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To develop a dispersive Raman spectroscopic method for measuring amylose-amylopectin ratios of corn starch mixtures, 67 mixtures were prepared by randomly mixing waxy and normal corn starches. Amylose contents were measured using a dual wavelength iodine binding colorimetric method. Raman data were collected from 250 to 3200 cm-1 using optimized instrument parameters. Partial least-squares (PLS) and principal components regression (PCR) were used to prepare multivariate calibration models; however, PLS commonly outperformed PCR. Truncating the spectra to 250 to 2000 cm-1 improved the results (r2 of validation = 0.831, SEP = 2.90%). Removal of a cold water swelling starch from the data also offered a slight improvement in results (r2 of validation = 0.860, SEP = 2.70%). Dispersive Raman spectroscopy may not be well suited for quantifying amylose content of starch mixtures; however, the method was easily capable of discriminating between waxy and normal starches. This may allow the method to be used for confirming the identity of starch shipments.
A dispersive Raman spectroscopic method for measuring retrogradation in corn starch gels was investigated. Thirty-six gels were prepared, stored at 4° C and measured at regular time intervals (0 h, 24 h, 48 h, 72 h, 120 h, 168 h after preparation). After each measurement, the gels were freeze-dried, then each resultant dried gel was ground into a powder and measured using X-ray diffraction. Relative crystallinity was determined, and intensity changes in the Raman band at 480 cm-1 were measured. No correlation was found between changes in the 480 cm-1 band and the relative crystallinity of the gels (r2 < .1). The low starch concentration used may have caused the poor Raman signal strength and the unpredictable changes in the X-ray diffraction data. The experiment found that measuring retrogradation in very dilute starch gels could be problematic, and that more development is needed in order to apply Raman spectroscopy to in a food system like white pan bread.
Advisor: Randy Wehling