with kcis rate constant of the chilling process, and khis rate constant of
the heat process. Both rate constants kcand khwill, as for all chemical
reactions, depend on temperature according to Arrhenius’ law:
kiki,ref e (7.3)
where kiis the rate constant of process i(cchilling injury, hhigh
temperature deterioration), ki,refis the rate constant of process iat ref-
erence temperature Tref(15°C), Eiis the energy of activation of that
process, and Tabsis the actual absolute temperature in the experiment.
Results
With these equations, the data of 20 species potted plants were ana-
lyzed using multiple nonlinear regression, and the parameters estimated.
In Figure 7.4 the acceptability is shown for six selected species as a
function of storage time, Figure 7.5 shows the acceptability of the same
six species as function of temperature. Except for two species, the ex-
plained variance (R^2 adj) exceeded 90%, and was more than 95% in 8 of
the 20 species. The kinetic parameters of the model can directly be in-
terpreted in terms of chilling and/or heat sensitivity. Fifteen species have
a distinct value for the reference rate for the chilling process (kcref) while
five species have no distinct value for that parameter. These results are
in agreement with the generally accepted behavior for these species.
From Figure 7.5 it is clear that the duration of storage in darkness has
a pronounced effect on the apparent rate of decrease in acceptability:
The longer a species has been stored or transported in darkness, the nar-
rower the optimal temperature region becomes, the faster the loss in ac-
ceptability becomes, assuming some plants are still saleable, and the
more pronounced differences due to temperature become. A practical
consequence is that more care should be taken in selecting the optimal
transport condition for transportation of longer duration.
From the model formulation it follows how the initial condition of
the potted plants (N 0 ) will affect the maximal acceptable transportation
period. N 0 also reflects the differences obtained in experiments (e.g.,
replications) with batches with apparently identical starting quality. The
more N 0 deviates from the maximum value Nmax, the sooner the plants
will become unacceptable at any temperature. Figure 7.6 gives an ex-
ample for the species Dieffenbachia,stored at 20°C with an initial num-
ber of acceptable potted plants ranging from 11.94 to 11.999 on a total
^1
Tabs
^1
Tref
Ei
RExamples of Modeling Accetability 133