Release profile of amino acids encapsulated in solid lipid particles during in vitro oro-gastrointestinal digestion.

Some amino acids are known to mediate immune responses through gut microbiota metabolism in both humans and monogastric animals. However, through the diet, most free amino acids are absorbed in the small intestine and only a small quantity reaches the microbiota-rich colon. To enhance microbial metabolism of amino acids and their potential health benefits, encapsulation strategies are developed for their protection and delivery to the colon. So far, the main encapsulation systems for amino acids are based on solid lipid particles, but their fate within the digestive tract has never been fully clarified. In this study, we investigated the release of various amino acids (branched-chain amino acid mixture, or lysine, or tryptophan) loaded in solid lipid particles during in vitro oro-gastrointestinal digestion mimicking the piglet. The loaded solid lipid particles were fully characterized for their composition, thermal behavior, molecular structure, crystalline state, surface morphology, and particle size distribution. Moreover, we investigated the effect of particle size by sieving solid lipid particles into two non-overlapping size fractions. We found that amino acid release was high during the gastric phase of digestion, mainly controlled by physical parameters, namely particle size and crystalline state including surface morphology. Large particle size and/or smooth ordered particle indeed led to slower and lower release. Although lipid hydrolysis was significant during the intestinal phase of digestion, the impact of the crystalline state and surface morphology was also observed in the absence of enzymes, pointing to a dominant water/solute diffusion mechanism through these porous solid lipid particles.

Influence of pH and lipid membrane on the liquid-liquid phase separation of wheat γ-gliadin in aqueous conditions.

Protein body (PB) formation in wheat seeds is a critical process influencing seed content and nutritional quality. In this study, we investigate the potential mechanisms governing PB formation through an in vitro approach, focusing on γ-gliadin, a key wheat storage protein. We used a microfluidic technique to encapsulate γ-gliadin within giant unilamellar vesicles (GUVs) and tune the physicochemical conditions in a controlled and rapid way. We examined the influence of pH and protein concentration on LLPS and protein-membrane interactions using various microscopy and spectroscopy techniques. We showed that γ-gliadin encapsulated in GUVs can undergo a pH-triggered liquid-liquid phase separation (LLPS) by two distinct mechanisms depending on the γ-gliadin concentration. At low protein concentrations, γ-gliadins phase separate by a nucleation and growth-like process, while, at higher protein concentration and pH above 6.0, γ-gliadin formed a bi-continuous phase suggesting a spinodal decomposition-like mechanism. Fluorescence and microscopy data suggested that γ-gliadin dense phase exhibited affinity for the GUV membrane, forming a layer at the interface and affecting the reversibility of the phase separation.

Human muscle stem cell responses to mechanical stress into tunable 3D alginate matrices.

Preclinical data acquired for human muscle stem (hMuStem) cells indicate their great repair capacity in the context of muscle injury. However, their clinical potential is limited by their moderate ability to survive after transplantation. To overcome these limitations, their encapsulation within protective environment would be beneficial. In this study, tunable calcium-alginate hydrogels obtained through molding method using external or internal gelation were investigated as a new strategy for hMuStem cell encapsulation. The mechanical properties of these hydrogels were characterized in their fully hydrated state by compression experiments using Atomic Force Microscopy. Measured elastic moduli strongly depended on the gelation mode and calcium/alginate concentrations. Values ranged from 1 to 12.5 kPa and 3.9 to 25 kPa were obtained for hydrogels prepared following internal and external gelation, respectively. Also, differences in mechanical properties of hydrogels resulted from their internal organization, with an isotropic structure for internal gelation, while external mode led to anisotropic one. It was further shown that viability, morphological and myogenic differentiation characteristics of hMuStem cells incorporated within alginate hydrogels were preserved after their release. These results highlight that hMuStem cells encapsulated in calcium-alginate hydrogels maintain their functionality, thus allowing to develop muscle regeneration protocols to improve their therapeutic efficacy.

