Effects of feed moisture, fat and corn starch levels and process temperature on physical properties of extrudates of defatted soy flouramylose corn starch-raw beef blends were investigated using response surface methodology. Contour plots showed a convex curve of expansion ratio (ER) with moisture, concave curves of bulk density (BD) and shear-force (SF) with moisture, and concave cmves of SF with each of the four extrusion variables. Fat decreased ER and increased BD, whereas corn starch increased ER. Products with high ER and low BD and SF tended to have prominent air cells, continuous protein matrices, and smooth cell wall surfaces in scanning electron micrographs. The optimum extrusion conditions for minimal SF values, with 20% non-dehydrated beef muscle and varied amounts of defatted soy flour, were: 29.1% feed moisture; 2.96% feed fat; 22% feed corn starch; and 162°C process temperature.

Response surface methodology (RSM) with a rotatable central composite design was used to determine an extrusion condition that would produce extrudates of a maximal expansion ratio from blends of catfish flesh (20%), corn flour and defatted soy flour (DSF) using a single‐screw laboratory extruder. Feed moisture, process temperature and DSF level were selected as independent variables. Analyses of the response indicated that the combination of 26.9% moisture, 160.1C and 4.95% DSF would result in extrudates with maximal expansion. The snack food made with the aforementioned combination and 74.74% corn flour in feed was slightly less dense than malted milk balls and much less hard than cocktail peanuts, according to a trained sensory panel. “Grain complex” was the most intense flavor note. When 1% garlic or onion powder was added to the feed formulation, the spice flavor notes were detected in extrudates. No fish flavor note was perceived in any of the extrudates.

Selected mixes consisting of Bf [high-beef (29%) low-fat (2.96%)], bf [low-beef (20%) low-fat] and BF [high-beef high-fat (S%)] which incorporated raw beef, defatted soy flour, and corn starch were extruded in a single-screw extruder. The products had no flavor additives and trained sensory panelists detected hay-like, beany or grainy flavors. Bf extrudate was more expanded than BF extrudate and rated least hard by the sensory panel, whereas bf extrudate was least susceptible to lipid oxidation. Bf and bf extrudates showed microstructures with large air cells. All three showed advantages of beef and soy flour in amino acid and fatty acid compositions, respectively, and were microbiologically safe during prolonged storage at 37°C.

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