Brix, pH and anthocyanin content determination in whole Port wine grape berries by hyperspectral imaging and neural networks

This work presents the results of measuring pH, sugars, and anthocyanin content of whole grape berries. The spectrum of each sample, composed of six whole grape berries, was collected using hyperspectral imaging in reflectance mode from 380 to 1028 nm. The spectra were converted to enological parameters by multilayer perceptrons created using 240 samples that were split for 7-fold cross-validation and test. The test set with 30 samples revealed R2 values of 0.73, 0.92 and 0.95 and RMSE of 0.18, 0.95 °Brix and 14 mg/l for pH, sugars and anthocyanin content, respectively. This is the only work, up to the authors’ knowledge, that reports the simultaneous determination of pH, sugars and anthocyanin with a spatial resolution smaller than the bunch size, by spectroscopy measurements done in reflectance mode. The results presented show an improvement of the state-of-the-art, for both reflectance and transmittance mode, that is particularly notorious for anthocyanin measurement.