Evaluating NIR instruments for quantitative and qualitative assessment of intact apple quality

Abstract

AbstractBACKGROUND: In recent years, near‐infrared reflectance (NIR) instruments have undergone radical changes, becoming much more versatile, more portable, cheaper and better adapted to hostile working areas. In this study, three commercially available spectrophotometers were evaluated for the determination of quality (soluble solid content, firmness and shelf‐life) in intact apples. The three instruments used, which differ primarily in terms of measurement principle and wavelength range, were a scanning monochromator (SM) with a range of 400–2500 nm, a combination of diode array and scanning monochromator (DASM) with a range of 350–2500 nm and a diode array (DA) with a range of 900–1700 nm.RESULTS: A total of 334 apples (Malus domestica Borkh.), cvs Fuji and Golden Delicious, were used to build calibration models in different spectral regions and using various spectral signal pretreatments. The three NIR instruments evaluated provided good precision for soluble solid content, with r2 values between 0.90 and 0.94 and standard error of cross‐validation (SECV) values ranging from 0.51 to 0.68°Brix; however, firmness measurements were less precise in all three cases (r2 = 0.52–0.57, SECV = 8.28–8.83 N). The performance of the three instruments in classifying apples by shelf‐storage duration (0, 8 and 14 days) was studied using partial least squares discriminant analysis to develop classification models. A total of 86.1% of samples from the mixed‐cultivar group were correctly assigned, compared with 86.6% of samples from single‐cultivar groups.CONCLUSION: The results obtained suggest that, in general, the three NIR instruments tested provided a similar level of accuracy for the measurement of soluble solid content, firmness and shelf‐life, being slightly better the prediction models developed with the DASM spectrophotometer. Copyright © 2009 Society of Chemical Industry