X-ray micro-computed tomography (μCT) evaluation of bubble structure to determine quality of dough and bread made from roasted wheat flour

Germishuys, Zandré (2021-04)

Thesis (PhD)--Stellenbosch University, 2021.

Thesis

ENGLISH ABSTRACT: Roasting of cereals has been shown to improve its sensory properties, increase its shelf life and inactivate proteolytic enzymes promoting increased loaf volume. The breadmaking process is a series of aeration stages which ultimately affects the final crumb structure of the bread. X-ray micro-computed tomography (μCT) is a non-invasive technique capable of producing high quality three-dimensional images enabling microstructural evaluation of food products. The aims of this study were to characterise white flour produced from roasted wheat differing in hardness and protein content using rheological and physicochemical analyses; to determine the optimal roasting conditions that would minimise the effect on the protein properties of the produced white flour; to evaluate the freeze drying of dough as a suitable sample preparation procedure to maintain the structure of the samples during X-ray μCT scanning for efficient analysis of the bubble structure of dough and foam properties of 10 g bread loaves produced from roasted wheat flour; and to evaluate the quality and shelf life of bread loaves prepared from roasted wheat flour by means of C-Cell and texture analysis. Hard, medium and soft textured wheat kernels were roasted for 140 s at 180°C using a forced convection continuous tumble (FCCT) roaster. This resulted in the largest reductions in hectolitre mass (7.36 hg/hl), flour yield (2.33%) and moisture content (2.87%) for the hard wheat. The largest increase in damaged starch (4.54%) and flour ash (0.06%) was observed for the hard and soft wheats, respectively. Roasting resulted in gluten protein changes as a gluten network could not be formed during dough mixing with the roasted flours. The use of composite flours (80% untreated flour and 20% flour from roasted wheat) displayed the largest increase in water absorption capacity (5.2%) for the medium textured wheat. Improved alveograph P/L ratios and higher levels of free starch was observed for the hard and medium textured wheat. The central composite design (CCD) showed no significant differences (p>0.05) for protein content, mixograph peak time and peak height for either the high or low protein roasted wheat. The roasting conditions chosen (based on trends observed) for X-ray μCT evaluation was 90°C and 86 Hz (ca. 130 s) as this combination maximised protein content and peak height and minimised peak time. To evaluate the bubble structure of dough and the foam structure of bread, 20- and 40 min proofed dough as well as 10 g bread samples, produced from roasted wheat flour based on the CCD, were subjected to X-ray μCT. The use of 10 g dough and bread samples enabled scanning at a much higher resolution. A finer crumb structure and softer texture was observed for the bread produced from roasted wheat flour due to decreased strut thicknesses. Lower mixograph peak heights and increased porosity suggested a weaker gluten strength for the roasted wheat samples. The roasting conditions used did not negatively impact the foam properties of the breads. C-Cell analysis showed a coarser crumb structure and a darker crumb colour for breads produced from roasted wheat flour although this did not negatively impact the breads texture. More importantly, texture analysis showed the use of flour produced from roasted wheat resulted in a softer bread (i.e., lower firmness) with an increased shelf life.

AFRIKAANSE OPSOMMING: Die rooster van grane verbeter die sensoriese eienskappe en verleng die rakleeftyd daarvan. Dit inaktiveer ook proteolitiese ensieme wat verhoogde brood volume bevorder. Die broodmaakproses is 'n reeks deurlugting fases wat uiteindelik die finale krummelstruktuur van die brood beïnvloed. X-straal mikro-berekende tomografie (μBT) is 'n nie-vernietigende tegniek wat in staat is om driedimensionele beelde van hoë gehalte te produseer wat dit moontlik maak om die mikrostruktuur van voedselprodukte te evalueer. Die doelwitte van hierdie studie was om wit broodmeel, geproduseer van geroosterde koring wat verskil in hardheid en proteïeninhoud, te karakteriseer met behulp van reologiese- en fisies-chemiese ontledings; om die optimale rooster kondisies te bepaal wat die effek op die proteïeneienskappe van die geproduseerde wit meel sal verminder; om die vriesdroog van deeg te evalueer as 'n geskikte monstervoorbereidings prosedure om die struktuur van die deegmonsters tydens X-straal μBT skandering te handhaaf vir 'n doeltreffende analise van die borrelstruktuur van deeg en skuim eienskappe van 10 g brode geproduseer van geroosterde koringmeel; en om die kwaliteit en rakleeftyd van brood berei vanaf geroosterde koringmeel te evalueer deur middel van C-Cell en tekstuur ontleding. Harde-, medium- en sagte-tekstuur koringpitte is vir 140 s by 180°C gerooster met behulp van 'n geforseerde konveksie aaneenlopende tuimel (GKAT) rooster. Dit het gelei tot die grootste afname in hektolitermassa (7.36 hg / hL), meel opbrengs (2.33%) en voginhoud (2.87%) vir harde koring. Die grootste toename in beskadigde stysel (4.54%) en asinhoud (0.06%) is onderskeidelik waargeneem vir die harde en sagte korings. Rooster het gelei tot veranderinge in glutenproteïene, siende dat 'n glutennetwerk nie gevorm kon word, tydens die deegmengproses, met die geroosterde meel nie. Die gebruik van saamgestelde meel (80% onbehandelde meel en 20% meel van geroosterde koring) het die grootste toename in waterabsorpsie kapasiteit (5.2%) vir die medium-tekstuur koring getoon. Verbeterde alveografie P/L verhoudings en hoër vlakke van vrye stysel is waargeneem vir die harde- en medium-tekstuur korings. Die sentrale saamgestelde ontwerp (SSO) het geen beduidende verskille (p> 0.05) getoon vir proteïeninhoud, miksograaf piektyd en -piekhoogte vir die hoë of lae proteïen geroosterde koring nie. Die gekose rooster kondisies (gebaseer op neigings waargeneem) vir X-straal μBT evaluering was 90°C en 86 Hz (ongeveer 130 s), siende dat hierdie kombinasie die proteïeninhoud en piekhoogte gemaksimeer het en piektyd geminimaliseer het. Om die borrelstruktuur van die deeg- en skuimstruktuur van die brood te evalueer, is deeg wat vir 20- en 40 min gerys is sowel as 10 g brood monsters, vervaardig met geroosterde koringmeel gebaseer op die SSO, blootgestel aan X-straal μBT skandering. Die gebruik van 10 g deeg- en broodmonsters het skandering teen 'n hoër resolusie moontlik gemaak. ‘n Fyner krummel struktuur en 'n sagter tekstuur is waargeneem vir die brood wat van geroosterde koringmeel geproduseer is as gevolg van ‘n dunner borrel selwand. Laer miksograaf piekhoogte en verhoogde porositeit dui op 'n swakker gluten sterkte vir die geroosterde koringmonsters. Die rooster kondisies wat gebruik is het nie die skuimeienskappe van die brood negatief beïnvloed nie. C-Cell analise het 'n growwer krummelstruktuur en 'n donkerder krummelkleur getoon vir brode wat met geroosterde koringmeel geproduseer is, alhoewel dit nie die brood tekstuur negatief beïnvloed het nie. Belangriker nog, die tekstuur analise het getoon dat die gebruik van meel geproduseer vanaf geroosterde koring gelei het tot 'n sagter brood (dit wil sê 'n laer fermheid) met 'n verlengde rakleeftyd.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/109867
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