The role of electrostatics in saliva-induced emulsion flocculation

Triglyceride Structure Modulates Gastrointestinal Digestion Fates of Lipids: A Comparative Study between Typical Edible Oils and Triglycerides Using Fully Designed in Vitro Digestion Model

Three typical edible oils (palm oil, PO; leaf lard oil, LO; rapeseed oil, RO) and triacylglycerols (TAGs) (glycerol tripalmitate, GTP; glycerol tristearate, GTS; glycerol trioleate, GTO) were selected to conduct digestion experiments using fully designed in vitro digestion model. The evolutions in mean particle diameter, ζ-potential, and microstructural changes during different digestion stages were investigated. Free fatty acid (FFA) release extent and kinetics were monitored by pH-Stat method. The particle characterization of different lipids during passage through the GIT depended on lipid type and the microenvironment they encountered. Absorbed surface protein can hardly be the obstacle for pancreas lipase to catalyze lipid hydrolysis after gastric digestion. The maximum FFA release level and apparent rate constant in small intestine digestion stage of the three oils and TAGs were: PO > RO > LO, GTP > GTS > GTO, respectively. PO showed the highest FFA release level and rate mainly due to the short chain length saturated palmitic acid (C16:0) specifically located in the Sn-1, 3 positions of TAG molecules in palm oil, while the Sn-1, 3 positions of TAG molecules in RO and LO were mainly mono- or polyunsaturated fatty acids (C18:1 or C18:2), restricting the continuous hydrolysis reaction. These findings can provide some basic understanding of the digestion differences of different lipids, which may be useful for their nutritional and functional evaluation and the applicability in the food area.

Is nano safe in foods? Establishing the factors impacting the gastrointestinal fate and toxicity of organic and inorganic food-grade nanoparticles

Nanotechnology offers the food industry a number of new approaches for improving the quality, shelf life, safety, and healthiness of foods. Nevertheless, there is concern from consumers, regulatory agencies, and the food industry about potential adverse effects (toxicity) associated with the application of nanotechnology in foods. In particular, there is concern about the direct incorporation of engineered nanoparticles into foods, such as those used as delivery systems for colors, flavors, preservatives, nutrients, and nutraceuticals, or those used to modify the optical, rheological, or flow properties of foods or food packaging. This review article summarizes the application of both inorganic (silver, iron oxide, titanium dioxide, silicon dioxide, and zinc oxide) and organic (lipid, protein, and carbohydrate) nanoparticles in foods, highlights the most important nanoparticle characteristics that influence their behavior, discusses the importance of food matrix and gastrointestinal tract effects on nanoparticle properties, emphasizes potential toxicity mechanisms of different food-grade nanoparticles, and stresses important areas where research is still needed. The authors note that nanoparticles are already present in many natural and processed foods, and that new kinds of nanoparticles may be utilized as functional ingredients by the food industry in the future. Many of these nanoparticles are unlikely to have adverse affects on human health, but there is evidence that some of them could have harmful effects and that future studies are required.

Physicochemical and colloidal aspects of food matrix effects on gastrointestinal fate of ingested inorganic nanoparticles

Inorganic nanoparticles, such as titanium dioxide, silicon dioxide, iron oxide, zinc oxide, or silver nanoparticles, are added to some food products and food packaging materials to obtain specific functional attributes, such as lightening, powder flow, nutrition, or antimicrobial properties. These engineered nanomaterials (ENMs) all have dimensions below 100nm, but may still vary considerably in composition, morphology, charge, surface properties and aggregation state, which effects their gastrointestinal fate and potential toxicity. In addition to their intrinsic physicochemical and morphological properties, the extrinsic properties of the media they are suspended in also affects their biotransformation, gastrointestinal fate and bioactivity. For instance, inorganic nanoparticles are usually consumed as part of a food or meal that contains numerous other components, such as lipids, proteins, carbohydrates, surfactants, minerals, and water, which may alter their gastrointestinal fate. This review article provides an overview of the potential effects of food components on the behavior of ENMs in the gastrointestinal tract (GIT), and highlights some important physicochemical and colloidal mechanisms by which the food matrix may alter the properties of inorganic nanoparticles. This information is essential for developing appropriate test methods to establish the potential toxicity and biokinetics of inorganic nanoparticles in foods.

