A rapid method for the simultaneous measurement of gluconic acid and glycerol, two important chemical markers of grape infection, was developed using Fourier-transform mid-infrared (FT-MIR) spectroscopy. The method used a combination of FT-MIR with partial-least squares (PLS) regression and compositional data of Trebbiano and Sangiovese grapes obtained with high performance ion-exchange chromatography (HPLC). A total of 320 grape samples were analyzed, including grapes hand picked in the vineyards (200 samples) and mechanically sampled from trucks upon arrival at the wineries (120 samples). Gluconic acid and glycerol increased with increasing percentage of grape infection assessed by visual inspection (r = 0.928). The best result was obtained for gluconic acid (R2 = 0.979; RMSECV = 0.63; RPD = 7.0), indicating that FT-MIR was suitable for process control.
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