| Being one of the biggest potato producers, China is accountable for more than one third of global potato production. Potato has competitive advantage comparing to other starch resources due to its physical nature. However, native starch defects have limited its usage in the food industry.The purpose of this research is to improve and amend physiochemical properties of potato starch (PS) through a pioneering and practical method of high hydrostatic pressure treatment at 200,300,400 and 600 MPa and enzyme modification with a-amylase at a concentration of (0.02%,0.04% and 0.06%, w/v) and pullulanase at a concentration of (40,160 and 320 U/g). The effect of varying concentration of a-amylase (0.02%,0.04% and 0.06%, w/v) at 25℃ on pre-HHP treated PS at 200,400 & 600 MPa on structure and physicochemical properties of starch were investigated. Also the effect of the combination of HHP-pullulanase at 200,300 and 400 MPa with concentration of 40,160 and 320 U/g at 60℃ on structural and physicochemical characteristics of PS was investigated. Moreover, the crystalline structure and some physicochemical properties of potato starch processed with a combination of HHP and a-amylase were investigated. According to the results of hydrolyzed pre-HHP treated starches, degree of hydrolysis and reducing sugar content of HHP-treated (600 MPa) (HHP600) PS exposed to a-amylase (0.06%, w/v) showed a significantly greater degree of hydrolysis and amount of reducing sugar released compared to a-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 HHP600 PS granules showed irregular and ruptured forms with several cracks and holes on the surface. Hydrolysis of HHP-treated PS by a-amylase could decrease the average granule size significantly (p<0.05) from 29.43±0.10 μm for HHP600 PS to 20.03±0.16 μm for hydrolyzed HHP600 PS with 0.06%(w/v) a-amylase. Swelling power decreased and solubility increased with increasing enzyme concentration and increasing pressure from 200-600 MPa, with the exception of the solubility of 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 a-amylase at a concentration 0.06%(w/v) changed to a B+V type with an additional peak at 20=19.36°. The HHP600 starch with 0.06% (w/v) a-amylase displayed the lowest value of To (onset temperature), Tc (conclusion temperature) and AHgel (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. HHP-pullulanase treatment at 60℃ could alter crystalline and amorphous region of PS. Modified starch at 400 MPa with 320 U/g showed the highest degree of hydrolysis as evidenced by amount of reducing sugar content. HHP treatment altered crystalline structure by a decrease in peak sharpness and the opposite trend was observed for HHP-Pullulanase treated starches due to the increase in enzyme concentration and crystallization of starch granule with conversion of B-type pattern to C-type pattern. Modified starch processed with a combination of HHP and a-amylase at 25℃ could alter some physico-chemical and morphological properties of PS. DSC curves revealed that the combination of HHP-a-amylase could not completely hydrolyzed crystalline region, Besides, X-ray diffraction analysis showed no changes in the diffraction pattern of starches but modified starch under respective conditions showed significantly decreased in peak sharpness due to partially destruct the crystalline structure. |
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