Lubrication of chocolate during oral processing

The structure of chocolate is drastically transformed during oral processing from a composite solid to an oil/water fluid emulsion. Using two commercial dark chocolates varying in cocoa solids content, this study develops a method to identify the factors that govern lubrication in molten chocolate and saliva's contribution to lubrication following oral processing. In addition to chocolate and its individual components, simulated boluses (molten chocolate and phosphate buffered saline), in vitro boluses (molten chocolate and whole human saliva) and ex vivo boluses (chocolate expectorated after chewing till the point of swallow) were tested. The results reveal that the lubrication of molten chocolate is strongly influenced by the presence of solid sugar particles and cocoa solids. The entrainment of particles into the contact zone between the interacting surfaces reduces friction such that the maximum friction coefficient measured for chocolate boluses is much lower than those for single-phase Newtonian fluids. The addition of whole human saliva or a substitute aqueous phase (PBS) to molten chocolate dissolves sugar and decreases the viscosity of molten chocolate so that thinner films are achieved. However, saliva is more lubricating than PBS, which results in lower friction coefficients for chocolate-saliva mixtures when compared to chocolate-PBS mixtures. A comparison of ex vivo and in vitro boluses also suggests that the quantity of saliva added and uniformity of mixing during oral processing affect bolus structure, which leads to differences in measured friction. It is hypothesized that inhomogeneous mixing in the mouth introduces large air bubbles and regions of non-emulsified fat into the ex vivo boluses, which enhance wetting and lubrication.

Influence of Lipid Content in a Corn Oil Preparation on the Bioaccessibility of β-Carotene: A Comparison of Low-Fat and High-Fat Samples

Some individuals with fat maldigestion have compromised digestive systems, which causes the incomplete hydrolyzation of ingested lipids within the gastrointestinal tract (GIT). We studied the influence of high-fat (20%) and low-fat (4%) contents on the bioaccessibility of a highly hydrophobic nutraceutical (β-carotene) through a simulated GIT model consisting of mouth, stomach, and small intestine phases. The low-fat and high-fat values were chosen to simulate low-fat and high-fat diets. The triglycerides in the low-fat system were fully digested, whereas those in the high-fat system were only partially digested, thereby mimicking the digestive systems of individuals who exhibit fat maldigestion. The carotenoids were initially solubilized within oil-in-water nanoemulsions prepared using a nonionic surfactant (Tween 20) as emulsifier and a long-chain triglyceride (corn oil) as the oil phase. After digestion, the total β-carotene concentration in the filtered micelle phase was much greater for the high-fat group (0.072 μg/mL) than for the low-fat group (0.032 μg/mL). Conversely, the β-carotene bioaccessibility of the high-fat group (39%) was much lower than that of the low-fat group (84%), which was attributed to a fraction of the carotenoids remaining in the nondigested lipid phase of the high-fat group. These results highlight the importance of delivering hydrophobic nutraceuticals in a form where the fat phase is fully digested.

Oral processing of emulsion systems from a colloidal perspective

This review discusses recent understanding of the oral destabilization of food emulsions from a colloidal perspective.

Nanostructuring Biomaterials with Specific Activities towards Digestive Enzymes for Controlled Gastrointestinal Absorption of Lipophilic Bioactive Molecules

This review describes the development of novel lipid-based biomaterials that modulate fat digestion for the enhanced uptake of encapsulated lipophilic bioactive compounds (e.g. drugs and vitamins). Specific focus is directed towards analysing how key material characteristics affect the biological function of digestive lipases and manipulate lipolytic digestion. The mechanism of lipase action is a complex, interfacial process, whereby hydrolysis can be controlled by the ability for lipase to access and adsorb to the lipid-in-water interface. However, significant conjecture exists within the literature regarding parameters that influence the activities of digestive lipases. Important findings from recent investigations that strategically examined the interplay between the interfacial composition of the lipid microenvironment and lipolysis kinetics in simulated biophysical environments are presented. The correlation between lipolysis and the rate of solubilisation and absorption of lipophilic compounds in the gastrointestinal tract (GIT) is detailed. Greater insights into the mechanism of lipase action have provided a new approach for designing colloidal carriers that orally deliver poorly soluble compounds, directly impacting the pharmaceutical and food industries.

