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United States Department of Agriculture

Agricultural Research Service

Research Project: OPTICAL PROPERTIES OF SMALL GRAINS FOR RAPID AND OBJECTIVE ASSESSMENT OF QUALITY AND SAFETY Title: Soluble Solids and Simple Sugars Measurement in Intact Mango Using Near Infrared Spectroscopy

Authors
item Delwiche, Stephen
item Mekwatanakarn, Weena - DEPT OF HORT, URU, THAI
item Wang, Chien

Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 25, 2008
Publication Date: July 1, 2008
Citation: Delwiche, S.R., Mekwatanakarn, W., Wang, C.Y. 2008. Soluble solids and simple sugars measurement in intact mango using near infrared spectroscopy. HortTechnology. 18(3):325-544.

Interpretive Summary: The level of dissolved sugars in fruit, generally measured by a refractometer calibrated to the percentage of soluble solids in its juice, is an important quality indicator that is used by the mango (Magnifera indica) industry. Although the refractometer method is relatively easy to perform, for the fresh fruit industry it has the drawback of being an invasive procedure. As an alternative, near-infrared (NIR) spectroscopy, a rapid and versatile technique that has found widespread use in food and agricultural applications, is a likely candidate for non-destructive assessment of mango quality. The objective of this study was to examine the potential of using NIR spectroscopy to measure total soluble solids content. Additionally, the technique was also applied to individual concentrations of fructose, glucose, and sucrose within the fruit. Ninety-three mangoes of one variety from one lot were purchased from a local market and stored for up to 11 days to produce varying degrees of ripeness (all edible stages between green underripe and yellow shriveled overripe). Near-infrared interactance, consisting of a fiber optic probe connected to a spectrometer, was used to collect spectra from opposite sides of each mango. From each scanned area, the juice from the underlying flesh was extracted and tested by refractometry for soluble solids content. Juice from a subset of flesh samples was also analyzed by gas chromatography for simple sugars concentrations. The results indicated that the NIR procedure has promise for the measurement of soluble solids, though less likelihood as a sufficiently accurate technique for the simple sugars. The expanding worldwide mango industry, including growers and marketers, are the intended beneficiaries of this work.

Technical Abstract: Total soluble solids content (TSS, °Brix), sucrose, glucose and fructose are important quality attributes of mango (Magnifera indica) fruit and have been shown to be useful for determining fruit maturity. The approach to develop a rapid, reliable, nondestructive method for quality evaluation of mangoes is very important and critical to the mango industry and international trade. Near-infrared (NIR) spectroscopy, which is a nondestructive method for the fruit quality evaluation, has become a very popular technique. The objective of this study was to determine the potential of NIR spectroscopy to predict total soluble solids content and individual concentrations (mg/g) of sucrose, glucose and fructose nondestructively in mango fruit (var Ataulfo). Ninety-three intact mangoes stored at two different temperatures (15 °C and 20 °C) were measured by NIR interactance (400–1098 nm) over a period of 11 days, starting when the fruit were underripe and extending to a few days past optimal average ripeness. Separate spectral and TSS measurements were collected on opposite sides of all mangoes. Simple sugar measurements were collected on a subset of these. Spectral preprocessing consisted of second derivative convolution (11 point Savitzky-Golay) followed by truncation of the wavelength region to 750–1088 nm. Partial least squares (PLS) regression with leave-one-out cross-validation was used to develop models for TSS (°Brix), individual sugar (mg/g), and the sum of the three sugars (mg/g). Such analyses yielded calibration equations with R2 = 0.83, 0.80, 0.61, 0.64, and 0.82; standard error of calibration (SEC) = 0.70, 8.3, 0.95, 4.2, and 9.6; and standard error of cross-validation (SECV) = 1.05, 13.7, 1.4, 6.4, and 14.8 for TSS, sucrose, glucose, fructose, and the sum of the three sugars respectively. These calibrations were sufficiently precise for determining TSS and the sum of the three sugars. Only slight improvements in modeling occurred when the storage temperatures were considered separately. These results indicate that NIR technology offers the possibility to assess fruit quality and maturity in intact mangoes, and may be useful for grading.

Last Modified: 7/23/2014