Walnut (Juglans regia L.) kernel oil bodies recovered by aqueous extraction for utilization as ingredient in food emulsions: Exploration of their microstructure, composition and the effects of homogenization, pH, and salt ions on their physical stability.

Natural oil-in-water emulsions containing plant oil bodies (OBs), also called oleosomes, rich in health-promoting omega-3 polyunsaturated fatty acids (ω3 PUFA) are of increasing interest for food applications. In this study, we focused on walnut kernel OBs (WK-OBs) and explored their microstructure, composition and physical stability in ionic environments as well as the impact of homogenization. A green process involving aqueous extraction by grinding of WK allowed the co-extraction of OBs and proteins, and centrifugation was used to recover the WK-OBs. Confocal laser scanning microscopy images showed the spherical shape of WK-OBs with an oil core envelopped by a layer of phospholipids (0.16 % of lipids) and embedded proteins. Their mean diameter was 5.1 ± 0.3 µm. The WK-OBs contained 70.1 % PUFA with 57.8 % ω6 linoleic acid and 12.3 % ω3 α-linolenic acid representing 68 % and 11.6 % of the total fatty acids in the sn-2 position of the triacylglycerols (TAG), respectively. Trilinolein was the main TAG (23.1 %). The WK-OBs also contained sterols (1223 ± 33 mg/kg lipids; 86 % ß-sitosterol), carotenoids (0.62 ± 0.01 mg/kg lipids; 49.2 % ß-carotene), and tocopherols (322.7 ± 7.7 mg/kg lipids; 89 % γ-tocopherol), confirming their interest as health-promoting ingredients. The decrease in the size of WK-OBs under high-pressure homogenization avoided phase separation upon storage. The anionic WK-OB surface at neutral pH was affected by stressful ionic environments (pH, NaCl, CaCl2), that induced aggregation of WK-OBs and decreased the physical stability of the emulsions. Emulsions containing WK-OBs are promising to diversify the market of the ω3-rich plant-based food products and beverages.

Optimized Lytic Polysaccharide Monooxygenase Action Increases Fiber Accessibility and Fibrillation by Releasing Tension Stress in Cellulose Cotton Fibers.

Lytic polysaccharide monooxygenase (LPMO) enzymes have recently shaken up our knowledge of the enzymatic degradation of biopolymers and cellulose in particular. This unique class of metalloenzymes cleaves cellulose and other recalcitrant polysaccharides using an oxidative mechanism. Despite their potential in biomass saccharification and cellulose fibrillation, the detailed mode of action of LPMOs at the surface of cellulose fibers still remains poorly understood and highly challenging to investigate. In this study, we first determined the optimal parameters (temperature, pH, enzyme concentration, and pulp consistency) of LPMO action on the cellulose fibers by analyzing the changes in molar mass distribution of solubilized fibers using high performance size exclusion chromatography (HPSEC). Using an experimental design approach with a fungal LPMO from the AA9 family (PaLPMO9H) and cotton fibers, we revealed a maximum decrease in molar mass at 26.6 °C and pH 5.5, with 1.6% w/w enzyme loading in dilute cellulose dispersions (100 mg of cellulose at 0.5% w/v). These optimal conditions were used to further investigate the effect of PaLPMO9H on the cellulosic fiber structure. Direct visualization of the fiber surface by scanning electron microscopy (SEM) revealed that PaLPMO9H created cracks on the cellulose surface while it attacked tension regions that triggered the rearrangement of cellulose chains. Solid-state NMR indicated that PaLPMO9H increased the lateral fibril dimension and created novel accessible surfaces. This study confirms the LPMO-driven disruption of cellulose fibers and extends our knowledge of the mechanism underlying such modifications. We hypothesize that the oxidative cleavage at the surface of the fibers releases the tension stress with loosening of the fiber structure and peeling of the surface, thereby increasing the accessibility and facilitating fibrillation.

