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

[摘要] 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 wheathardness scenario of the Southern and Western Cape in South Africa.The effect of differences in sample holder composition on FT-NIR calibrationand prediction results were investigated. Different calibrations were derived forprotein and moisture content of 92 South African whole wheat flour samples usingthree different sample holders. Best results were achieved with borosilicate-glassvials, followed by soda-glass vials and the conventional sample cup with a sapphire glassbase provided with the spectrophotometer. Differences in results due to theuse of different sample holders were investigated using correlation coefficients (r) andmaximum distances (d) of a number of individual spectra and by performing analysisof variance (ANOVA) on the predicted values for independent validation of thedifferent calibration models. The effect of compositional differences within both theborosilicate-glass and the soda-glass vials were investigated by means of ANOVA onthe predicted values of a single sample presented to the spectrophotometer in anumber of individual vials. Ail differences were found to be statistically insignificant(P ≤ 0.05). The sapphire-glass sample cup provided with the spectrophotometercould therefore be replaced by one of the vial-types investigated in which eachsample could be stored and presented to the spectrophotometer individually.The bread wheat hardness scenario of the Southern and Western Cape wereinvestigated by deriving a FT-NIR hardness calibration for 198 ground bread wheatsamples and using the particle size index (PSI) test as reference method. Particlesize index results indicate that the investigated bread wheat cultivars have a verywide hardness range of 37.05 - 60.50%. The influence of genotype, location, proteincontent and moisture content on wheat hardness was investigated by means ofANOVA, Student's t-test, correlation analysis and regression analysis. Significantdifferences (P ≤ 0.05) in hardness was found over culitvars, while a positive linearrelationship with protein content and a negative linear relationship with moisturecontent exist. The wheat samples - were subsequently presented to thespectrophotometer in individual borosilicate-glass vials. A FT-NIR calibration was derived by performing PLS regression on baseline-corrected spectra and the modelvalidated 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 meansof a comparative scanning electron microscopy (SEM) study performed on SouthAfrican and Canadian wheat cultivars of different hardnesses. For each cultivar across section of the endosperm and a sample of the whole wheat flour wereexamined. The South African durum wheat, Kronos and the Canadian durum wheathad similar kernel endosperm and flour structures with tightly-packed protein-starchmatrixes and a high degree of starch damage. Canadian and South African breadwheats reveal a large range of hardnesses and therefore a great difference in kernelendosperm and flour structure. The continuity of the protein-starch matrix, the degreeof starch damage and the structure of starch granules differ within the bread wheatclass, with T4 and SST 75 being, respectively, the hardest and the softest of theexamined South African cultivars. The structure of the South African and Canadiansoft wheat cultivars have a high resemblance, both revealing a discontinuous matrix,free starch granules and little. or no starch damage. Results confirm the theory thatwheat hardness is determined by the strength of the protein-starch bond and thathardness-related structural differences exist within especially the South African andCanadian bread wheats.It can be concluded that the bread wheat class of the Southern and WesternCape is significantly (P ≤ 0.05) influenced by genotype, protein and moisture contentand encompasses wheats of a very wide hardness range. A new system ofcategorising South African wheats for commercial purposes that acknowledges thesedifferences by including kernel hardness measurements, could be beneficial to themilling and baking industries. The PSI method and FT-NIR spectroscopy have beenestablish as successful methods for such determinations on South African wheatcultivars.

[发布机构] Stellenbosch University