Physico-chemical properties of starch in sago palm (Metroxylon sagu) at different growth stages
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Date
2005
Authors
Stages Adrina Tie Pei, Lang
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Abstract
This study aimed to characterise the physico-chemical properties of sago starch from
base and mid heights of palms at different growth stages, namely, ‘Plawei’, ‘Bubul’,
‘Angau Muda’, ‘Angau Tua’ and ‘Late Angau Tua’. The starch content and the
composition of associated components in the sago pith were determined as well. The
characterisation of physico-chemical properties of sago starch involved determination of
swelling factor, particle size and distribution profile, flow behaviour of the starch paste,
pasting characteristics and retrogradation profiles analysis. The starch content was
found to increase as the palms matured from Plawei to Angau Muda stages and decrease
from Angau Tua to Late Angau Tua stages. The scanning electron micrographs of sago
starch showed oval-shaped granules of 10 - 30 μm in different proportion. Variation was
observed in the granule size of starch whereby the starch at base height of all the stages
was larger in mean diameter than mid height. The pasting profile showed four different
pattern of pasting curves from the combination of the mean results. No prominent
variation was observed in the results of swelling factor, flow behaviour measurement
and thermal properties of sago starch from the different growth stages. All the starch
samples showed the highest swelling factor at 70 °C. The best fit curve of shear stress
versus shear rate indicated all the samples fitted the Herschel-Bulkley model. The
relationship between the log viscosity and log shear rate suggested that the starch
dispersion is susceptible to shear-thinning or pseudoplastics behaviour. The thermal profile showed similar thermograms with To in the range of 70.2 - 73.1 °C, Tp of 75.1 -
77.0 °C, Tc of 97.4 - 101.4 °C and ΔHG of 17.5 - 19.2 Jg-1 in all the starch samples.
Similarly, the thermograms of retrograded starch showed a broad endotherm occurring
at transition temperatures of 25 - 29 °C and ΔHR of 8 - 9 Jg-1 lower than that of
gelatinised starch. No significant difference was observed in the composition of
associated components of sago pith from the different growth stages. The soluble
carbohydrate ranged from 4.5 - 8.5 %. The phenolic compound was less than 1 %
whereas the lignin content ranged from 9 - 22 %. The non-starch polysaccharides in the
form of total, insoluble and soluble non-starch polysaccharides ranged from 57.5 - 105.4
%, 43.5 - 86.4 % and 12.4 - 23.9 %, respectively. In conclusion, the best stage for
harvesting is Angau Muda stage whereas the variation in the physico-chemical
properties of sago starch from base and mid heights of different stages will govern its
application in the different industries according to the individual commercial needs.
Description
Master
Keywords
Industrial technology , Physicochemical