Characteristics of snack-like products from twin-screw extrusion of corn flour or wheat flour blended with tuna flesh

Pilot scale twin-screw extruder was employed for production of extrudates with cereal and tuna flesh at 3, 6, and 10% levels (w/w, as is basis), and with 18% moisture contents under pre-optimized conditions. Protein contents of the products ranged 8.3-14.5% depending on the content of tuna flesh added. Corn snacks showed higher expansion ratio (ER) and lower bulk density (BD) values when compared with wheat ones. Incorporation of tuna, up to 6%, slightly increased (corn) or decreased (wheat) ER values, which then stabilized at 10%, while opposite tendency was observed for BD values. Brittleness increased (corn) or decreased (wheat), while hardness decreased with tuna flesh addition, although excess tuna (10%) was detrimental, for both products. Water absorption ratio resembled the general tendencies of ER and brittleness. Increase in tuna flesh addition resulted in lighter (corn), darker (wheat), reddish (wheat) or greenish (corn) extrudates, while yellow tone was less affected.