Gelatinization and viscosity behavior of single-screw extruded african breadfruit (treculia africana) mixtures
2006
NWABUEZE, T.U.
Mixtures of African breadfruit (Treculia africana), corn and soybean were extruded in a single-screw extruder. Feed composition (fc), feed moisture (fm) and screw speed (ss) were three process variables investigated at five level conditions. The fc was at 40:5:55, 55:5:40, 70:5:25, 85:5:10 and 100:0:0% (breadfruit, corn and soybean, respectively), fm was at 15, 18, 21, 24 and 27% while ss was at 100, 120, 140, 160 and 180 rpm level conditions using a second-order response surface composite design. Process variable conditions that did not completely gelatinize the blends were further studied for proximate composition, energy demand and levels of gelatinization and viscosity. Crude protein significantly (P <= 0.05) increased from 17.52% in the control (100% breadfruit) to 34.14% in the mixture containing 40% of breadfruit. Carbohydrate reduced significantly (P <= 0.05) from 63.18% in the control to 40.41% in the mixture. Pellets were obtained at 15% fm while strands were produced at 21%, irrespective of other variables. The unextruded control showed an increasingly higher starch viscosity, ranging from 350 BU at peak to 365 BU on cooling to 52C than the mixtures. Soy addition increased gelatinization temperatures from 77.30 to 87.90C and from 68.80 to 78.90C in unextruded and extruded samples, respectively. Gelatinization and viscosity behavior of extrudates was most influenced at 100 rpm except where minimum fm was replicated. Specific mechanical energy for extrudate transformation ranged from 167 to 241 KJ/Kg in the mixtures while the changes in expansion ratio were not significant (P > 0.05).
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