Effect of pulsed light and ascorbic acid/CaCl2 dipping on rheological properties of fresh-cut apples

GÓMEZ, P.; SALVATORI, D.; ALZAMORA, S.M.

Atenas

Congreso; 11th International Congress on Engineering and Food; 2011

School of Chemical Engineering, National Technical University of Athens

The aim of this work was to evaluate the changes on linear viscoelastic properties of fresh-cut apples irradiated with pulsed light (PL) subjected or not to an antibrowning pretreatment. Apple slices (3 cm diameter and 0.6 cm thickness) were dipped into a 1% (w/v) ascorbic acid + 0.1 % (w/v) calcium chloride solution for 5 min at 4ºC. The PL treatments were performed with a RS-3000B Steripulse-XL system, which produced polychromatic radiation (200 to 1100 nm) and generated high intensity pulsed light. Samples were exposed to irradiation for 60 s at 10 cm from the lamp (fluence: 72 J/cm2). Slices irradiated with and without the antibrowning pretreatment were compared to a control throughout a week of storage at 4-5ºC. Dynamic oscillatory shear and creep/recovery tests were performed at 0 and 7 day. Creep behavior was fitted with a mechanical model (a spring, two Kelvin-Voigt elements and a dashpot). Light microscopy observations were made after processing and storage. Storage moduli (G’) of apples exposed to PL were lower than those of the fresh fruit, both at 0 and 7 day. The decrease was more pronounced when apples were pretreated with the antibrowning solution. The instantaneous compliance (J0) and the retarded compliance (J2) increased after 7 day storage in samples irradiated, denoting that these tissues became more deformed. The changes in compliances were greater in irradiated samples previously dipped into the antibrowning solution. Rheological response of apple tissue was correlated with microstructure and ultrastructure features. Pulsed light at the dose tested induced changes in viscoelastic properties of apple tissue that led to both a loss of stiffness and higher capacitance values. These changes were increased by ascorbic acid/CaCl2 treatment and during storage. However, due to the fact that PL irradiation has low penetration, changes in viscoelasticity would be given mainly in superficial region of irradiated samples.