Construction of starch-sodium alginate interpenetrating polymer network and its effects on structure, cooking quality and in vitro starch digestibility of extruded whole buckwheat noodles

The effects of different concentrations and crosslinking methods of sodium alginate (SA) on the structure, cooking quality and in vitro starch digestibility of extruded whole buckwheat noodles were investigated. The results showed that SA could interact with starch through hydrogen bonding, resulting in decrease of the relative crystallinity of starch and improvement of thermal stability. Addition of 1% SA significantly decreased the cooking loss from 15.33% to 8.64%, predicted glycemic index (pGI) from 84.76 to 78.92, and increased the noodle hardness from 2260.16 g to 2809.34 g，as well as the content of resistant starch (RS) from 37.25 to 45.47. Two different crosslinking methods, dynamic blending crosslinking (DBC) and in-situ polymerization crosslinking (ISPC) of SA at 1% induced by CaCl2 were attempted to further improve the properties of extruded buckwheat noodle. SEM showed that both starch gel network and SA gel network existed. DBC induced fast gelation of SA molecules, and the aggregated SA gels disrupted the continuity of the starch gel network. As a comparison, SA network was evenly distributed in starch network when ISPC was applied, indicating Starch-SA interpenetrating polymer network (IPN) was successfully constructed. The resultant cooking loss, surface adhesion and pGI value significantly decreased to 6.58%, −19.59 g s, 69.25, while the noodle hardness and content of RS increased to 6220.90 g, 61.03%, respectively. In a word, the formation of Starch-SA IPN enhanced cooking quality and reduced starch digestibility of extruded whole buckwheat noodles.