Evolution of mechanical characteristics of tomatoes of two varieties during ripening

Mechanical characteristics of tomatoes of two varieties (Pusa Ruby and Vashali hybrid) were studied at various stages of ripening by whole fruit compression (WFCT) and Magness-Taylor penetration (MTPT) tests on an Instron Universal Testing Machine, Model 1 140. Rupture/penetration force, deformation at rupture/penetration, stiffness, and work done were computed from the respective force-deformation curves for WFCT and MTPT for various ripening stages of both varieties. All the parameters, except deformation at rupture under WFCT, showed highly significant variations with ripening. The fruits of both varieties showed significant differences in all parameters obtained by WFCT except in stiffness. The tomatoes of the Vashali hybrid were firmer requiring 20-50 % extra force to rupture/puncture at all stages of ripening compared with Pusa Ruby. The deformation at penetration increased four times more rapidly, with ripening, for Pusa Ruby compared with the Vashali hybrid. After breaker stage, Pusa Ruby fruits required more energy (work) for penetration as most of the energy was spent in deformation rather than puncturing. The overestimate of work of compression or penetration when approximated by linear force deformation curve was significant at the 99.9 % level. Except for deformation under WFCT (for the Vashali hybrid) and work done under MTPT (for Pusa Ruby), all the other parameters showed good correlations between them. Empirically selected inverse and power law models adequately described the variation in most of the parameters with ripening index and both the models were equally suited for the purpose.

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