Effect of Emulsifier Concentration and Physical State on the In Vitro Digestion Behavior of Oil-in-Water Emulsions

In vitro digestion study comparing a predigested glycerolysis product versus long-chain polyunsaturated fatty acid-rich oils (LCPUFA) as a strategy for administering LCPUFA to preterm neonates

BACKGROUND & AIMS

Maintaining an adequate supply of arachidonic acid (ARA) and docosahexaenoic acid (DHA) is essential for optimal growth of preterm infants. This study aims to evaluate and compare the digestibility and bioaccessibility of ARA and DHA oils compared to their predigested product through an in vitro digestion model.

METHODS

An in vitro gastrointestinal digestion model was used in two stages: gastric digestion and intestinal digestion. Samples of two polyunsaturated rich oils (ARA and DHA oils) and their predigested product (2:1, ARA: DHA) produced by enzymatic glycerolysis have been digested for 120 min. The final digestion product obtained was composed of three phases: an upper oily phase (OP) containing the undigested species, an intermediate micellar phase (MP) containing digested and bioaccessible lipids, and a precipitate phase (PP) with insoluble compounds. The reaction was monitored by taking aliquots and their subsequent lipid extraction and analysis.

RESULTS

Poorer digestibility for ARA and DHA oils was observed based on the percentage of the oily phase (26.7% and 20%, respectively) found compared to the glycerolysis product (GP) oily phase (13.9%). The highest micellar phase was found in the GP (approx. 83%). On the other hand, the monoglyceride (MAG) content was lower in the digestion product (DP) from ARA and DHA oils, 4.3% and 9.2%, respectively, compared to the MAG observed in the DP of GP (15%).

CONCLUSION

Considering the percentage of oily phase, micellar phase, and the MAG content, it can be concluded that the GP is more digestible and ARA and DHA are more bioaccessible than in its precursor oils.

Predigested Mixture of Arachidonic and Docosahexaenoic Acids for Better Bio-Accessibility

A predigested product from arachidonic acid oil (ARA) and docosahexaenoic acid (DHA) oil in a 2:1 (w/w) ratio has been developed and evaluated in an in vitro digestion model. To produce this predigested lipid mixture, first, the two oils were enzymatically hydrolyzed up to 90% of free fatty acids (FFAs) were achieved. Then, these two fatty acid (FA) mixtures were mixed in a 2:1 ARA-to-DHA ratio (w/w) and enzymatically esterified with glycerol to produce a mixture of FFAs, mono-, di-, and triacylglycerides. Different glycerol ratios and temperatures were evaluated. The best results were attained at 10 °C and a glycerol-to-FA molar ratio of 3:1. The bio-accessibility of this predigested mixture was studied in an in vitro digestion model. A total of 90% of the digestion product was found in the micellar phase, which contained 30% monoacylglycerides, more than 50% FFAs, and a very small amount of triacylglycerols (3% w/w). All these data indicate an excellent bio-accessibility of this predigested mixture.

Exploring the fates and molecular changes of different diacylglycerol-rich lipids during in vitro digestion

This study aimed to support the pursuit of healthy oils and investigate the relationships between lipid compositions and digestion fates of diacylglycerol (DAG)-rich lipids using an in vitro digestion model. Soybean-, olive-, rapeseed-, camellia-, and linseed-based DAG-rich lipids (termed SD, OD, RD, CD, and LD, respectively) were selected. These lipids exhibited identical lipolysis degrees (92.20-94.36 %) and digestion rates (0.0403-0.0466 s^-1). The lipid structure (DAG or triacylglycerol) was a more important factor affecting the lipolysis degree than other indices (glycerolipid composition and fatty acid composition). For RD, CD and LD with similar fatty acid compositions, the same fatty acid had different release levels, probably due to their different glycerolipid compositions (causing different distributions of the fatty acid in UU-DAG, USa-DAG and SaSa-DAG; U: unsaturated fatty acids, Sa: saturated fatty acids). This study provides insights into the digestion behaviors of different DAG-rich lipids and supports their food or pharmaceutical applications.

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 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.

