Influence of environmental and instrumental variables on the non-invasive prediction of Brix in pineapple using near infrared spectroscopy

The Brix content of pineapple fruit can be non-invasively predicted from th e second derivative of near infrared reflectance spectra. Correlations obta ined using a NIRSystems 6500 spectrophotometer through multiple linear regr ession and modified partial least squares analyses using a post-dispersive configuration were comparable with that from a pre-dispersive configuration in terms of accuracy (e.g. coefficient of determination, R-2, 0.73; standa rd error of cross validation, SECV, 1.01 degrees Brix). The effective depth of sample assessed was slightly greater using the post-dispersive techniqu e (about 20 mm for pineapple fruit), as expected in relation to the higher incident light intensity, relative to the pre-dispersive configuration. The effect of such environmental variables as temperature, humidity and extern al light, and instrumental variables such as the number of scans averaged t o form a spectrum, were considered with respect to the accuracy and precisi on of the measurement of absorbance at 876 nm, as a key term in the calibra tion for Brix, and predicted Brix. The application of post-dispersive near infrared technology to in-line asse ssment of intact fruit in a packing shed environment is discussed.