Robustness of NIR Calibrations for Soluble Solids in Intact Melon and Pineapple

Abstract

The soluble solids content of intact fruit can be measured non-invasively by near infrared spectroscopy, allowing "sweetness" grading of individual fruit. However, little information is available in the literature with respect to the robustness of such calibrations. We developed calibrations based on a restricted wavelength range (700-1100 nm), suitable for use with low-cost silicon detector systems, using a stepwise multiple linear regression routine. Calibrations for total soluble solids (°Brix) in intact pineapple fruit were not transferable between summer and winter growing seasons. A combined calibration (data of three harvest dates) validated reasonably well against a population set drawn from all harvest dates (r 2 = 0.72, SEP = 1.84°Brix). Calibrations for Brix in melon were transferable between two of the three varieties examined. However, a lack of robustness of calibration was indicated by poor validation within populations of fruit harvested at different times. Further work is planned to investigate the robustness of calibration across varieties, growing districts and seasons.

Application of commercially available, low-cost, miniaturised NIR spectrometers to the assessment of the sugar content of intact fruit

“…The relatively good performance of the purpose-built instrumentation is ascribed to the low SNR of the MMS1 detector and optimisation of the system in terms of optical geometry of incident light, sample and detector. We will employ this system to collect spectra of melons of various cultivars, growing districts and seasons to further develop the consideration of Guthrie et al (1998) of calibration robustness. Harvested rockmelon fruit vary between 6 and 14 o Brix, with 10 o Brix commonly accepted as a quality standard.…”

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

“…Thus this work extends the consideration of Guthrie et al (1998), using the partial transmittance instrumentation characterised in Walsh et al (2000), and the model updating procedure described for mandarins in Guthrie et al (2005b). In all, 22 populations of various varieties of rockmelons (each of approx.…”

“…of 0.76% TSS. Work in Australia followed, with Guthrie et al (1998) using a reflectance geometry with a NIRSystems 6500 to achieve a RMSEP of 0.9% TSS on a combined variety population of fruit with a s.d. of 3.2% TSS.…”

“…He reported on the use of a calibration model developed in 1 season to predict a single lot from the subsequent season. The only published work on TSS model robustness in intact melons across multiple populations, varieties, and seasons is that of Guthrie et al (1998). In this work, stepwise multiple linear regression (MLR) models were developed using 3-5 wavelengths, rather than modified partial least squares (MPLS) regression of the full spectrum, from reflectance spectra.…”

“…Eastern Star and El Dorado) were attributed to the nature of the skin (irregular and thicker epidermal layers) of these varieties. Further, as there is a poor correlation between skin and inner mesocarp TSS, Guthrie et al (1998) suggested that the correlation of mesocarp TSS with spectral data may represent a secondary correlation with another constituent of the skin and green flesh layers. A breakdown in this secondary correlation could be responsible for the lack of model robustness.…”