Preparation Of Peach Gum Polysaccharide And Its Application In Emulsion Stabilization

Rosaceae plants such as peach trees（Prunus persica）secret peach gum exudate when subjected to external stresses such as mechanical injuries,infections and insects.At ambient temperature,raw peach gum becomes hard crystalline-like solid with very poor solubility,thereby greatly restricting its application in food industry.Peach gum polysaccharide is the main component of raw peach gum.It is an acidic heteropolysaccharide with highly branched macromolecular structure.Owing to the large molecular weight,a number of hydroxyl groups and carboxylic groups,peach gum polysaccharide has exhibited excellent performance in stabilizing emulsions and forming hydrogels.The present study focused on the hot water extraction and ultrasonic-assisted green extraction（UAGE）of peach gum polysaccharides from raw peach gum.The as extracted peach gum polysaccharides were applied for emulsion stabilization.The study provides fundamental support for the high-value utilization of raw peach gum.The main research contents and results are as follows:1.Response surface methodology（RSM）was used to optimize the parameters for UAGE of polysaccharide from raw peach gum（UPGP）.Meanwhile,the physicochemical properties and bioactivities of UPGP and hot water extracted peach gum polysaccharide（PGP）were compared.The maximum extraction rate of UPGP was up to 80.1%under the optimized UAGE conditions of 5 h extraction time,90 m L/g water to material ratio and 532 W ultrasonic intensity at 95^oC.The PGP and UPGP had similar monosaccharide composition,both mainly consisted of arabinose（Ara）,galactose（Gal）and mannose（Man）.The molecular weight of UPGP（8.18×10⁶ g/mol）was lower than PGP（1.24×10⁷ g/mol）,leading to reduced intrinsic viscosity and apparent viscosity,and increased solubility.Moreover,UPGP exhibited better ABTS radical scavenging activity,α-amylase andα-glucosidase inhibitory activity than PGP.These results revealed that UAGE was an efficient,convenient and green method to extract higher yield and value-added peach gum polysaccharides from raw peach gum.2.Zein and PGP based biopolymeric nanoparticles were fabricated to stabilize the Pickering emulsion and deliver curcumin.Effects of the PGP addition order during and after anti-solvent precipitation process on the properties of nanoparticles（NPs）were discussed.When preparation zein-PGP NPs,PGP was added during the anti-solvent precipitation process.When preparation zein/PGP NPs,PGP was added after the anti-solvent precipitation process.The zein-PGP NPs were spherical with mean size of 172.8nm,while zein/PGP NPs were rod-like with mean size of 207.5 nm.Both zein-PGP and zein/PGP NPs were negatively charged with the wettability of 93.5^o and 90.3^o,respectively.Compared to the zein NPs,zein-PGP and zein/PGP NPs stabilized emulsions had smaller droplet size,better storage and environmental stabilities.The release rates（2 h）of curcumin in zein-PGP NPs and zein/PGP NPs stabilized emulsions were 23.4%and 26.7%,respectively in simulated gastric fluid（SGF）.The curcumin release rates（2 h）in zein-PGP NPs and zein/PGP NPs stabilized emulsions were 32.5%and 24.0%,respectively in simulated intestinal fluid（SIF）.These findings might promote an effective delivery system for bioactive food ingredients using zein and PGP based complex nanoparticles.3.Whey protein isolate（WPI）and PGP complexes（WPI-PGP complexes）were synthesized near the isoelectric point（p H 3,4 and 5）of WPI.Their sizes were 598,274and 183 nm,respectively.And theirζ-potentials were+2.9,-8.6 and-22.8 m V,respectively.Their emulsifying performance were firstly investigated.Interface rheological experiment showed that at p H 3 more WPI-PGP complex adsorbed at the oil droplet surface,which lowered the surface tension,and formed a softer film compared to the complexes at p H 4 and 5.Microfluidic experiments showed that all WPI-PGP complexes were able to stabilize droplets against coalescence within short timescales（milliseconds）.Freshly prepared emulsion samples at p H 3,4 and 5 had a droplet size(D_3,2)of 1.19,0.69 and 0.89μm,respectively.At p H 4 and 5,the emulsions were stable over 16 days storage,but aggregation and creaming occurred at p H 3 after storage for 8 days.Our study confirmed that the aggregation stability of the emulsion was mainly determined by the surface charge of the complex,while the coalescence stability of emulsion was determined by both surface charge and surface load of the complex,which provided new insights into how to prepare stable food emulsions.4.Telechelic DNA was creatively introduced in food emulsion to link the oil droplets,and further mediate their aggregation at the molecular scale to improve their viscoelastic properties.A stable emulsion with 70%oil fraction was prepared by 40mg/m L of WPI-PGP complex at the mass ratio of 1:1.The addition of telechelic DNA（0.125 to 0.375μmol/L）resulted in the changing of emulsion state from cream-like to self-supporting gel.Rheological experiments confirmed that the telechelic DNA could improve the yield stress,storage modulus/loss modulus（G’/G”）and apparent viscosity of emulsion gel in a concentration-dependent manner.Inverted fluorescence images manifestly showed the inter-droplet network of emulsion gel,which further confirmed the cross-linking effect of telechelic DNA.For 3D printing,the emulsion gel with a higher concentration（0.375μmol/L）of telechelic DNA displayed a better surface quality and dimensional resolution,indicating an improved printability.The telechelic DNA-based emulsion gel showed great potential as edible inks for 3D printing.In summary,this study optimized the extraction process of peach gum polysaccharide,and confirmed the effects of different extraction methods on the physicochemical properties and biological activities of peach gum polysaccharide.Then,various PGP-protein complexes were successfully prepared under different conditions for emulsion stabilization.This study provides the theoretical basis for the application of raw peach gum in the food industries.