Fig. 4. Validation scatter plots of actual against predicted values for (top) N and (bottom) total soluble polyphenol concentrations. Calibration models were developed with TreeNet stochastic gradient boosting using a random selection of 75% of the total number of samples and validated on the remaining 25% holdout sample. No outliers were removed from either calibration or validation data sets. Root mean square errors (RMSE) are also given.

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