In Vitro Gastrointestinal Digestibility of Crystalline Oil-in-Water Emulsions: Influence of Fat Crystal Structure

Controlling release of astaxanthin in β-sitosterol oleogel-based emulsions via different self-assembled mechanisms and composition of the oleogelators

In this study, three types of β-sitosterol-based oleogels (β-sitosterol + γ-oryzanol oleogels, β-sitosterol + lecithin, oleogels and β-sitosterol + monostearate oleogels), loaded with astaxanthin, were employed as the oil phase to create oleogel-based emulsions (SO, SL, and SM) using high-pressure homogenization. The microstructure revealed that fine-scale crystals were dispersed within the oil phase of the droplets in the β-sitosterol oleogel-based emulsion. The bioaccessibility of astaxanthin was found to be 58.13 %, 51.24 %, 36.57 %, and 45.72 % for SM, SL, SO, and the control group, respectively. Interestingly, the release of fatty acids was positively correlated with the availability of astaxanthin (P = 0.981). Further analysis of FFAs release and kinetics indicated that the structural strength of the oil-phase in the emulsions influenced the degree and rate of lipolysis. Additionally, the micellar fraction analysis suggested that the nature and composition of the oleogelators in SM and SL also impacted lipolysis and the bioaccessibility of astaxanthin. Furthermore, interfacial binding of lipase and isothermal titration calorimetry (ITC) measurements revealed that the oleogel network within the oil phase of the emulsion acted as a physical barrier, hindering the interaction between lipase and lipid. Overall, β-sitosterol oleogel-based emulsions offer a versatile platform for delivering hydrophobic molecules, enhancing the bioavailability of active compounds, and achieving sustained release.

Mechanisms of interesterified fat digestibility in a muffin matrix using a dynamic gastric model

Industrially generated trans-fats have been linked with cardiovascular disease (CVD) and have thus been replaced by interesterified (IE) fats, in foods. Interesterification rearranges fatty acids on the glycerol backbone of a triacylglycerol molecule. However, the impact of IE fat on health is unknown. We recently reported differences in lipid absorption kinetics between IE and rapeseed oil (RO). Here, we investigated the mechanisms underpinning IE fat digestion kinetics in the same muffins baked using an IE fat, non-IE fat [with the same fatty acid composition] and rapeseed oil (RO) under simulated conditions. IE and non-IE fats were largely solid in the gastric phase and strongly associated within the muffin matrix, whereas RO formed liquid droplets which separated from the matrix. No significant difference in lipolysis rates was detected between IE and non-IE fats. The lipolysis of the RO fat was slower, due to long-chain PUFAs. Interesterification itself did not affect digestibility, but the strong interaction between the hard fats and the muffin matrix resulted in extensive creaming of the matrix in the stomach, leading to delayed gastric emptying compared to the RO sample. The rate and extent of lipolysis were determined by the amount of fat available and the structure of the fat. This demonstrates the importance of the physical behaviour of the fats during digestion and provides a mechanistic understanding of the overall lipid digestion of IE fats, which relates to their physiological response.

Influence of Proteins on Bioaccessibility of α-Tocopherol Encapsulation within High Diacylglycerol-Based Emulsions

α-Tocopherol has been widely used in medicine, cosmetics, and food industry as a nutritional supplement and antioxidant. However, α-tocopherol showed low bioaccessibility, and there is a widespread α-tocopherol deficiency in society today. The preparation of oil-in-water emulsions with high safety and low-calorie property is necessary. The aim of this research was to investigate the effects of different protein emulsifiers (whey protein isolate (WPI), soy protein isolate (SPI), and sodium casein (SC)) on the properties of emulsions delivery system, and diacylglycerol (DAG) was picked as a low-accumulated lipid. The interfacial changes, microstructural alterations, and possible interactions of the protein-stabilized DAG emulsions were investigated during the in vitro digestion. The results show that different proteins affect the degree of digestibility and α-tocopherol bioaccessibility of the emulsions. Both WPI- and SPI-coated emulsions showed good digestibility and α-tocopherol bioaccessibility (77.64 ± 2.93%). This might be due to the strong hydrolysis resistance of WPI (β-lactoglobulin) and the good emulsification ability of SPI. The SC-coated emulsion showed the lowest digestibility and α-tocopherol bioaccessibility, this might be due to the emulsification property of hydrolysis products of SC and the potential interaction with calcium ions. This study provides new possibilities for the application of DAG emulsions in delivery systems.

