The role of electrostatics in saliva-induced emulsion flocculation

Perspective on oral processing of plant-based beverages

Around the world, the market for plant-derived beverages is one of the fastest-expanding segments in the functional and specialty beverage areas of newer food product development. Consumers are increasingly likely to choose alternatives to bovine beverages due to factors including lactose intolerance, hypercholesterolemia prevalence, allergies to bovine beverages, and preference for vegan diets that contain functionally active ingredients with health-promoting characteristics. Due to health, ecological, and ethical concerns, many customers are interested in reducing their usage of animal products like bovine milk. A variety of plant-based beverage substitutes are being created by the food sector as a result. To create viable alternatives, it is first necessary to provide an overview of the chemical composition, structure, features, and nutritional attributes of ordinary bovine milk. Sensory acceptability in the case of substitutes for beverages made from legumes is a significant barrier to their widespread acceptance, and thus saliva acts as a sophisticated fluid that serves a variety of purposes in the cavity of the mouth. Designing and producing next-generation plant-based beverages that mimic the physicochemical and functional qualities of conventional bovine-based beverages is gaining popularity, and many of these products can be thought of as colloidal materials that contain the particles or polymers that give them their unique qualities NG-PB foods can have a wide range of rheological qualities, such as fluids with low viscosity (such as plant-based beverages), high-viscosity liquids (like creams), soft liquids (like yogurt), as well as hard solids (such as some cheeses).

The effect of cations and epigallocatechin gallate on in vitro salivary lubrication

Ionic valency influences oral processing by changing salivary behavior and merits more attention since little is known. In this study, the influence of three ionic valences (monovalent, divalent and trivalent), ionic strength and epigallocatechin gallate (EGCG) on lubricating properties of saliva were investigated. Tribological measurements were used to characterize the lubrication response of KCl, MgCl2, FeCl3, and AlCl3 in combination with EGCG to the ex vivo salivary pellicle. KCl at 150 mM ionic strength provided extra lubrication via hydration lubrication. Contrarily, trivalent salts aggregated together with the salivary mucins via ionic cross-link interactions, which led to a decrease in salivary lubrication. FeCl3 and AlCl3 affected the salivary lubrication differently, which was attributed to changes in the pH. Finally, in presence of EGCG, FeCl3 interacted with EGCG via chelating interactions, preventing salivary protein aggregation. This resulted in less desorption of the salivary film, retaining the lubrication ability of salivary proteins.

Capturing the onset of oral processing: Merging of a model food emulsion drop with saliva

The events occurring before and during the merging of a model liquid food emulsion with saliva have been captured ex vivo using confocal microscopy. In the order of a few seconds, millimeter-sized drops of liquid food and saliva touch and are deformed; the two surfaces eventually collapse, resulting in the merging of the two phases, in a process reminiscent of emulsion droplets coalescing. The model droplets then surge into saliva. Based on this, two distinct stages can be distinguished for the insertion of a liquid food into the oral cavity: A first phase where two intact phases co-exist, and the individual viscosities and saliva-liquid food tribology should be important to texture perception; and a second stage, dominated by the rheological properties of the liquid food-saliva mixture. The importance of the surface properties of saliva and liquid food are highlighted, as they may influence the merging of the two phases.

Food protein glycation: A review focusing on stability and in vitro digestive characteristics of oil/water emulsions

Recently, increasing studies have shown that the functional properties of proteins, including emulsifying properties, antioxidant properties, solubility, and thermal stability, can be improved through glycation reaction under controlled reaction conditions. The use of glycated proteins to stabilize hydrophobic active substances and to explore the gastrointestinal fate of the stabilized hydrophobic substances has also become the hot spot. Therefore, in this review, the effects of glycation on the structure and function of food proteins and the physical stability and oxidative stability of protein-stabilized oil/water emulsions were comprehensively summarized and discussed. Also, this review sheds lights on the in vitro digestion characteristics and edible safety of emulsion stabilized by glycated protein. It can further serve as a research basis for understanding the role of structural features in the emulsification and stabilization of glycated proteins, as well as their utilization as emulsifiers in the food industry.

