Use of near infrared hyperspectral tools for the screening of extractable polyphenols in red grape skins

Abstract

a b s t r a c tHyperspectral images of intact grapes were recorded at harvest time using a near infrared hyperspectral imaging system (900-1700 nm). Spectral data have been correlated with red grape skin extractable polyphenols (total phenolic, anthocyanins and flavanols) by modified partial least squares regression (MPLS) using a number of spectral pretreatments. The obtained results (coefficient of determination (RSQ) and standard error of prediction (SEP), respectively) for the developed models were: 0.82 and 0.92 mg g À1 of grape skin for extractable total phenolic content, 0.79 and 0.63 mg g À1 of grape skin for extractable anthocyanin content, 0.82 and 0.45 mg g À1 of grape skin for extractable flavanol content. The obtained results present a good potential for a fast and reasonably inexpensive screening of the extractable polyphenolic compounds in intact grapes. Moreover, the heterogeneity of extractable polyphenols within the ripeness stage has been also evaluated using the proposed method.

Relationship between hyperspectral indices, agronomic parameters and phenolic composition of Vitis vinifera cv Tempranillo grapes

“…Vegetation indices developed from spectral observations in the visible‐near infrared (NIR) regions are highly correlated with several plant stand parameters, such as green leaf area index, chlorophyll content, percentage ground cover of vegetation, etc . These non‐destructive techniques also have demonstrated their estimation abilities with respect to determining both technological maturity and the extractable polyphenols of grapes . However, no studies have correlated such indices with the detailed phenolic composition of grapes.…”

“…11,17,18 These non-destructive techniques also have demonstrated their estimation abilities with respect to determining both technological maturity 19 and the extractable polyphenols of grapes. 20 However, no studies have correlated such indices with the detailed phenolic composition of grapes. A good correlation between NIR-imaging technology, 21,22 NIR spectroscopy 23 and the phenolic composition of seeds and intact grapes has also been reported when measurements are performed directly on the seeds and grapes, respectively.…”

Digital photography provides a fast, reliable, and noninvasive method to estimate anthocyanin pigment concentration in reproductive and vegetative plant tissues

“…Finally, our methodology performs well when analyzing variation among samples in concentration of the same anthocyanin type (e.g., cyanidin derivatives). However, when samples differ in the type of pigment (e.g., anthocyanin vs. carotenoid), type of anthocyanin (cyanidin vs. pelargonidin), or in their biochemical modifications (glycosylation & acylation; Merken & Beecher, ; Nogales‐Bueno, Baca‐Bocanegra, Rodríguez‐Pulido, Heredia, & Hernández‐Hierro, ), digital images will capture the visible color, but there will be no associated changes in the raw anthocyanin concentration. In these cases, other indices may show improved performance, but require further study.…”

Linking ATR-FTIR and Raman features to phenolic extractability and other attributes in grape skin

“…Near infrared spectroscopy (NIRS) has been used in order to screen total or extractable phenolic compounds in grapes obtaining quite good results [14][15][16][17][18][19]. However, despite the fact that features in the near infrared region can be used to relate skin cell wall composition to phenolic compounds extractability, it is not possible to interpret this relationship in detail.…”

“…NH ≤ 0.6 is usually applied for grouping samples for similar purposes. In this way, the distribution of samples in the spectral space is optimal for accurate predictions [16,32,33]. Thus, 34 groups with different spectral characteristics were created.…”