Effect of α-Amylase Degradation on Physicochemical Properties of Pre-High Hydrostatic Pressure-Treated Potato Starch

The effect of high hydrostatic pressure (HHP) on the susceptibility of potato starch (25%, w/v) suspended in water to degradation by exposure to bacterial alpha-amylase (0.02%, 0.04% and 0.06%, w/v) for 40 min at 25 degrees C was investigated. Significant differences (p < 0.05) in the structure, morphology and physicochemical properties were observed. HHP-treated potato starch (PS) exposed to alpha-amylase (0.06%, w/v) showed a significantly greater degree of hydrolysis and amount of reducing sugar released compared to alpha-amylase at a concentration of 0.04% (w/v) or 0.02% (w/v). Native PS (NPS) granules have a spherical and elliptical form with a smooth surface, whereas the hydrolyzed NPS (hNPS) and hydrolyzed HHP-treated PS granules showed irregular and ruptured forms with several cracks and holes on the surface. Hydrolysis of HHP-treated PS by alpha-amylase could decrease the average granule size significantly (p < 0.05) from 29.43 to 20.03 mu m. Swelling power decreased and solubility increased with increasing enzyme concentration and increasing pressure from 200-600 MPa, with the exception of the solubility of HHP-treated PS at 600 MPa (HHP600 PS). Fourier transform infrared spectroscopy (FTIR) showed extensive degradation of the starch in both the ordered and the amorphous structure, especially in hydrolyzed HHP600 PS. The B-type of hydrolyzed HHP600 PS with alpha-amylase at a concentration 0.06% (w/v) changed to a B+V type with an additional peak at 2 theta = 19.36 degrees. The HHP600 starch with 0.06% (w/v) alpha-amylase displayed the lowest value of To (onset temperature), T-c (conclusion temperature) and Delta H-gel (enthalpies of gelatinization). These results indicate the pre-HHP treatment of NPS leads to increased susceptibility of the granules to enzymatic degradation and eventually changes of both the amorphous and the crystalline structures.