Structural and physicochemical characterization of enzymatically hydrolyzed porous starch isolated from Vigna unguiculata

Abstract To overcome the limitations of native starch (NS), particularly its low surface area and limited adsorption capacity, porous starch (PS) has been utilized to enhance starch functionality. Porous starch from indigenous, underutilized, alternative sources such as cowpea ( Vigna unguiculata ), may provide an ideal medium for the adsorption and encapsulation of bioactive compounds. This study, therefore, focused on (i) synthesizing PS from cowpea through enzymatic hydrolysis utilizing amyloglucosidase and (ii) characterizing the structural and physicochemical properties of the PS produced. Scanning electron microscopy revealed that the treatment led to notable alterations in the surface characteristics of the PS33 and PS66 starch samples, exhibiting porous structures with a varied porosity distribution. The XRD analysis of NS and PS samples revealed a C-type crystalline pattern typically observed in legumes with two distinct peaks at 15 and 23 and dual peaks at 17 and 18°. The DSC results obtained outlined a clear distinction between the PS and NS samples, with the PS66 sample exhibiting an increased onset, peak temperature and a greater gelatinization enthalpy. Enzymatic hydrolysis led to a notable increase in the water and oil adsorption capacity of the PS33 (234.67±13.26; 154.67±9.42) and PS66 (260.67±11.61; 159.33±8.57) samples when compared to the NS (96.67±3.46; 75.33±3.46). This improvement can be linked to the increased specific surface area and porosity, which effectively trap and retain water/oil. The findings from this study indicate that PS66 shows considerable promise as a carrier for active compounds.