Flavor release and stability comparison between nano and conventional emulsion as influenced by saliva

Flavour release and emulsion stability depend on volatile organic compounds' environmental conditions, food microstructure, and physicochemical properties. The effect of pH (3.5 vs 7.0) and saliva addition on stability and flavour release from nano and conventional emulsions was investigated using particle size, charge and Lumisizer measurments. Larger particle sizes were observed at lower pressures and in saliva-containing emulsions. At 1700 bar, nano-emulsions (below 150 nm) were created at pH 3.5 and 7.0 including saliva-containing emulsions. As was clear from the creaming velocity measurements, saliva addition decreased the emulsion stability by reducing particle charges and increased viscosity by more than 50%, especially when prepared at pH 3.5 closer to the isoelectric point of the used emulsifier β-lactoglobulin (pH 5.2). (5.2). Flavour release from emulsions was measured at equilibrium using a phase ratio variation to determine partition coefficients and dynamically using an electronic nose. Partition coefficients of the flavour compounds for most conditions were two to four times lower in emulsions prepared at pH 7.0 than at pH 3.5 and in emulsions without saliva. Emulsions prepared with higher pressures showed stronger flavor release rates, while additional salvia dropped the release rate for ethyl acetate at pH 3.5. The physicochemical properties of flavour compounds, saliva addition and pH of emulsions influenced flavour release more than homogenization pressures. The potential in using nano-emulsions in food applications an be attributed higher stability and enhanced flavor release.

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 Soybean Oil Body as a Milk Fat Substitute on Ice Cream: Physicochemical, Sensory and Digestive Properties

Soybean oil body (SOB) has potential as a milk fat substitute due to its ideal emulsification, stability and potential biological activity. In this study, SOB was used as a milk fat substitute to prepare ice cream, expecting to reduce the content of saturated fatty acid and improve the quality defects of ice cream products caused by the poor stability of milk fat at low temperatures. This study investigated the effect of SOB as a milk fat substitute (the substitution amount was 10–50%) on ice cream through apparent viscosity, particle size, overrun, melting, texture, sensory and digestive properties. The results show SOB substitution for milk fat significantly increased the apparent viscosity and droplet uniformity and decreased the particle size of the ice cream mixes, indicating that there were lots of intermolecular interactions to improve ice cream stability. In addition, ice cream with 30% to 50% SOB substitution had better melting properties and texture characteristics. The ice cream with 40% SOB substitution had the highest overall acceptability. Furthermore, SOB substitution for milk fat increased unsaturated fatty acid content in ice cream and fatty acid release during digestion, which had potential health benefits for consumers. Therefore, SOB as a milk fat substitute may be an effective way to improve the nutritional value and quality characteristics of dairy products.

Colloidal dynamics of emulsion droplets in mouth

The interaction of emulsions with the tongue is key to the sensory appeal of food and can potentially be exploited for oral/buccal pharmaceutical delivery. Whilst there is good understanding of the different mucoadhesive forces governing emulsion interaction with the tongue, their relative importance is not well understood. In addition, the physical location of emulsions within the saliva papillae on the tongue is not understood at all. A combination of ex vivo salivary film, and in vivo oral coating experiments were used to determine the importance of different mucoadhesive forces. Mucoadhesion of cationic emulsions was largely driven by electrostatic complexation. SDS-PAGE of the in vivo saliva coating highlighted that mucins were largely responsible for cationic emulsion mucoadhesion. Anionic emulsions were bound via hydrophobic/steric interactions to small salivary proteins typically located away from the mucin anchor points. The physical location and clustering of emulsions relative to the salivary film/papillae was probed via the invention of a fluorescent oral microscope. Cationic emulsions were densely clustered close to the papillae whilst anionic emulsions were suspended in the salivary film above the papillae. Interestingly, non-ionic emulsions were also trapped within the salivary film above the papillae as individual droplets. These findings highlight that whilst electrostatic complexation with saliva is a powerful mucoadhesive force, hydrophobic and steric interactions also act to induce oral retention of emulsions. The differences in physical location and clustering of emulsions within the salivary film hint at the 3D locations of the different salivary proteins driving each mucoadhesive interaction. This novel understanding of emulsion saliva/papillae interactions has potential to aid efficacy of buccal pharmaceutical delivery and the reduction of astringency in plant-based foods.