The Role of the Food Matrix and Gastrointestinal Tract in the assessment of biological properties of ingested engineered nanomaterials (iENMs): State of the science and knowledge gaps

Many foods contain appreciable levels of engineered nanomaterials (ENMs) (diameter < 100 nm) that may be either intentionally or unintentionally added. These ENMs vary considerably in their compositions, dimensions, morphologies, physicochemical properties, and biological responses. From a toxicological point of view, it is often convenient to classify ingested ENMs (iENMs) as being either inorganic (such as TiO₂, SiO₂, Fe₂O₃, or Ag) or organic (such as lipid, protein, or carbohydrate), since the former tend to be indigestible and the latter are generally digestible. At present there is a relatively poor understanding of how different types of iENMs behave within the human gastrointestinal tract (GIT), and how the food matrix and biopolymers transform their physico-chemical properties and influence their gastrointestinal fate. This lack of knowledge confounds an understanding of their potential harmful effects on human health. The purpose of this article is to review our current understanding of the GIT fate of iENMs, and to highlight gaps where further research is urgently needed in assessing potential risks and toxicological implications of iENMs. In particular, a strong emphasis is given to the development of standardized screening methods that can be used to rapidly and accurately assess the toxicological properties of iENMs.

Gelation of Soy Milk with Hagfish Exudate Creates a Flocculated and Fibrous Emulsion- and Particle Gel

Hagfish slime is an ultra dilute, elastic and cohesive hydrogel that deploys within milliseconds in cold seawater from a glandularly secreted exudate. The slime is made of long keratin-like fibers and mucin-like glycoproteins that span a network which entraps water and acts as a defense mechanism against predators. Unlike other hydrogels, the slime only confines water physically and is very susceptible to mechanical stress, which makes it unsuitable for many processing operations and potential applications. Despite its huge potential, little work has been done to improve and functionalize the properties of this hydrogel. To address this shortcoming, hagfish exudate was mixed with a soy protein isolate suspension (4% w/v) and with a soy emulsion (commercial soy milk) to form a more stable structure and combine the functionalities of a suspension and emulsion with those of the hydrogel. Hagfish exudate interacted strongly with the soy systems, showing a markedly increased viscoelasticity and water retention. Hagfish mucin was found to induce a depletion and bridging mechanism, which caused the emulsion and suspension to flocculate, making "soy slime", a cohesive and cold-set emulsion- and particle gel. The flocculation network increases viscoelasticity and substantially contributes to liquid retention by entrapping liquid in the additional confinements between aggregated particles and protein fibers. Because the mucin-induced flocculation resembles the salt- or acid-induced flocculation in tofu curd production, the soy slime was cooked for comparison. The cooked soy slime was similar to conventional cooked tofu, but possessed a long-range cohesiveness from the fibers. The fibrous, cold-set, and curd-like structure of the soy slime represents a novel way for a cold coagulation and fiber incorporation into a suspension or emulsion. This mechanism could be used to efficiently gel functionalized emulsions or produce novel tofu-like structured food products.

Kinetics of bread crumb hydration as related to porous microstructure

An in vitro approach enabled to investigate the relationship between bread crumb porous micro structure and kinetics of hydration.

Enhancement of carotenoid bioaccessibility from carrots using excipient emulsions: influence of particle size of digestible lipid droplets

The influence of initial lipid droplet size on the ability of excipient emulsions to increase carotenoid bioaccessibility from carrots was investigated using a simulated gastrointestinal tract (GIT).

Influence of olive oil phenolic compounds on headspace aroma release by interaction with whey proteins

The release of volatile compounds in an oil-in-water model system obtained from olive oil-whey protein (WP) pairing was investigated by considering the effect of phenolic compounds. Human saliva was used to simulate mouth conditions by retronasal aroma simulator (RAS) analysis. Twelve aroma compounds were quantified in the dynamic headspace by SPME-GC/MS. The results showed significant influences of saliva on the aroma release of virgin olive oil (VOO) volatiles also in the presence of WP. The interaction between WP and saliva leads to lower headspace release of ethyl esters and hexanal. Salivary components caused lower decrease of the release of acetates and alcohols. A lower release of volatile compounds was found in the RAS essay in comparison to that in orthonasal simulation of only refined olive oil (without addition of saliva or WP), with the exception of hexanal and 1-penten-3-one, where a significantly higher release was found. Our results suggest that the extent of retronasal odor (green, pungent) of these two volatile compounds is higher than orthonasal odor. An extra VOO was used to verify the release in model systems, indicating that WP affected aroma release more than model systems, while saliva seems to exert an opposite trend. A significant increase in aroma release was found when phenolic compounds were added to the system, probably due to the contrasting effects of binding of volatile compounds caused by WP, for the polyphenol-protein interaction phenomenon. Our study could be applied to the formulation of new functional foods to enhance flavor release and modulate the presence and concentrations of phenolics and whey proteins in food emulsions/dispersions.

