Modulating in vitro gastric digestion of emulsions using composite whey protein-cellulose nanocrystal interfaces

Pseudosciaena crocea roe protein-stabilized emulsions for oral delivery systems: In vitro digestion and in situ intestinal perfusion study

Benzyl isothiocyanate (BITC) was encapsulated in oil-in-water emulsions stabilized by Pseudosciaena crocea roe protein isolate (PRPI). The stability, lipid digestion, BITC bioavailability, and retention rate of the emulsions were characterized using a simulated gastrointestinal tract model. Tween-corn and PRPI-medium-chain triglycerides (MCT) emulsions were used as controls. The membrane permeability and BITC absorption from these emulsions were investigated by in situ single-pass intestinal perfusion. The results showed that the PRPI-stabilized emulsions were stable under nonacidic environment conditions. Moreover, the PRPI-corn emulsion had more obvious protective effects than PRPI-MCT and Tween-corn emulsions. Atomic force and confocal laser scanning microscopy images showed that the protein hydrolyzed and oil droplets aggregated during simulated gastric phase digestion. Following the exposure of oil droplets in the small intestine phase, the PRPI-corn emulsion had a high rate of free fatty acid release (99.13 ± 2.49%), and the retention rate and bioavailability of BITC from the PRPI-corn emulsion were 75.93 ± 7.17% and 77.32 ± 5.36%, respectively, which were significantly higher than those measured for the other emulsions (P < 0.05). Moreover, the K_a and P_eff of the PRPI-corn emulsion reached the maximum value at 45 min and then decreased slowly. These results suggest that the PRPI-corn emulsion delivery system is effective in encapsulating, delivering, and protecting BITC. PRACTICAL APPLICATION: This study provides some useful information for the food industry to develop a Pseudosciaena crocea roe protein isolate (PRPI) emulsion that could be successfully used to construct a BITC delivery system and improve benzyl isothiocyanate (BITC) bioavailability. The protective effect on BITC assessed in vitro simulated gastrointestinal tract and in situ single-pass intestinal perfusion are discussed.

Pickering emulsions stabilized by colloidal gel particles complexed or conjugated with biopolymers to enhance bioaccessibility and cellular uptake of curcumin

The aim of this study was to investigate the fate of curcumin (CUR)-loaded Pickering emulsions with complex interfaces during in vitro gastrointestinal transit and test the efficacy of such emulsions on improving the bioaccessibility and cellular uptake of CUR. CUR-loaded Pickering emulsions tested were whey protein nanogel particle-stabilized Pickering emulsions (CUR-E_WPN) and emulsions displaying complex interfaces included 1) layer-by-layer dextran sulphate-coated nanogel-stabilized Pickering emulsions (CUR-DxS+E_WPN) and 2) protein+dextran-conjugated microgel-stabilized Pickering emulsions (CUR-E_WPDxM). The hypothesis was that the presence of complex interfacial material at the droplet surface would provide better protection to the droplets against physiological degradation, particularly under gastric conditions and thus, improve the delivery of CUR to Caco-2 intestinal cells. The emulsions were characterized using droplet sizing, apparent viscosity, confocal and cryo-scanning electron microscopy, zeta-potential, lipid digestion kinetics, bioaccessibility of CUR as well as cell viability and uptake by Caco-2 cells. Emulsion droplets with modified to complex interfacial composition (i.e. CUR-DxS+E_WPN and CUR-E_WPDxM) provided enhanced kinetic stability to the Pickering emulsion droplets against coalescence in the gastric regime as compared to droplets having unmodified interface (i.e. CUR-E_WPN), whereas droplet coalescence occurred in intestinal conditions irrespective of the initial interfacial materials. A similar rate and extent of free fatty acid release occurred in all the emulsions during intestinal digestion (p > 0.05), which correlated with the bioaccessibility of CUR. Striking, CUR-DxS+E_WPN and CUR-E_WPDxM significantly improved cellular CUR uptake as compared to CUR-E_WPN (p < 0.05). These results highlight a promising new strategy of designing gastric-stable Pickering emulsions with complex interfaces to improve the delivery of lipophilic bioactive compounds to the cells for the future design of functional foods.

