In vitro gastric and intestinal digestion of a walnut oil body dispersion

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 % β-sitosterol), carotenoids (0.62 ± 0.01 mg/kg lipids; 49.2 % β-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.

Effect of Heat Treatment on the Digestive Characteristics of Different Soybean Oil Body Emulsions

Soybean oil body (SOB) emulsions were prepared using OBs extracted at pH 11.0 and pH 7.0. The pH 11.0-SOB comprised oleosins, whereas pH 7.0-SOB comprised extrinsic proteins and oleosins. All SOB emulsions were heated at 60-100 °C for 15 min. Heating may lead to the release of extrinsic proteins from the surface of pH 7.0-SOB due to heat-induced denaturation. The total proportion of α-helix and β-sheets gradually decreased from 77 (unheated) to 36.2% (100 °C). During stomach digestion, the extrinsic protein hydrolysis of heated pH 7.0-SOB emulsions was fast between 60 and 80 °C, and it then slowed between 90 and 100 °C; heating inhibited the oleosin hydrolysis of pH 7.0- and 11.0-SOBs. Heat treatment promoted aggregation and coalescence, and it resulted in increased particle sizes for all emulsions. Larger aggregates were found in heated pH 7.0-SOB emulsions, and larger oil droplets were found in heated pH 11.0-SOB emulsions. After intestinal digestion, the droplets of all SOB emulsions gradually dispersed, and particle sizes decreased. Different heating temperatures had lesser effects on particle sizes and microstructures. Lipolysis was affected by the extraction pH and heating. For pH 11.0-SOB emulsions, the FFA release tendency was greatly affected by the heating temperature, and heating to 80 °C resulted in the highest FFA release (74%). However, all pH 7.0-SOB emulsions had similar total FFA releases. In addition, the droplet charges of heated pH 7.0-SOB emulsions were lower than those of unheated pH 7.0-SOB emulsions in both the intestine and stomach phases; however, the charge changes in different pH 11.0-SOB emulsions showed the opposite tendency. This study will offer guidance regarding the application of SOB emulsions in food.

Understanding the structure, interfacial properties, and digestion fate of high internal phase Pickering emulsions stabilized by food-grade coacervates: Tracing the dynamic transition from coacervates to complexes

Although protein-polysaccharide complexes have shown tremendous potential in stabilizing high internal phase Pickering emulsions (HIPPEs), it is unclear whether coacervates have the same potential to be used as effective Pickering stabilizers. In this study, HIPPEs were prepared by ovalbumin (OVA)-pectin (PE) coacervates during the transition from coacervates to complexes. The results showed that enhanced OVA-PE interactions significantly affected the wettability and surface-tension reduction ability of the OVA-PE coacervates. At pH 2, the coacervate-stabilized HIPPEs exhibited smaller oil droplet sizes (21.3±2.3 μm), tighter droplet packing, and finer solid-like structures through the bridging of droplets and the generation of stronger gel-like network structures to prevent coalescence and lipid oxidation. The gastrointestinal digestion results proved that the OVA-PE coacervates promoted lipid hydrolysis and improved the bioaccessibility (from 19.7±0.7% to 36.5±2%) of curcumin-loaded HIPPEs. Our work provides new ideas for the development of biopolymer particles as effective Pickering stabilizers in the food industry.

Preparation, identification, and molecular docking of novel elastase inhibitory peptide from walnut (Juglans regia L.) meal

This study aimed to isolate bioactive peptides with elastase inhibitory activity from walnut meal via ultrasonic enzymatic hydrolysis. The optimal hydrolysis conditions of walnut meal protein hydrolysates (WMPHs) were obtained by response surface methodology (RSM), while a molecular weight of<3 kDa fraction was analyzed by LC-MS/MS, and 556 peptides were identified. PyRx virtual screening and Autodock Vina molecular docking revealed that the pentapeptide Phe-Phe-Val-Pro-Phe (FFVPF) could interact with elastase primarily through hydrophobic interactions, hydrogen bonds, and π-sulfur bonds, with a binding energy of -5.22 kcal/mol. The verification results of inhibitory activity showed that FFVPF had better elastase inhibitory activity, with IC₅₀ values of 0.469 ± 0.01 mg/mL. Furthermore, FFVPF exhibited specific stability in the gastric environment. These findings suggest that the pentapeptide FFVPF from defatted walnut meal could serve as a potential source of elastase inhibitors in the food, medical, and cosmetics industries.

