Agriculture Reference
In-Depth Information
Perceived sweetness is higher the lower the acidity (Visser
et al.
,
): a sport of
'Jonagored' characterized by its sweetness of taste was found to be identical in
sugar content but much less acid than the parent type (Lott,
). For pears,
which are less acid, perceived sweetness is higher the juicier the fruit. Sugar
and acid content are inherited independently and change independently over
time and in response to controlling factors. Therefore, although perceived taste
depends on the balance of sugar and acids (Yahia,
) its variability and
management are generally approached at the individual component, sugar
and acid, level. There is no single desirable level of sugar, acid, or sugar/acid
ratio that applies to all cultivars. Corrigan
et al.
(
) showed soluble solids
content to range from
.
%to
.
%, malic acid from
.
%to
.
% and
the soluble solids to acid ratio from
between five cultivars of current
commercialimportance.Thispresumablyshowsthatdifferentconsumershave
different tastes, but consistency in matching the expected taste of a cultivar is
important.
to
Aroma
Much of the character of apple and pear fruits depends on their aroma, re-
sulting from trace amounts of volatile organic substances. Between
and
volatiles, out of more than
identified, are responsible for apple aroma
(Yahia,
).Typicalaromavolatilesincludeesters(e.g.hexylhexanoate),lipid
oxidation products (e.g. (E)-
-damascenone.
Different cultivars have different characteristic aroma volatiles. When
amino-acid precursors are fed to different cultivars they are converted into
different volatiles, for example 'Granny Smith' converts isoleucine to ethyl
-hexenal) and the terpenoid
β
-methylbutanoate whereas 'Red Delicious' apples also show conversion to
-methyl-
-butenyl esters (Rowan
et al.
,
).
Changes during maturation
and ripening
Physical properties
Cell separation occurs during the growth of apples so that at maturity about
% of the fruit volume is air space between the cells (Khan and Vincent,
). This increase in air space may account for the decline in firmness
during growth (Knee,
) and may be difficult to separate from ripening-
related changes in fruit texture. Hesse and Hitz (
) found
a slow decline in firmness, as measured by pressure tests, from late August to
early October whereas the best eating quality was achieved by harvest in late
) and Smock (
