Non destructive detection of brown heart in ‘Braeburn’ apples by time-resolved reflectance spectroscopy

Brown Heart (BH) is an internal disorder which is visible only when fruit are cut open. The aim of this work was to test whether time-resolved reflectance spectroscopy (TRS) can be used to detect BH in intact ‘Braeburn’ apples stored for 3 and 6 months in BH inducing (1% O2 + 5% CO2) and not-inducing (2.5% O2 + 0.7% CO2) conditions. At each storage time, at d0 and d14 of shelf life at 18 °C, thirty apples were measured by TRS at 670 nm and in the spectral range 740-1100 nm on four points (A-D) around the equator. Afterwards, each fruit was cut open and evaluated for BH (position and severity), firmness, intercellular space volume (RISV), and pulp colour (in correspondence of TRS points). Fruit affected by BH showed significantly higher μa in the 740-900 nm spectral range than healthy ones, with the highest difference recorded at 740 nm. The μa740 and a* increased and L* and H decreased in fruit with moderate and severe BH and when BH was localized in the pulp. In parallel, RISV showed the lowest percentage in healthy apples and the highest when cavities were associated to browning. High correlations were found between μa740 and pulp L*, a* and H°; considering the correlation with L*, at μa740<0.038 cm−1 only healthy pulp can be detected, while at μa740>0.08 cm−1 only severely browned pulp can be found.