Plant oil bodies and their membrane components: new natural materials for food applications

Plants store triacylglycerols in the form of oil bodies (OBs) as an energy source for germination and subsequent seedling growth. The interfacial biomaterials from these OBs are called OB membrane materials (OBMMs) and have several applications in foods, e.g., as emulsifiers. OBMMs are preferred, compared with their synthetic counterparts, in food applications as emulsifiers because they are natural, i.e., suitable for clean label, and may stabilize bioactive components during storage. This review focuses mainly on the extraction technologies for plant OBMMs, the functionality of these materials, and the interaction of OB membranes with other food components. Different sources of OBs are evaluated and the challenges during the extraction and use of these OBMMs for food applications are addressed.

Gastric digestion of cow milk, almond milk and oat milk in rats

In this study, gastric digestion of isocaloric and iso-macronutrient cow milk, almond milk and oat milk were compared in rats euthanized at different post-feeding times.

Digestibility and oxidative stability of plant lipid assemblies: An underexplored source of potentially bioactive surfactants?

Most lipids in our diet come under the form of triacylglycerols that are often redispersed and stabilized by surfactants in processed foods. In plant however, lipid assemblies constitute interesting sources of natural bioactive and functional ingredients. In most photosynthetic sources, polar lipids rich in ω3 fatty acids are concentrated. The objective of this review is to summarize all the knowledge about the physico-chemical composition, digestive behavior and oxidative stability of plant polar lipid assemblies to emphasize their potential as functional ingredients in human diet and their potentialities to substitute artificial surfactants/antioxidants. The specific composition of plant membrane assemblies is detailed, including plasma membranes, oil bodies, and chloroplast; emphasizing its concentration in phospholipids, galactolipids, peculiar proteins, and phenolic compounds. These molecular species are hydrolyzed by specific digestive enzymes in the human gastrointestinal tract and reduced the hydrolysis of triacylglycerols and their subsequent absorption. Galactolipids specifically can activate ileal break and intrinsically present an antioxidant (AO) activity and metal chelating activity. In addition, their natural association with phenolic compounds and their physical state (Lα state of digalactosyldiacylglycerols) in membrane assemblies can enhance their stability to oxidation. All these elements make plant membrane molecules and assemblies very promising components with a wide range of potential applications to vectorize ω3 polyunsaturated fatty acids, and equilibrate human diet.

Structural and Physicochemical Characteristics of Oil Bodies from Hemp Seeds (Cannabis sativa L.)

The structural and physicochemical characteristics of oil bodies from hemp seeds were explored in this study. Oil bodies from several plant-based sources have been previously studied; however, this is the first time a characterisation of oil bodies from the seeds of industrial hemp is provided. The morphology of oil bodies in hemp seeds and after extraction was investigated using cryo-scanning electron microscopy (cryo-SEM), and the interfacial characteristics of isolated oil bodies were studied by confocal laser scanning microscopy (CLSM). Proteins associated with oil bodies were characterised using sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The effect of pH and ionic strength on colloidal properties of the oil bodies was investigated. Oil bodies in hemp seeds appeared spherical and sporadically distributed in the cell, with diameters of 3 to 5 μm. CLSM images of isolated oil bodies revealed the uniform distribution of phospholipids and proteins at their interface. Polyunsaturated fatty acids were predominant in the lipid fraction and linoleic acid accounted for ≈61% of the total fatty acids. The SDS-PAGE analysis of washed and purified oil bodies revealed major bands at 15 kDa and 50–25 kDa, which could be linked to membrane-specific proteins of oil bodies or extraneous proteins. The colloidal stability of oil bodies in different pH environments indicated that the isoelectric point was between pH 4 and 4.5, where oil bodies experienced maximum aggregation. Changes in the ionic strength decreased the interfacial charge density of oil bodies (ζ-potential), but it did not affect their mean particle size. This suggested that the steric hindrance provided by membrane-specific proteins at the interface of the oil bodies could have prevented them from flocculation at low interfacial charge density. The results of this study provide new tertiary knowledge on the structure, composition, and colloidal properties of oil bodies extracted from hemp seeds, which could be used as natural emulsions or lipid-based delivery systems for food products.

