Data of Texture Profile Analysis performed by different input settings on stored ‘Nui’ and ‘Rahi’ blueberries
Data of the average results obtained by the evaluation of four storage humidity for 21 d at 4.5 °C on mechanical properties of hardness (N), hardness slope (kN m-1), resilience (-), and apparent modulus of elasticity (MPa) obtained by using two compression distances (15 % or 30 % strain) as target displacement for operating texture analyzer in two blueberries cultivars, ‘Nui’ and ‘Rahi’ Data of the average results obtained by the evaluation of four storage humidity for 21 d at 4.5 °C on mechanical properties of cohesiveness (-) and springiness (-). Cohesiveness and springiness were measured by using four operational conditions obtained by the matrix combination of two compression distance (15 % and 30 % strain) and two times duration between compression cycles (2 s and 10 s) as TPA operational settings in two blueberries cultivars, ‘Nui’ and ‘Rahi’
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Mechanical properties of Texture Profile Analysis (TPA) were assessed at 20 °C on ‘Nui’ (highbush blueberry) and ‘Rahi’ (rabbiteye blueberries) previously-stored for 21 d at 4.5 °C in four storage humidity of 73 %, 88 %, 92 % and 95% for ‘Nui’; and of 74 %, 81 %, 89 %, and 93 % for ‘Rahi’. Texture Analyser (TA.XT plus, Stable Micro Systems, Surrey, UK) equipped with a 5 kg load cell and a 25 mm cylindrical flat-ended probe (P/25, Stable Micro Systems). Mechanical properties of hardness, resilience, cohesiveness, hardness slope, and springiness were estimated from the double compression graph using Exponent software (Version 184.108.40.206, Stable Micro Systems). Hardness, hardness slope and resilience were obtained using the first compression cycle immediately before the waiting time has started, and cohesiveness and springiness, using both compression cycles. Hardness was calculated as the maximum force (N) to achieve 15 % or 30 % strain. Hardness slope or chord stiffness as the slope of a straight line drawn between the trigger force of 0.06 N and the maximum force at 15 % or 30 % strain. Resilience was calculated as the ratio of the area of work (force X displacement) during withdrawal (upstroke) of the first compression to the area of work during the downstroke of the first compression. Cohesiveness was calculated as the ratio of the area of work during the second compression cycle to the area of work during the first compression cycle. Springiness was calculated as the ratio of displacement (mm) during downstroke compression of the second cycle to the displacement (mm) during downstroke compression of the first cycle . The apparent modulus of elasticity (MPa) was calculated following the equation for parallel plate contact of spherical samples of viscoelastic behaviour (Eq. 1). E= (0.338 F (1-µ^2))/D^(3/2) × [K_U× (1/R_U +1/(R_U^' ))^(1/3)+K_L 〖×(1/R_L +1/(R_L^' ))〗^(1/3) ]^(3/2) (Eq. 1) Where, E is the apparent modulus of elasticity (Pa); F is the force (N) at selected deformation distance (15 % or 30 % strain); D is the probe displacement (m) at selected deformation distance; µ is the blueberry Poisson’s ratio (dimensionless); RU and R’U are the minimum and maximum, respectively, radii of curvature (m) of convex shape object at the upper point of contact (plate probe); RL and R’L are the minimum and maximum, respectively, radii of curvature (m) of convex shape object at the lower point of contact (platform support). KU and KL are constants calculated from the geometry of the upper and lower point of contact, respectively. A Poisson’s ratio (µ) of 0.4 was assumed for blueberries. Assumptions for spherical objects were considered, thus RU, R’U, RL, R’L were equals to the radii of curvature (R) and KU=KL=1.351 . Radii of curvature were calculated for each berry by the equatorial diameter obtained from Texture Analysis readings.