Effect of Pyrodextrinization, Crosslinking and Heat- Moisture Treatment on In vitro Formation and Digestibility of Resistant Starch from African Locust Bean (<i>Parkia biglobosa</i>)

Abstract

Purpose: This investigation was carried out to determine the impact of Parkia biglobosa starch modification on the fractions, namely rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS). Methods: Aqueous solution of sodium hypochlorite and potassium hydroxide was used to extract starch prior to modification by pyrodextrinization, cross-linking and heat-moisture treatment. Solubility, swelling power, x-ray diffraction, scanning electron microscopy (SEM) and thermal properties of the native and modified starches were also studied. Results: Pyrodextrinization (PD), cross-linking (CL), and heat-moisture treatment (HMT) reduced the swelling power to 6.73, 4.17 and 5.57 g/g, respectively but increased solubility by 59.0, 41, 41.5 and 39.5 %, respectively, and tended to decrease gelatinization enthalpy (ΔH). Starch yield was 25.7 % on a whole seed basis. RS content significantly (p < 0.05) increased to 46.3, 49.2 and 45.3 %, respectively following PD, CL and HMT. X-ray diffraction resulrs indicate the presence of V-type crystallinity in the modified parkia starch while SEM showed PD and CL starch structures were more compact and dense than HMT starch which was irregularly-shaped formed. Conclusion: Native parkia starch modified by pyrodextrinization, cross-linking and heat-moisture treatment showed appreciably higher thermal stability which makes it suitable for incorporation in foods that are subject to high temperature processing and high shear.