Fabrication and characterization of β-carotene emulsions stabilized by soy oleosin and lecithin mixtures with a composition mimicking natural soy oleosomes

Natural soy oleosomes are known to have a remarkable stability, given the advantage of their sophisticated membrane. The aim of the present study is to examine the concept of fabricating a β-carotene emulsion stabilized by soy oleosin (OLE) and lecithin (LEC) mixtures mimicking the membrane composition of soy oleosomes while providing preferable stability and bioaccessibility. For this, the fabricated emulsion was characterized in terms of droplet size distribution, and emulsion structure, stability and digestion (release and absorption of lipophilic β-carotene). Compared to SPI/LEC (10 : 1) stabilized emulsions, the OLE/LEC (10 : 1) mixture stabilized emulsion exhibited the highest emulsifying activity index (EAI) and emulsifying stability index (ESI) values, and higher encapsulation efficiency. Results show that the β-carotene emulsion stabilized by OLE and LEC mixtures at the ratio of 10 : 1 (w/w) has the most uniform droplet distribution and highest stability. The in vitro gastrointestinal digestion test revealed that the β-carotene emulsion stabilized by OLE and LEC mixtures was digested more rapidly than the emulsion stabilized by soy protein isolate (SPI) and LEC mixtures. In turn, the bioaccessibility and cellular uptake of β-carotene were enhanced, resulting in a higher absorption, a desirable feature of nutrition delivery systems. Our results demonstrated a promising way to fabricate emulsions mimicking natural soy oleosomes.

Effect of simulated saliva components on the in vitro digestion of peanut oil body emulsion

The digestion properties of natural oil bodies (OBs) are very important to their potential applications such as traditional fat replacement or bioactive delivery systems. However, study on the complete digestion behaviours of OBs has not been reported yet. In this paper, peanut OBs were extracted by an aqueous medium method, and their digestion behaviour was studied using completed in vitro oral-gastric-intestinal digestion simulation. In particular, the effects of saliva components, mainly α-amylase and mucin, on the digestion of the peanut OBs were systematically investigated. The OB emulsion microstructure, average particle size d_4,3, ζ-potential, and surface protein compositions during oral, gastric and intestinal digestion, and the free fatty acid (FFA) release rate of the peanut OBs during intestinal digestion were determined. Interestingly, it was revealed from both the periodic acid-Schiff staining technique and the confocal laser microscopy characterization that glycosidic bonds exist on the surface of the peanut OBs, though how they were produced was unknown. The results from the digestion measurements showed that α-amylase in saliva can break the glycosidic bonds in oral digestion, promoting the digestion of the OBs in the gastric and intestinal environments. Saliva mucin caused bridging flocculation of OBs by electrostatic attraction in the gastric tract, and depletion flocculation of OBs in the intestinal tract. The former hindered the fusion of oil droplets, and the latter promoted FFA release rate by increasing the contacting surface area of OBs with bile salts.

Glycosidic bonds exist on the surface of OBs, and α-amylase in saliva breaks the glycosidic bonds, promoting gastrointestinal digestion of OBs.

Dietary lysophospholipids reduce lymphatic cholesterol transport compared with dietary phospholipids in thoracic lymph-duct cannulated rats