Effects of Sucrose Replacement by Polyols on the Dough-Biscuit Transition: Understanding by Model Systems.

This study investigated the impacts of the complete substitution of sucrose by maltitol and/or sorbitol on the dough-crumb transition in biscuits. To this end, the phenomena of starch gelatinization/melting were studied at different moisture contents, both in the biscuit dough and model systems, by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and by environmental scanning electron microscopy (ESEM). Observation of doughs in ESEM revealed sorbitol had a structure very different from sucrose and maltitol crystals. After forming the dough pieces, it could be seen that at least some sugar and maltitol crystals were still present while sorbitol flakes were solubilized. At a limiting real water content (~20% dry basis), adding sweeteners to the mixture increased the gelatinization temperature, more markedly for sucrose and maltitol, as well as increasing the enthalpy. These results were confirmed by the model systems analyses. The calorimetric study with mixing batch cells revealed that sorbitol dissolved completely while maltitol and sucrose competed with the flour constituents to capture water. The proportion of water available for the sorption of the starch grain and its gelatinization was therefore different according to the affinity of the sweetener for water, and might influence the degree and temperature of starch gelatinization/melting.

Oil Bodies from Chia (Salvia hispanica L.) and Camelina (Camelina sativa L.) Seeds for Innovative Food Applications: Microstructure, Composition and Physical Stability.

Exploring and deciphering the biodiversity of oil bodies (OBs) recovered from oilseeds are of growing interest in the preparation of sustainable, natural and healthy plant-based food products. This study focused on chia (Salvia hispanica L.) and camelina (Camelina sativa L.) seed OBs. A green refinery process including ultrasound to remove mucilage, aqueous extraction by grinding and centrifugation to recover OBs from the seeds was used. The microstructure, composition and physical stability of the OBs were examined. Confocal laser scanning microscopy images showed that chia and camelina seed OBs are spherical assemblies coated by a layer of phospholipids and proteins, which have been identified by gel electrophoresis. The mean diameters determined by laser light scattering measurements were 2.3 and 1.6 µm for chia and camelina seed OBs, respectively. The chia and camelina seed OBs were rich in lipids and other bioactive components with, respectively, 64% and 30% α-linolenic acid representing 70% and 53% of the total fatty acids in the sn-2 position of the triacylglycerols, 0.23% and 0.26% phospholipids, 3069 and 2674 mg/kg oil of ß-sitosterol, and lipophilic antioxidants: 400 and 670 mg/kg oil of γ-tocopherol. Phenolic compounds were recovered from the aqueous extracts, such as rutin from camelina and caffeic acid from chia. Zeta-potential measurements showed changes from about -40 mV (pH 9) to values that were positive below the isoelectric points of pH 5.1 and 3.6 for chia and camelina seed OBs, respectively. Below pH 6.5, physical instability of the natural oil-in-water emulsions with aggregation and phase separation was found. This study will contribute to the development of innovative and sustainable food products based on natural oil-in-water emulsions containing chia and camelina seed OBs for their nutritional and health benefits.

Impact of cell wall non-cellulosic and cellulosic polymers on the mechanical properties of flax fibre bundles.

Fibre bundles are groups of elementary fibres glued together thanks to the middle lamella, and are the main fraction in plant fibre composites. In this study, relationship between the mechanical properties of flax fibre bundles, chemical composition and cellulose structure were investigated. To do so, a sequential biopolymer extraction was implemented. Fibre bundles were first depectinated by oxalate extraction, and then the hemicelluloses were extracted by LiCl/dimethyl sulfoxide (DMSO) and KOH. The oxalate extract consisted of homogalacturonans and type I rhamnogalacturonans, while the LiCl extract was composed mainly of glucomannans and the KOH extract of xyloglucans. The KOH stage resulted in the appearance of cellulose II in flax bundles. The extraction of pectin and hemicelluloses led to the disappearance of the middle lamella concomitant with a decrease in the tensile Young's modulus and maximum strength. Finally, the fibre bundle composition, ultrastructure and mechanical properties are discussed together in view of the thin middle lamella.

