The Gelation And The Effect On Starch Physicochemical Properties Mechanism Of Pectin From Creeping Fig

Pectin is widely used in the food industry as a thickening agent,gelling agent,stabilizer,etc.Commercial pectins are mainly derived from citrus peels and apple pomace and are high methoxylation pectins.In order to obtain pectin with a lower degree of methoxylation,it can only be de-esterified through processing,so it is urgent to seek natural resources of pectin with a lower degree of methoxylation.Creeping fig female fruit seeds are often used to make"Liangfen".It has been confirmed that this is because it is rich in pectin,a high-quality pectin resource,and has a low degree of methoxylation.However,there is a lack of systematic research on the molecular structure and gel properties of pectin from creeping fig seeds.In this study,the pectin from creeping fig seeds was extracted by water extraction and alcohol precipitation,its basic components and fine structure were characterized,and the applicability between structural characteristics and characterization methods was discussed.The gel properties of creeping fig seeds pectin were studied and its mechanism and the driving force were clarified.Pectin gelation was further induced by p H and monovalent ions by regulating the gel driving force.In food formulations,pectin and starch are often used in combination.Therefore,this study also took creeping fig seeds pectin as an example to illustrate the influence mechanism of non-starch polysaccharides on starch properties from the perspective of starch granules adsorbing pectin.The main research conclusions are as follows:1.The pectin from creeping fig seeds was extracted by water extraction and alcohol precipitation.The yield of pectin was found to be 12.53%,and the content of galacturonic acid,protein and ferulic acid was found to be 89.60%,0.95%and 0.24%,respectively.Pectin was accompanied by a small number of metal ions,mainly K,Ca,Mg,Na and Al,which were presented in amorphous and crystalline forms and acetyl groups were absent.The degree of methoxylation before and after acidification of pectin was 92.27%and 56.30%,respectively,indicating that the carboxyl group on the pectin molecule was in the form of carboxylate.Comparing the results of the degree of methoxylation determined by acid-base titration and infrared spectroscopy,it showed that in order to obtain accurate results,infrared spectroscopy required that the unmethylated carboxyl groups in pectin were in the form of carboxylate,while the acid-base titration method required it in the form of carboxylic acid.The molecular weight of pectin was dependent on naturally present metal ions,which facilitated the entanglement and aggregation of pectin chains,resulting in exhibited higher molecular weight.Pectin has polydispersity and was in solution in a rod-like conformation.The results of neutral sugar showed that the molecular chain of pectin was mainly homopolygalacturonic acid（89.14%HG and 1.52%RG-I）,and the side chain was short.Pectin was inferior in emulsifying activity and emulsifying stability.Pectin has no toxicity to mouse macrophages in a 12.5-50μg/m L concentration range,and could significantly increase the release of NO,in a concentration-dependent.2.Creeping fig seeds pectin could form a spontaneous gel at a concentration of0.75%（w/v）,showing obvious thermal hysteresis and poor thixotropy.The analysis of the driving force of spontaneous gelation showed that the combined action of Ca²⁺,hydrophobic interactions and hydrogen bonds induced pectin to form gels.Although a small amount of Ca²⁺contained in pectin was insufficient to induce the gelling of pectin,it could promote the formation of a dimer"egg box"model,resulting in a pectin chain that could closer and produce hydrophobic interactions to form a gel,while hydrogen bonds mainly play a role in stabilizing the gel network structure.0.5%（w/v）acidified pectin solution could gelation by adding slightly soluble calcium salt（Ca CO₃）without GDL.With the increase of Ca CO₃ concentration,the gelation time was shortened,the gel strength increased,and the thixotropy was enhanced.This was responsible for the hydrolysis of Ca CO₃ by the unmethylated carboxyl groups of pectin,releasing Ca²⁺into pectin solution and forming a gel.3.The pectin produced a viscous solution at p H 4.5 and forms a strong gel when the p H was lowered by the addition of GDL.This was mainly responsible for the reduction of electrostatic repulsion between pectin chains with decreasing p H,which promotes chain association mainly through hydrogen bonding.It was also found that the lower the p H of the solution,the faster the rate of gel formation.Hydrophobic interactions resulting from the carboxyl groups and covalently bound ferulic acid on the pectin chain may also be involved in the gelation.Pectin gelation could also be induced by Na⁺and K⁺salts.The gel strength depends on the concentration and nature of the electrolyte and was consistent with the Lyotropic series.This indicated that the added electrolyte reduced the electrostatic repulsions between the pectin chains,thereby promoting the association of the pectin chains to form a gel.4.Adsorption isotherms have been determined to investigate the nature of the interaction between pectin molecules and rice,potato and pea starch granules.The amount of pectin adsorbed was found to be very much higher for potato and pea starches（～50 mg/m²）compared to rice starch（～5 mg/m²）.This indicated that a significant amount of pectin penetrated into the interior of the granules through the surface pores and channels for potato and pea starch,while for rice starch the penetration was much less and most of the pectin may be accommodated on the granule surface.The adsorption/absorption of pectin molecules significantly reduced the amount of amylose leaching out of the granules at room temperature in excess water suggesting that the granule channels and pores were blocked by the pectin.The adsorption/absorption also led to a reduction in the swelling of the granules on heating and to a slight increase in the gelatinization temperatures and enthalpies.The pectin had a significant influence on the viscosity profile of starch dispersions on heating and cooling under shear.This has been attributed to initial heating to the adsorbed/absorbed pectin molecules influencing the gelatinization process by reducing granule swelling and then the following gelatinization on cooling to thermodynamic incompatibility of starch and pectin molecules in solution and their tendency to segregate.