Dietary phospholipids have been traditionally known to affect micelle formation. Egg yolk-derived lysophospholipids (LysoPL) are commercially available. We investigated the effects of dietary LysoPL on lymphatic lipid transport. We also compared sn-1 LysoPL and sn-2 LysoPL, which have different fatty acyl esterification positions. Thoracic lymph duct-cannulated rats were fed a diet supplemented with egg yolk-derived sn-1 LysoPL, sn-2 LysoPL, or phospholipids (PL). The amount of lymphatic lipid transport was also evaluated. Time courses of transport were applied to the one-compartment model as one of the pharmacokinetic analyses. The solubility of cholesterol in bile acid micelles was measured. Compared to the PL diet, the sn-1 and sn-2 LysoPL diets significantly reduced the lymphatic transport of cholesterol. There were no differences in the lymphatic PL and TAG transport. There was no difference in cholesterol transport between the sn-1 LysoPL group and the sn-2 LysoPL group; however, the transport rate constant at a decrease in lymphatic cholesterol was lower in the sn-1 LysoPL group than in the sn-2 LysoPL group. Cholesterol solubility in bile acid micelles was significantly decreased in the sn-1 LysoPL and sn-2 LysoPL groups compared to that in the PL group. Dietary LysoPL affects the behavior of intestinal cholesterol and suppresses lymphatic cholesterol transport.

Encapsulation of phenolic compounds within nano/microemulsion systems: A review

Phenolic compounds (phenolics) have received great attention in the food, pharmaceutical and nutraceutical industries due to their health-promoting attributes. However, their extensive use is limited mainly due to their poor water dispersibility and instability under both processing conditions and/or gastrointestinal interactions, affecting their bioavailability/bioaccessibility. Therefore, different nanocarriers have been widely used to encapsulate phenolics and overcome the aforementioned challenges. To the best of our knowledge, besides many research studies, no comprehensive review on encapsulation of phenolics by microemulsions (MEs) and nanoemulsions (NEs) has been published so far. The present study was therefore attempted to review the loading of phenolics into MEs and NEs. In addition, the fundamental characteristics of the developed systems such as stability, encapsulation efficiency, cytotoxicity, bioavailability and releasing rate are also discussed. Both MEs and NEs are proved as appropriate vehicles to encapsulate and protect phenolics which may expand their applications in foods, supplements and pharmaceuticals.

Stability to oxidation and interfacial behavior at the air/water interface of minimally-processed versus processed walnut oil-bodies

Oil bodies (OB), the form of triacylglycerol storage in seeds, are interesting natural assemblies for nutritional applications. In walnuts, OB contain an important amount of polyunsaturated fatty acids that could be interesting food ingredients but may be prone to oxidation. The oxidative and interfacial behavior of walnut OB, either minimally-processed or after processing, were compared with processed complex walnut juice. The good oxidative stability of minimally-processed OB over 10 days (PV ≤ 8.4 meq O₂/kg, TBARS = 1.4 mmol eq MDA/kg) and of processed walnut complex matrixes over 20 days (PV ≤ 4.8 meq O₂/kg, TBARS = 1.4 mmol eq MDA/kg) was evidenced. In comparison, processing of OB promoted their oxidation. The interfacial studies led to the proposition of a new model of adsorption for minimally-processed OB that will be useful to design functional emulsion or foam in which OB act as emulsifiers.

Effect of food on orally-ingested titanium dioxide and zinc oxide nanoparticle behaviors in simulated digestive tract

Nanomaterials have been widely utilized in human daily life. The interaction between nanoparticles (NPs) and food matrices through oral ingestion is important for fate and potential toxicity of NPs. In this study, the interaction between NPs (i.e., titanium dioxide (TiO₂) and zinc oxide (ZnO)) and food matrices (namely sucrose, protein powder, and corn oil) was investigated by use of an in vitro physiological model. Measurement using asymmetrical flow field-flow fractionation (AF₄) showed that particle size of TiO₂ NPs in saliva fluid decreased from 102 ± 6.21 nm (control) to 69.2 ± 6.90 and 81.9 ± 4.30 nm in protein powder and corn oil. Similar trend was also observed for ZnO. Compared with gastric fluid, micelles formed by corn oil in intestinal fluid further dispersed NPs, as indicated by approximately 11.1% and 13.2% decrease in particle size of TiO₂ and ZnO NPs, respectively. Characterization of TEM, FTIR and AFM showed that a layer of biological corona was attached on surface of NPs in protein and oil. The XPS demonstrated that oil bound with NPs through forming covalent bonds, while protein bound with NPs through van der Waals force and electrostatic force for TiO₂ and ZnO NPs, respectively. The result here demonstrated the importance of considering food effect when investigating the morphology and behavior of NPs after oral ingestion. This understanding was valuable in assessment of environmental fate and biological effects of NPs.

