Comparative Study on the Use of a Non-Destructive Optical Sensor (Multiplex®3) for the Monitoring of the Anthocyanin Content in Red Berry Fruit

The preliminary results of a comparative study on the determination of the anthocyanin content in red grape and plum by a portable fluorescence-based optical sensor (Multiplex®3) are reported. Commercially available Multiplex®3 was used for measuring the "Fluorescence Excitation Ratio Anthocyanin Relative Index" (FERARI) in red plums (Prunus domestica, L., cv Nero Sardo, Dore A. and Stanley) and red grapes (Vitis vinifera, L., cv Monica and Cagnulari). In both species the FERARI was related with the total anthocyanin content determined by UV-Vis spectrophotometry and expressed as mg/100 g peel of malvidin 3-glucoside and mg/100 g peel of cyanidin 3-glucoside for grape and plum, respectively. A good correlation between the fluorescence index and the peel anthocyanin content in all the plum cultivars was observed. On the contary, only for one grape cultivar (Cagnulari) correlation was found. Moreover, FERARI and anthocyanin content showed a linear relationship in plum while it was logarithmic in grape. Finally, a larger range of anthocyanin content detectable with Multiplex®3 was observed for plum compared to grape. Preliminary results showed that the fluorimetric-based optical sensor Multiplex®3 can be an effective tool for monitoring anthocyanin content in the peel of red plum. Moreover, a marked difference in its use depending the species was observed.