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.

Effects of acetylated cassava starch on the physical and rheological properties of multicomponent protein emulsions

The present study investigates the effect of different acetylated cassava starch (ACS) concentrations on the physical and rheological properties of multicomponent emulsion-based products at specific pH values. The emulsion-based products were made by mixing 2% (w/v) prepared lipid droplets that were stabilized by either native or heated whey proteins, 0.01% (w/v) flaxseed gum and 0-6.0% (w/v) ACS. The results indicated that particle size, apparent viscosity and rheological moduli of multicomponent emulsion-based products were significantly enhanced with increasing addition amounts of ACS (P < 0.05). Moreover, the microscopic morphology showed that the addition of ACS contributed to the formation of a more compact, uniform, and continuous comb-like network. However, higher ACS concentration was prone to induce visibly larger aggregations and coarser textures, lending to some negative impact on visual appearance and overall acceptability. Moreover, acidic conditions could obviously promote droplet aggregation via electrostatic interactions, whereas neutral conditions had no effect on droplet aggregation. Additionally, when compared with native whey proteins, lipid droplets stabilized by their heated protein forms induced significantly higher apparent viscosities and rheological moduli of multicomponent emulsion-based products (P < 0.05). Our results potentially provide some information for the creation of multicomponent emulsion-based products with various desirable quality attributes.

Protein-saliva interactions: a systematic review

Food industries are challenged to reformulate foods and beverages with higher protein contents to lower fat and sugar content. However, increasing protein concentration can reduce sensory acceptability due to astringency perception. Since the properties of food-saliva mixtures govern mouthfeel perception, understanding how saliva and protein interact is key to guide development of future protein-rich reformulations with optimal sensory attributes. Hence, this systematic review investigated protein-saliva interaction using both model and real human saliva, including a quality assessment. A literature search of five databases (Medline, Pubmed, Embase, Scopus and Web of Science) was undertaken covering the last 20 years, yielding 36 604 articles. Using pre-defined criteria, this was reduced to a set of 33 articles with bulk protein solutions (n = 17), protein-stabilized emulsions (n = 13) and protein-rich food systems (n = 4). Interaction of dairy proteins, lysozyme and gelatine with model or human saliva dominated the literature. The pH was shown to have a strong effect on electrostatic interaction of proteins with negatively-charged salivary mucins, with greater interactions occurring below the isoelectric point of proteins. The effect of protein concentration was unclear due to the limited range of concentrations being studied. Most studies employed a 1 : 1 w/w protein : saliva ratio, which is not representative of true oral conditions. The interaction between protein and saliva appears to affect mouthfeel through aggregation and increased friction. The searches identified a gap in research on plant proteins. Accurate simulation of in vivo oral conditions should clarify understanding of protein-saliva interaction and its influence on sensory perception.

Influence of oil matrixes on stability, antioxidant activity, bioaccessibility and bioavailability of astaxanthin ester

BACKGROUND

Astaxanthin ester (Asta-E) is used as functional nutraceuticals in many food products. Unfortunately, Asta-E utilization is currently limited owing to its chemical instability and low bioavailability. The purpose of this study is to investigate the promotion effect of oil matrixes on the stability, antioxidant activity, bioaccessibility and bioavailability of Asta-E.