Separation, identification, and molecular docking of tyrosinase inhibitory peptides from the hydrolysates of defatted walnut (Juglans regia L.) meal

Defatted walnut meal protein was hydrolyzed using alcalase to yield tyrosinase inhibitory peptides. After separation by ultrafiltration and Sephadex G-25, the fraction with the highest tyrosinase inhibitory activity was identified using liquid chromatography-tandem mass spectrometry and 606 peptides were obtained. Then, molecular docking was used to screen for tyrosinase inhibitory peptides and to clarify the theoretical interaction mechanism between the peptides and tyrosinase. A peptide with the sequence Phe-Pro-Tyr (FPY, MW: 425.2 Da) was identified and the synthesized peptide inhibited tyrosine monophenolase and diphenolase with IC₅₀ values of 1.11 ± 0.05 and 3.22 ± 0.09 mM, respectively. The inhibition of tyrosinase by FPY was competitive and reversible. Good stability of FPY toward digestion was observed in an in vitro gastrointestinal digestion simulation experiment. These results indicated that FPY can be used as a potential tyrosinase inhibitor in the food, medicine, and cosmetics industries.

Nature-Assembled Structures for Delivery of Bioactive Compounds and Their Potential in Functional Foods

Consumers are demanding more natural, healthy, and high-quality products. The addition of health-promoting substances, such as bioactive compounds, to foods can boost their therapeutic effect. However, the incorporation of bioactive substances into food products involves several technological challenges. They may have low solubility in water or poor stability in the food environment and/or during digestion, resulting in a loss of their therapeutic properties. Over recent years, the encapsulation of bioactive compounds into laboratory-engineered colloidal structures has been successful in overcoming some of these hurdles. However, several nature-assembled colloidal structures could be employed for this purpose and may offer many advantages over laboratory-engineered colloidal structures. For example, the casein micelles and milk fat globules from milk and the oil bodies from seeds were designed by nature to deliver biological material or for storage purposes. These biological functional properties make them good candidates for the encapsulation of bioactive compounds to aid in their addition into foods. This review discusses the structure and biological function of different nature-assembled carriers, preparation/isolation methods, some of the advantages and challenges in their use as bioactive compound delivery systems, and their behavior during digestion.

Deciphering the Structural Network That Confers Stability to High Internal Phase Pickering Emulsions by Cross-Linked Soy Protein Microgels and Their In Vitro Digestion Profiles

High internal phase Pickering emulsions (HIPPEs) stabilized by food-grade particles have received much attention in recent years. However, the stabilizing mechanism (e.g., structural network) in the continuous phase of HIPPEs stabilized by proteins is not well understood. In this work, we deciphered the stabilizing mechanisms that confer stability to HIPPEs produced from sunflower oil and soy protein microgels (SPMs). HIPPEs were fabricated at the protein concentrations of 1.50-2.00 wt % and oil volume fraction of 0.78-0.82. The cryo-scanning electron microscopy (cryo-SEM) observations indicated that there were two possible stabilizing mechanisms for HIPPEs at the protein concentrations of 1.50-2.00 wt %: the first is a stabilization provided by the shared monolayer of SPMs (at a protein concentration of 1.50%), and the other is stabilization provided by the distinct monolayer of SPMs (at protein concentrations of 1.75 and 2.00 wt %). The latter protein concentration created a thick network, formed by interacting SPMs, which trapped oil droplets. Results also confirmed that HIPPEs have an open-cell porous structure, forming a sponge-like morphology, where the internal phase was located. This study also investigated the digestibility of HIPPEs, suggesting a slower free fatty acid-releasing profile in in vitro intestinal digestion.

