Characterisation and quantification of microstructure, physicochemical and functional properties of oven and forced convection continuous tumble roasted cereal grains
dc.contributor.advisor | Manley, Marena | en_ZA |
dc.contributor.advisor | Du Plessis, Anton | en_ZA |
dc.contributor.author | Schoeman, Letitia | en_ZA |
dc.contributor.other | Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science. | en_ZA |
dc.date.accessioned | 2017-01-30T16:12:27Z | |
dc.date.accessioned | 2017-03-29T11:35:02Z | |
dc.date.available | 2017-01-30T16:12:27Z | |
dc.date.available | 2017-03-29T11:35:02Z | |
dc.date.issued | 2017-03 | |
dc.description | Thesis PhD(Food Sc)--Stellenbosch University, 2017. | en_ZA |
dc.description.abstract | ENGLISH ABSTRACT: The use of roasted cereal grains in foods can improve organoleptic properties, enhance shelf life, ease incorporation into ready-to-eat products and increase antioxidant activity. Structural, physicochemical and functional changes will inevitably occur during roasting and this study aimed to investigate these properties. X-ray micro-computed tomography (μCT) was used as a non-destructive technique for characterising and quantifying microstructural changes in individual cereal grains induced by conventional oven and forced convection continuous tumble (FCCT) roasting at 180°C for 140 s. X-ray μCT uses differences in X-ray attenuation arising from differences in density within a sample. X-ray tomograms of the raw and roasted wheat and maize kernels were obtained, using a General Electric Phoenix model V|Tome|X L240 X-ray μCT system with a source voltage of 60 kV and an electron current set at 240 μA. Analysis of the whole kernel and regions-of-interest (ROIs) was performed with VGStudio Max 2.2 three-dimensional (3D) software. Qualitative results were depicted as two-dimensional (2D) transmission images and 3D volumes. Internal structural changes were observed as a loss of endosperm integrity, detected as a decrease in attenuation. For both cereal grains oven roasting was associated with a larger increase in kernel volume (wheat=4.47%; maize=10.76%) than FCCT roasting (wheat=1.57%; maize=3.41%), as well as larger relative density decreases (wheat=2.76%; maize=6.33%) in comparison to FCCT roasting (wheat=0.55%; maize=1.92%). During FCCT roasting the material density (excluding air) remained unaffected. Structural changes can strongly influence physicochemical and functional properties. Kernel hardness and hectolitre mass (HLM) can be helpful to assess the milling yield, which was not affected (P>0.05) by either roasting methods. Scanning electron microscopy (SEM) illustrated the starch-protein morphology, where both roasting methods resulted in a partially disintegrated protein network and swollen and/or ruptured starch granules in the oven-roasted samples. Quantification of these structural differences included crystallinity determinations using X-ray diffraction (XRD), thermal properties using differential scanning calorimetry (DSC) and pasting properties employing a Rapid Visco Analyser (RVA). The reduction in crystallinity for both FCCT (wheat=0.12%; maize=0.45%) and oven (wheat=0.16%; maize=1.83%) roasting was consistent with the decrease in gelatinisation enthalpy (ΔH). Only partial gelatinisation occurred in both the oven (wheat=17.16%; maize=25.27%) and FCCT-roasted (wheat=10.14%; maize=16.23%) samples. Oven roasting caused more adverse changes in most of the measured properties, being a more destructive process. With FCCT roasting the samples are continuously moving, resulting in an even heat transfer in comparison to oven roasting where the samples are stationary. FCCT roasting maintained more of the favourable characteristics, i.e. microstructure, hardness and milling yield and will thus result in a more acceptable final product. This study demonstrated the capability of X-ray μCT in combination with image analysis as a non-invasive technique to study microstructural changes in cereal grains, induced by roasting, both in a qualitative and quantitative manner and at a relatively high spatial resolution of 12 micron. The results integrate qualitative and quantitative information that could be useful for understanding structure-property relationships in terms of further processing and utilisation, e.g. the development of value-added products with improved digestibility and viscosity or delayed staling phenomenon. | en_ZA |
