Viscoelastic properties of Tarocco orange fruit
Moresi, M.; Pallottino, F.; Costa, C.; Menesatti, P.
FOOD AND BIOPROCESS TECHNOLOGY
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In this work, the rheometrical behaviour of Tarocco orange fruit was assessed via stress–relaxation testing under constant engineering strain (?z) in the range of 5–20% of the initial fruit height, each test being prolonged for 15 min and replicated 20 times. The time course of the experimental dimensionless relaxation modulus (G*) was typical of a viscoelastic solid and was reconstructed by considering two Maxwell elements in parallel to an elastic spring element. In a more restricted ?z range (i.e. 5–10%), the dimensionless viscoelastic constants (Ai) were found to be approximately constant, the elastic component responsible for the equilibrium residual stress representing about 42% of the initial relaxation modulus. After any orange fruit had been submitted to stress–relaxation testing and decompressed for 5 min, it exhibited a practically negligible mass loss (0.04±0.03%) and a permanent volume contraction rising from 1.7±1.0% to 3.0±0.9% as ?z was increased from 5% to 10%. Thus, by tasting the orange fruit firmness at ?z ?5%, fruit response, being of the viscoelastic type, is expected to give rise to nearly irrelevant deformations.