Effect of thymol and Pickering stabilization on in-vitro digestion fate and oxidation stability of plant-derived flaxseed oil emulsions

The aim of this study was to evaluate the effect of Pickering stabilization by biopolymer-based particles (bioparticles), consisting of flaxseed protein and polysaccharides, and of the addition of thymol to the oil phase on the oxidation stability, and digestion fate of flaxseed oil (FO) emulsions, compared to bulk FO and conventional emulsions stabilized by polysorbate 80 (PS80). Applying Pickering stabilization and thymol simultaneously was a successful approach to retard FO oxidation. Moreover, lipid digestion was slower in bioparticle-stabilized emulsions compared to PS80 stabilized emulsions. The thymol bioaccessibility increased after incorporation into FO Pickering emulsions in comparison to the bulk oil. The results suggested that the combination of Pickering stabilization and thymol addition to the oil phase can be used as a promising way of protecting highly unsaturated oils such as FO against oxidation. These emulsions are also applicable for designing functional foods with controlled lipid digestion.

Adsorption and interfacial structure of nanocelluloses at fluid interfaces

Nanocelluloses (NCs), more specifically cellulose nanocrystals and nanofibrils, are a green alternative for the stabilization of fluid interfaces. The adsorption of NCs at oil-water interfaces facilitates the formation of stable and biocompatible Pickering emulsions. In contrast, unmodified NCs are not able to stabilize foams. As a consequence, NCs are often hydrophobized by covalent modifications or adsorption of surfactants, allowing also the stabilization of foams or functional inverse, double, and stimuli-responsive emulsions. Although the interfacial stabilization by NCs is readily exploited, the driving force of adsorption and stabilization mechanisms remained long unclear. Here, we summarize the recent advances in the understanding of NC adsorption regarding kinetics, isotherms, and energetic aspects, as well as their interfacial structure, surface coverage, and contact angle. We thereby distinguish unmodified NCs, covalently modified NCs, and surfactant enhanced adsorption.

Water-in-Oil Pickering Emulsions Stabilized by Synergistic Particle-Particle Interactions

Here, we report a novel "double Pickering stabilization" of water-in-oil (W/O) emulsions, where complex formation at the interface between Pickering polyphenol particles adsorbing from the oil side and whey protein microgel (WPM) particles coadsorbing from the aqueous side of the interface is investigated. The interfacial complex formation was strongly dependent on the concentration of WPM particles. At low WPM concentrations, both polyphenol crystals and WPM particles are present at the interface and the water droplets were stabilized through their synergistic action, while at higher concentrations, the WPM particles acted as "colloidal glue" between the water droplets and polyphenol crystals, enhancing the water droplet stability for more than 90 days and prevented coalescence. Via this mechanism, the addition of WPM up to 1 wt % gave a significant improvement in the stability of the W/O emulsions, allowing an increase to a 20 wt % water droplet fraction. The evidence suggests that the complex was probably formed due to electrostatic attraction between oppositely charged polyphenol Pickering particles on the oil side of the interface and WPM Pickering particles mainly on the aqueous side of the interface. Interfacial shear viscosity measurements and monolayer (Langmuir trough) experiments at the air-water interface provided further evidence of this strengthening of the film due to the synergistic particle-particle complex formation at the interface.

Enhanced Chemical Stability, Intestinal Absorption, and Intracellular Antioxidant Activity of Cyanidin-3-O-glucoside by Composite Nanogel Encapsulation

A composite nanogel was developed for cyanidin-3-O-glucoside (C3G) delivery by combining Maillard reaction and heat gelation. The starting materials utilized were ovalbumin, dextran, and pectin. C3G-loaded nanogel was spherical with a diameter of ∼185 nm, which was maintained over a wide range of pH and NaCl concentrations. The composite nanogel enhanced the chemical stability of C3G under accelerated degradation models and a simulated gastrointestinal tract. Clathrin-mediated, caveolae-mediated, and macropinocytosis-related endocytosis contributed to the higher cellular uptake of nano-C3G than that of free-C3G. The apparent permeability coefficients of C3G increased 2.16 times after nanoencapsulation. The transcytosis of the C3G-bearing nanogel occurred primarily through the clathrin-related pathway and macropinocytosis and followed the "common recycling endosomes-endoplasmic reticulum-Golgi complex-basolateral plasma membrane" route. Moreover, nano-C3G was more efficient in restoring the viability of cells and activities of endogenous antioxidant enzymes than free-C3G in oxidative models, which may be attributed to the former's high cellular absorption.