Network Structure and Nanoplatelet Characterization of the Edible Fat Crystallization in Low-Fat W/O Emulsions

Fat crystals provided the strength of the colloidal network in W/O emulsions and stabilized water droplets. To understand the stabilizing effect of fat-regulated emulsions, W/O emulsions with different edible fats were fabricated. The result indicated that more stable W/O emulsions were produced by palm oil (PO) and palm stearin (PS), whose proportions of fatty acids were similar. Meanwhile, water droplets inhibited the crystallization of emulsified fats but participated in the formation of the colloidal network with fat crystals in emulsions, and the Avrami equation showed a slower crystallization rate of emulsified fats than the corresponding fat blends. However, water droplets participated in the formation of a colloidal network of fat crystals in emulsions, and the adjacent fat crystals were connected through a bridge constructed by water droplets. Fats in the emulsion containing palm stearin crystallized faster and more easily formed the β-polymorph. The small-angle X-ray scattering (SAXS) data were interpreted by the unified fit model to determine the average size of crystalline nanoplatelets (CNPs). The larger CNPs (>100 nm) with a rough surface of emulsified fats and a uniform distribution of their aggregates was confirmed.

Strategies for modulating the lipid digestion of emulsions in the gastrointestinal tract

The structural changes in emulsion products can be used to control the bioavailability of fatty acids and lipophilic compounds. After ingestion, lipid droplets undergo breakdown and structural changes as they pass through the gastrointestinal tract. The oil-water interface plays a critical role in modulating the digestive behavior of lipid droplets because changes in the interfacial layer control the adsorption of lipase and bile salts and determine the overall rate and extent of lipid digestion. Therefore, lipid digestibility can be tuned by selecting the appropriate types and levels of stabilizers. The stabilizer can change the lipase accessibility and exposure of lipid substrates, resulting in variable digestion rates. However, emulsified lipids are not only added to food matrixes but are also co-ingested from other dietary components. Therefore, overall consumption behaviors can affect the digestion rate and digestibility of emulsified lipids. Although designing an emulsion structure is challenging, controlling lipid digestion can improve the health benefits of products. Therefore, a thorough understanding of the process of emulsified lipid digestion is required to develop food products that enable specific physiological responses. The targeted or delayed release of lipophilic molecules and fatty acids through emulsion systems has significant applications in healthcare and pharmaceuticals.

Surfactant-free oleogel-based emulsion stabilized by co-assembled ceramide/lecithin crystals with controlled digestibility

BACKGROUND

There is increasing interest in the development of oleogel-based emulsions. However, they usually contained surfactants for stabilization, especially small-molecular weight surfactants, which may have adverse health impacts.

RESULTS

Herein, a surfactant-free oleogel-based emulsion stabilized by co-assembled ceramide/lecithin (CER/LEC) crystals was developed. The formation and stabilization mechanisms were explored. The different molar ratios of gelator (LEC and CER) in emulsions resulted in different crystal morphology, crystallinity as well as different emulsion properties. This suggested that appropriate crystallinity, crystal size, and interfacial distribution of these crystals provided higher surface coverage against droplets coalescence, thus better emulsion stabilization. Both X-ray diffractograms and contact angle results confirmed that the crystals which were primarily responsible for emulsion stabilization, are co-assembled crystals consisted of both gelators (CER and LEC). Furthermore, the percentage of free fatty acids (FFAs%) results revealed a negative relationship between lipid digestibility and crystal concentration.

CONCLUSIONS

This strategy greatly enriched surfactant-free oleogel-based emulsion formulations, as well as their potential applications in healthy lipid-based products and novel food delivery systems with controlled lipid digestibility. © 2022 Society of Chemical Industry.

Tracing distribution and interface behavior of water droplets in W/O emulsions with fat crystals

Sucrose palmitate (P170) and sucrose laurate (L195) were used as emulsifiers to control the crystallization behavior of AMF and to stabilize W/O emulsions. In this study, the P170 promoted crystallization and led to strong fat crystal networks with smaller AMF crystals (60-80 μm) in emulsions, retaining flocculation. Water droplets were squeezed into irregular shapes between the strong network but the P170 formed an interface layer with better strength to resist the aggregation. Contrarily, the L195 inhibited crystallization and formed larger AMF spherulites (more than 100 μm) resulting in a low strength of fat crystal networks and unstable emulsions. Meanwhile, the water droplets were easily fixed on the surface of AMF crystals because of the existence of sucrose esters. Protruding crystals on the surface of larger spherulites could pierce the water-oil interface, leading to a greater coalescence and forming larger water droplets. Therefore, a weak crystal network could not prevent the sedimentation and phase separation caused by gravity.