RESULTS

The results showed that the stability of Asta-E in six oil matrixes was improved. Based on the 2, 2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity experiment, the antioxidant activity of Asta-E was positively correlated with the degree of unsaturation of the oil matrixes, but not with the side chain length. The in vitro gastrointestinal tract (GIT) simulation model and in vivo experiment using mice were also employed to investigate the digestion and absorption characteristics of Asta-E in various oil matrixes. The results demonstrated that the bioaccessibility and bioavailability of Asta-E increased with the increase of fatty acid chain length of oil matrixes (triglyceride oleate > triglyceride caprylate > triglyceride butyrate), as well as with the decrease of unsaturation degree (olive oil > corn oil > fish oil).

CONCLUSION

Monounsaturated fatty acids (MUFA) and long-chain triglyceride (LCT) in an oil matrix were the factors that could efficiently improve the bioavailability of Asta-E. Moreover, the size of the mixed micelles of Asta-E during digestion was the main factor influencing the bioaccessibility of Asta-E. This study provides references for the design of suitable oil matrixes for Asta-E. © 2020 Society of Chemical Industry.

Contributions of viscosity and friction properties to oral and haptic texture perception of iced coffees

Creaminess is affected by bulk properties (i.e. viscosity) and surfaces properties (i.e. friction). This study aimed (i) to assess contributions of viscosity and friction properties to creaminess, thickness and slipperiness perception; and (ii) to compare oral and haptic thickness and slipperiness perception of iced coffees. Three iced coffees differing in viscosity and friction properties were prepared: low viscosity - high friction (LV-HF); low viscosity - low friction (LV-LF) and high viscosity - low friction (HV-LF) iced coffee. Viscosity of iced coffees was adjusted by addition of maltodextrin, and viscosity of HV-LF was 2.5 times higher than that of LV-HF and LV-LF (10 vs. 4 mPa s at 100 s-1). Friction coefficients of LV-LF were reduced by addition of polyethylene glycol (PEG, Mw 6000), and were up to 25% lower than those of LV-HF. Forty-seven untrained panellists (18-27 years) performed two-alternative forced choice (2-AFC) and rank-rating tests to compare creaminess by oral assessment, and thickness and slipperiness by oral and haptic assessment. Results from 2-AFC and rank-rating congruently showed that HV-LF was creamier, thicker and more slippery than LV-HF and LV-LF, both orally and haptically. LV-LF was orally perceived as less creamy and less thick, but haptically as more slippery than LV-HF. Creaminess was more strongly correlated to thickness than to slipperiness. Oral and haptic evaluation of thickness was congruent, whereas differences between oral and haptic slipperiness evaluation were product-dependent. We conclude that increasing viscosity enhances creaminess, whereas increasing lubrication is not necessarily sufficient to increase creaminess in iced coffees.

Use of Milk Fat/Cellulose Ether Emulsions in Spreadable Creams and the Effect of In Vitro Digestion on Texture and Fat Digestibility

This study investigated the texture properties and fat digestibility of new spreadable chocolate creams formulated with an emulsion composed of milk fat and a cellulose ether as a fat source. The spreadability was analysed at 20 °C and compared with a commercial spreadable cream formulated with palm fat. Structural changes in the creams after the in vitro oral and gastric digestion stages were evaluated; lipid digestibility was determined by titration with NaOH during intestinal digestion. Spreadability tests showed the spreads were similar. After oral digestion, the commercial spread showed an increase in extrusion force because of flocculation induced by saliva, an effect not observed in spreads with cellulose ether. Digestibility determination showed lower values for the reformulated spreads. Therefore, milk fat-cellulose ether based emulsions offer an alternative to achieve reformulated spreadable creams, with physical properties similar to those of commercial products but providing reduced fat content and lower lipid digestibility, without compromising the quality of the final product.

