Assessment of internal quality attributes of mandarin fruit. 1. NIR calibration model development

Abstract

Abstract. The utility of near infrared spectroscopy as a non-invasive technique for the assessment of internal eating quality parameters of mandarin fruit (Citrus reticulata cv. Imperial) was assessed. The calibration procedure for the attributes of TSS (total soluble solids) and DM (dry matter) was optimised with respect to a reference sampling technique, scan averaging, spectral window, data pre-treatment (in terms of derivative treatment and scatter correction routine) and regression procedure. The recommended procedure involved sampling of an equatorial position on the fruit with 1 scan per spectrum, and modified partial least squares model development on a 720-950-nm window, pre-treated as first derivative absorbance data (gap size of 4 data points) with standard normal variance and detrend scatter correction. Calibration model performance for the attributes of TSS and DM content was encouraging (typical R c 2 of >0.75 and 0.90, respectively; typical root mean squared standard error of calibration of <0.4 and 0.6%, respectively), whereas that for juiciness and total acidity was unacceptable. The robustness of the TSS and DM calibrations across new populations of fruit is documented in a companion study.Additional keywords: spectral window, non-invasive.

NIR model development and robustness in prediction of melon fruit total soluble solids

“…Model performance for prediction of TSS in intact rockmelon fruit was inferior to previous work on mandarins (Guthrie et al 2005a(Guthrie et al , 2005b. This was ascribed to the heterogenous distribution of TSS (sugars) within the fruit and poor penetration of light through the irregular fruit skin.…”

“…The WINISI software forced the removal of at least 1 MPLS factor, on the basis that the first MPLS factor is indicative of the scattering of light in the sample due to particle size and not the attribute of interest. Calibration performance for both 'local' and 'global' MPLS procedures was assessed in terms of R v 2 , RMSEP, standard deviation ratio (SDR = s.d./RMSECV or RMSEP), slope, and bias of the validation populations as per Guthrie et al (2005a). The SDR statistic facilitates comparison of different populations with differing s.d.s.…”

“…7.0) -PLS toolbox (ver. 3.5 by Eigenvector) (Guthrie et al 2005a). The combined populations of years 1 and 2 (17 populations comprising 1467 spectra) were used, with second-derivative (WINISI gap size 4 without scatter correction) absorbance data interpolated to 3-nm steps.…”

“…Peiris et al 1998;McGlone et al 2003). For further review, see Guthrie et al (2005a). In a previous exercise with mandarins (Guthrie et al 2005b), it was demonstrated that model updating following addition to the calibration population of a relatively small number of samples (<20), chosen by any procedure (e.g.…”

Assessment of internal quality attributes of mandarin fruit. 2. NIR calibration model robustness

“…In a companion manuscript (Guthrie et al 2005) the reference sampling procedure and data pre-processing techniques were optimised for the development of partial least squares (PLS) calibration models on intact mandarin fruit for total soluble solids (TSS) and dry matter (DM), using short wavelength (720-950 nm) near infrared (NIR) spectra acquired in an interactance mode (Greensill and Walsh 2000). Chemometric descriptive terms were also defined and will be used in the current manuscript.…”