Firmness, dry-matter and soluble-solids assessment of postharvest kiwifruit by NIR spectroscopy

NIR spectroscopy was used to test whether postharvest ripeness and physicochemical properties of kiwifruit (Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson cv. 'Hayward') could be determined non-destructively. Multivariate models for predicting firmness, dry matter, and soluble solids were developed from NIR interactance measurements using a narrow spectral range from 800 to 1100 nm. Dry matter and soluble solids could both be predicted with very good accuracy. Overall regression statistics in prediction were: R-2 = 0.90, root mean square error of prediction (RMSEP)= 0.42% for dry-matter; and R-2 = 0.90, RMSEP = 0.39 degrees Brix for soluble solids content. Firmness was not well predicted with overall prediction statistics of R-2 = 0.66 and RMSEP = 7.8 N. Within a narrow fruit data set, in terms of orchard origin and size, a better firmness model could be produced (R-2 = 0.76, RMSEP = 7.0 N). However this model performed poorly against independent data sets, suggesting the influence of secondary correlations due to fruit characteristics that are not directly related to fruit firmness. (C) 1998 Elsevier Science B.V. All rights reserved.