| Potato protein is a kind of high nutritional value plant protein.At present,commercial potato protein is mainly derived from potato starch industry by-product.However,the functional properties of the potato protein are deteriorated during the recovery process becaues of the heat treatment.That greatly limits its application in the food industry and leads to lowering its value.Although enzymatic hydrolysis can improve its functional properties,conventional enzymolysis usually has the disadvantage of low reaction time and low protein conversion efficiency.Therefore,the effect of ultrasonic pretreatment on the enzymatic hydrolysis of potato protein and the mechanism of improving the enzymolysis efficiency were discussed.Additionaly,The digestion of potato protein hydrolyzate was investigated to understand the effect of ultrasound pretreatment of potato protein on the bioaccessibility of potato protein hydrolyzate by in vitro simulatedgastrointestinal digestion.The main results of the research are summarized as follows:(1)Firstly,the effects of ultrasonic frequency,ultrasonic time and ultrasonic power density on the enzymolysis of potato protein were investigated by degree of hydrolysis(DH)and protein convertion rate(CR).The optimal ultrasonic parameters for improving the DH and CR were obtained by single factor experiments as follows: ultrasonic frequency of 20/40 kHz,pretreatment time of 10 min,power density of 250 w/L.Compared with enzymolysis without ultrasound pretreatment,ultrasound pretreatment increased the DH and CR by 18.1% and 8.6% respectively.(2)Secondly,the effects of ultrasonic pretreatment on the morphology and molecular structure of potato protein were investigated by particle size distribution,electron microscopy and molecular spectroscopy.The results of the particle size distribution,scanning electron microscopy and atomic force microscopy showed that the large particles of potato protein are dispersed into smaller particles and increases the surface roughness of the protein after ultrasound pretreatment,which increasing the contact probability between enzyme and protein.The results of UV second-order spectroscopy,fluorescence spectroscopy,CD and FT-RS showed that ultrasound pretreatment leaded to unfolding of potato protein by exposing hydrophobic groups and changing the relative content of secondary structure.(3)Then,the effects of ultrasound pretreatment on the thermodynamics and kinetics of potato hydrolysis were investigated by thermodynamic parameters(Ea,?H and ?S)and kinetic parameters(reaction rate constant,KM and kcat).The results showed that,compared with the traditional enzymatic hydrolysis,the thermodynamics parameters Ea,?H and ?S of enzymolysis were reduced by 19.2%,20.4% and 1.6%,indicating that the enzymatic reaction is easier to be carried out.The values of reaction rate constant for ultrasound pretreatment were increased by 55.2%,41.6%,16.1% and 14.3% at the tempemture of 303,313,323 and 333 K respectively.The results of kinetics study indicated that,ultrasonic pretreatment decreased the KM by 37.5% and 36.5% resulting from substrate depletion and product accumulation respectively.This showed that the ultrasonic pretreatment increased the affinity between enzyme and potato protein.However,the apparent break-down rate constan(kcat)of ultrasound-assisted enzymolysis was lower than the traditional enzymatic hydrolysis.(4)Again,the effects of ultrasound pretreatment of potato protein on the bioaccessibility and antioxidation activity of potato protein hydrolyzate after simulated gastrointestinal digestion were investigated by static and dynamic digestion model using the content of peptide,the content of free amino group,molecular weight distribution,free amino acid composition and antioxidant activity of potato protein hydrolyzate as indicators.The resultes indicated that ultrasonic pretreatment improved the content of polypeptide,the content of free amino groups and the free radical scavenging ability and ferrous ion chelating ability of the final digest product of potato protein hydrolyzate during the static digestion.The content of oligopeptides decreased obviously,and the contents of peptides and amino acids increased significantly after potato protein hydrolysate digestion.Moreover,ultrasonic pretreatment could increase the total free amino acid content of potato protein hydrolysate after intestinal digestion.(5)Finally,The effect of ultrasonic pretreatment on the bioavailability and lipid digestion of the emulsion prepared with potato protein hydrolysate after simulated gastrointestinal digestion were investigated by static and dynamic digestion model using the content of free amino group,molecular weight distribution,free amino acid composition of potato protein hydrolyzate in the emulsion liquid phase and lipid digestibility in the emulsion as indicators..The resultes indicated that the ultrasonic pretreatment can increase the growth rate of the free amino acid content in the emulsion during the dynamic digestion model.After digestion,the molecular weight distribution of the aqueous phase becomed more concentrated in the small molecule peptide,and there is no significant difference between static state and dynamic state.Moreover,ultrasonic pretreatment could increase the total free amino acids in the aqueous phase after the emulsion digestion.Moreover,the rate and extent of the release of free fatty acids in the emulsion prepared by the traditional enzymatic hydrolysates of potato protein was significantly higher than that of the emulsion prepared by ultrasonic assisted enzymatic hydrolysis during the static digestionIn summary,ultrasonic pretreatment improved the enzymatic hydrolysis of potato protein by unfolding of potato protein,reducing the activation energy of enzymolysis and improving the affinity of potato protein and enzyme.Ultrasonic pretreatment might improve the bioavailability of potato protein.Different food structure environments(solutions and emulsions)would affect the digestion of potato protein hydrolysates. |
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