Deciphering the properties of hemp seed oil bodies for food applications: Lipid composition, microstructure, surface properties and physical stability.

Hemp seed oil bodies (HSOBs) are of growing interest in response to the demand of consumers for healthy and natural plant-based food formulations. In this study, we used minimal processing including aqueous extraction by grinding and centrifugation to obtain HSOBs. We determined the lipid composition of HSBOs, their microstructure, and the impact of the homogenization pressure, pH and minerals on their surface properties and the physical stability of the emulsions. HSOBs contain high levels of well-balanced PUFA with LA/ALA = 2.9, γ-tocopherol, lutein and phytosterols. The mean diameter of HSOBs was 2.3 ± 0.1 µm with an isoelectric point in the range of pH 4.4 to 4.6. Homogenization of hemp seed extracts induced a decrease in the size of HSOBs but did not eliminate the sedimentation of the protein bodies composed of the globulin edestin. By changing the surface properties of HSOBs, pH values below 6 and NaCl induced the aggregation of HSOBs, while CaCl2 induced both aggregation and membrane-fusion mediated coalescence of HSOBs by involving probably the anionic phospholipids together with membrane proteins. This study will contribute to extend the range of novel food products and designed emulsions containing hemp seed proteins and oil bodies.

Cellulose Nanofibrils/Xyloglucan Bio-Based Aerogels with Shape Recovery.

Bio-based aerogels containing cellulose nanofibrils (CNFs) are promising materials due to the inherent physical properties of CNF. The high affinity of cellulose to plant hemicelluloses (xyloglucan, xylan, pectin) is also an opportunity to develop biomaterials with new properties. Here, we prepared aerogels from gelled dispersions of CNFs and xyloglucan (XG) at different ratios by using a freeze-casting procedure in unidirectional (UD) and non-directional (ND) manners. As showed by rheology analysis, CNF and CNF/XG dispersions behave as true gels. We investigated the impact of the freezing procedure and the gel's composition on the microstructure and the water absorption properties. The introduction of XG greatly affects the microstructure of the aerogel from lamellar to cellular morphology. Bio-based aerogels showed high water absorption capacity with shape recovery after compression. The relation between morphology and aerogel compositions is discussed.

Hydroxyl groups on cellulose nanocrystal surfaces form nucleation points for silver nanoparticles of varying shapes and sizes.

In this study, we investigate the interactions between the cellulose surface and Ag nanoparticles (AgNPs) for the purpose of manufacturing hybrid nanomaterials using bacterial cellulose nanocrystals (BCNs) as a model substrate. We focus on the role of the BCN surface chemistry on the AgNP nucleation obtained by chemical reduction of Ag+ ions. Homogeneous hybrid suspensions of BCN/AgNP are produced, regardless of whether the BCNs are quasi-neutral, negatively (TBCNs) or positively charged (ABCNs). The characterization of BCN/AgNP hybrids identifies the -OH surface groups as nucleation points for AgNPs, of about 20 nm revealing that surface charges only improve the accessibility to OH groups. X-ray Absorption technics (XANES and EXAFS) revealed a high metallic Ag0 content ranging from 88% to 97%. Moreover, the grafting of hydrophobic molecules on a BCN surface (HBCNs) does not prevent AgNP nucleation, illustrating the versatility of our method and the possibility to obtain bifunctional NPs. A H2O2 redox post-treatment on the hybrid induces an increase in AgNPs size, up to 90 nm as well as a shape variation (i.e., triangular). In contrast, H2O2 induces no size/shape variation for aggregated hybrids, emphasizing that the accessibility to -OH groups ensures the nucleation of bigger Ag nano-objects.

