Quality characteristics of air-dried apple rings: Influence of storage time and fruit maturity measured by time-resolved reflectance spectroscopy

With the aim of studying the influence of maturity and of cold storage time on the quality characteristics of air-dried apple rings, 60 apples (cv Pink Lady®) were measured at harvest by time-resolved reflectance spectroscopy (TRS) at 670 nm, ranked on the basis of decreasing absorption coefficient at 670 nm (μa670, increasing maturity) and hence classified based on the ranking order as less mature (LeM), medium mature (MeM,) and more mature (MoM). The sixty fruit were, then, randomized into 3 batches corresponding to 3 storage times (0, 3 and 5 months in normal atmosphere at +1 °C), and, at each storage time, 3 rings/fruit were air-dried at 80 °C up to a constant weight using a pilot air circulated drier. Quality characteristics of fresh fruit and of air-dried rings were analysed by ANOVA and PCA statistical analyses. Stored fruit compared to fruit at 0m were softer, had lower stiffness and energy-to-rupture, and higher soluble solids content (SSC), relative intercellular space volume (RISV) and L*f. LeM class had lower SSC and dry matter, and the MoM class higher a*f and lower b*f than the other two classes. 3m-Apples showed the highest differences with respect to fresh ring in browning index (BI), total colour, chroma and hue, compared to fruit processed at 0m and 5m. Air-dried rings from less mature apples (i.e. those processed at 0m and of LeM class) had higher Fmax, Emod, E and BI than those from more mature fruits (i.e. those processed after storage and of MoM class). PCA underlined the positive relationship between mechanical characteristics of fresh fruit with those of dried rings and ring shrinkage, which were opposite to RISV, SSC and weight loss.