Structural and physicochemical changes in almond milk during in vitro gastric digestion: impact on the delivery of protein and lipids

Almond milk (about 3% protein and 7% lipids) was prepared using wet disintegration of raw almonds and then subjected to in vitro gastric digestion using an advanced dynamic digestion model (i.e., a human gastric simulator). Microstructural changes, physicochemical behavior, and protein digestion were examined; the release of lipids and protein during digestion was quantified. Under acidic gastric conditions, almond oil bodies flocculated. Proteolysis by pepsin led to destabilization and coalescence of the oil bodies, resulting in creaming and phase separation. This phase separation significantly delayed the delivery of lipids to the small intestine. After 225 min of digestion, ∼42% of the lipids remained in the stomach. In contrast, protein release was not significantly affected by the gastric behavior of the almond oil bodies. This study provides a better understanding of how the digestive system manages plant lipids, and may be useful in the microstructural design of foods to achieve a controlled physiological response during digestion.

Energy extraction from nuts: walnuts, almonds and pistachios

The bioaccessibility of fat has implications for satiety and postprandial lipidaemia. The prevailing view holds that the integrity of plant cell wall structure is the primary determinant of energy and nutrient extraction from plant cells as they pass through the gastrointestinal (GI) tract. However, comparisons across nuts (walnuts, almonds and pistachios) with varying physical properties do not support this view. In the present study, masticated samples of three nuts from healthy adults were exposed to a static model of gastric digestion followed by simulated intestinal digestion. Primary outcomes were particle size and lipid release at each phase of digestion. Walnuts produced a significantly larger particle size post-mastication compared with almonds. Under gastric and intestinal conditions, the particle size was larger for walnuts compared with pistachios and almonds (P < 0·05). However, the masticated and digesta particle sizes were not related to the integrity of cell walls or lipid release. The total lipid release was comparable between nuts after the in vitro intestinal phase (P > 0·05). Microstructural examination showed ruptured and fissured cell walls that would allow digestion of cellular contents, and this may be governed by internal cellular properties such as oil body state. Furthermore, the cell walls of walnuts tend to rupture rather than separate and as walnut tissue passes through the GI tract, lipids tend to coalesce reducing digestion efficiency.

Structure and functions of oleosomes (oil bodies)

Oleosomes are natural oil droplets, abundant in plants and more specifically in seeds, composing 20-50 wt% of their mass. The structure of oleosomes is the mechanism that seeds developed to safely store energy in the form of triacylglycerols and use it during germination. For this, the phospholipid/protein membrane that covers and protects the triacylglycerols has been wisely developed during evolution to grant them extreme stability against physical and chemical stresses. The remarkable property-performance relationships of oleosomes have generated a lot of interest to incorporate them in oil-in-water emulsions and take advantage of their sophisticated membrane. However, the structure-function relationship of the molecular components in the oleosome membrane is still not well understood and requires more attention in order to take complete advantage of their potential functions. The aim of this review is to give insights into the architecture of the oleosomes and to discuss the exploitation of their properties in advanced and broad applications, from carrying and protecting sensitive molecules to bio-catalysis.

Physicochemical and oxidative stability of a soybean oleosome-based emulsion and its in vitro digestive fate as affected by (-)-epigallocatechin-3-gallate

Oleosomes, which are pre-emulsified oil bodies found naturally in plants, have excellent stability, therefore making their use more popular in the food industries. However, the mechanism of EGCG in regulating the physicochemical and oxidative stability, and digestion of oleosome emulsions is not yet clear. In this study, the effect of EGCG on the properties of soybean oleosome emulsions (SOE) was examined at different pH values (5.0, 7.0, and 9.0). EGCG was significantly more effective in maintaining the stability of SOE at pH 5.0 and 7.0 over the 14 days of storage, but less effective at pH 9.0. Furthermore, lipid oxidation of SOE at pH 7.0 was successfully retarded by incorporating EGCG, but not at pH 5.0 and 9.0. The in vitro gastrointestinal results suggested that EGCG retarded the digestion rate of SOE based on a 20% reduction in free fatty acid release. The results of this study will help food technologists to design slow-digestive oleosome-based products that will satisfy health-conscious consumers' demand for healthier food choices.

