Effective production of resistant starch using pullulanase immobilized onto magnetic chitosan/Fe3O4 nanoparticles

•Immobilized pullulanase with high stability was used for the production of RS.•High RS content was obtained via optimizing process condition.•Debranching effects due to free vs. immobilized pullulanase were compared.•Immobilized pullulanase gave higher stability and RS content compared to free enzyme.•Operational Stabilities of enzymes immobilized by the two methods were compared.

In this study, pullulanase was firstly immobilized by covalent bonding onto chitosan/Fe3O4 nanoparticles or encapsulation in sol-gel after bonding onto chitosan/Fe3O4 nanoparticles, and then the immobilized pullulanase was used for the effective production of resistant starch (RS). The highest RS content (35.1%) was obtained under the optimized condition of pH 4.4, enzyme concentration of 10 ASPU/g and hydrolysis time of 12 h when debranched by free pullulsanase, indicating that RS content was significantly (p < 0.05) increased when compared to native starch (4.3%) and autoclaved starch (12.5%). Under these conditions, the immobilized pullulanase (10 ASPU/g dry starch) yielded higher RS content compared to free enzyme (10 ASPU/g dry starch), especially, the pullulanse immobilized by sol-gel encapsulation yielded the highest RS content (43.4%). Moreover, compared to starches hydrolyzed by free pullulanase, starches hydrolyzed by immobilized pullulanase showed a different saccharide profile of starch hydrolysate, including a stronger peak C (MW = 5.0 × 103), as well as exhibited an additional absorption peak around 140 °C. Reusability results demonstrated that pullulanase immobilized by sol-gel encapsulation had the advantages of producing higher RS content as well as better operational stability compared to pullulanase immobilized by cross-linking. The resulting enhanced RS content generated by the process described in this work could be used as an adjunct in food processing industries.