dc.description.abstract | AFRIKAANSE OPSOMMING: Die gebruik van geroosterde grane in voedsel kan organoleptiese eienskappe verbeter, rakleeftyd verleng, byvoeging in gereed-vir-eet produkte en ontbytgrane vergemaklik en antioksidant aktiwiteit verhoog. Dit is onvermydelik dat strukturele, fisies-chemiese en funksionele veranderinge sal plaasvind tydens rooster en dus was die doel van die studie om hierdie eienskappe te ondersoek. X-straal mikro-berekende tomografie (μBT) was gebruik as ‘n nie-vernietigende tegniek vir die karakterisering en kwantifisering van mikrostrukturele veranderinge in individuele grane, geïnduseer deur konvensionele oond- en geforseerde konveksie aaneenlopende tuimel (GKAT) rooster by 180°C vir 140 s. X-straal μBT gebruik verskille in X-straal attenuasie, wat voortspruit uit verskille in digtheid in ‘n monster. X-straal tomogramme van die rou en geroosterde koring en mieliepitte is verkry met ‘n General Electric Phoenix model V|Tome|X L240 X-straal μBT sisteem met ‘n bronspanning van 60 kV en ‘n elektronstroom gestel op 240 μA. Analise van die heelpit en areas-van-belang (AVBs) is uitgevoer met VGStudio Max 2.2 drie-dimensionele (3D) sagteware. Kwalitatiewe resultate is uitgebeeld as twee-dimensionele (2D) transmissiebeelde en 3D volumes. Interne strukturele veranderinge is waargeneem as ‘n verlies van endosperm integriteit, bespeur as ‘n afname in attenuasie. Vir beide grane is oond rooster geassosieer met 'n groter toename in pitvolume (koring=4.47%; mielie=10.76%;) as vir GKAT rooster (koring=1.57%; mielie=3.41%), sowel as ‘n groter afname in relatiewe digtheid (koring=2.76%; mielie=6.33%) in vergelyking met GKAT rooster (koring=0.55%; mielie=1.92%). Gedurende GKAT rooster het die materiaal digtheid (lug uitgesluit) onveranderd gebly. Strukturele veranderinge kan fisies-chemiese en funksionele eienskappe beïnvloed. Pit hardheid en hektolitermassa (HLM) is nuttig om maalopbrengs te evalueer, wat nie geaffekteer is (P>0.05) deur beide rooster metodes. Skandeer-elektronmikroskopie (SEM) het die stysel-proteïen morfologie geïllustreer, waar beide rooster metodes tot ‘n gedeeltelike gedisintegreerde proteïen netwerk en geswelde en/of gebarste stysel granules in die oond geroosterde monsters gelei het. Kwantifisering van hierdie strukturele veranderinge het kristalliniteit-bepalings met X-straal diffraksie (XSD), termiese eienskappe met differensiële skandeer kalorimetrie (DSK) en plak eienskappe met behulp van ‘n Rapid Visco Analyser (RVA) ingesluit. Die afname in kristalliniteit vir beide GKAT (koring=0.12%; mielie=0.45%) en oond (koring=0.16%; mielie=1.83%) rooster was konsekwent met die afname in gelatinisasie entalpie (ΔH). Slegs gedeeltelike gelatinisasie het in beide die oond (koring=17.16%; mielie=25.27%) en GKAT geroosterde (koring=10.14%; mielie=16.23%) monsters plaasgevind. Oond rooster het meer ongunstige veranderinge in meeste van die gemete eienskappe veroorsaak, wat 'n meer vernietigende proses impliseer. Met GKAT rooster beweeg die monsters voortdurend, wat lei tot ‘n eweredige hitte-oordrag in vergelyking met oond rooster waar die monsters stilstaande is. Tydens GKAT rooster het meeste van die gunstige eienskappe, soos mikrostruktuur, hardheid en maalopbrengs behoue gebly en dit sal aanleiding gee tot ‘n meer aanvaarbare eindproduk. Hierdie studie demonstreer die vermoë van X-straal μBT in kombinasie met beeld-analise as ‘n nie-vernietigende tegniek om mikrostrukturele veranderinge in graan, veroorsaak deur rooster, in beide ‘n kwalitatiewe en kwantitatiewe wyse en teen 'n relatiewe hoë ruimtelike resolusie van 12 mikron te bestudeer. Die resultate integreer kwalitatiewe en kwantitatiewe inligting wat nuttig is vir die begrip van struktuur-eienskap verhoudings in terme van verdere verwerking en gebruik, byvoorbeeld vir die ontwikkeling van toegevoegde waarde produkte met verbeterde verteerbaarheid en viskositeit of vertraagde verouderingsverskynsel. | af_ZA |
dc.description.sponsorship | National Research Foundation (NRF) | en_ZA |
dc.format.extent | 293 pages : illustrations | en_ZA |
dc.identifier.uri | http://hdl.handle.net/10019.1/100822 | |
dc.language.iso | en_ZA | en_ZA |
dc.publisher | Stellenbosch : Stellenbosch University | en_ZA |
dc.rights.holder | Stellenbosch University | en_ZA |
dc.subject | Roasted cereal grains | en_ZA |
dc.subject | Cereal grains -- Characterisation | en_ZA |
dc.subject | Microstructural changes in cereal grains | en_ZA |
dc.subject | Forced convection continuous tumble (FCCT) roasting | en_ZA |
dc.subject | Food -- Composition | en_ZA |
dc.subject | UCTD | en_ZA |
dc.title | Characterisation and quantification of microstructure, physicochemical and functional properties of oven and forced convection continuous tumble roasted cereal grains | en_ZA |
dc.type | Thesis | en_ZA |