In vitro lipid digestion in raw and roasted hazelnut particles and oil bodies

Previous studies have proved that the physical encapsulation of nutrients by the cell walls of plant foods modulates macronutrient bioaccessibility during human digestion. In this study, we investigated structural factors that modulate lipid hydrolysis during in vitro digestion of raw and roasted hazelnut particles and isolated oil bodies. Isolated oil bodies exhibited a significantly higher lipid hydrolysis compared to hazelnut particles. Moreover, roasting had an impact on the structure of hazelnut cell walls implying a more efficient diffusion of digestive fluids and enzymes into the hazelnut cells. Heat treatment also caused destabilization of oil body interfacial protein membranes, facilitating their proteolysis under gastric conditions, altering the emulsion properties and enhancing fatty acid release during intestinal digestion. This study underlined the barrier role played by the plant cell wall as well as the impact of heat processing on lipid bioaccessibility in hazelnuts.

Re-evaluation of the mechanisms of dietary fibre and implications for macronutrient bioaccessibility, digestion and postprandial metabolism

The positive effects of dietary fibre on health are now widely recognised; however, our understanding of the mechanisms involved in producing such benefits remains unclear. There are even uncertainties about how dietary fibre in plant foods should be defined and analysed. This review attempts to clarify the confusion regarding the mechanisms of action of dietary fibre and deals with current knowledge on the wide variety of dietary fibre materials, comprising mainly of NSP that are not digested by enzymes of the gastrointestinal (GI) tract. These non-digestible materials range from intact cell walls of plant tissues to individual polysaccharide solutions often used in mechanistic studies. We discuss how the structure and properties of fibre are affected during food processing and how this can impact on nutrient digestibility. Dietary fibre can have multiple effects on GI function, including GI transit time and increased digesta viscosity, thereby affecting flow and mixing behaviour. Moreover, cell wall encapsulation influences macronutrient digestibility through limited access to digestive enzymes and/or substrate and product release. Moreover, encapsulation of starch can limit the extent of gelatinisation during hydrothermal processing of plant foods. Emphasis is placed on the effects of diverse forms of fibre on rates and extents of starch and lipid digestion, and how it is important that a better understanding of such interactions with respect to the physiology and biochemistry of digestion is needed. In conclusion, we point to areas of further investigation that are expected to contribute to realisation of the full potential of dietary fibre on health and well-being of humans.

In vitro digestion of infant formulations with hydrolysed and non-hydrolysed proteins from dairy and soybean

Digestion of hydrolysed and non-hydrolysed dairy (casein and whey proteins) and soy proteins commonly used in infant formulations was studied underin vitrogastrointestinal (without lipases) conditions for 60 and 120 minutes in the stomach and small intestine, respectively.

Physicochemical properties of whey protein, lactoferrin and Tween 20 stabilised nanoemulsions: Effect of temperature, pH and salt

Oil-in-water nanoemulsions were prepared by emulsification and solvent evaporation using whey protein isolate (WPI), lactoferrin and Tween 20 as emulsifiers. Protein-stabilised nanoemulsions showed a decrease in particle size with increasing protein concentration from 0.25% to 1% (w/w) level with Z-average diameter between 70 and 90 nm. However, larger droplets were produced by Tween 20 (120-450 nm) especially at concentration above 0.75% (w/w). The stability of nanoemulsions to temperature (30-90°C), pH (2-10) and ionic strength (0-500 mM NaCl or 0-90 mM CaCl2) was also tested. Tween 20 nanoemulsions were unstable to heat treatment at 90°C for 15 min. WPI-stabilised nanoemulsions exhibited droplet aggregation near the isoelectric point at pH 4.5 and 5 and they were also unstable at salt concentration above 30 mM CaCl2. These results indicated that stable nanoemulsions can be prepared by careful selection of emulsifiers.

Impact of extraneous proteins on the gastrointestinal fate of sunflower seed (Helianthus annuus) oil bodies: a simulated gastrointestinal tract study