Properties of oil/water emulsions affecting the deposition, clearance, and after-feel sensory perception of oral coatings

The aims of this study were to investigate the influence of (i) protein type, (ii) protein content, and (iii) viscosity of o/w emulsions on the deposition and clearance of oral oil coatings and after-feel perception. Oil fraction (m(oil)/cm(2)(tongue)) and after-feel perception differed considerably between emulsions which do not flocculate under in mouth conditions (Na-caseinate) and emulsions which flocculate under in mouth conditions (lysozyme). The irreversible flocculation of lysozyme stabilized emulsions caused slower oil clearance from the tongue surface compared to emulsions stabilized with Na-caseinate. Protein content had a negative relation with oil fraction for lysozyme stabilized emulsions and no relation for Na-caseinate stabilized emulsions immediately after expectoration. Viscosity differences did not affect oil fraction, although the presence of thickener decreased deposition of oil on tongue. We conclude that after-feel perception of o/w emulsions is complex and depends on the deposited oil fraction, the behavior of proteins in mouth, and thickeners.

Effect of human saliva on the consistency of thickened drinks for individuals with dysphagia

BACKGROUND

Thickening of foods and fluids is commonly used in the management of dysphagia to reduce the risk of aspiration. The use of starch-based thickeners is established. However, the use of gums in thickeners is gaining interest as they are resistant to salivary amylase, which may promote safer swallowing.

AIMS

To compare the effect of human saliva on the consistency of drinks thickened with a gum-containing (GC) thickener with that of drinks thickened with four starch-based (SB) thickeners.

METHODS & PROCEDURES

Three drinks (artificial tap water, hot coffee and full-fat milk) were thickened to custard consistency with the different thickeners. Compression force and amount of thin liquid formed were determined after 10 and 50 min of contact with human saliva with standardized amylase activity and compared with a control inoculated with water.

OUTCOMES & RESULTS

Drinks thickened with GC thickener were significantly less sensitive to thinning by human saliva compared with drinks thickened with all four SB thickeners (p < 0.05). Moreover, incubation of SB-thickened drinks with human saliva resulted in the formation of at least 10 g of decantable liquid, while for GC-thickened drinks, almost no liquid was formed.

CONCLUSIONS & IMPLICATIONS

These results show that GC thickeners contain their consistency better in contact with human saliva than SD thickeners. This may enhance the swallowing safety of people with dysphagia.

Influence of physical state of β-carotene (crystallized versus solubilized) on bioaccessibility

β-Carotene has potentially beneficial biological effects. However, its use is currently limited because of its low water-solubility, high melting point, and low oral bioavailability. This study investigated the influence of physical state (crystalline versus solubilized) on the bioaccessibility of β-carotene using a simulated gastrointestinal tract (GIT) model. Three delivery systems were compared: (1) β-carotene predissolved in a nanoemulsion; (2) β-carotene crystals mixed with a nanoemulsion; and (3) β-carotene crystals mixed with a phosphate-buffered saline (PBS). The changes in the microstructure of the delivery systems were characterized after each stage of the GIT model. The β-carotene bioaccessibility decreased in the order of delivery system 1 ≫ 2 > 3, which indicated that carotenoids solubilized within a oil phase were much more bioaccessible than those that formed crystals. This study provides important information for developing effective delivery systems for lipophilic bioactive components in food and beverage applications.