Impact of curcumin delivery system format on bioaccessibility: nanocrystals, nanoemulsion droplets, and natural oil bodies

Curcumin, a hydrophobic yellow-orange crystalline substance derived from plants, is claimed to exhibit a broad range of biological activities. Its application in functional foods and beverages is often limited by its low solubility in aqueous media, chemical instability, and low bioavailability. Previously, we have shown that curcumin can be successfully loaded into emulsions using the pH-shift method. In this study, we compared the efficacy of curcumin crystals dispersed in water (control) with three delivery systems produced using the pH-shift method: curcumin nanocrystals; curcumin-loaded nanoemulsions; and curcumin-loaded soy oil bodies. The nanoemulsions and oil bodies formed creamy yellow dispersions that were stable to creaming, whereas the nanocrystals formed a cloudy yellow-orange suspension that was prone to sedimentation. The gastrointestinal fate of the delivery systems was assessed using a static in vitro digestion model consisting of mouth, stomach, and small intestine phases. The nanoemulsions and oil bodies were rapidly and fully digested, while the nanocrystals were not. All three systems were relatively stable to chemical transformation in the in vitro digestion model. The nanocrystals gave a low bioaccessibility but the other two systems gave a high bioaccessibility, which was attributed to their ability to form mixed micelles to solubilize the curcumin. These results have important implications for the creation of more effective delivery systems for curcumin.

Human saliva and model saliva at bulk to adsorbed phases - similarities and differences

Human saliva, a seemingly simple aqueous fluid, is, in fact, an extraordinarily complex biocolloid that is not fully understood, despite many decades of study. Salivary lubrication is widely believed to be a signature of good oral health and is also crucial for speech, food oral processing and swallowing. However, saliva has been often neglected in food colloid research, primarily due to its high intra- to inter-individual variability and altering material properties upon collection and storage, when used as an ex vivo research material. In the last few decades, colloid scientists have attempted designing model (i.e. 'saliva mimicking fluid') salivary formulations to understand saliva-food colloid interactions in an in vitro set up and its contribution on microstructural aspects, lubrication properties and sensory perception. In this Review, we critically examine the current state of knowledge on bulk and interfacial properties of model saliva in comparison to real human saliva and highlight how far such model salivary formulations can match the properties of real human saliva. Many, if not most, of these model saliva formulations share similarities with real human saliva in terms of biochemical compositions, including electrolytes, pH and concentrations of salivary proteins, such as α-amylase and highly glycosylated mucins. This, together with similarities between model and real saliva in terms of surface charge, has led to significant advancement in decoding various colloidal interactions (bridging, depletion) of charged emulsion droplets and associated sensory perception in the oral phase. However, model saliva represents significant dissimilarity to real saliva in terms of lubricating properties. Based on in-depth examination of properties of mucins derived from animal sources (e.g. pig gastric mucins (PGM) or bovine submaxillary mucin (BSM)), we can recommend that BSM is currently the most optimal commercially available mucin source when attempting to replicate saliva based on surface adsorption and lubrication properties. Even though purification via dialysis or chromatographic techniques may influence various physicochemical properties of BSM, such as structure and surface adsorption, the lubricating properties of model saliva formulations based on BSM are generally superior and more reliable than the PGM counterpart at orally relevant pH. Comparison of mucin-containing model saliva with ex vivo human salivary conditioning films suggests that mucin alone cannot replicate the lubricity of real human salivary pellicle. Mucin-based multi-layers containing mucin and oppositely charged polyelectrolytes may offer promising avenues in the future for engineering biomimetic salivary pellicle, however, this has not been explored in oral tribology experiments to date. Hence, there is a strong need for systematic studies with employment of model saliva formulations containing mucins with and without polycationic additives before a consensus on a standardized model salivary formulation can be achieved. Overall, this review provides the first comprehensive framework on simulating saliva for a particular bulk or surface property when doing food oral processing experiments.

