GG was selected for mass transfer studies, as it had shown least
oil uptake during puri frying (17.22%). The frying time period was
extended upto 35 s (beyond its optimum frying time (25 s)) for the
purpose of getting pseudo-equilibrium points for moisture content
(mN) and oil content (oN). There will not be any real equilibrium
existing in the present case of deep fat frying unlike in drying
operation. However, the system behaves as if there exists an
equilibrium (dm/dt and do/dt¼ 0) mainly due to the physical
changes that occur in the product during frying, that restrict the
mass transfer of moisture and oil. Since mN and oN do not represent
the physical driving potential for water and oil transfer, they
are considered as pseudo-co-efficients. But these co-efficients have been referred to as equilibrium moisture and oil content in the text
for the sake of convenience. Same model was also used by Sukumar
et al. (2003) to study the effect of pre-drying on kinetics of moisture
loss and oil uptake in chickpea flour-based snack food.
Therewas a significant reduction in the moisture content of puri
upto 30 s of frying time and later the extent of reduction was
insignificant. The curve of moisture content drawn against frying
time (Fig. 4) became plateaued beyond 30 s. This trend was similar
even in case of GG sample. The oil content of puri, in both CON and
GG samples, increased significantly upto 30 s of frying time and
later the plateau appeared in the curves of oil content in puri. In
case of GG sample, the rates of moisture loss (dm/dt) as well as the
rate of oil uptake (do/dt) were lower when compared to those for
CON sample which is evident from the MC/FC versus frying time
curves. Hence, themN for CON (0.21%) samplewas less than that for
GG sample (0.28%), while oN for CON (0.28%) was more than that
for GG (0.18%).
On plotting ln(Mr) versus frying time for both CON and GG
samples (Fig. 5), the linear equations for both lines were obtained.
The slope of these lines which give Km values showed that the CON
sample had significantly higher Km value (0.126 s1) than the Km
value of GG sample (0.090 s1). This clearly indicates that addition
of GG helped in retention of moisture in the product and hence
made puri softer and pliable compared to CON.
Similarly, the Ko values for both CON and GG samples were
determined by plotting ln(Or) versus frying time. The Ko value for
CON (0.152 s1)was found to be significantly higher than that of GG
sample (0.086 s1). This indicates that the addition of GG in puri has
greater influence on the mass transfer co-efficient for oil uptake in
puri. Hydrocolloids seemed to have formed a coating around the
proteinestarch network and hence prevented them from absorbing
more oil during frying.
Table 3
Nutritional quality parameters of puri.
Parameters Samples
CON GG
Moisture content