Effects of Extrusion and Enzymatic Hydrolysis on the in Vitro Starch Digestibility, Protein Structure and Rheological Properties of Pea Flour

The effects of extrusion alone and followed by enzymatic hydrolysis on the microstructure and physicochemical properties of pea flour were investigated.

The structures of raw, extruded and hydrolysed pea flours were determined using scanning electronic microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), a rapid viscosity analyzer (RVA), and a rheometer, and the in vitro starch digestibility was measured.

Extrusion partially destroyed the structure of pea flour, as manifested by a decrease in relative crystallinity, I_{1045 cm^-1}/I_{1022 cm^-1}, viscosity, breakdown and retrogradation value. The relative crystallinity of starch in hydrolyzed extruded pea flour was increased, the viscosity was reduced, and the resistance to shearing and retrogradation was enhanced compared with extruded pea flour. Extrusion and enzymatic treatment had significant effects on the secondary structure of proteins in pea flour, as shown by a reduction (extrusion) or even disappearance (enzymatic treatment) of α-helix, a decrease in β-sheet and an increase in β-turn and random coil. In addition, extrusion and enzymatic treatment increased the content of slowly digestible starch (SDS) and decreased the content of resistant starch (RS). The viscoelasticity and temperature stability of pea flour was improved by enzymatic treatment.

Pea flour extrudate and its enzymatic hydrolysate can be used as high-quality ingredients for high-SDS foods, and can be blended with cereals due to the increased protein digestibility and high lysine content.