Comparing density and NIR methods for measurement of Kiwifruit dry matter and soluble solids content

Abstract

Abstract Density and near infrared (NIR) predictions of dry matter (DM) and soluble solids content (SSC) have been made on kiwifruit ( Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Fergusion var. Hayward). The data set consisted of 360 kiwifruit harvested unripe, late in the commercial harvest period, from four orchards and examined either immediately or after ripening. Density measurements were made by flotation and the NIR measurements were made with a polychromatic spectrometer operating over the range 300–1140 nm. Both the density and NIR methods accurately predicted DM (as % fresh weight), on both unripe and ripe fruit, and SSC (as % fresh juice) on ripe fruit. The root mean square error of prediction (RMSEP) was around 0.5% or less, irrespective of whether DM or SSC was being predicted, with the better results obtained on ripe fruit and with the NIR method. For the situation of most practical interest, the grading of unripe fruit at harvest time, the accuracy of the NIR and density methods were fairly similar, with RMSEPs of 0.39 and 0.53%, respectively, in terms of predicting the final SSC of the fully ripened, ready to eat fruit.