•Crosslinking chitosan with genipin generated microgels with finely tunable size.•The microgels showed unique performance to prepare HIPEs and macroporous materials.•The HIPEs and macroporous materials have a cellular and tunable pore structure.•The HIPEs could resist mechanical perturbation and were maintained for months.•The microgels stabilized HIPEs due to the reduced size and increased lipophilicity.Simply crosslinking chitosan (CS) aggregates with genipin in an aqueous solution was found to form biocompatible polymer microgel particles with a finely tunable size and unique emulsifying property for solely stabilizing high internal phase emulsions (HIPEs). The size of the microgel particles was controlled by changing the degree of crosslinking. Such microgel particles showed a concentration advantage of more than 100-fold in emulsifying HIPEs compared with other CS analogs. In addition, the fabrication process avoided the drawbacks of labor-intensive and usage of toxic chemical reagents and solvents in other previous studies. The HIPEs and macroporous polymer materials thus formed had a cellular and tunable pore structure that could resist mechanical perturbation and were maintained for months. The strong emulsifying performance of the microgel particles was attributable to a simultaneous reduction in the size and size distribution and increase in lipophilicity during the crosslinking. This study paves the way for a promising green approach to facilely fabricate macromolecule microgel particles with tunable properties and functions for the development of HIPEs and macroporous polymer materials, which are expected to have extensive applications as biocompatible materials for delivery and scaffold design.

Modification of chitosan (CS) through grafting with caffeic acid (CA, CA-g-CS) and ferulic acid (FA, FA-g-CS) significantly improved its solubility under neutral and alkaline environments. Spherical and physicochemically stable nanocomplexes assembled from the phenolic acid grafting CS and caseinophosphopeptide (CPP) were obtained with particle size <300 nm and zeta potential of <+30 mV. The net polymer nanocomplexes composed with the phenolic acid grafting CS and CPP showed strong antioxidant activity. The encapsulation efficiencies of epigallocatechin-3-gallate (EGCG) in the CA-g-CS–CPP nanocomplexes and FA-g-CS–CPP nanocomplexes were 88.1 ± 6.7 and 90.4 ± 4.2%, respectively. Improved delivery properties of EGCG were achieved after loading with the antioxidant nanocomplexes, including controlling release of EGCG under simulated gastric environments and preventing its degradation under neutral and alkaline environments.

The present study provided a new approach to enhance the stability of protein-emulsified nanoemulsions and to control the lipase digestibility of lipid droplets through spontaneous cross-linking of the interfacial layer with genipin, a functional ingredient isolated from the fruit of Gardenia jasminoides E. Cross-linking casein-emulsified nanoemulsions under different genipin/casein mass ratios (1:20, 1:10, 1:5) significantly (p < 0.05) or very significantly (p < 0.01) enhanced their stability under harsh gastric pH environments and prevented nanoemulsion flocculation. As observed by transmission electron microscope (TEM), under the pH 1.2 condition, the genipin cross-linked nanoemulsion showed more compact microstructure with clear and defined contour as well as “core–shell” structure caused by the swelling of the surface protein film. Interestingly, the intestinal digestibility of lipid droplets was delayed very significantly (p < 0.01) after cross-linking the interfacial casein layer with genipin, which was enhanced by the increase in genipin/casein mass ratio and cross-linking time.

Genipin-cross-linked caseinophosphopeptide (CPP)–chitosan (CS) nanoparticles (smaller than 300 nm) showed significantly improved stability and adjustable release profile in the gastrointestinal (GI) tract. Optimal purification of the nanoparticles was established by centrifugation to terminate the cross-linking reaction, which was further confirmed and characterized by FT-IR. Results from transmission electron microscopy (TEM), dynamic light scattering (DLS), and electrophoretic mobility (ζ-potential) measurements revealed that genipin cross-linking significantly prevented the bursting of the CPP–CS nanoparticles in simulated stomach acid and their precipitation under neutral intestinal environment. Pepsin showed little impact on the nanoparticle colloid stability; however, trypsin induced their aggregations. Genipin cross-linking slowed the burst release of (−)-epigallocatechin-3-gallate (EGCG) from the nanoparticles. The EGCG-loaded nanoparticles showed strong cytotoxicity against cancer cells; meanwhile, the net nanoparticles demonstrated high biocompatibility. The findings in the present work provide fundamental information for the rational design of biopolymer nanoparticles as an effective delivery systems for polyphenols.

•The nanoparticles fabricated from protein, polysaccharides and lipid.•The enhancement effect of food macromolecule nanoparticles on bioavailability of polyphenol.•The structure behavior of nanoparticles during digestion.•The metabolism of polyphenols after encapsulation in the nanoparticles.Diet polyphenols—primarily categorized into flavonoids (e.g., flavonols, flavones, flavan-3-ols, anthocyanidins, flavanones, and isoflavones) and nonflavonoids (with major subclasses of stilbenes and phenolic acids)—are reported to have health-promoting effects, such as antioxidant, antiinflammatory, anticarcinoma, antimicrobial, antiviral, and cardioprotective properties. However, their applications in functional foods or medicine are limited because of their inefficient systemic delivery and poor oral bioavailability. Epigallocatechin-3-gallate, curcumin, and resveratrol are the well-known representatives of the bioactive diet polyphenols but with poor bioavailability. Food macromolecule based nanoparticles have been fabricated using reassembled proteins, crosslinked polysaccharides, protein–polysaccharide conjugates (complexes), as well as emulsified lipid via safe procedures that could be applied in food. The human gastrointestinal digestion tract is the first place where the food grade macromolecule nanoparticles exert their effects on improving the bioavailability of diet polyphenols, via enhancing their solubility, preventing their degradation in the intestinal environment, elevating the permeation in small intestine, and even increasing their contents in the bloodstream. We contend that the stability and structure behaviors of nanocarriers in the gastrointestinal tract environment and the effects of nanoencapsulation on the metabolism of polyphenols warrant more focused attention in further studies.Download high-res image (209KB)Download full-size image