Physicochemical characteristics of calcium-treated jackfruit (Artocarpus heterophyllus ) pulps during chilled storage
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Date
2009
Authors
Ramli, Rafidah Aida
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Abstract
This work study the changes in physicochemical characteristics of jackfruit pulps at
different maturity levels, of ripe jackfruit pulps during storage at 8 C and of the
effect of different calcium-infiltration method of ripe jackfruit pulps. In the maturity
study, there was a significant increase in the total soluble solid (TSS) from 5oBrix
in green pulps to 28oBrix in ripe jackfruit pulps. The total pectin and chelatorsoluble
pectin registered a significant decrease from green to ripe stage, while the
water-soluble pectin showed an increase. The increase in pH coincided with the
decrease in titratable acids (TA). Although the polygalacturonase (PG) and pectin
esterase (PE) activities were low in green and mature pulps, the ripe pulps
exhibited a sharp increase in both activities. These changes resulted in the jackfruit
to be suitable for human consumption.
The ripe jackfruit pulps stored at 8 oC exhibited an increased in PE activity and a
decrease in pectin content and firmness during storage. Although the pulps started
to lose its firmness by day 3, the lost was significant by day 8, making it appeared
limp and unattractive. Partial purification and characterization of PG and PE from
ripe jackfruit pulps gave purification 0f 1.4% for PG and 19.7 % for PE which could
be due to the instability of the enzymes during purification. The molecular weight of
PG was 46.6 kDa and PE 46.6 and 42 kDa. Isoelectric points for PG were at pH
7.0 and 7.7; while PE had isoelectric points at pH 7.1 and 7.6.
The methods of calcium infusions evaluated were blanching, immersion and
vacuum-assisted infusion at two levels of calcium concentration, i.e. at 0.5% and
1.0% (w/v). The blanched ripe pulps lost its texture after 3 days and exhibited
“cooked” characteristic. Blanched pulps were not considered in further study. The
calcium-treated ripe pulps lost their texture slower than untreated pulps. The colour
index indicated a darkening in all samples regardless of treatment. The ascorbic
acid content of all the samples reduced during the 14 days of storage. Immersed
ripe jackfruit pulps gave off higher liquid loss, followed by vacuum-assisted ripe
jackfruit pulps and control pulps. The cell walls and middle lamella of vacuuminfused
pulps were intact, while other samples showed sign of middle lamella
dissolution. Based on textural characteristics and sensory evaluation, the ripe
jackfruit pulps vacuum-infused with calcium at 1.0% have a shelf life of up to 14
days stored at 8oC.
Description
PhD
Keywords
Chemical science , Calcium-treated jackfruit , Chilled storage