Adsorption of xyloglucan and cellulose nanocrystals on natural fibres for the creation of hierarchically structured fibres.

Green treatment of natural fibres is a major issue in paper, textile and biocomposites industries to design innovative and eco-friendly products. In this work, hierarchical structuring of flax woven fabrics by the adsorption of xyloglucan (XG) and cellulose nanocrystals (CNC) is studied. Indeed, CNC have high mechanical properties, high specific surface area and great potential for functionalization. The adsorption of XG and CNC has been investigated in terms of localization by confocal and scanning electron microscopy (SEM) and quantification through adsorption isotherms. Adhesion force measurements have also been performed by Atomic Force Microscopy (AFM). XG and CNC are homogeneously adsorbed on flax fabric and adsorption isotherms reach plateau values around 20 mg /gfibres for both. The pre-adsorption of XG on flax fabric influences the amount of adsorbed CNC in the high concentrations and also creates entanglements and strong interactions between XG and CNC with the formation of an extensible network.

Tuning of Ag Nanoparticle Properties in Cellulose Nanocrystals/Ag Nanoparticle Hybrid Suspensions by H2O2 Redox Post-Treatment: The Role of the H2O2/AgNP Ratio.

Hybrid nanoparticles involving 10-nm silver nanoparticles (AgNPs) nucleated on unmodified rod-like cellulose nanocrystals (CNCs) were prepared by chemical reduction. H2O2 used as a post-treatment induced a size-shape transition following a redox mechanism, passing from 10-nm spherical AgNPs to 300-nm triangular or prismatic NPs (AgNPrisms), where CNCs are the only stabilizers for AgNPs and AgNPrisms. We investigated the role of the H2O2/AgNP mass ratio (α) on AgNPs. At α values above 0.20, the large amount of H2O2 led to extensive oxidation that produced numerous nucleation points for AgNPrisms on CNCs. On the contrary, for α below 0.20, primary AgNPs are only partially oxidized, releasing a reduced amount of Ag+ ions and thus preventing the formation of AgNPrisms and reforming spherical AgNPs. While XRD and EXAFS reveal that the AgNP fcc crystal structure is unaffected by the H2O2 treatment, the XANES spectra proved that the AgNP-AgNPrism transition is always associated with an increase in the metallic Ag fraction (Ag0). In contrast, the formation of new 15-nm spherical AgNPs keeps the initial Ag0/Ag+ ratio unmodified. For the first time, we introduce a complete guide map for the fully-controlled preparation of aqueous dispersed AgNPs using CNC as a template.

Self-assembly, foaming, and emulsifying properties of sodium alkyl carboxylate/guanidine hydrochloride aqueous mixtures.

Unsaturated fatty acids may be extracted from various agricultural resources and are widely used as soaps in the industry. However, there also exist a large variety of saturated and hydroxy fatty acids in nature, but their metal salts crystallize at room temperature in water, hampering their use in biological and chemical studies or for industrial applications. Addition of guanidine hydrochloride (GuHCl) to sodium salt of myristic acid has been shown to prevent its crystallization in water, forming stable flat bilayers at room temperature. Herein, we extend this finding to two other saturated fatty acids (palmitic and stearic acids) and two hydroxyl fatty acids (juniperic and 12 hydroxy stearic acids) and study more deeply (by using small angle neutron scattering) the supramolecular assemblies formed in both saturated and hydroxyl fatty acid systems. In addition, we take the advantage that crystallization no longer occurs at room temperature in the presence of GuHCl to study the foaming and emulsifying properties of those fatty acid dispersions. Briefly, our results show that all fatty acids, even juniperic acid, which is a bola lipid, are arranged in a bilayer structure that may be interdigitated. Depending on the nature of the fatty acid, the systems exhibit good foamability and foam stability (except for juniperic acid), and emulsion stability was good. Those findings should be of interest for using saturated long chain (and hydroxyl) fatty acids as surfactants for detergency or even materials chemistry.