Nanostructured lipid carriers for the encapsulation of phloretin: preparation and in vitro characterization studies

Phloretin is a powerful antioxidant with many effects, such as anti-cancer, anti-inflammatory, promoting cell renewal, delaying aging and so on. However, the application of phloretin was limited by its low water solubility, low absorption in vivo and unstable properties. A phloretin-loaded nanostructured lipid carrier was designed with a high-pressure homogenization technique. The mean particle size of phloretin NLC was 137.40 ± 3.27 nm, and the Polydispersity index (PdI) value was 0.237 ± 0.005. The encapsulation efficiency was 96.68% ± 0.06%. Transmission electron microscopy images showed that the phloretin-loaded nanostructured lipid carriers were spherical. Phloretin in NLC showed a sustained release pattern in vitro. The results showed that phloretin NLC is more suitable for absorption than phloretin ethanol solution, and NLC can be a promising carrier for phloretin in the food industry.

Upper digestion fate of citrus pectin-stabilized emulsion: An interfacial behavior perspective

Citrus pectin can serve as a naturally digestion-resistant emulsifier, although how it achieves this effect is still unknown. In this study, the upper digestion fate of an emulsion stabilized by different concentrations of citrus pectin, and changes in its interfacial properties during digestion, were investigated. Emulsions stabilized by high-concentration citrus pectin (3 %) were relatively stable during digestion and had a lower free fatty acid (FFA) release rate than emulsions stabilized by low-concentration citrus pectin (1 %). At the low concentration, the citrus pectin interface had a thin absorbing layer and was largely replaced by bile salts, while at high concentration the citrus pectin interface possessed a uniform and thick adsorbing layer that resisted the replacement of bile salts and enabled lipase adsorption. This study has improved our understanding of the digestion of emulsion from the interface and will be useful for designing emulsion-based functional foods that can achieve targeted release.

Effect of different structural flaxseed lignans on the stability of flaxseed oil-in-water emulsion: An interfacial perspective

The influences of the different structural flaxseed lignans on flaxseed oil (FO) emulsions during storage and digestion were investigated, focusing on their interfacial behavior. From perspective of interface, more than 60% of secoisolariciresinol (SECO) and the acidic hydrolysates of flaxseed lignan macromolecule (FLEH) were located on the interface of FO emulsions. It improved the stability of FO emulsions both during storage and digestion by inhibiting of free radical penetration and improving their targeted antioxidative activity. By comparison, the secoisolariciresinol diglucoside (SDG) and the alkaline hydrolysates of flaxseed lignan macromolecule (FLE) largely located in the aqueous and exerted lower antioxidative efficiency in emulsions. Moreover, SDG, SECO, FLE and FLEH slowed down the digestive rate of FO in emulsions, which might be due to flaxseed lignans inhibited the activity of digestive enzymes. These findings suggested that the different structural flaxseed lignans had the potential as antioxidants in emulsions during storage and digestion.

Improving the bioavailability of oil-soluble vitamins by optimizing food matrix effects: A review

The potency of oil-soluble vitamins (vitamins A, D, E and K) in fortified foods can be improved by understanding how food matrices impact their bioavailability. In this review, the major food matrix effects influencing the bioavailability of oil-soluble vitamins are highlighted: oil content, oil composition, particle size, interfacial properties, and food additives. Droplet size and aggregation state in the human gut impact vitamin bioavailability by modulating lipid digestion, vitamin release, and vitamin solubilization. Vitamins in small isolated oil droplets typically have a higher bioavailability than those in large or aggregated ones. Emulsifiers, stabilizers, or texture modifiers can therefore affect bioavailability by influencing droplet size or aggregation. The dimensions of the hydrophobic domains in mixed micelles depends on lipid type: if the domains are too small, vitamin bioavailability is low. Overall, this review highlights the importance of carefully designing food matrices to improve vitamin bioavailability.

The lipid type affects the in vitro digestibility and β-carotene bioaccessibility of liquid or solid lipid nanoparticles

Solid lipid nanoparticles (SLNs) are emulsion-based carriers of lipophilic bioactive compounds. However, their digestibility may be affected by the solid lipid phase composition. Hence, the aim of this work was to study the in vitro lipolysis kinetics as well as the relationship between the lipid digestion, micelle fraction composition and β-carotene bioaccessibility of SLNs with different solid lipids, being blends of medium chain triglyceride (MCT) oil, glyceryl stearate (GS) or hydrogenated palm oil (HPO) as compared to liquid lipid nanoparticles (LLNs) with pure MCT. SLNs formulated with GS were fully digested, similarly to LLNs. However, HPO-containing SLNs presented slower lipolysis kinetics during the intestinal phase at increasing HPO concentration. Despite this, HPO-SLNs showed higher β-carotene bioaccessibility, which was related to the higher amount of monounstaturated free fatty acids in the micelle fraction. Thus, this work provides valuable insight for designing delivery systems of bioactive compounds with optimal functionality.