Nanomaterials for the theranostics of obesity

As a chronic and lifelong disease, obesity not only significant impairs health but also dramatically shortens life span (at least 10 years). Obesity requires a life-long effort for the successful treatment because a number of abnormalities would appear in the development of obesity. Nanomaterials possess large specific surface area, strong absorptivity, and high bioavailability, especially the good targeting properties and adjustable release rate, which would benefit the diagnosis and treatment of obesity and obesity-related metabolic diseases. Herein, we discussed the therapy and diagnosis of obesity and obesity-related metabolic diseases by using nanomaterials. Therapies of obesity with nanomaterials include improving intestinal health and reducing energy intake, targeting and treating functional cell abnormalities, regulating redox homeostasis, and removing free lipoprotein in blood. Diagnosis of obesity-related metabolic diseases would benefit the therapy of these diseases. The development of nanomaterials will promote the diagnosis and therapy of obesity and obesity-related metabolic diseases.

Role of protein-cellulose nanocrystal interactions in the stabilization of emulsion

HYPOTHESIS

The interactions between two bio-based emulsifiers, namely cellulose nanocrystals (CNC) and the surface active sodium caseinate (CAS), can influence the formation and stability of oil-in-water emulsion (O/W).

EXPERIMENTS

After studying the interactions between CNC and CAS, in bulk, and at air-water and liquid-liquid interfaces, emulsions have been prepared through different routes of addition, at pH 7 and 3, at which CNC and CAS had repulsive and attractive interactions, respectively. The routes of addition were (1) CAS and CNC simultaneously, (2) CAS first followed by CNC in a subsequent emulsification step and (3) CNC first, followed by CAS. The emulsions were characterized by laser diffraction and optical microscopy.

FINDINGS

At pH 7, in the case of repulsive interactions, the surface activity of CAS was balanced by the irreversible adsorption of CNC, irrespectively of the route of emulsification. At pH 3, in the case of attractive interactions, using route (1), the aggregates CAS-CNC provided better emulsification than CNC and CAS alone. For emulsions prepared by route (2) and (3), gelling was observed which could be controlled through the order of addition. Emulsions prepared at pH 7 then adjusted to pH 3 exhibited an increase in viscosity, while the droplet size was not affected.

Microgels at fluid-fluid interfaces for food and drinks

Various aspects of microgel adsorption at fluid-fluid interfaces of relevance to emulsion and foam stabilization have been reviewed. The emphasis is on the wider non-food literature, with a view to highlighting how this understanding can be applied to food-based systems. The various different types of microgel, their methods of formation and their fundamental behavioral traits at interfaces are covered. The latter includes aspects of microgel deformation and packing at interfaces, their deformability, size, swelling and de-swelling and how this affects their surface activity and stabilizing properties. Experimental and theoretical methods for measuring and modelling their behaviour are surveyed, including interactions between microgels themselves at interfaces but also other surface active species. It is concluded that challenges still remain in translating all the possibilities synthetic microgels offer to microgels based on food-grade materials only, but Nature's rich tool box of biopolymers and biosurfactants suggests that this field will still open up important new avenues of food microstructure development and control.

In vitro investigation of the influence of nano-fibrillated cellulose on lipid digestion and absorption

Nanocellulose, including nano-fibrillated cellulose (NFC), has been a topic of significant interest and a number of studies have focused on using it for the fabrication of stable oil-in-water emulsions. However, limited studies have been performed to understand the potential influence of NFC on lipid digestion and absorption. In this study, a simulated digestion model, consisting of salivary, gastric and intestinal digestion phases, was used to investigate the effects of NFC on lipid digestion and absorption. To better understand the mechanisms behind, the effects of NFC on lipase activity, micellar solubility of cholesterol and bile acid diffusion were studied in addition to the cholesterol adsorption capacity of NFC, with conventional cellulose as a comparison. Results showed that NFC slightly reduced lipase activity, but NFC or cellulose at concentrations up to 1.1% (w/w) did not significantly influence lipid digestion under simulated intestinal conditions. Moreover, NFC showed greater bile acid retardation effect than cellulose, and slightly higher cholesterol adsorption capacity probably due to its larger specific surface area. Nonetheless, NFC did not significantly affect micellar solubility of cholesterol. These results suggest that NFC, when added into fat-rich foods, may have health benefits via its viscosity effect and retardation effect on bile acid absorption.