Self-assembly and foaming properties of fatty acid-lysine aqueous dispersions.

We report on dispersions of fatty acid-lysine salts in aqueous solutions which are further used to produce foams. The alkyl chain length is varied from dodecyl to stearic. In aqueous solutions, the lysine salt of the dodecyl chain yields an isotropic solution, probably micelles, whereas for longer alkyl chains, vesicles formed but crystallized upon resting at room temperature or when kept at 4 degrees C. Solid-state NMR showed that in vesicles fatty acids are embedded in a lamellar arrangement passing from a gel to a fluid state upon heating; the transition temperature at which it occurs was determined by DSC. Those results are confirmed by small-angle neutron scattering which also give additional information on the bilayer structure. Incredibly stable foams are obtained using the palmitic acid/Lys salt whereas for other alkyl chain length, poor or no foam is formed. We conclude that the foamability is related to the phase behavior in aqueous solution.

12-Hydroxystearic acid lipid tubes under various experimental conditions.

There is a growing interest for constructing supramolecular hollow tubes from amphiphilic molecules. Aqueous solutions of the ethanolamine salt of 12-hydroxystearic acid are known to form tubes of several tens of micrometers in length with a temperature-tunable diameter. However, the phase behavior of this system has not been fully studied. Herein, we report the variation of various physico-chemical parameters on the self-assembling properties of this system. The effects of the ionic strength, ethanol, doping with other lipids, pH, concentration, and the fatty acid/ethanolamine molar ratio R were investigated by both phase-contrast microscopy and DSC. We observed the formation of tubes in a wide range of parameters. For instance, the molar ratio R can be modified from 2/3 to 5/2 without altering the formation of tubes. In some but not all cases, the tube diameter still varied with temperature. These findings show that tubes form under various experimental conditions. This should increase the interest in producing such self-assemblies from low-cost fatty acids.

Self assembly of anastomosis-like superstructures in fatty acid/guanidine hydrochloride aqueous dispersions.

A mixture between 1% sodium myristate and guanidine hydrochloride at a molar ratio of 1 in water forms a gel of membranes below a phase transition of ca. 21 degrees C and a viscous limpid and isotropic solution above. As observed by both TEM and AFM, we report the formation of interconnected superstructures in that latter phase. Those assemblies exhibit a size of ca. 4-40 nm width and several tens of mum length with unexpected disconnections and re-connections between them having the appearance of an anastomosis-like superstructure.

Beta-lactoglobulin aggregates in foam films: effect of the concentration and size of the protein aggregates.

Single foam films made from mixtures of nonaggregated proteins and protein aggregates have been studied using a thin film balance apparatus. Their features (heterogeneity, stability and resistance to pressure change) are dependent on the aggregate size and on the ratio between nonaggregated proteins and protein aggregates. A phase diagram of these foam films has been drawn and a correlation of the structural properties of foam film and stability of real foams has been found. In particular, the formation of a gel-like network within the foam film coincides with the stability of the corresponding 3-D foams.

Synthesising gold nanoparticles within bola fatty acid nanosomes.

We report on the synthesis of gold nanoparticles (Au-NP) stabilized by a layer of mercapto and/or hydroxyl bola palmitic acid-tetrabutyl ammonium salts (TBAOH) which form nanosomes in water. Mixing both bola fatty acids in water in various proportions allowed to tune the nanoparticle diameter from 1 to 10 nm using NaBH(4) as a reductor. Those nanoparticles could be phase transferred to dichloromethane by adding a more hydrophobic counter-ion than TBAOH, its derivative with octyl chains (TOAOH). Finally, we used those Au-NP to formulate emulsions, the stability of which was followed as a function of particle size and time. The emulsions were stable but creamed after several hours. We conclude that bola fatty acid nanosomes are then good candidates to synthesize gold nanoparticles dispersed either in water, organic solvents and emulsions.