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

To investigate how the fat crystal structure affects lipid in vitro digestibility, 30% palm stearin-in-water emulsions were prepared after storage at different temperatures (4, 25, and 37 °C) for 1 h, which consisted of different polymorphic forms, sizes, and quantities of fat crystals. The variation of particle size ( d_4,3), zeta potential, and microstructure during the gastrointestinal digestion and the free fatty acid (FFA) released in small intestine phase were investigated. After oral and gastric digestion, all of the emulsions underwent partial or complete coalescence and flocculation. During intestinal digestion, the d_4,3 and zeta potentials did not notably affect lipid digestion. The FFA-released assay results indicated that the lipid digestion extent decreased as the fat crystal size and content of the β polymorph increased, and there was no obvious relationship between FFA release and fat crystal quantity or solid fat content (SFC). This study highlighted the crucial roles of fat crystal size and polymorphic form in regulating the digestion behavior of lipid-based O/W emulsions.

Interactions of salivary mucins and saliva with food proteins: a review

Mucins are long glycoprotein molecules responsible for the gel nature of the mucous layer that covers epithelial surfaces throughout the body. Mucins, as the major salivary proteins, are also important proteins for the food oral processing and digestion. The interactions of salivary mucins and saliva with several food proteins and food protein emulsions, as well as their functional properties related to the food oral processing were reviewed in this paper. The target food proteins of focus were whey proteins (lactoferrin and beta-lactoglobulin) and non-whey proteins (casein, gelatin, galectin/lectin, and proline-rich proteins). Most of the studies suggest that electrostatic attraction (between positively charged food proteins with negatively charged moieties of mucin mainly on glycosylated region of mucin) is the major mode of interaction between them. On the other hand, casein attracts the salivary proteins only via non-covalent interactions due to its naturally self-assembled micellar structure. Moreover, recent studies related to β-lactoglobulin (BLG)-mucin interactions have clarified the importance of hydrophobic as well as hydrophilic interactions, such as hydrogen bonding. Furthermore, in vitro studies between protein emulsions and saliva observed a strong aggregating effect of saliva on caseinate and whey proteins as well as on surfactant-stabilized emulsions. Besides, the sign and the density of the charge on the surface of the protein emulsion droplets contribute significantly to the behavior of the emulsion when mixed with saliva. Other studies also suggested that the interactions between saliva and whey proteins depends on the pH in addition to the flow rate of the saliva. Overall, the role of interactions of food proteins and food protein emulsions with mucin/saliva-proteins in the oral perception, as well as the physicochemical and structural changes of proteins were discussed.

Colloidal aspects of digestion of Pickering emulsions: Experiments and theoretical models of lipid digestion kinetics

