A Maturity Index for Blueberries Using Light Transmittance1

Light transmittance curves of intact blueberries, ‘Wolcott’ and ‘Bluecrop’ cul-tivars4, were recorded in the visible and infrared with the ASCO Biospect5 and correlated with anthocyanin content. Correlation coefficients were computed for a large number of possible maturity indexes to determine the optimum index. In all cases the index involves the measurement of the optical density of the intact fruit at 2 wavelengths and computation of the optical density difference. From the ‘Wolcott’ blueberry correlation data, the highest correlations, 0.925 and 0.967, were found in the infrared region between ∆OD(760–800 nm) vs anthocyanin content per berry and between ∆OD(760–800 nm) vs anthocyanin content per g fresh weight of tissue, respectively. For the ‘Bluecrop’ blueberry, the highest correlations, 0.933 and 0.916, were found in the infrared region between ∆OD(740–800 nm) vs anthocyanin content per berry and between ∆OD(740–800 nm) vs anthocyanin content per g fresh weight of tissue, respectively. Thus, optical density difference measurements of individual intact fruits afford a reliable maturity index for blueberries.