Abstract: This study investigated the influence of different extrusion conditions including pea starch moisture content (25%, 35%, 40%, 45% and 55%), barrel temperature (50, 60, 70, 80 and 90 ℃) and screw speed (100, 120, 140, 160 and 180 r/min) on the in vitro starch digestibility and rheological properties of pea starch. Hydrolysis degree (HD) was measured using an in vitro digestion model, and rheological properties were determined through steady shear test, frequency sweep test and temperature sweep test. The results showed that after extrusion treatment, HD and the relative content of slowly digestible starch (SDS) increased whereas the relative content of resistant starch (RS) decreased. The maximum relative content of SDS of 34.41% was obtained under the following extrusion conditions: moisture content 25%, barrel temperature 70 ℃ and screw speed 140 r/min. When screw speed increased to 180 r/min with moisture content 40%, barrel temperature 70 ℃, the relative content of RS reached the minimum value of 10.49%. Particle size was positively correlated with SDS relative content and consistency coefficient (K value) (r = 0.60 and r = 0.61, P < 0.05). The extruded pea starch suspension was pseudoplastic. In frequency and temperature sweep tests, storage and loss moduli increased with the degree of starch damage increasing caused by extrusion. The results showed that the extruded pea starch exhibited enhanced structure and elastic gel properties. Therefore, extrusion can affect the in vitro starch digestibility and rheological properties of pea starch, thereby improving food functionality and quality.

Key words: extrusion; pea starch; starch digestibility; rheological properties