Study On De-esterified Modification And Its Gel Properties Of Pectin By High Hydrostatic Pressure Assisted Enzymatic Method

Pectin is a kind of complex polysaccharide,which is widely distributed in the cell wall of plants.It has the functions of thickening,emulsifying and gelling.At present,most of pectin extracted commercially is high methoxyl pectin,which require de-esterified modification to obtain low methoxyl pectin.Different sources and modification methods lead to different physical and chemical properties and functional properties of pectin.At present,the alkali de-esterification is widely used and it reduce the molecular weight of pectin and affect the quality of pectin.Enzymatic method is a method that uses pectin methylesterase(PME)to specifically de-esterified.It does not change the molecular weight of pectin but the reaction efficiency is low.High hydrostatic pressure(HHP)is a non-thermal processing technology,which reported to promote the enzymatic reaction of PME to a certain extent.Therefore,this thesis uses the HHP assisted enzymatic method to prepare low methoxyl pectin(HHP-pectin),and systematically studies the effect of de-esterification modification of pectin on the physical and chemical properties and molecular structure.On this basis,this thesis studies the gel characteristics of modified low methoxyl pectin,constructs hydrogel and emulsion gel systems,and explores the application of HHP assisted enzymatic low methoxyl pectin gel in the delivery of low-calorie food gels and fat-soluble nutrients potential applications.The study used atmospheric pressure enzymatic low methoxyl pectin(E-pectin)and traditional alkaline method low methoxyl pectin(A-pectin)as controls.The main research contents and results are as follows:1.Study on the physicochemical properties and molecular structure of low methoxyl pectin with HHP assisted enzymatic method:HHP assisted enzymatic method has the highest de-esterified efficiency.The degree of methyl-esterification of HHP-pectin drops from 75.07%to 25.81%within 12 min,and it took 2.5 hours and 25minutes for E-pectin and A-pectin to decrease to the same level,respectively.The de-esterification method has a great influence on the physical and chemical properties and molecular structure of pectin.Compared to A-pectin,HHP-pectin and E-pectin exhibited higher viscosity,accompanied by larger average molecular weight.HHP-pectin has a higher degree of molecular chain branching and a higher content of neutral sugar side chains.However,the content of galacturonic acid in the three types of pectins was not significantly different during the de-esterification process with similar crystal structures.These results clearly demonstrated that HHP-assisted enzymatic method is a more efficient for pectin de-esterification,particularly for preparing low methoxyl pectin with better thickening properties.2.Study on properties of low methoxyl pectin hydrogel with HHP assisted enzymatic method:Results showed that the de-esterification method had a strong influence on gelling properties of pectin.The hydrogel of all pectin was significantly affected by pectin concentration,Ca²⁺concentration and pH of the solution,but enzymatically de-esterified pectin formed gels withhigher gel strength,WHC and better viscoelasticity than those from alkaline de-esterified method.When the concentration of pectin more than 40 mg/g,HHP-pectin showed the highest gel strength and water holding capacity,under the same Ca²⁺concentration and pH conditions.On this basis,HHP-pectin sugar alcohol gel was prepared.Both sugar alcohol type and concentration had significant effects on sugar alcohol gel.Gel strength,elasticity,and storage modulus G'decreased with increasing sugar alcohol concentration,but erythritol-gels always showed the highest value,and sorbitol-gels the lowest at the same sugar alcohol concentration.All sugar alcohol gels had good water holding capacity(>97%)when the sugar alcohols concentration was less than 20%(w/v).At a concentration of 20%sugar alcohol,erythritol gel formation speed is the fastest,the gel point is 56.6?,while the gel points of xylitol and sorbitol are 43.1?and 28.8?,respectively.All these results indicated that HHP-pectin hydrogel have greater application potential in the field of health food due to their excellent gel properties and low-calorie characteristics.3.Study on the gel properties of HHP assisted enzymatic low methoxyl pectin emulsion:All of the emulsions exhibited good stability at acidic conditions.Although A-pectin emulsion has the smallest average particle size and better centrifugal stability,HHP-pectin emulsion has the best long-term stability during 21 d storage,with the smallest increase in particle size(11.12%),compared to E-pectin(33.05%)and A-pectin(84.50%).On this basis,HHP-pectin emulsion gel was prepared.Compared with emulsions,high-strength emulsion gels can inhibit the digestion and decomposition of oils,and the FFA release rate drops from 72.23%(emulsion)to 42.36%(emulsion gel).The retention rate of curcumin in the small intestine of emulsion and emulsion gel is at the same level(81.17%-74.09%).The release rate of curcumin in the emulsion gel is as low as 24.19%,while the emulsion is as high as 72.33%indicating that the emulsion gel loaded with curcumin can effectively inhibit the fat and protect the release of curcumin in the oral,stomach and intestinal digestion stages.In summary,the HHP assisted enzyme method has high de-esterification efficiency.and excellent gel performance.Hydrogel with Sugar alcohol and emulsion gels prepared on this basis have great application potential in the field of low-sugar and low-fat health foods and the direction of fat soluble nutrients delivery.