Submitted to: Rice Utilization Workshop Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: May 13, 1999
Publication Date: N/A
Technical Abstract: NIR-FT/Raman spectroscopy was investigated to provide a rigorous spectroscopic method by which to analyze rice flour for protein and apparent amylose content using a chemometric approach. Ninety rice samples from a 1996 collection of short, medium and long grain rices (grown in 4 states of the U.S., Taiwan, Korea and Austr.) were investigated. Milled rice flour samples were scanned in rotating cups with a 1064 nm NIR laser at 500 mW of power and Raman scatter was collected with a Ge (LN2) detector at 16 cm-1 resolution. Only Raman data over the shift range of 200-3600 cm-1 was utilized. Duplicate spectra of 128 scans each that were averaged and preprocessed with baseline correction and normalization gave the best results. The model for protein (n=86, with 1 spectral and 3 chemical outliers removed) using 7 factors gave r2=0.988 with SECV=0.157% and bias = -0.0003%, over a range of 5.05-10.35%. The model for apparent amylose (n=86, with 4 chemical outliers removed) using 12 factors gave r2=0.982 with SECV=1.09% and bias=0.026%, over a range of 0.50-24.94%. Unlike infrared absorbance methods, Raman is insensitive to interference by water and signals are more likely to be responding to direct compositional differences of the components of interest. Therefore, the C-O bands at 384, 446, and 484 cm-1 and the C-H stretch band at 2929 cm-1 were the primary spectral variables for amylose and amylopectin. The amide I band ca.1670 cm-1 was the primary variable for protein. Thus, there is no interference from O-H bands that could ambiguously be related to either carbohydrate or water content. The results obtained for prediction of protein and apparent amylose content by Raman spectroscopy were nearly statistically equivalent to those obtainable by NIR spectroscopy.