Improved fluorescence-based evaluation of flavonoid in red and white winegrape cultivars

Background and Aims: Modern viticulture requires robust, fast, non-destructive methods to assess berry composition. Wetested 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 dependenton the cultivar anthocyanin profile. In Nebbiolo, in which dihydroxylated anthocyanins prevail, ANTH_RG was 2.4 times higherthan in Barbera, in which trihydroxylated anthocyanins prevail. Considering the profiles of the two cultivars at similar anthocyaninconcentration and their relative in vitro absorbance, a bathochromic shift of 10 nm emerged, which can explain the differentscreening effect exerted by anthocyanin on chlorophyll fluorescence. As to flavanols, we propose the calibration of a new spectroscopicindex, the FLAV_UV, in coloured and white berries, finding good correlation with flavonol concentration determinedanalytically (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 anew 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.