A review on versatile applications of blends and composites of CNC with natural and synthetic polymers with mathematical modeling

Cellulose is world's most abundant, renewable and recyclable polysaccharide on earth. Cellulose is composed of both amorphous and crystalline regions. Cellulose nanocrystals (CNCs) are extracted from crystalline region of cellulose. The most attractive feature of CNC is that it can be used as nanofiller to reinforce several synthetic and natural polymers. In this article, a comprehensive overview of modification of several natural and synthetic polymers using CNCs as reinforcer in respective polymer matrix is given. The immense activities of CNCs are successfully utilized to enhance the mechanical properties and to broaden the field of application of respective polymer. All the technical scientific issues have been discussed highlighting the recent advancement in biomedical and packaging field.

Development of Nanocomplexes for Curcumin Vehiculization Using Ovalbumin and Sodium Alginate as Building Blocks: Improved Stability, Bioaccessibility, and Antioxidant Activity

Type I (Complex I) and type II nanocomplexes (Complex II) were created in this work for curcumin (Cur) delivery using ovalbumin (OVA, 1.0% w/w) and sodium alginate (ALG, 0.5% w/w) as building blocks. OVA was heated at 90 °C for 5 min at pH 7.0 and then coated with ALG at pH 4.2 to produce Complex I; OVA-ALG electrostatic complex was created at pH 4.0, which was treated at 90 °C for 5 min thereafter yielding Complex II. Complex I presented an irregular elliptical shape with a diameter of ∼250 nm, whereas Complex II adopted a defined spherical structure of a smaller size (∼200 nm). Complex II did not dissociate at the pH range of 5-7, which was different from Complex I. Cur was loaded into the nonpolar matrix of nanocomplexes through hydrogen bonding and hydrophobic interactions, and Complex II displayed a higher loading capacity than Complex I. Nanocomplexes were resistant to pepsinolysis during simulated gastrointestinal digestion, which enhanced the stability and controlled release of loaded Cur, thereby improving Cur bioaccessibility from ∼20% (free form) to ∼60%. Additionally, nanocomplexes contributed to the cellular antioxidant activity (CAA) of Cur by promoting its cellular uptake. The CAA of Cur was also better preserved in nanocomplexes especially in Complex II after digestion owing to the increased stability and bioaccessibility. Results from this work highlighted the effect of nanocomplex encapsulation on the performance of Cur and revealed the critical role of preparation method in the physicochemical attributes of nanocomplexes.

Colloidal aspects of digestion of Pickering emulsions: Experiments and theoretical models of lipid digestion kinetics

