Simulated Gastrointestinal Tract Model Research Articles

Impact of protein-nanoparticle interactions on gastrointestinal fate of ingested nanoparticles: Not just simple protein corona effects

The interaction of nanoparticles (NPs) with proteins in their surroundings is a key factor determining their biological fate. The formation of a protein corona around ingested NPs in complex food matrices and in the gastrointestinal tract (GIT) is known to impact their gastrointestinal fate. In this study, the interaction between titanium dioxide (TiO2) NPs from a common food additive (E171) and casein, an abundant milk protein was characterized. The impact of these interactions on the potential gastrointestinal fate of the NPs was examined using a simulated GIT model. Our results showed that a series of complex molecular events occurred when the TiO2 NPs were added to casein solutions, including dissociation of casein micelles, NP-protein complex formation, and complex aggregation. Extensive aggregation was observed under conditions where charge neutralization occurred, which was attributed to a reduction in the electrostatic repulsion between the NP-protein complexes and to a polymer bridging effects. There was a pronounced decrease in the rate and extent of gastric digestion of the casein in the presence of the TiO2 NPs, indicating that complex formation reduced the access of pepsin to the peptide bonds. These findings stress the importance of taking into account the interactions of ingested NPs with food matrix and gastrointestinal components. Moreover, our findings show that the simple concept of a protein corona does not adequately explain the complex structural changes that occur when proteins and NPs interact.

Controllable Viscoelastic Properties of Whey Protein-Based Emulsion Gels by Combined Cross-Linking with Calcium Ions and Cinnamaldehyde.

Whey protein-based emulsion gels were fabricated by combined covalent cross-linking with cinnamaldehyde and ionic cross-linking with calcium ions. The structural and rheological properties of these emulsion gels were characterized by microscopy, macrorheometry, and microrheometry. Soft to hard emulsion gels could be fabricated by altering the Ca2+ level. However, water separation occurred in the emulsion gels at high calcium levels, indicating that an appropriate balance of protein cross-linking was essential for a good functional performance of the emulsion gels. At a constant calcium ion level, cross-linking with cinnamaldehyde softened the texture of the emulsion gels and reduced the level of water separation. Thermal treatment could be used to strengthen the interaction between the whey proteins and calcium ions, presumably due to protein unfolding and aggregation. Rheology demonstrated that cross-linking reactions occurred between the whey protein and cinnamaldehyde at the oil-water interface, which decreased the viscosity of the emulsion gels, but increased their viscoelasticity. Microstructural changes observed by fluorescence microscopy were in agreement with the rheology results. Scanning electronic microscopy showed that the microstructure of the emulsion gels was strongly impacted by the presence of cinnamaldehyde, which led to a more uniform and smaller pore size. The gastrointestinal fate of the emulsion gels was determined using a simulated gastrointestinal tract model. The oral and gastric processing of the emulsion gels was strongly influenced by cinnamaldehyde cross-linking, with less aggregation being observed. The information obtained in this study may facilitate the development of more innovative protein-based products with novel functional attributes for use in foods and other applications.

Nanoemulsion-Based Delivery Systems for Nutraceuticals: Influence of Long-Chain Triglyceride (LCT) Type on In Vitro Digestion and Astaxanthin Bioaccessibility

Astaxanthin (AST) exerts biological activities that is potentially beneficial to human health, but its utilization as a nutraceutical in foods and supplements is currently limited by its low oral bioavailability. The influence of three long chain triglyceride (LCT) oils (flaxseed, olive and corn oil) on the bioaccessibility of AST encapsulated within oil-in-water nanoemulsions was evaluated using a simulated gastrointestinal tract (GIT) model. The microstructure and particle properties (size and charge) of all three nanoemulsions followed similar patterns in simulated mouth, stomach, and small intestinal regions, which were appreciably different from the control (no lipid). Moreover, all three nanoemulsions significantly increased the bioaccessibility of AST compared to the control, which was attributed to their ability to form mixed micelles that could solubilize the hydrophobic carotenoids. However, LCT type did have an impact on lipid digestion and carotenoid bioaccessibilty, with the final amount of free fatty acids (FFAs) released and bioaccessibility decreasing in the following order: olive oil > flaxseed oil > corn oil. These effects were attributed to the impact of FFA unsaturation and chain length on lipid digestion and micelle formation. The results of this study highlight the potential of nanoemulsions for enhancing AST bioavailability in functional foods and supplements.

Impact of Titanium Dioxide on the Bioaccessibility of β-Carotene in Emulsions with Different Particle Sizes

Commercial, titanium dioxide (TiO2) ingredients used as color additives (E171) in foods and beverages contain an appreciable fraction of particles in the nanoscale range. At present, little information is available regarding the potential impact of food-grade TiO2 nanoparticles on the gastrointestinal fate of co-ingested bioactives, such as nutraceuticals. In this study, the impact of TiO2 on the bioaccessibility of β-carotene solubilized in model food emulsions was investigated using a simulated gastrointestinal tract model. Raman spectroscopy showed that there was no charge transfer between β-carotene and TiO2 but that some β-carotene absorbed to the surface of TiO2 particles. The initial particle size of the food emulsion did not significantly affect β-carotene bioaccessibility, probably because the same amount of free fatty acids (FFAs) was released by the end of digestion. The addition of TiO2 at levels typically found in foods also had no significant impact on β-carotene bioaccessibility and FFA release, which suggested that this type of inorganic particle does not interfere with the gastrointestinal fate of these lipophilic bioactive agents. This information is important for ensuring the safety of inorganic nanoparticle utilization within the food industry.

