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Adsorption isotherm
modeling of soy-melon-enriched and un-enriched ‘gari’ using
GAB equation
M. O. Oluwamukomi
1Department
of Food Science and Technology, Federal University of
Technology, Akure (FUTA), Nigeria.
*Corresponding author. E-mail:
mukomi2003@yahoo.com.
Accepted 20
March, 2009 |
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Fresh
samples of soy-melon enriched and un-enriched (control)
“gari” (a
fermented, dewatered and toasted granule from cassava) widely
consumed all over West Africa and in Brazil, were prepared
and used to determine their sorption isotherms. The sorption
isotherms were determined within a range of water activities
of (0.20 - 0.92) at three different temperatures of 20, 30
and 40oC using the static gravimetric method.
Results showed that the water sorption was temperature
dependent as typical of food systems. The higher the
temperature, the lower the equilibrium moisture content
(EMC) at constant water activity (aw). EMC for
soy-melon “gari” ranged between 0.022 kgkg-1 (db)
and 0.320 kgkg-1(db) within the temperature range
of 20 and 40oC; while those of un-enriched
(control) “gari” ranged between 0.054 kgkg-1(db)
and 0.335 kgkg-1(db). The GAB monolayer moisture
values (Mo) were 0.044, 0.032 and 0.023 kgkg-1(db)
at 20, 30, and 40oC respectively for soy-melon “gari”;
while for the control “gari” samples, they were 0.080,
0.059, and 0.050 kgkg-1 (db). The ‘Mean relative
percent modulus’ (E%) values were 9.45, 7.37, and 9.61% at
20, 30 and 40oC respectively for soy-melon “gari”
samples; while for the control samples they were 3.76, 2.48,
and 2.04%. The RSS values ranged from 0.0002 to 0.0008 for
soy-melon gari while they ranged from 0.0001 to 0.0004 for
the un-enriched gari at temperature between 20 and 40oC.
All the E% values were below 10%. These showed that there
was perfect fitness between the experimental moisture
sorption and the predicted GAB sorption. However, the values
for un-enriched (control) “gari” samples were consistently
lower than those of the enriched gari showing that GAB model
could be used to predict the moisture equilibrium of control
“gari” samples better than those of soy-melon “gari” at the
range of water activities used in this study.
Key
words:
Soy-melon “gari”, supplementation, EMC, sorption isotherm. |