Control of β-carotene bioaccessibility using starch-based filled hydrogels

β-Carotene was incorporated into three types of delivery system: (i) "emulsions": protein-coated fat droplets dispersed in water; (ii) "hydrogels": rice starch gels; and (iii) "filled hydrogels": protein-coated fat droplets dispersed in rice starch gels. Fat droplets in filled hydrogels were stable in simulated mouth and stomach conditions, but aggregated under small intestinal conditions. Fat droplets in emulsions aggregated under oral, gastric, and intestinal conditions. β-Carotene bioaccessibility was higher when encapsulated in filled hydrogels than in emulsions or hydrogels, which was attributed to increased aggregation stability of the fat droplets leading to a larger exposed lipid surface area. β-Carotene bioaccessibility in starch hydrogels containing no fat was very low (≈1%) due to its crystalline nature and lack of mixed micelles to solubilise it. The information presented may be useful for the design of rice-starch based gel products fortified with lipophilic nutraceuticals.

Nutraceutical nanoemulsions: influence of carrier oil composition (digestible versus indigestible oil) on β-carotene bioavailability

BACKGROUND

Carotenoids, such as β-carotene, are widely used in foods and beverages as natural colorants and nutraceuticals. We investigated the influence of carrier oil composition (ratio of digestible to indigestible oil) on the physical stability, microstructure and bioaccessibility of β-carotene nanoemulsions using a simulated gastrointestinal tract model.

RESULTS

β-Carotene nanoemulsions (d < 150 nm) were formed by high-pressure homogenization using sucrose monoester and lysolecithin as emulsifiers, and mixtures of corn oil (digestible) and lemon oil (indigestible) as the lipid phase. All of the nanoemulsions underwent extensive droplet aggregation under mouth, stomach and small intestine conditions. The extent of free fatty acid production in the small intestine increased as the amount of digestible oil in the droplets increased. The bioaccessibility of β-carotene also increased with increasing digestible oil content, ranging from ∼5% for the pure lemon oil system to ∼76% for the pure corn oil system. This effect was attributed to the ability of mixed micelles formed from triglyceride digestion products (free fatty acids and monoglycerides) to solubilize β-carotene.

CONCLUSIONS

This study provides important information for developing effective delivery systems for lipophilic bioactive components in food and beverage applications.

Volatile release from whey protein isolate-pectin multilayer stabilized emulsions: effect of pH, salt, and artificial salivas

Whey protein isolate (WPI) and pectin can form a multilayer at the oil-water interface when they are oppositely charged. In this study, effects of pH, salt, and artificial salivas on emulsion stability and volatile release from multilayer emulsions were investigated. Results showed that emulsions (0.5 wt % WPI, 10 wt % oil) with pectin content ≤0.1 wt % had rapid phase separation at pH 4 and 5, and emulsions with higher pectin content (≥0.2 wt %) had good stability. Due to an electrostatic screening effect, multilayer emulsions collapsed when subjected to ≥150 mM NaCl solutions at pH 5. When diluted with artificial salivas containing salts, mucin, and/or α-amylase, multilayer emulsions showed rapid droplet aggregation. GC headspace analysis found that volatiles had significantly lower initial headspace concentration (C(initial)) in multilayer emulsions, and the C(initial) correlated negatively with pectin content in emulsions. Emulsions at pH 7 had more volatiles released to the headspace than emulsions at pH 5. However, changes in pectin content and pH did not show a significant effect on release rate of most volatile compounds. In salt-treated multilayer emulsions, C(initial) and release rates of volatiles increased with NaCl content. Addition of salivas triggered higher release of hydrophobic volatiles and lower release of hydrophilic volatiles, which was mostly due to dilution effect and saliva-induced emulsion instability.

Volatile release and structural stability of β-lactoglobulin primary and multilayer emulsions under simulated oral conditions

The relationship between emulsion structure and the release of volatile organic compounds (VOCs) was investigated using a model mouth system under oral conditions (tongue mastication, artificial saliva, pH and salt). The VOCs were monitored on-line by proton transfer reaction mass spectrometry (PTR-MS). Two types of emulsion system were compared: primary and multilayer oil-in-water (P-O/W, M-O/W) emulsions consisting of soy oil coated by β-lactoglobulin and pectin layers. The P-O/W emulsions showed intensive flocculation at pH 5 and above 200 mM NaCl where the electrostatic repulsive charge was at a minimum. Bridging and depletion flocculation were mostly observed for P-O/W emulsions containing artificial saliva with 1 wt% mucin. The VOC release was found to increase when the emulsion droplets flocculated, thus changing the oil volume phase distribution. The adsorbed pectin layer stabilised the emulsion structure under conditions of short-time oral processing, and hindered the release of hydrophobic VOCs.