Gelling Mechanism And Application Of Citrus RG-? Pectin

Pectin is the most complex and widely distributed polysaccharide from plant cell walls,mainly composed of linear homogalacturonan(HG),rhamnogalacturonan-I(RG-?)and rhamnogalacturonan-?(RG-?).RG-? pectin is abundant in fruits and vegetables processing waste and has been reported unique physiological functions superior to traditional HG pectin.However,the RG-? domain is removed during the extraction of pectin by the traditional hot-acid method and not used as hydrocolloid in the food industry,which is considered to improve gelling properties.Previous research has reported that RG-? pectin showed the potential to form gel in sugar-free or low-sugar system,but the mechanism is unknow and rheological properties wait to be improved.In this study,a comprehensive structure-function relationship of RG-? pectin was established and the gel properties were improved by synergistic gelation,then the delivery system was based on RG-? blend pectin gel.The main contents and results of this research are as follows:(1)Gelling mechanism of RG-? enriched citrus pectinThe RG-? enriched pectin with a low degree of esterification recovered from citrus canning basic processing water(PB)and the enzymatically de-branched RG-? enriched pectin(DPB)were prepared.The rheological properties and microstructure of gels were compared to establish a comprehensive structure-function relationship for RG-? pectin.RG-? enriched pectin with abundant arabinose sugar side-chains can form gels under both cation and acid conditions and its side-chains improve network formation:In cation-induced gelation,abundant divalent cations,such as Ca²⁺and Zn²⁺,generally interact with carboxyl groups on galacturonic acid of HG region and form egg-box junction zones,while side-chains of the RG-? region stabilize both the chain-chain and dimer-dimer structures through entanglements.These entanglements make the gel network denser and limit network chain mobility,and thus,improving gel strength.For acid-induced gelation,low p H promotes the formation of hydrogen bonds and hydrophobic interactions between pectin chains and the side-chains play an active role in hydrogen bond interactions to strengthen the gel network.Moreover,side-chain entanglements create a tighter conformation,eventually allowing for stronger hydrophobic interactions and hydrogen bonding in HG.(2)Synergistic gelling mechanism of RG-? enriched citrus pectinBased on the structure and gelling mechanism of PB,RG-? pectin recovered from citrus canning acidic processing water with a moderate degree of esterification(PA)was chosen to mix with PB,in order to improve the gelling properties.Rheological properties and microstructure of RG-? pectin gels were investigated to elucidate the synergistic gelation mechanism of PA and PB.The network of PA gel was mainly composed of hydrogen bonds between methoxylated galacturonic acid residues.PB gels relied on ionic cross-link junction-zones,stabilized by side-chain entanglements.PA/PB blend gel(PA/PB=1)showed improved rheological properties compared with pure gels.Ca-bridges connected pectin aggregates and promoted the three-dimensional structure of PA/PB blend gels,while neutral sugar side-chains prompted hydrogen bonds and strengthened gel network.(3)Curcumin-loaded emulsion gel based on RG-? enriched citrus pectinBased on the matrix of PA/PB blend pectin gel,the emulsion gel was prepared by calcium induced gelation and the influence of different preparation methods and oil ratios on the mechanical properties of emulsion gel was investigated.The emulsion gels of different preparation methods were applied to deliver curcumin,and the stability and in vitro simulated digestion characteristics was explored.The results showed that the RG-? blend pectin can be used as a matrix of emulsion gel which can store the curcumin.In the process of simulated digestion in vitro,emulsion filled gel(EFG)exhibited the highest curcumin bioaccessibility in the small intestine stage(43.95%),while emulsified microgel(EPG)has the most stable matrix structure and may be in poor conditions.Flavor nutrient embedding application has potential.