Nonthermal starch hydrolysis using ultra high pressure: I. Effects of acids and starch concentrations

Corn starches with 2 mol/l hydrochloric acid (HCl), 2 mol/l sulfuric acid (H2SO4) and 2 mol/l oxalic acid (C2H2O4) were pressurized at 600 MPa for 30 min. Corn starch with C2H2O4 formed a gel after ultra-high-pressure (UHP) treatment. Corn starch with HCl showed partial disintegration but starch with H2SO4 maintained its shape. Corn starch with HCl showed higher (0.42-0.47) degree of hydrolysis compared to starch with C2H2O4 (about 0.14) and H2SO4 (0.13-0.14) regardless of increasing starch concentration up to 20 g/100 g sample. Main component of starch hydrolysate was maltose for HCl and oligosaccharides for H2SO4 and C2H2O4. Crystallinity of starch with HCl decreased with decreasing starch concentration as observed by both differential scanning calorimetry (DSC) and X-ray diffraction. Therefore, UHP can be used for nonthermal starch hydrolysis and HCl would be a good catalyst for UHP starch hydrolysis compared to H2SO4 and C2H2O4. This work provides a potential of nonthermal UHP processing for new starch hydrolysis method.