Lipid digestion is a bio-interfacial process that is largely governed by the binding of the lipase-colipase-biosurfactant (bile salts) complex onto the surface of emulsified lipid droplets. Therefore, engineering oil-water interfaces that prevent competitive displacement by bile salts and/or delay the transportation of lipase to the lipidoidal substrate can be an effective strategy to modulate lipolysis in human physiology. In this review, we present the mechanistic role of Pickering emulsions i.e. emulsions stabilised by micron-to-nano sized particles in modulating the important fundamental biological process of lipid digestion by virtue of their distinctive stability against coalescence and resilience to desorption by intestinal biosurfactants. We provide a systematic summary of recent experimental investigations and mathematical models that have blossomed in the last decade in this domain. A strategic examination of the behavior and mechanism of lipid digestion of droplets stabilised by particles in simulated biophysical environments (oral, gastric, intestinal regimes) was conducted. Various particle-laden interfaces were considered, where the particles were derived from synthetic or biological sources. This allowed us to categorize these particles into two classes based on their mechanistic role in modifying lipid digestion. These are 'human enzyme-unresponsive particles' (e.g. silica, cellulose, chitin, flavonoids) i.e. the ones that cannot to be digested by human enzymes, such as amylase, protease and 'human enzyme-responsive particles' (e.g. protein microgels, starch granules), which can be readily digested by humans. We focused on the role of particle shape (spherical, anisotropic) on modifying both interfacial and bulk phases during lipolysis. Also, the techniques currently used to alter the kinetics of lipid digestion using intelligent physical or chemical treatments to control interfacial particle spacing were critically reviewed. A comparison of how various mathematical models reported in literature predict free fatty acid release kinetics during lipid digestion highlighted the importance of the clear statement of the underlying assumptions. We provide details of the initial first order kinetic models to the more recent models, which account for the rate of adsorption of lipase at the droplet surface and include the crucial aspect of interfacial dynamics. We provide a unique decision tree on model selection, which is appropriate to minimize the difference between experimental data of free fatty acid generation and model predictions based on precise assumptions of droplet shrinkage, lipase-binding rate, and nature of lipase transport process to the particle-laden interface. Greater insights into the mechanisms of controlling lipolysis using particle-laden interfaces with appropriate mathematical model fitting permit better understanding of the key lipid digestion processes. Future outlook on interfacial design parameters, such as particle shape, size, polydispersity, charge, fusion, material chemistry, loading and development of new mathematical models that provide closed-loop equations from early to later stages of kinetics are proposed. Such future experiments and models hold promise for the tailoring of particle-laden interfaces for delaying lipid digestion and/or site-dependent controlled release of lipidic active molecules in composite soft matter systems, such as food, personal care, pharmaceutical, healthcare and biotechnological applications.

Saliva could act as an emulsifier during oral processing of oil/fat

Human saliva is a fluid naturally secreted in the oral cavity that interacts with food and food components for bolus formation, structure degradation, as well as lubrication. Because of the presence of salivary proteins, we speculate that saliva could also function as an effective emulsifier during oral processing of oil/fat. In this preliminary work, experiments were then designed to test this hypothesis. Whole human saliva from three healthy subjects were collected and analyzed for protein content, surface tension, and molecular weight distribution. Saliva emulsions were obtained both in vitro one and in situ for all three participating subjects. Droplet size distribution, zeta potential, and microstructure of such emulsions were examined immediately after the emulsification. Results show that stable saliva emulsions can be produced during oral processing of either pure oil (rapeseed oil) or fat food (pork belly in this work). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed that protein fractions of 27 and 55 kDa molecular weights were favored for emulsion formation. This work suggests that human saliva could function as an effective emulsifier and oral emulsification could be an important mechanism for the oral processing of oil/fat. Despite being preliminary, findings from this work provide a new scientific insight to our understanding of the oral behavior of oil/fat and their sensory perception. PRACTICAL APPLICATIONS: Food industry is currently under a growing pressure to use novel techniques and ingredients to minimize the use of oil/fat in food products but without compromising its sensory quality. However, food industry has limited progresses because of the lack of understanding of the mechanisms of oral sensation and perception of oil/fat. Whereas there have been extensive debates about the sensory mechanisms of oil/fat, this work takes a step back by examining the oral behavior of oil/fat. Findings show that saliva can actually function as emulsifier to oil/fat, which means that ingested oil/fat will be dispersed and converted into an emulsion at the oral stage. The findings from this work offer food industry new insight on the sensory mechanisms of oil/fat.

Impact of Delivery System Type on Curcumin Bioaccessibility: Comparison of Curcumin-Loaded Nanoemulsions with Commercial Curcumin Supplements