Lipid digestion is a bio-interfacial process that is largely governed by the binding of the lipase-colipase-biosurfactant (bile salts) complex onto the surface of emulsified lipid droplets. Therefore, engineering oil-water interfaces that prevent competitive displacement by bile salts and/or delay the transportation of lipase to the lipidoidal substrate can be an effective strategy to modulate lipolysis in human physiology. In this review, we present the mechanistic role of Pickering emulsions i.e. emulsions stabilised by micron-to-nano sized particles in modulating the important fundamental biological process of lipid digestion by virtue of their distinctive stability against coalescence and resilience to desorption by intestinal biosurfactants. We provide a systematic summary of recent experimental investigations and mathematical models that have blossomed in the last decade in this domain. A strategic examination of the behavior and mechanism of lipid digestion of droplets stabilised by particles in simulated biophysical environments (oral, gastric, intestinal regimes) was conducted. Various particle-laden interfaces were considered, where the particles were derived from synthetic or biological sources. This allowed us to categorize these particles into two classes based on their mechanistic role in modifying lipid digestion. These are 'human enzyme-unresponsive particles' (e.g. silica, cellulose, chitin, flavonoids) i.e. the ones that cannot to be digested by human enzymes, such as amylase, protease and 'human enzyme-responsive particles' (e.g. protein microgels, starch granules), which can be readily digested by humans. We focused on the role of particle shape (spherical, anisotropic) on modifying both interfacial and bulk phases during lipolysis. Also, the techniques currently used to alter the kinetics of lipid digestion using intelligent physical or chemical treatments to control interfacial particle spacing were critically reviewed. A comparison of how various mathematical models reported in literature predict free fatty acid release kinetics during lipid digestion highlighted the importance of the clear statement of the underlying assumptions. We provide details of the initial first order kinetic models to the more recent models, which account for the rate of adsorption of lipase at the droplet surface and include the crucial aspect of interfacial dynamics. We provide a unique decision tree on model selection, which is appropriate to minimize the difference between experimental data of free fatty acid generation and model predictions based on precise assumptions of droplet shrinkage, lipase-binding rate, and nature of lipase transport process to the particle-laden interface. Greater insights into the mechanisms of controlling lipolysis using particle-laden interfaces with appropriate mathematical model fitting permit better understanding of the key lipid digestion processes. Future outlook on interfacial design parameters, such as particle shape, size, polydispersity, charge, fusion, material chemistry, loading and development of new mathematical models that provide closed-loop equations from early to later stages of kinetics are proposed. Such future experiments and models hold promise for the tailoring of particle-laden interfaces for delaying lipid digestion and/or site-dependent controlled release of lipidic active molecules in composite soft matter systems, such as food, personal care, pharmaceutical, healthcare and biotechnological applications.

In Vitro Digestion of Oil-in-Water Emulsions Stabilized by Regenerated Chitin

Regenerated chitin (R-chitin) can stabilize oil-in-water (O/W) emulsions containing up to 50% oil at a low chitin dosage of 2 mg/g oil. The mean droplet size of the resulting emulsion decreased as more R-chitin was used. Confocal laser scanning microscopy (CLSM) demonstrated the adsorption of R-chitin on emulsion droplets surface, confirming the emulsions were stabilized via Pickering mechanism. The effects of R-chitin concentration on storage stability, microstructure, and lipid digestion properties were investigated. Pickering emulsions stabilized by R-chitin above 1.0% w/w exhibited outstanding physical stability against coalescence and Ostwald ripening. In particular, highly consistent emulsions that remained almost unchanged during oral, gastric, and intestine digestion could be prepared using R-chitin. The emulsions could enhance fullness and satiety perceptions at gastric level, and R-chitin could be used as a substitute for food emulsifiers for weight management via increasing satiation perception and reducing lipid digestion.

Water-In-Oil Pickering Emulsions Stabilized by Water-Insoluble Polyphenol Crystals

In recent years, there has been a resurgence of interest in Pickering emulsions because of the recognition of the unique high steric stabilization provided by particles at interfaces. This interest is particularly keen for water-in-oil (W/O) emulsions because of the limited range of suitable Pickering stabilizers available. We demonstrate for the first time that W/O emulsions can be stabilized by using crystals from naturally occurring polyphenols (curcumin and quercetin particles). These particles were assessed based on their size, microstructure, contact angle, interfacial tension, and ζ-potential measurements in an attempt to predict the way that they act as Pickering stabilizers. Static light-scattering results and microstructural analysis at various length scales [optical microscopy, confocal laser scanning microscopy (CLSM), and scanning electron microscopy (SEM)] confirmed that the quercetin particles has a nearly perfect crystalline rod shape with a high aspect ratio; that is, the ratio of length to diameter ( L/ D) was ca. 2.5:1-7:1. On the other hand, the curcumin particles ( d_3,2 = 0.2 μm) had a polyhedral shape. Droplet sizing and CLSM revealed that there was an optimum concentration (0.14 and 0.25 wt % for quercetin and curcumin, respectively) where smaller water droplets were formed ( d_3,2 ≈ 6 μm). Interfacial shear viscosity (η _i) measurements confirmed that a stronger film was formed at the interface with quercetin particles (η _i ≈ 25 N s m^-1) rather than with curcumin particles (η _i ≈ 1.2 N s m^-1) possibly because of the difference in the shape and size of the two crystals. This study provides new insights into the creation of Pickering W/O emulsions with polyphenol crystals and may lead to various soft matter applications where Pickering stabilization using biocompatible particles is a necessity.

