The bread wheat hardness scenario of the Southern and Western Cape : introducing the particle size index (PSI) method and fourier transform near infrared (FT-NIR) spectroscopy calibrations

Van Zyl, Louise (1999-12)

Dissertations (M.Sc.Voedselwet.) -- University of Stellenbosch, 1999.

Thesis

ENGLISH ABSTRACT: Fourier transform near infrared spectroscopy (FT-NIR), the particle size index (PSI) method and scanning electron microscopy were used to investigated the bread wheat hardness scenario of the Southern and Western Cape in South Africa. The effect of differences in sample holder composition on FT-NIR calibration and prediction results were investigated. Different calibrations were derived for protein and moisture content of 92 South African whole wheat flour samples using three different sample holders. Best results were achieved with borosilicate-glass vials, followed by soda-glass vials and the conventional sample cup with a sapphire glass base provided with the spectrophotometer. Differences in results due to the use of different sample holders were investigated using correlation coefficients (r) and maximum distances (d) of a number of individual spectra and by performing analysis of variance (ANOVA) on the predicted values for independent validation of the different calibration models. The effect of compositional differences within both the borosilicate-glass and the soda-glass vials were investigated by means of ANOVA on the predicted values of a single sample presented to the spectrophotometer in a number of individual vials. Ail differences were found to be statistically insignificant (P ≤ 0.05). The sapphire-glass sample cup provided with the spectrophotometer could therefore be replaced by one of the vial-types investigated in which each sample could be stored and presented to the spectrophotometer individually. The bread wheat hardness scenario of the Southern and Western Cape were investigated by deriving a FT-NIR hardness calibration for 198 ground bread wheat samples and using the particle size index (PSI) test as reference method. Particle size index results indicate that the investigated bread wheat cultivars have a very wide hardness range of 37.05 - 60.50%. The influence of genotype, location, protein content and moisture content on wheat hardness was investigated by means of ANOVA, Student's t-test, correlation analysis and regression analysis. Significant differences (P ≤ 0.05) in hardness was found over culitvars, while a positive linear relationship with protein content and a negative linear relationship with moisture content exist. The wheat samples - were subsequently presented to the spectrophotometer in individual borosilicate-glass vials. A FT-NIR calibration was derived by performing PLS regression on baseline-corrected spectra and the model validated using independent validation. Excellent results were achieved with a SEP, RMSEP and r of 2.13%, 4.53% and 0.89, respectively. Wheat hardness of South African cultivars was further investigated by means of a comparative scanning electron microscopy (SEM) study performed on South African and Canadian wheat cultivars of different hardnesses. For each cultivar a cross section of the endosperm and a sample of the whole wheat flour were examined. The South African durum wheat, Kronos and the Canadian durum wheat had similar kernel endosperm and flour structures with tightly-packed protein-starch matrixes and a high degree of starch damage. Canadian and South African bread wheats reveal a large range of hardnesses and therefore a great difference in kernel endosperm and flour structure. The continuity of the protein-starch matrix, the degree of starch damage and the structure of starch granules differ within the bread wheat class, with T4 and SST 75 being, respectively, the hardest and the softest of the examined South African cultivars. The structure of the South African and Canadian soft wheat cultivars have a high resemblance, both revealing a discontinuous matrix, free starch granules and little. or no starch damage. Results confirm the theory that wheat hardness is determined by the strength of the protein-starch bond and that hardness-related structural differences exist within especially the South African and Canadian bread wheats. It can be concluded that the bread wheat class of the Southern and Western Cape is significantly (P ≤ 0.05) influenced by genotype, protein and moisture content and encompasses wheats of a very wide hardness range. A new system of categorising South African wheats for commercial purposes that acknowledges these differences by including kernel hardness measurements, could be beneficial to the milling and baking industries. The PSI method and FT-NIR spectroscopy have been establish as successful methods for such determinations on South African wheat cultivars.

