Influence of waxy wheat flour blends on dough and bread baking quality as well as shelf life

Kleyn, Megan Elizabeth (2018-03)

Thesis (MSc Food Sc)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: Waxy wheats are a naturally occurring genetic mutation of the hexaploid bread wheat Triticum aestivum. They contain only amylopectin starch due to the absence of the protein responsible for producing amylose, called granule bound starch synthase (GBSS). The amylopectin content retards starch retrogradation as amylopectin retrogrades more slowly than amylose. This can be utilised to increase the shelf life of bread by slowing down the staling process in which starch retrogradation is involved. One hundred percent waxy wheat cannot be used to make bread because of a resulting undesirable loaf appearance. Blends of waxy wheat and non-waxy wheats were thus used to create a loaf of bread which not only had an extended shelf life but also a desirable appearance. The starch granule morphology and percentage crystallinity of starch isolated from four waxy wheat lines (375, 376, 377 and 378), was determined using a scanning electron microscope and X-ray diffraction respectively. A non-waxy wheat control was used. No differences were seen in granule size and morphology between the lines and the control but more B-type granules were observed in control. The control was found to have an unusually high percentage crystallinity (36.5%) but was still lower than, or equal to, the waxy wheat lines (36.5 – 38%). Flour of each line was blended with the control in ratios of 10, 15, 20 and 25% waxy wheat to non-waxy wheat. Pasting properties were determined by the Rapid Visco Analyser (RVA). Blends of lines 375, 376 and 377 were found to have a lower peak viscosity, a faster peak time and a lower final viscosity than the control, while line 378 was similar in values to the control. No significant differences were seen between the blends and the control for the arrival time, water absorption, and stability as determined by the Farinograph. Likewise, no significant differences were seen for the peak time, peak height and tail height determined by the Mixograph between all blends and the control. Biaxial extension of the dough from each blend using the Alveograph showed no significant differences from the control for the P, L, P/L and W parameters. The blends were baked into loaves of bread to determine final loaf quality and shelf life. The C-Cell showed no significant differences for the cell and hole number, cell area and slice brightness between the blends and control. Lines 375 and 377 had the highest percentage concavity and therefore the worst appearance. Line 376 and 378 had the best appearance with the highest amount of waxy wheat. The texture analyser showed that waxy wheats create a softer initial loaf. On day six, only blends from line 376 successfully decreased the firmness compared to the control. The addition of up to 25% waxy wheats to non-waxy wheats marginally affects the processing properties of dough but negatively affects the outward appearance of bread. Bread baked with blends of 20 – 25% of line 376 had an improved shelf life, whilst still being visually appealing.

AFRIKAANSE OPSOMMING: Wasagtige korings is ‘n genetiese mutasie van die heksaploiede broodkoring, Triticum aestivum, wat natuurlik voorkom. Hierdie broodkorings bevat slegs een tipe stysel, amilopektien, omdat die proteïen wat verantwoordelik is daarvoor om amilose te vervaardig naamlik, granulêr gebonde stysel sintase (GBSS), nie teenwoordig is nie. Aangesien amilopektien stadiger retrogradeer as amilose, word stysel retrogradasie vertraag in wasagtige korings. Stysel retrogradasie is betrokke by die verouderingsprosess van brood. Die hoë amilopektieninhoud van wasagtige korings kan dus gebruik word om die rakleeftyd van brood te verleng, Die gebruik 100% wasagtige koring in die bak van brood is nie ideaal is nie, aangesien dit ‘n ongewensde voorkoms aan die brood verleen. Mengsels van wasagtige en nie-wasagtige korings word gebruik om brood te bak wat ‘n aanvaarbare voorkoms, sowel as verlengde rakleeftyd het. Stysel van vier wasagtige koring lyne (375, 376, 377 en 378) is op grond van die stysel se granulêre morfologie en persentasie kristalliniteit, deur middel van ‘n skanderings elektron mikroskoop en x-straal diffraksie onderskeidelik, geïsoleer en geklassifiseer. ‘n Nie-wasagtige koring is as kontrole gebruik. Daar is geen verskille in die grootte van die granule, sowel as die morfologie tussen die toetslyne en die kontrole opgemerk nie. Die stysel van die kontrole-koring het meer B-tipe granules bevat, asook ‘n uitsonderlike hoë persentasie kristalliniteit (36.5%) gehad. Hierdie persentasie was steeds laer of gelyk aan die wasagtige koringlyne, waarvan die persentasie kristalliniteit gewissel het van 36.5 tot 38%. Meel van elkeen van die toetslyne koring is in verhoudings van 10, 15, 20 en 25% wasagtige koring tot nie-wasagtige koring van met die meel van die kontrole-koring gemeng. Gom-eienskappe van die mengsels is deur ‘n Rapid Visco Analyser (RVA) bepaal. Die mengsels met koring lyne van 375, 376 en 377 het ‘n laer piekviskositeit, ‘n vinniger piektyd en ‘n laer finale viskositeit as die kontrole getoon, terwyl lyn 378 soortgelyke waardes as die kontrole gehad het. Daar was geen beduidende verskille tussen enige van die mengsels en die kontrole, ten opsigte van die aankomstyd, waterabsorbsie en stabiliteit, soos gemeet deur ‘n Farinograaf, nie. Eweneens was daar geen beduidende verskille tussen die piektyd, piekhoogte en sterthoogte, soos bepaal deur ‘n Miksograaf, vir enige van die mengsels en die kontrole nie. Die tweeassige uitstrekking van die deeg is bepaal met behup van ‘n Alveograaf. Daar was geen beduidende verskille vir die P, L, P/L en W parameters tussen die toetslyne en die kontrole nie. Om die finale brood kwaliteit en rakleeftyd te bepaal, is daar van elke een van die mengsels, sowel as die kontrole, brode gebak. Die C-cell het geen beduidende verskille gewys vir die selgrootte, die -hoeveelheid, -area en die sny helderheid tussen die verskillende mengsels en die kontrole nie. Lyne 375 en 377 het die hoogste persentasie konkaviteit en dus die swakste voorkoms gehad. Lyne 376 en 378 het die beste voorkoms getoon met die hoogste wasagtige koring inhoud. Die tekstuurontleder het aangedui dat wasagtige koring aanvanklik sagter brood maak, alhoewel slegs mengsels van koringlyn 376 die fermheid van die brood op dag ses, suksesvol kon verlaag teenoor die kontrole. Die prosesseringseienskappe van deeg word tot ‘n geringe mate beïnvloed deur die toevoeging van tot 25% wasagtige koring by die nie-wasagtige koring. Dit lei egter tot negatiewe effekte op die uiterlike voorkoms van brood. Die brood wat met 20% tot 25% van koringlyn 276 gemaak is, het ‘n verbeterde rakleeftyd gehad, terwyl dit steeds ‘n aanvaarbare voorkoms behou het.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/103755
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