A review of recent progress in improving the bioavailability of nutraceutical-loaded emulsions after oral intake

Increasing awareness of the health benefits of specific constituents in fruits, vegetables, cereals, and other whole foods has sparked a broader interest in the potential health benefits of nutraceuticals. Many nutraceuticals are hydrophobic substances, which means they must be encapsulated in colloidal delivery systems. Oil-in-water emulsions are one of the most widely used delivery systems for improving the bioavailability and bioactivity of these nutraceuticals. The composition and structure of emulsions can be designed to improve the water dispersibility, physicochemical stability, and bioavailability of the encapsulated nutraceuticals. The nature of the emulsion used influences the interfacial area and properties of the nutraceutical-loaded oil droplets in the gastrointestinal tract, which influences their digestion, as well as the bioaccessibility, metabolism, and absorption of the nutraceuticals. In this article, we review recent in vitro and in vivo studies on the utilization of emulsions to improve the bioavailability of nutraceuticals. The findings from this review should facilitate the design of more efficacious nutraceutical-loaded emulsions with increased bioactivity.

Effects of lipid type and toxicological properties on the digestion of cellulose nanocrystals in simulated gastrointestinal tract

This study aimed to understand the impact of different oil types on the cellulose nanocrystals (CNCs) to modulate lipid digestion and the in vitro gastrointestinal toxicity of CNCs in food systems. We explored the ability of CNCs to modulate lipid digestion in a simulated gastrointestinal system and monitored the gastrointestinal fate of CNC-based emulsions with different oil types. Finally, a small intestine epithelial model was used to evaluate the influence of cytotoxicity. The results suggested that the addition of 0.6 wt% CNCs in the high-fat food model reduced the hydrolysis of free fatty acids (FFAs) from triglycerides by 37.8% after the small intestine phase. CNCs showed the best effect in reducing lipid digestion in emulsions with high unsaturation triglycerides. In addition, the toxicology results suggest that 0.6 wt% CNCs had only a slight effect on reactive oxygen species and cytotoxicity, and no significant change in cell-layer integrity.

Effects of the Distribution Site of Crystallizable Emulsifiers on the Gastrointestinal Digestion Behavior of Double Emulsions

Double emulsions (DEs) are promising delivery vehicles for the protective and programmed release of bioactive compounds. Herein, DEs with monoglycerides crystallized at the internal- or external interface or oil phase were fabricated. The results suggested that the crystallization site of monoglycerides exerts a significant role in retarding the structural degradation and lipid digestion of DEs by affecting the available contact area of lipase. At the initial stage of intestinal digestion, compared with noncrystalline DEs (82.1%, 3.7 min), the burst release of internal markers in the internal interface crystallized emulsions was decreased by 42.4% and the lag time of free fatty acid (FFA) release was delayed by 5.8 min in the external interface crystallized emulsions. The structural integrity and digestion kinetics of the external interface crystallized DEs were synchronized with the retention time of the interfacial crystals. Therefore, crystallizable emulsifiers exhibit unique and fine regulatory effects on the digestive properties of emulsions.

In vitro gastrointestinal digestibility of corn oil-in-water Pickering emulsions stabilized by three types of nanocellulose

The effect of three nanocellulose (various in crystalline allomorph and morphology) on lipid in vitro gastrointestinal digestibility was investigated. Corn oil-in-water emulsions were prepared by CNCs-I, CNCs-II and CNFs respectively. The variations of droplets diameter D[4,3], zeta potential, and microstructure were measured during gastrointestinal digestion (mouth, stomach and small intestine), and the free fatty acid (FFA) released in the small intestine phase were examined. The FFA-released test results indicated that both crystalline allomorph and morphology of nanocellulose affected the degree of lipid digestion, especially the morphology. FFA released amount was ranked in the order of CNCs-I (56.60%), CNCs-II (48.67%) and CNFs (28.21%). This is mainly due to the difference in the self-assembly behavior of nanocellulose at the interface. Our findings provide an innovative solution that using nanocellulose as food-grade particle stabilizer to modulate the digestion of Pickering emulsified lipids, which would benefit the development of given functional foods.

