Application of proximal sensing in viticulture: Comparison of different berry state conditions

Previous works have analyzed the relation between the total anthocyanins content in fresh grape berries and some fluorimetric indices. This study aimed to investigate the different fluorescence sensor responses when used to analyze anthocyanins content in grape berries under different conditions: in open field or laboratory, on fresh or frozen berries. The study was conducted in 2016 in a commercial vineyard, cv. Cannonau, located in Nurra Valley (Sardinia, Italy) during the ripening period. A portable fluorescence-based optical sensor (Multiplex®3) was used to measure the "Excitation Fluorescence Anthocyanin ratio Relative Index" (FERARI) on 12 vines in the field (Field Berries = BF), and on 36 Multiplex plates in laboratory on fresh (Fresh Berries = BSH) and frozen (Berries Frozen = BZ) samples. Analysis were performed using two instrument configurations, CFG 2 and CFG 4. A statistical correlation between the fluorescence index and the anthocyanins content in berry skin was observed in all treatments. The highest values were obtained for the frozen samples (CFG 2 ρ = 0.89 R2 = 0.80; CFG 4 ρ = 0.89 R2 = 0.80), while the lowest were acquired for BF (CFG 2 ρ = 0.64 R2 = 0:42; CFG 4 ρ = 0.79 R2 = 0.62). In conclusion, we observed that the CFG4 configuration on frozen fruits gave the best agreement between FERARI index and total anthocyanins content in Cannonau berries.