Study On Preparation Of Corn Porous Starch With Enzymatic Hydrolysis And Application As Absorbent

Porous starch, a new type of modified starch, relies on capillary absorption action of pores to form physical adsorption on target substances which are easily oxidized, decomposed or volatile. Thus, it can be used to encapsulate volatile and labile functional food ingredient to provide protection while allowing their controlled-release.In this study, native corn starch was selected as the experimental material to prepare porous starch with two different enzymes mixed at varied ratios. Other parameters including pH, temperature, reaction time, and concentration of starch were also investigated. Both single-factor experiment and orthogonal experiment were used to obtain the optimum preparative conditions. The best hydrolysis conditions obtained are showed as follows: amount of enzymes 1.0%, ratio of enzymes (α-amylase: glucoamylase) 1:3, temperature 45 oC, reaction time 20 h, pH 5.4, and concentration of starch 30%. Under these conditions, the product yield was 51.15%, and the capacity of oil absorption was 79.27%, which was 2.9 times as much as that of native starch.Based on the principle that closing to gelatinization onset temperature, amylose dissolves from starch granule and granules swell lightly, which can be easily hydrolyzed by amylase, pretreatment technology of heat moisture treatment was studied. Before enzymatic hydrolysis, native starch was heat moisture treated at 65 oC, 66 oC for 8 min, 5 min, respectively, oil absorption capacity of porous starch produced was increased by 7.9%, 4.0% , respectively, compared with the porous starch untreated.Amylose content of starch samples prepared under various conditions in the course of optimization experiment were measured. The percentage of amylose first increased and then decreased with the increase of the enzymatic hydrolysis time and enzyme amount. It verified that amylopectin has higher sensitivity than amylose to amylase. Using scanning electron microscopy and laser particle size analysis instrument to study the microstructure and particle size distribution of porous starch samples, the number of pore on the starch granule changed from less to more, pore size became larger, and pore changed from shallow to deep, the average particle diameter decreased slightly. Weight average molecular weight(Mw) and Molecular rotation radius(RMS) of porous starch samples prepared under various conditions were measured with HPSEC-MALLS-RI technology. Mw and RMS decreased in the enzymatic hydrolysis process with the branch of amylopectin being partial cut, amylose chain being cut shorter. Enzymatic supernatant components was studied by HPLC-RID analysis, components were glucose and a series of oligosaccharides such as maltose, trisaccharide, tetrasaccharide, pentasaccharide and so on and with the increase of enzyme amount and enzymatic hydrolysis time, macromolecular carbohydrate was hydrolyzed to monosaccharides and disaccharides.Porous starch was used as the adsorbent of vitamin E and peppermint oil to prepare dry vitamin E and peppermint oil porous starch powder with the loading rate of 28.71%, 38.42%, respectively. During one month storage, the radical scavenging capacity of vitamin E absorbed by porous starch decreased from 90% to about 60%, while radical scavenging rate of vitamin E without being adsorbed reduced from 87.90% to less than 30%; exposure at room temperature for 40 days, retention rate of peppermint oil absorbed with porous starch stayed at 54.68%, however, the peppermint oil retention rate without adsorption was down to 23.82%. In conclusion, porous starch has good protection and controlled-release effect on target substances.