Maturity, Ripening, and Quality Relationships 59
apples harvested less mature show very little difference in softening, whereas fruit
harvested at more mature stages shows differentials in softening rate dependent on
its size (Johnston et al., 2002b). In later-harvested apples, small fruits soften at a
slower rate than do large fruits.
There are cases where fruits do not appear to soften after harvest. Strawberries
are progressively softer when picked at 50%, 100%, and after full red color. No
matter at which stage the fruits are harvested, strawberries do not soften after harvest
for up to 5 days of cool storage plus 2 days at shelf temperature (Forney et al.,
1998). A partial explanation for this observation is that postharvest softening does
not occur in strawberries within a 6- to 7-day period after harvest. Similar observa-
tions have been made over short storage durations for fresh-cut apple slices. Under
a short shelf-life expectation (6 days or less) softening does not appear to be
significant; however, if shelf life expectations exceed 6 days, softening becomes a
determinant for the end of shelf life (Kim et al., 1993). Therefore, the length of
storage must be considered when evaluating whether textural changes will be impor-
tant.
Another effect of harvest maturity in some fruit is the susceptibility to significant
textural disorders in storage. For instance, ‘Songold’ plums were found to develop
gel breakdown sooner and more severely if they were harvested past optimum
maturity (Taylor et al., 1995). In that case, the optimal maturity was defined as fruit
with an average firmness of 64 N, while fruit harvested at an average firmness of
44 N had severe incidence of the disorder.
In attempting to understand the influence of maturity at harvest on firmness and
texture changes during storage, allowance must be made for understanding differ-
ences in relation to cultivar. In apples, rates of softening in response to exposure to
low chilling temperatures can vary significantly for different cultivars (Johnston et
al., 2001a,b). Also in apples, harvest maturity in some cultivars is extremely critical
in determining the firmness and crispness in fruit after storage (Zerbini et al., 1999).
In sweet cherries, softer cultivars have a shorter lag phase after pit hardening than
do firmer cultivars (Choi et al., 2002). Similar findings have been reported for
nectarines; firmer cultivars are described as “slow-ripening” (Brecht et al., 1984).
3.2.2 FLAVOR
As with texture, flavor can be significantly affected by the maturity of the fruit at
harvest. The perception of flavor is considered to be a rather complex issue and
involves the combined impact of acidity (titratable acidity and pH), soluble solids
(individual sugars and sugar alcohols), and aroma volatiles (Young et al., 1996;
Baldwin et al., 1998; Harker et al., 2002b). While there are general relationships
among acidity, soluble solids, aroma volatiles, and flavor, the relationship of indi-
vidual components to final flavor impact can be inconsistent (Harker et al., 2002b).
Therefore, this discussion will focus on effects of maturity on the individual com-
ponents and their change in postharvest situations.
Generation of aroma volatiles in fruit is linked with metabolism at the latter
stages of maturity (Girard and Lau, 1995; Song and Bangerth, 1996; Fellman et al.,
2003), and hence fruit picked at a more mature stage would be expected to have a