In this study, we examined the physicochemical nature of sunflower seed oil bodies (in the absence and presence of added protein) exposed to gastrointestinal conditions in vitro: crude oil bodies (COB); washed oil bodies (WOB); whey protein isolate-enriched oil bodies (WOB-WPI); and, sodium caseinate enriched-oil bodies (WOB-SC). All oil body emulsions were passed through an in vitro digestion model that mimicked the stomach and duodenal environments, and their physicochemical properties were measured before, during, and after digestion. Oil bodies had a positive charge under gastric conditions because the pH was below the isoelectric point of the adsorbed protein layer, but they had a negative charge under duodenal conditions which was attributed to changes in interfacial composition resulting from adsorption of bile salts. Oil bodies were highly susceptible to flocculation and coalescence in both gastric and duodenal conditions. SDS-PAGE analysis indicated degradation of oleosin proteins (ca. 18-21 kDa) to a greater or lesser extent (dependent on the emulsion) during the gastric phase in all emulsions tested; there is evidence that some oleosin remained intact in the crude oil body preparation during this phase of the digestion process. Measurements of protein displacement from the surface of COBs during direct exposure to bile salts, without inclusion of a gastric phase, indicated the removal of intact oleosin from native oil bodies.

Cooking increases net energy gain from a lipid-rich food

Starch, protein, and lipid are three major sources of calories in the human diet. The unique and universal human practice of cooking has been demonstrated to increase the energy gained from foods rich in starch or protein. Yet no studies have tested whether cooking has equivalent effects on the energy gained from lipid-rich foods. Using mice as a model, we addressed this question by examining the impact of cooking on the energy gained from peanuts, a lipid-rich oilseed, and compared this impact against that of nonthermal processing (blending). We found that cooking consistently increased the energy gained per calorie, whereas blending had no detectable energetic benefits. Assessment of fecal fat excretion showed increases in lipid digestibility when peanuts were cooked, and examination of diet microstructure revealed concomitant alterations to the integrity of cell walls and the oleosin layer of proteins that otherwise shield lipids from digestive lipases. Both effects were consistent with the greater energy gain observed with cooking. Our findings highlight the importance of cooking in increasing dietary energy returns for humans, both past and present.

Entrapment of a volatile lipophilic aroma compound (d-limonene) in spray dried water-washed oil bodies naturally derived from sunflower seeds (Helianthus annus)

Oil bodies are natural emulsions that can be extracted from oil seeds and have previously been shown to be stable after spray drying. The aim of the study was to evaluate for the first time if spray dried water-washed oil bodies are an effective carrier for volatile lipophilic actives (the flavour compound d-limonene was used as an example aroma compound). Water-washed oil bodies were blended with maltodextrin and d-limonene and spray dried using a Buchi B-191 laboratory spray dryer. Lipid and d-limonene retention was 89–93% and 24–27%. Samples were compared to processed emulsions containing sunflower oil and d-limonene and stabilised by either lecithin or Capsul. Lecithin and Capsul processed emulsions had a lipid and d-limonene retention of 82–89%, 7.7–9.1% and 48–50%, 55–59% respectively indicating that water-washed oil bodies could retain the most lipids and Capsul could retain the most d-limonene. This indicates that whilst additional emulsifiers may be required for future applications of water-washed oil bodies as carriers of lipophilic actives, oil bodies are excellent agents for lipid encapsulation.

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Spray dried water-washed oil bodies were prepared with d-limonene and maltodextrin

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Water-washed oil bodies were compared to processed emulsions

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Water-washed oil bodies were most effective at retaining lipid during spray drying

Bioaccessibility of Cd, Cu, Fe, Mn, Pb, and Zn in hazelnut and walnut kernels investigated by an enzymolysis approach

Bioaccessibility of four essential (Fe, Cu, Mn, Zn) and two toxic (Cd, Pb) elements in kernels of four walnut and four hazelnut cultivars was investigated using sequential enzymolysis approach and atomic absorption spectrometry. It was found that the assimilable part of elements was not dependent on nut cultivar. The bioaccessible fraction of Cu, Mn, and Zn was definitely higher for hazelnuts (62% Cu, 39% Mn, 58% Zn) than for walnuts (14% Cu, 21% Mn, 15% Zn). Bioaccessible Fe was 20-24% from its total content for both nut types. Solubility in the simulated intestinal juice is affected by both formation of stable soluble complexes and back sorption of dissolved elements on nut solid residues. Lead shows strong insolubility due to the high sorption affinity of lead ions to the insoluble fraction of nuts. Thus, walnuts and hazelnuts could act as effective biosorbents for lead detoxication.