Characterizing apple texture during storage through mechanical, sensory and optical properties

Texture is a sensory property affecting consumer acceptability and it is dependent on pulp structure. Often, changes in fruit texture are accompanied by changes in the optical properties of the flesh. The absorption (?) and the scattering (?') coefficients, non-destructively measured in the fruit pulp by time-resolved reflectance spectroscopy (TRS), have been found to be linked to firmness, intercellular spaces, pectic composition and additionally to be correlated with sensory attributes. This research aimed at characterizing apple texture through mechanical, sensory and optical properties during long-term storage in order to understand whether optical measurements can be used to discriminate apples with different textural properties. 'Braeburn' apples, picked with 1 week interval at beginning, mid and end of the optimal harvest window for controlled atmosphere storage, were measured at harvest by TRS at 670 nm (?670), ranked by decreasing ?670 (increasing maturity), classified as less (LeM), medium and more (MoM) mature, randomized into 3 batches of 30 fruit/harvest for analyses at harvest and after 3 and 7 months of cold storage (1.3°C) in controlled atmosphere (1.5% O, 1.3% CO), respectively. LeM and MoM fruit were measured by TRS in the 540-880 nm range and analyzed for mechanical (firmness, stiffness, energy-to-rupture) and sensory (firm, crispy, juicy, mealy) attributes. Cluster analysis applied on mechanical attributes produced four data sets having distinctive textural profiles. W1 apples were characterized by a very firm texture, and showed the highest scores for sensory firmness, crispness and juiciness and the highest ?670 values. In contrast, W3 apples having a soft texture, were judged as the most mealy and the least firm, juicy and crispy and had the lowest ?670 values and the highest scatterer density. TRS optical properties allowed to distinguish well enough very firm apples from mealy ones, while they did not separate apples with intermediate texture due to the fact that these fruit differed for mechanical properties but not so clearly for sensory and optical characteristics.