Fruit and Vegetable Quality

plant example, as it is based on data gathered from experiments using
exclusively fixed acceptability limits. To develop models that include
variable quality criteria, we have to search deeper into the mechanisms
involved in quality decay. In the model on keeping quality (Tijskens,
1995; Tijskens and Polderdijk, 1994d, 1996a), these aspects are worked
out for the four most commonly occurring mechanisms. All four mech-
anisms resulted in the same generic formulation of keeping quality show
in Equation (7.4):

KQ (7.4)

where KQis the keeping quality, kis the rate constant for each of the
occurring quality decaying processes iand KQrefis the keeping quality
at reference temperature. Keeping quality may be defined as the time
the product’s quality remains acceptable during storage or transport.
Shelf life may be defined as the keeping quality at standardized condi-
tions. The definition of acceptability, that is, which product properties
are included and which quality limits are applied, remains rather unde-
fined and changes from produce to produce, from consumer to consumer
and from situation to situation.

Effect of Quality Limits

To be flexible and generic, the quality limit, applied by a consumer
or group of consumers, has to be included in the model formulation.
Based on an assumed exponential mechanism as an example for the qual-
ity attribute(s) involved, the model on keeping quality is explained and
the effects of different limits and initial qualities are shown. Other mech-
anisms are possible, with a different relation for the limit applied.

KQ (7.5)

where Qis the quality of the produce, 0 at initial time, and lthe limit
value. The relation deduced for keeping quality of perishable products
is shown in Equation (7.5). We see that (for this exponential mechanism

ln

Q

Q

0

l







N

i 1

ki

KQref





N

i 1

ki

Examples of Modeling Accetability 135