Modulating the in vitro gastrointestinal digestibility of crystalline oil-in-water emulsion: Different fat crystal sizes and polymorphic forms under the same SFC

The effects of the fat crystal structure on lipid droplets digestion behaviors were investigated using an in vitro digestion model. The crystalline oil-in-water emulsions containing the same solid fat content (SFC) with different fat crystal sizes and polymorphic forms were fabricated by different storage protocols: constant-temperature and inconstant-temperature storage. Oral and gastric processing led to a significant increase (p < 0.05) in the d_4,3 values of the two emulsions, and the two emulsions underwent partial coalescence and flocculation/aggregation. The free fatty acid (FFA) release profiles showed that the lipolysis extent decreased due to a larger crystal size. In addition, the two emulsions showed differences in beta polymorphism. This work further demonstrated that the FFA release could be modulated by the physical properties of the fat.

Enhancing the bioaccessibility of puerarin through the collaboration of high internal phase Pickering emulsions with β-carotene

Puerarin is a medicinal and edible flavonoid compound found in the traditional Chinese medicine Pueraria lobata rhizome that has potential biological benefifits, including for the treatment of diabetes and memory...

Biophysical insights into modulating lipid digestion in food emulsions

During the last decade, major scientific advances on understanding the mechanisms of lipid digestion and metabolism have been made, with a view to addressing health issues (such as obesity) associated with overconsumption of lipid-rich and sucrose-rich foods. As lipids in common foods exist in the form of emulsions, the structuring of emulsions has been one the main strategies for controlling the rate of lipid digestion and absorption, at least from a colloid science viewpoint. Modulating the kinetics of lipid digestion and absorption offers interesting possibilities for developing foods that can provide control of postprandial lipaemia and control the release of lipophilic compounds. Food emulsions can be designed to achieve considerable differences in the kinetics of lipid digestion but most research has been applied to relatively simple model systems and in in vitro digestion models. Further research to translate this knowledge into more complex food systems and to validate the results in human studies is required. One promising approach to delay/control lipid digestion is to alter the stomach emptying rate of lipids, which is largely affected by interactions of emulsion droplets with the food matrices. Food matrices with different responses to the gastric environment and with different interactions between oil droplets and the food matrix can be designed to influence lipid digestion. This review focuses on key scientific advances made during the last decade on understanding the physicochemical and structural modifications of emulsified lipids, mainly from a biophysical science perspective. The review specifically explores different approaches by which the structure and stability of emulsions may be altered to achieve specific lipid digestion kinetics.

Stability and bioaccessibility of curcumin emulsions stabilized by casein hydrolysates after maleic anhydride acylation and pullulan glycation

The effects of maleic anhydride (MA) acylation and pullulan glycation on casein hydrolysates (CH) and the physicochemical stability of modified or unmodified CH-stabilized emulsions were explored. Compared with casein, the solubility of CH was improved, and CH₁ (hydrolysis degree 4%) exhibited the optimal emulsifying properties. After the acylation of MA, degrees of acylation (DA) increased with increasing addition of MA. Fourier-transform infrared spectroscopy revealed that a covalent bond was formed between MA and CH₁. The results of pullulan glycation indicated that the degree of glycation decreased with increasing DA. Acylation combined with glycation effectively reduced the surface hydrophobicity of CH. Results of analysis of physicochemical stability and gastrointestinal fate of curcumin in emulsions revealed that CH modified by MA acylation and pullulan glycation played a positive role in enhancing the stability and bioaccessibility of curcumin loaded in emulsions.

In Vitro Gastrointestinal Digestion of Palm Olein and Palm Stearin-in-Water Emulsions with Different Physical States and Fat Contents

The impacts of lipid physical state and content on lipid digestion behavior were investigated using 4 and 20% palm olein-in-water emulsions (4% PO and 20% PO) and 4 and 20% palm stearin-in-water emulsions (4% PS and 20% PS). The changes of lipid physical state, particle size, and microstructure during gastrointestinal digestion; the free fatty acid (FFA) released in the intestinal phase; and the fatty acid composition of micellar phases were investigated. After gastric digestion, all emulsions underwent flocculation and coalescence, with 20% PS showing the most extensive aggregation. During intestinal digestion, the FFA release rate and level decreased as the lipid content increased from 4 to 20%, with 4% PO presenting the highest digestion rate and extent. Besides, the solid fat in 4% PS and 20% PS decreased and increased the maximum lipid digestibility, respectively. These results highlighted the combined roles of lipid physical state and content in modulating dietary lipid digestion.

