Improved fluorescence-based evaluation of flavonoids in red and white wine-grape varieties

Background and Aims: Modern viticulture requires robust, fast, non-destructive methods to assess berry composition. We
tested a chlorophyll fluorescence screening method to estimate berry phenolic substances.
Methods and Results: We focused on anthocyanin and flavonol in red and white cultivars. The ANTH_RG indexwas dependent
on the cultivar anthocyanin profile. In Nebbiolo, in which dihydroxylated anthocyanins prevail, ANTH_RG was 2.4 times higher
than in Barbera, in which trihydroxylated anthocyanins prevail. Considering the profiles of the two cultivars at similar anthocyanin
concentration and their relative in vitro absorbance, a bathochromic shift of 10 nm emerged, which can explain the different
screening effect exerted by anthocyanin on chlorophyll fluorescence. As to flavanols, we propose the calibration of a new spectroscopic
index, the FLAV_UV, in coloured and white berries, finding good correlation with flavonol concentration determined
analytically (R2 higher than 0.7).
Conclusions: Spectroscopic indices can estimate the concentration of anthocyanin and flavonol in grape berries.
Significance of the Study: A calibration curve for Nebbiolo, which has a distinctive anthocyanin profile, and the calibration of a
new index, the FLAV_UV, able to estimate flavonol concentration in both red and white cultivars, are described for the first time.
These indices can effectively be applied for non-destructive assessment of grape flavonoid.