AFRIKAANSE OPSOMMING: Fourier transformasie naby infrarooi (FT-NIR) spektroskopie, die partikelgrootteindeks (PGI) metode en skandeer-elektronmikroskopie (SEM) is gebruik om die broodkoringhardheid . scenario van die Suid- en Wes-Kaap in Suid-Afrika te ondersoek. Die effek van verskille in monsterhouerkomposisie op FT-NIR kalibrasie en voorspellingsresultate is ondersoek. Verskillende kalibrasies is ontwikkel vir proteien en voginhoud van 92 Suid-Afrikaanse heelkoringmeelmonsters deur gebruik te maak van drie verskillende monsterhouertipes. Die beste resultate is verkry met borosilikaat-glasflessies, gevolg deur soda-glasflessies en die konvensionele monsterhouer met 'n saffier-glasbasis wat saam met die spektrofotometer verskaf is. Verskille in resultate as gevolg van die gebruik van verskillende monsterhouers is ondersoek deur gebruik te maak van die korrelasiekoeffisiente (r) en maksimum afstande (d) van 'n aantal individuele spektra en deur analise van variansie (ANOVA) op voorspelde waardes vir onafhanklike validasie van die verskillende kalibrasiemode lie. Die effek van komposisionele verskille binne die borosilikaat-glas en sodaglasflessies is ondersoek deur middel van ANOVA op voorspelde waardes van 'n enkele monster wat blootgestel is aan die spektrofotometer in 'n aantal individuele flessies. Daar is gevind dat aile verskille statisties onbeduidend is (P ≤ 0.05). Die saffier-glasmonsterhouer wat saam met die spektrofotometer verskaf word, kan dus vervang word met een van die ondersoekte flessie tipes waarin elke monster individueel gestoor en aan die spektrofotometer blootgestel kan word. Die broodkoringhardheid scenario van die Suid- en Wes-Kaap is ondersoek deur 'n FT-NIR hardheid kalibrasie vir 198 gemaalde broodkoringmonsters te ontwikkel waar die partikelgrootte-indeks (PGI) metode as verwysingsmetode gebruik is. Volgens die PGI resultate het die ondersoekte broodkoringkultivars 'n wye hardheidsreeks van 37.05 - 60.50%, wat daarop dui dat die broodkoringklas in die Suid- en Wes-Kaap korings van 'n besondere wye reeks van hardhede bevat. Die invloed van genotipe, lokaliteite, proteien- en voginhoud op graanhardheid is met behulp van statistiese ontledings ondersoek. Betekenisvolle verskille in hardheid is gevind in monsters van verskillende genotipe (P ≤ 0.05). Hardheid toon verder 'n positiewe linieere verband met proteien- en 'n negatiewe linieere verband met voginhoud. Monsters is aan die spektrofotometer blootgestel in individuele borosilikaatglasfiessies. 'n FT-NIR kalibrasie is gevolglik ontwikkel deurdat die som van kleinste kwadrate (PLS) regressie uitgevoer is op basislyn-gekorrigeerde spektra. Die model is gevalideer met behulp van onafhanklike validasieprosedures. Goeie resultate is verkry met In standaardfout van voorspelling (RMSEP), standaardfout van voorspelling gekorrigeer vir oorhelling (SEP) en 'n korrelasiekoeffisient (r) van onderskeidelik 4.53%, 2.13% en 0.89 behaal. Die resultate van die studie dui daarop dat beide die PGI en die FT-NIR metodes suksesvol gebruik kan word om korrelhardheid van Suid-Afrikaanse broodkorings te bepaal. Om die koringhardheid van Suid Afrikaanse korings verder te bestudeer, is 'n vergelykende skandeer-elektronmikroskopie studie op In aantal Suid-Afrikaanse en Kanadese koringkultivars van verskillende hardhede uitgevoer. 'n Kruisseksie van die endosperm en 'n monster van die heelkoringmeel van elke kultivar is ondersoek. Die Suid-Afrikaanse durumkoring, Kronos, en die Kanadese durumkoring het eenderse endosperm- en meelstrukture met styfgepakte proteien-stysel matrikse en 'n hoe graad van styselbeskadiging getoon. Suid-Afrikaanse en Kanadese broodkorings het 'n groot variasie in hardheid en dus ook in endosperm- en meelstruktuur openbaar. Die. kontinuiteit van die proteien-stysel matriks, die graad van styselbeskadiging en die struktuur van die styselgranules het onderlinge verskille getoon met T4 en SST 75 wat, onderskeidelik, die hardste en die sagste van die ondersoekte Suid-Afrikaanse broodkorings was. Die struktuur van die Suid-Afrikaanse en Kanadese sagtekoringmonsters toon 'n groot ooreenkoms. Seide het 'n los matriks, vry styselgranules en min of geen styselbeskadiging. Resultate van die SEM studie staaf die teorie dat koringhardheid bepaal word deur die sterkte van die proteien-styselbinding en dui ook op hardheidsverwante strukturele verskille binne en tussen veral die Suid-Afrikaanse en Kanadese broodkorings. Daar kan verder ook afgelei word dat die broodkorings van die Suid- en WesKaap betekenisvol beinvloed word deur genotipe, proteien- en voginhoud en dat die broodkoringklas korings van 'n baie wyer reeks hardhede insluit. Daarom is 'n nuwe sisteem vir die katagorisering van Suid Afrikaanse broodkorings wat korrelhardheidbepalings insluit, moontlik nodig. Die PGI metode en FT-NIR spektroskopie is daargestel as suksesvolle metodes vir sulke bepalings op Suid-Afrikaanse koringkultivars.

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