Degradation of starch in pasta induced by extrusion below gelatinization temperature.

Abstract

The structural deformation of starch during pasta extrusion leads to varied effects on pasta quality. We investigated the impact of shearing force on the starch structure of pasta and pasta quality by varying the screw speed (100, 300, 500 and 600rpm) with a temperature range of 25 to 50 ℃ in increments of 5 ℃, from the feeding zone to the die zone. The higher screw speeds were associated with more specific mechanical energy input (157, 319, 440, and 531kJ/kg for pasta produced at 100, 300, 500 and 600rpm, respectively), resulting in a lower pasting viscosity (1084, 813, 522 and 480mPa·s for pasta produced at 100, 300, 500 and 600rpm, respectively) in the pasta due to the loss of starch molecular order and crystallinity. Size-exclusion chromatography revealed that pasta produced at 600rpm screw speed had a lower amylopectin size distribution which indicated molecular breakdown during extrusion. Pasta produced at 600rpm had higher in vitro starch hydrolysis (both raw and cooked) than the pasta made at 100rpm. The research provides relationship of how the screw speed can be manipulated to design pasta with varied texture and nutritional functionality.