Agriculture Reference
In-Depth Information
and starch with some sucrose and glucose. Starch concentration in young
fruitlets declines from an initial level of less than
mg g
−
fresh weight to
a minimum of less than
mg at
days after anthesis then increases to a
mg g
−
at
maximum of above
-
days after anthesis. It declines to
a very low level by
-
days from anthesis in 'Royal Gala' and 'Fuji',
respectively (Brookfield
et al.
,
). In general starch hydrolysis begins in the
later stages of fruit growth, usually
weeks before the increase of ethylene
production (ethylene climacteric) in apples (Lau,
or
,
) and about
days before the respiration climacteric in European pears (North,
). Fruit
abscission in some apple cultivars always occurs at a fixed starch concentration
(Poapst
et al.
,
), suggesting a close linkage between starch content and
natural ripening and senescence processes. The amount of starch present and
its distribution can be assessed by exposing the cut surface of fruits cut in half
equatorially for about
% potassium
iodide. The starch stains blue-black and the amount and distribution can be
quantified by comparison with standard charts for the cultivar (North,
seconds to a
% solution of iodine in
;
Smith,
). The starch index
values so obtained provide valuable guidance to the level of fruit maturity and
the appropriate time of harvesting for immediate consumption or long-term
storage.
The starch hydrolysis is accompanied by the appearance of sucrose but
the amount of sucrose is much greater than can be accounted for solely by
starch hydrolysis (Whiting,
; Lau,
; Knee
et al.
,
; Kingston,
). Sucrose is then slowly hydrolysed to form
more glucose and fructose. Starch phosphorylase (EC
.
.
.
),
α
-amylase
(EC
) are probably important. The con-
centration of sugars changes little during storage (Lott,
.
.
.
) and
β
-amylase (EC
.
.
.
; Knee,
;
Table
.
).
Table
.
Changes in some fruit characteristics during storage: 'Bramley's
Seedling' apples stored in
◦
C
-
%CO
at
.
Days in store after harvest
Variable
-
-
-
(
n
=
)
Peel chlorophyll
.
.
.
.
.
(
µ
gcm
−
)
Total sugar (mg g
−
)
.
.
.
.
.
Titratable acid
.
.
.
.
.
(mg g
−
)
Firmness (kg)
.
.
.
.
.
Data from Knee (
). Reproduced with permission.
