To investigate the robustness with respect to maturity, samples
of two maturity color stages (4 and 5 from both seasons) were
combined to develop the calibration model, which was then
externally validated three times: 1) with the samples from both
stages in the prediction set, 2) with the samples from stage 4, and 3)
with samples from stage 5. Additionally, the robustness in terms of
seasonality was examined.