Non-destructive quality measurement system for cane stalks using a portable NIR instrument

Sugar content of cane at the farm is important information for farmers and millers in Japan because cane prices are determined by pol in cane. While NIR systems have been used to measure cane quality at the mill, portable measurement systems for cane to detect chemical properties in the field have not been developed, although there are some commercially available instruments for fruits. We investigated direct non-destructive measurements for sugar content using a portable near infrared spectrophotometer. A portable fruit tester comprising a NIR spectrophotometer was modified for use in the transmittance mode and employed to quantify brix and pol levels in cane stalks. Reflectance and transmittance spectra in the 600 to 1100 nm range were obtained from 100 cane stalk samples. Brix and pot values were measured with a refractometer and polarimeter. Potassium (K), calcium (Ca) and other chemical components were also measured by an ICP (Inductivity Coupled Plasma) method. Calibration models using a partial least-squares regression analysis were developed for predicting these parameters in cane stalks from the spectra. Calibration models for brix values using transmittance spectra were more suitable than those from reflectance spectra. The model for pol yielded a correlation coefficient of 0.87 with a root mean square error of cross-validation (RMSECV) of 1.0%. Some calibration models for minerals were also developed, although accuracy of the models was not as accurate as pol models. Based on this study, the portable NIR spectrophotometer will be useful for measuring pol and brix values of sugarcane.