In this study, nanoemulsion-based delivery systems fabricated using three different methods were compared with three commercially available curcumin supplements. Powdered curcumin was dispersed into the oil-in-water nanoemulsions using three methods: the conventional oil-loading method, the heat-driven method, and the pH-driven method. The conventional method involved dissolving powdered curcumin in the oil phase (60 °C, 2 h) and then forming a nanoemulsion. The heat-driven method involved forming a nanoemulsion and then adding powdered curcumin and incubating at an elevated temperature (100 °C, 15 min). The pH-driven method involved dissolving curcumin in an alkaline solution (pH 12.5) and then adding this solution to an acidified nanoemulsion (pH 6.0). The three commercial curcumin products were capsules or tablets purchased from an online supplier: Nature Made, Full Spectrum, and CurcuWin. Initially, the encapsulation efficiency of the curcumin in the three nanoemulsions was determined and decreased in the following order: pH-driven (93%) > heat-driven (76%) > conventional (56%) method. The different curcumin formulations were then subjected to a simulated gastrointestinal tract (GIT) model consisting of mouth, stomach, and small intestine phases. All three nanoemulsions had fairly similar curcumin bioaccessibility values (74-79%) but the absolute amount of curcumin in the mixed micelle phase was highest for the pH-driven method. A comparison of these nanoemulsions and commercial products indicated that the curcumin concentration in the mixed micelles decreased in the following order: CurcuWin ≈ pH-driven method > heat-driven method > conventional method ≫ Full spectrum > Nature Made. This study provides valuable information about the impact of the delivery system type on curcumin bioavailability. It suggests that encapsulating curcumin within small lipid particles may be advantageous for improving its absorption form the GIT.

Material properties of ex vivo milk chocolate boluses examined in relation to texture perception

The texture perception of chocolate products is a major driver for consumer liking and the popularity of this confectionary category. Whilst some texture attributes are clearly linked to the material properties of the chocolate bar itself, others are closer related to the properties of the chocolate bolus. However, little is known about the material properties of chocolate boluses. Hence the aim of this study was to gain more in-depth insights into this area and to evaluate how chocolate bolus material properties link to texture and mouthfeel perception. Boluses prepared from four milk chocolates were analysed for microstructure, particle size, composition and friction properties. The boluses showed the expected oil-in-water emulsion microstructure. The emulsion droplets were composed of fat and milk protein with clear evidence for the presence of milk protein not only at the droplet interface but also in the droplet bulk phase. The type of adsorbed milk protein depended on the presence or absence of interfacially adsorbed cocoa solids, grouping the four chocolates into two pairs. The chocolate boluses showed increased friction compared to saliva and at low sliding speed the friction coefficients were lower for boluses with interfacially adsorbed cocoa solids. The perceived differences in mouthcoating were reflected in the mixed regime of the Stribeck curve. Thickness perception on the other hand was reflected in the hydrodynamic regime of the friction curves. This research has highlighted the promise in analysing the material properties of chocolate boluses in view of understanding the perceived texture.

Relationship between sensory analysis for texture and instrument measurements in model strawberry jam

The primary objective of this study was to investigate the correlations between instrument measurements and sensory attributes of strawberry jam. For this purpose, a series of low sugar strawberry jams were prepared by using different contents of pectin from different sources, which were evaluated by sensory analysis for sensory attributes and by instrument measurements for specific physical properties. Model strawberry jams showed an elastic behavior that increased with higher low-methoxyl (LM) pectin content. These results showed that the apparent viscosity from viscosity measurements was highly correlated with each sensory attribute. As jam is a non-Newtonian fluid, the apparent viscosity was dependent on the shear rate. Moreover, the secondary objective of this study was to discern the physical properties affecting human texture perception based on these relationships. Hence, the instrumental texture perception based on the oral cavity condition was able to predict human texture perception based on the shear rate, which was obtained from the apparent viscosity. These results indicated that human texture perception is judged by apparent viscosity as determined by controlling tongue movement and oral cavity condition (e.g., temperature, saliva, and shear rate).

PRACTICAL APPLICATIONS

We could demonstrate the importance of texture measurement using replicated oral processing for each sensory attribute. Specifically, viscosity measurement results indicated that shear rate is a very important factor for texture perception. Moreover, our findings clarified that human texture perception is modified by apparent viscosity corresponding to shear rate. We anticipate that this technology might be applied as a measure of apparent viscosity to control texture for jam quality improvement.