Production of slowly digestible corn starch using hyperthermophilic Staphylothermus marinus amylopullulanase in Bacillus subtilis

We describe a novel method for enzymatic production of slowly digestible starch (SDS) at 100 degrees C. A hyperthermophilicamylopullulanase from archaeon Staphylothermus marinus (SMApu) was expressed in a generally recognised as safe (GRAS) microorganism, Bacillus subtilis. Purified SMApu at 80-240 U/g substrate was incubated with 0.1 g/mL of corn starch in a boiling water bath for 2 h. SDS content of the SMApu-modified starch increased significantly from 17.4 to 42.7% (P < 0.05). Molecular weight and amylopectin branch chains A (DP 6-12) of SMApu-modified starch were significantly lower, and amylose content and amylopectin branch chains B1 (DP 13-24) significantly higher (P < 0.05), than those of natural corn starch. These changes in molecular structure partially explained the reduced digestibility. High optimal temperature of SMApu facilitated the simultaneous gelatinisation and hydrolysis of cereal starch. These results demonstrate that SMApu has potential applications in the production of SDS during thermal processing of cereal foods.