The influence of oil composition on the transformation, bioaccessibility, and intestinal absorption of curcumin in nanostructured lipid carriers

In this study, the influences of liquid medium-chain triglyceride (MCT) and solid glyceryl tristearate (GTS) contents in the lipid matrix of nanostructured lipid carriers (NLCs) on their delivering capacities with respect to curcumin (Cur) were investigated by using a simulated gastrointestinal tract and Caco-2 monolayer models. The transformation of the encapsulated Cur decreased on increasing the MCT content in the lipid matrix of NLCs because it facilitated their lipolysis and promoted the exposure of Cur to a harsher exterior environment. Cur bioaccessibility was positively correlated with the level of micellized stearic acid resulting from GTS hydrolysis, which might be attributed to the fact that it could afford large hydrophobic domains to accommodate Cur. This value initially increased with an increase in the MCT content, reaching a maximum at 20% (w/w) and decreasing thereafter. The intestinal absorption of micellar Cur ranged from 26.06% to 38.76%, and a majority of the transported molecules were its reductive and conjugative metabolites. Overall, NLC containing 20% MCT in the lipid matrix afforded the highest Cur bioavailability, followed by that containing 10, 0, 40, 60, and 100% MCT. This work provides useful insights into the rational design of NLCs to optimize the bioavailability of the loaded agent.

Capacitive sensing of triglyceride film reactions: a proof-of-concept demonstration for sensing in simulated duodenal contents with gastrointestinal targeting capsule system

Ingestible capsule systems continue to evolve to overcome drawbacks associated with traditional gastrointestinal (GI) diagnostic and therapeutic processes, such as limitations on which sections of the GI tract can be accessed or the inability to measure local biomarker concentrations. We report an integrated capsule sensing system, utilizing a hybrid packaging scheme coupled with triglyceride film-coated capacitive sensors, for measuring biochemical species present in the duodenum, such as pancreatic lipase and bile acids. The system uses microfabricated capacitive sensors interfaced with a Bluetooth low-energy (BLE)-microcontroller, allowing wireless connectivity to a mobile app. The triglyceride films insulate the sensor surface and react either with 0.01-1 mM lipase via hydrolysis or 0.07-7% w/v bile acids via emulsification in simulated fluids, leading to measurable changes in capacitance. Cross reactivity of the triglyceride films is evaluated in both phosphate buffered saline (PBS) as well as pancreatic trypsin solutions. The film morphology is observed after exposure to each stimulus to better understand how these changes alter the sensor capacitance. The capsule utilizes a 3D-printed package coated with polymers that remain intact in acid solution (mimicking gastric conditions), then dissolve at a duodenum-mimicking neutral pH for triggered opening of the sensing chamber from which we can subsequently detect the presence of pancreatic lipase. This device strategy represents a significant step towards using embedded packaging and triglyceride-based materials to target specific regions of the GI tract and sensing biochemical contents for evaluating gastrointestinal health.

Exploration of the Stabilization Mechanism and Curcumin Bioaccessibility of Emulsions Stabilized by Whey Protein Hydrolysates after Succinylation and Glycation in Different Orders

The combined effects of succinic anhydride (SA) succinylation and linear dextrin (LD) glycation on whey protein hydrolysates (WPH) and their stabilized emulsions were evaluated. Degree of succinylation (DS), degree of glycation (DG), and degree of browning of samples suggested that a competitive displacement of reactive groups existed when WPH reacted with SA and LD in different orders. Attenuated total reflection Fourier transform infrared (ATR-FTIR) and far-UV circular dichroism (CD) indicated that the order of modification methods had a significant effect on secondary structures of WPH. Succinylation combined with glycation effectively reduced the surface hydrophobicity and increased the molecular flexibility of WPH. Meanwhile, the total free -SH content decreased, and the exposed free -SH content increased. Results of storage stability and gastrointestinal fate of the curcumin-loaded emulsion revealed that the modified WPH with higher DS was more effective for improving the curcumin bioaccessibility, while that with higher DG was more effective for enhancing the stability of the emulsion.

In vitrogastrointestinal digestibility of phytosterol oleogels: influence of self-assembled microstructures on emulsification efficiency and lipase activity

The objective of this study was to investigate the influence of a self-assembled microstructure on lipid digestibility of phytosterol (γ-oryzanol and β-sitosterol) oleogels, including the oil emulsification process and further lipolysis.