Distinct effects of different α-amylases on cross-linked tapioca starch and gel-improving mechanism

Considering the weak gel of tapioca starch and generally incomplete gel-advancing mechanism of α-amylase modification, two commercial α-amylases (named A- and N-amylase) with different reaction patterns were used to improve the gel strength of cross-linked tapioca starch. SEM showed that A-amylase exhibited surface erosion pattern, compared to an extensive erosion pattern of N-amylase. XRD, SAXS, and HPGPC-MALLS-RI revealed that A-amylase mainly attacked amorphous regions, while N-amylase hydrolyzed both amorphous regions and amorphous lamella of crystalline regions. Analysis of the pasting and gelling properties indicated that with similar degree of hydrolysis, A-amylase increased the storage modulus (G′) of cross-linked starch gels by about 10%, without significantly changing pasting properties, whereas N-amylase modified cross-linked starch formed a solid gel in 15 min, and the G’ of the starch gel increased by nearly 30% after 23 h of hydrolysis. Notably, the observed phenomena can fit the starch gelation model of “Filler in matrix”.