| The traditional enzymolysis preparation of porous starch has the disadvantage of long time and excessive hydrolysis leading to structural collapse,which increases the energy consumption of industrial production and reduces the production efficiency.Therefore,this paper studies and discusses an enhanced modification process that can save energy consumption and improve production efficiency.It mainly studied the preparation process and physicochemical properties of porous starch modified by pulsed electric fields with enzymatic pretreatment,and explores the mechanism of pulsed electric fields on modifying porous starch.The main findings are as follows:1)The effects of single factor(enzyme ratio,enzyme content and enzymolysis time)on the adsorption properties(OA value)of porous starch were investigated.Based on this,the effect of the PEF strength,the PEF effective treatment time and starch concentration on the adsorption properties of the modified porous starch were evaluated.Finally,the main influencing factors were:the enzymolysis time,the electric field strength,and the PEF effective treatment time.On the basis of single factor,the composite modification process of enzymolysis and PEF treatment was optimized using response surface method(RSM)and obtained the optimum conditions:3.9 hours of enzymolysis time,11.5 kV/cm of PEF strength,and 18 ms of PEF effective treatment time.Through experimental verification,the highest OA value is 129.892±0.11%,which is basically consistent with the theoretical prediction.2)The structural properties of composite modified porous starch and traditional enzymolyzed porous starch with different OA values were studied:SEM and LSCM observations showed that the pulsed electric fields had a significant role in increasing the pore size,pore depth of porous starch on the basis of enzymolysis.And the bigger BET-specific surface area made the adsorption performance of porous starches significantly.The treatment of PEF led to collapse and reduce the specific surface area of porous starch structure with the4.5 h hydrolysis.The XRD analysis showed that PEF treatmenton the enzymolyzed porous starch has the significantly effect of the crystallinity of porous starch,increasing from 38.7%to 45.7%at the maximum;FTIR shows that PEF treatments had no obvious effect on the chemical structure of the enzymolyzed porous starch,but obviously changed the spatial structure of tightly folded starch granules,which resulted in a very significant increase in the stretching vibration intensity of many functional groups of porous starch.3)The changes of physicochemical properties of porous starches by PEF treatment were studied,and the results showed that:PEF significantly enhanced the hydration ability and the adsorption capacity of methyl violet of porous starch,respectively;The best results were achieved at the best point of the response surface method experiment(3.9 hours of enzymolysis time,11.5 kV/cm of PEF strength,18 ms of PEF effective treatment time)and2.5 hours of enzymolysis time,9.0 kV/cm of PEF strength,and 14.4 ms of PEF effective treatment time,respectively.PEF intensified the solubility of traditional porous starches and compensated for the lack of swelling force,which made the porous starch pastes from combination treatments with extremely excellent transparency,achieving a 93%transparency at the best point of the RSM;traditional enzymatic hydrolysis and PEF combined with enzymatic treatment both had good effect on improving the freeze-thaw stability of the starch paste,but when the enzymolysis time was too long,the pores of the structure was too large and the freeze-thaw stability tended to decrease.The combination of the two treatments could achieve best freeze-thaw stability under the conditions of enzymolysis 3.5 h,PEF strength 15kV/cm and PEF effective processing time 10.8 ms.Only 11.36%water was separated out after being frozen and thawed for three times,revealing a stronger water-holding capacity than that of the original starch(38.02%water was separated out after being frozen and thawed only for one times).4)The gelatinization characteristics,amylose content and digestibility of the porous starch treated by traditional enzymatic hydrolysis and combining PEF treatment were studied.The results of DSC indicated that the enzymolysis treatment would increase the peak temperature T_p and?H value of gelatinization of the original starch.While the PEF treatment can reduce the T_p and?H values on the basis of enzymatic hydrolysis of starch,thereby achieving an effect of reverse complementation,then the prepared porous starch has both excellent adsorption performance and low gelatinization temperature.The amylose content of porous starch was improved by PEF treatment,and the most obvious increase occurred at 2.5 h after enzymolysis.Vitro digestibility experiments showed that:PEF treatment can further improve the digestion performance of porous starch,rapid digestion starch(RDS)was significantly improved,and resistance starch(RS)was decreased.Two modifications have superimposed strengthening effect.5)The mechanism of porous starch preparation by PEF-assisted(electrical breakdown theory)was initially discussed.The energy input and space charge fragmentation of porous starch from PEF caused the porous starch structure to be destroyed and lead to further formatting pore and cavity;the greater enzymolysis degree of porous starch,the greater the energy that can be absorbed,resulting in destructive structure collapses. |
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