Abstract:
Blends of sorghum and soybean flours were processed
in a co-rotating twin screw
extruder to prepare expanded product. Response surf
ace methodology (RSM) was used to
study the effect of soya level (SL), feed moisture
(FM), barrel temperature (BT) and screw
speed (SS) on extruder system parameters and physic
al properties of the extrudate.
Response variables were product temperature (PT), m
otor torque (MT), specific
mechanical energy (SME), expansion ratio (ER), bulk
density (BD), hardness (H),
crispness (C), water absorption index (WAI), and wa
ter solubility index (WSI). Second
order polynomial models were developed to determine
the responses as a function of
process variables.
FM
,
BT
, and
SS
had a significant effect on all the responses exce
pt
BT
on
WAI
, while
SL
considerably affected
ER
,
BD
,
H, C
, and
WAI
. All the models were
found to be statistically significant (R
2
> 0.85; insignificant lack of fit). Sorghum-soya
extruded product was found to be feasible and the o
ptimum values of processing variables
were:
SL
: 14 per cent;
FM:
14 per cent wb;
BT
: 129°C; and
SS
: 422 rpm.
Keywords:
Extrusion, RSM, SME, Sorghum, Soybean.