A review of natural polysaccharides for drug delivery applications: Special focus on cellulose, starch and glycogen

Natural polysaccharides are renewable with a high degree of biocompatibility, biodegradability, and ability to mimic the natural extracellular matrix (ECM) microenvironment. Comprehensive investigations of polysaccharides are essential for our fundamental understanding of exploiting its potential as bio-composite, nano-conjugate and in pharmaceutical sectors. Polysaccharides are considered to be superior to other polymers, for its ease in tailoring, bio-compatibility, bio-activity, homogeneity and bio-adhesive properties. The main focus of this review is to spotlight the new advancements and challenges concerned with surface modification, binding domains, biological interaction with the conjugate including stability, polydispersity, and biodegradability. In this review, we have limited our survey to three essential polysaccharides including cellulose, starch, and glycogen that are sourced from plants, microbes, and animals respectively are reviewed. We also present the polysaccharides which have been extensively modified with the various types of conjugates for combating last-ditch pharmaceutical challenges.

Reducing Intestinal Digestion and Absorption of Fat Using a Nature-Derived Biopolymer: Interference of Triglyceride Hydrolysis by Nanocellulose

Engineered nanomaterials are increasingly added to foods to improve quality, safety, or nutrition. Here we report the ability of ingested nanocellulose (NC) materials to reduce digestion and absorption of ingested fat. In the small intestinal phase of an acellular simulated gastrointestinal tract, the hydrolysis of free fatty acids (FFA) from triglycerides (TG) in a high-fat food model was reduced by 48.4% when NC was added at 0.75% w/w to the food, as quantified by pH stat titration, and by 40.1% as assessed by fluorometric FFA assay. Furthermore, translocation of TG and FFA across an in vitro cellular model of the intestinal epithelium was significantly reduced by the presence of 0.75% w/w NC in the food (TG by 52% and FFA by 32%). Finally, in in vivo experiments, the postprandial rise in serum TG 1 h after gavage with the high fat food model was reduced by 36% when 1.0% w/w NC was administered with the food. Scanning electron microscopy and molecular dynamics studies suggest two primary mechanisms for this effect: (1) coalescence of fat droplets on fibrillar NC (CNF) fibers, resulting in a reduction of available surface area for lipase binding and (2) sequestration of bile salts, causing impaired interfacial displacement of proteins at the lipid droplet surface and impaired solubilization of lipid digestion products. Together these findings suggest a potential use for NC, as a food additive or supplement, to reduce absorption of ingested fat and thereby assist in weight loss and the management of obesity.

Microgel-in-Microgel Biopolymer Delivery Systems: Controlled Digestion of Encapsulated Lipid Droplets under Simulated Gastrointestinal Conditions

Structural design principles are increasingly being used to develop colloidal delivery systems for bioactive agents. In this study, oil droplets were encapsulated within microgel-in-microgel systems. Initially, a nanoemulsion was formed that contained small whey protein-coated oil droplets ( d₄₃ = 211 nm). These oil droplets were then loaded into either carrageenan-in-alginate (O/M_C/M_A) or alginate-in-carrageenan (O/M_A/M_C) microgels. A vibrating nozzle encapsulation unit was used to form the smaller inner microgels ( d₄₃ = 170-324 μm), while a hand-held syringe was used to form the larger outer microgels ( d₄₃ = 2200-3400 μm). Calcium alginate microgels (O/M_A) were more stable to simulated gastrointestinal tract (GIT) conditions than potassium carrageenan microgels (O/M_C), which was attributed to the stronger cross-links formed by divalent calcium ions than the monovalent potassium ions. As a result, the microgel-in-microgel systems had different gastrointestinal fates depending upon the nature of the external microgel phase; i.e., the O/M_C/M_A system was more resistant to rupture than the O/M_A/M_C system. The rate of lipid digestion under simulated small intestine conditions decreased in the following order: free oil droplets > O/M_C > O/M_A > O/M_A/M_C > O/M_C/M_A. This effect was attributed to differences in the integrity and dimensions of the microgels in the small intestine, because a hydrogel network surrounding the oil droplets inhibits lipid hydrolysis by lipase. The structured microgels developed in this study may have interesting applications for the protection or controlled release of bioactive agents.