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.