The application of discriminant analysis to on-line near infrared spectroscopy of prepared sugar cane

Near Infrared (NIR) reflectance spectra of prepared cane and accompanying conventional analytical measurements (i.e. fibre, juice pol and juice brix) were collected over two harvest seasons (1998-1999) at Proserpine sugar mill. The spectra were separated by harvest year, cane variety, harvest method (i.e. burnt or green) and cane age (i.e. one year old or standover cane). To a limited extent discriminant analysis was able to correctly assign cane to harvest year, cane variety, harvest method and cane age. This discriminant analysis was simplified to three types (i.e. Ql24 green harvested. all other varieties green harvested and all varieties burnt harvested), and this analysis correctly assigned spectra to types. NIR calibrations for juice pol and juice brix based on all spectra (local calibrations) and on the three types (type calibrations) were developed and compared to global calibrations reported in the literature. The standard errors of calibration of local calibrations are superior to those of global calibrations. Some further improvement in calibration is achieved by using type calibrations, but not enough to justify the effort required to maintain type calibrations.