Influence of harvest maturity and storage technology on mechanical properties of blueberries

The present study contributes to the search of methodological procedures to accurately evaluate and ascribe meaning to the mechanical parameters of blueberry. To generate populations of berries with different mechanical properties, 'Nui' and 'Rahi' blueberries were harvested at three maturity stages and stored in five storage technologies for 42 d at 4.6 ?. Storage technologies included two humidity levels in air (high: 99% or low: 80% RH) and three CAs of 5 kPa, 10 kPa, or 20 kPa of CO2 combined with 4 kPa of O-2 at high humidity (94-99% RH). Two mechanical tests, Texture Profile Analysis (TPA) and penetration test, were used to determine ten mechanical parameters. The mechanical parameter that best separated the blueberry population varied depending on the cause of textural variation. Force at skin break provided the best differentiation of harvest maturities at harvest time and after the storage period. However, force at skin break did not differentiate the effect of storage humidity. Hardness slope, skin break slope, and displacement at skin break provided good differentiation of berries stored in different technologies. In addition, hardness slope and skin break slope separated berries obtained by the combined effect of harvest maturity and storage technology after 42 d of storage and were able to detect both softening and firming throughout the storage period. Consequently, the results suggest that the loading slope of the force/deformation graph obtained by any of both mechanical tests (TPA plate compression or needle penetration test) separated stored berries with variable textural characteristics. Hence loading slope may be the most suitable mechanical parameter to track quality changes of stored blueberries.