Browsing by Author "Van Zyl, Louise"
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- ItemThe 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(Stellenbosch : Stellenbosch University, 1999-12) Van Zyl, Louise; Manley, M.; Osborne, B. G.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.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.