf 33 na 93. Die ligter ekstrak kleur is voordelig vir toepassing in die bakproses. Die fisiese-chemiese eienskappe van AX beïnvloed hul funksionalitiet in die brood maak proses. Die hoë water bindingskapasiteit van AX laat toe vir toenemende deeg water absorpsie wat veranderinge in brood gewig en volume tot gevolg het. Alhoewel, by optimale AX toevoegingsvlakke en meel verwyderingsvlakke kan hierdie brood eienskappe behou word. Dit was moontlik deur toevoeging van 0.8% AX en meel verwydering van 2.5%, terwyl water absorpsie met bykans 2% toegeneem het. Die enigste opmerkbare verksil tussen brode met AX toevoeging en die kontrole was die kleur, as gevolg van die donker kleur van die ekstrak self. Die toevoeging van ‘n ontkleuringstap tydens die ekstraksie proses van E2 het ‘n aansienlike ligter finale produk tot gevolg gehad, in vergelyking met E1. Vergelyking van E1 en E2 met kommersiële AX het gelei tot finale produkte met ooreenstemmende eienskappe. Dit dui daarop dat die suiwerheid van die AX ekstrak nie sy prestasie beïnvloed het nie. Verder, toevoeging van die oksidatiewe ensiem, laccase, het ‘n finale produk met ‘n sagter tekstuur tot gevolg gehad. Die produksie koste van AX was beraam as R110/ kg. Hierdie koste het gelei tot ‘n hoër produksie koste vir brode met AX toevoeging in vergelyking met kommersiële witbrood. Om wins marge te behou moet die verkoopprys van brode met AX toevoeging na beraming 9.2% meer wees. Ten slotte, geëkstraeerde AX, vanaf graan semels, is ‘n realistiese kandidaat vir toepassing in die brood maak proses as ‘n gedeeltelike meel vervanger.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98435
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