Applications of simulated gastro-intestinal model in foodborne pathogens: tolerance and pathogenesis

We evaluated the tolerance and pathogenesis of foodborne pathogens with a simulated gastro-intestinal tract model that simulates the chemical, physical and biological effects of human digestion process under laboratory conditions. This could be used to study the tolerance, pathogenesis, gut microbiota interaction and vaccine development of foodborne pathogens, so as to contribute to control and treatment of foodborne pathogens. This review introduces the applications of simulated gastro-intestinal tract model tp evaluate foodborne pathogens, which includes in-vitro static gastro-intestinal model, in-vitro dynamic gastro-intestinal model, conventional animal model and humanized animal model. And the concepts and characteristics of all models are described in detail. Also, the shortcomings of existing models are analyzed, and improvements of artificial gastro-intestinal tract model are prospected. In conclusion, this review could provide comprehensive data for promoting the progress of studying tolerance and pathogenesis of foodborne pathogens.

Encapsulation of vitamin D3 in pickering emulsions stabilized by nanofibrillated mangosteen cellulose: Impact on in vitro digestion and bioaccessibility

Oil-in-water Pickering emulsions stabilized by nanofibrillated cellulose (NFC) were used to encapsulate and deliver vitamin D3. NFC was extracted from a waste product of the food industry, mangosteen (Garcinia mangostana L.) rind, using dissolution in a hot sodium hydroxide solution, bleaching using hydrogen peroxide, and shearing using a high-pressure homogenizer. This yielded cellulose fibers with a diameter of around 60 nm and a length of several micrometers. Emulsions containing 10% w/w oil (0.01% w/w vitamin D3 and 9.99% w/w soybean oil), 0.10–0.70% w/w NFC as emulsifier, and phosphate buffer (pH 7) were prepared. The effect of NFC on lipid digestion and vitamin bioaccessibility was investigated using a simulated gastrointestinal tract (GIT) model, which included mouth, stomach and small intestine phases. The rate and extent of lipid digestion, as well as the vitamin bioaccessibility, decreased with increasing NFC concentration. Numerous physicochemical phenomena may account for this effect, including the ability of NFC to: act as a physical barrier at the lipid droplet surfaces; to promote droplet flocculation in the gastric phase; and, to increase the viscosity of the aqueous phase. The slight decrease in vitamin D3 bioaccessibility at higher NFC levels, was probably due to the lower level of lipid digestion. Our results indicate that mangosteen fiber can be used to stabilize oil-in-water emulsions, and only has a minor effect on lipid digestion and vitamin bioaccessibility when used at relatively low levels. This information may be useful for the rational design of functional foods from natural waste-products, such as mangosteen rind.

Carotenoprotein from Pacific white shrimp (Litopenaeus vannamei ) shells extracted using trypsin from albacore tuna (Thunnus alalunga ) spleen: Antioxidant activity and its potential in model systems

Antioxidative activities of carotenoprotein from Pacific white shrimp shells extracted by trypsin from albacore tuna spleen were investigated. Carotenoprotein exhibited increased DPPH, ABTS radical scavenging activities, ferric reducing antioxidant power (FRAP), metal chelating activity, hydrogen peroxide, and hydroxyl radical scavenging activities as concentration increased up to 5 mg/mL (p < .05). ABTS radical scavenging activity of carotenoprotein was stable over a wide pH range (2–11) and temperature up to 100°C for 180 min. It was also stable in a simulated gastrointestinal tract model system. Carotenoprotein was able to reduce lipid oxidation in a dose-dependent manner. During storage at room temperature, light and dark, 4°C and −20°C for 12 weeks, the ABTS radical scavenging activity of carotenoprotein was stable with more than 75.75% activity retention. Therefore, Pacific white shrimp carotenoprotein may be used as an alternative source of natural antioxidants. Practical applications Carotenoprotein from Pacific white shrimp shells, the by-products from shrimp processing industry, can be extracted using tuna trypsin. This product possessed antioxidative activities and could serve as natural antioxidant to prevent lipid oxidation in foods.

Controlling the potential gastrointestinal fate of β-carotene emulsions using interfacial engineering: Impact of coating lipid droplets with polyphenol-protein-carbohydrate conjugate.

The impact of interfacial coatings comprised of polyphenol-protein-carbohydrate conjugates on the properties of nutraceutical-fortified lipid droplets during digestion was investigated. Surface-active chlorogenic acid-lactoferrin-polydextrose (CA-LF-PD) conjugate was synthesized as emulsifier to stabilize lipid droplets in β-carotene-enriched oil-in-water emulsions. Changes in droplet size, charge, and microstructure were monitored as β-carotene emulsions were passed through a simulated gastrointestinal tract model (mouth, stomach, small intestine). LF-coated droplets were unstable to flocculation at pH 8.0-9.0, due to the reduction in electrostatic repulsion, but CA-LF-PD conjugate-coated droplets were stable. Emulsions stabilized by ternary conjugate had better stability to droplet aggregation under simulated GIT conditions than other systems, which increased β-carotene bioaccessibility. The importance of including an oral phase in the simulated GIT model was also demonstrated. The ternary conjugate-stabilized emulsions developed in this study have potential applications as protectors and carriers of hydrophobic drugs, supplements and nutraceuticals.

Potential physicochemical basis of Mediterranean diet effect: Ability of emulsified olive oil to increase carotenoid bioaccessibility in raw and cooked tomatoes

Excipient emulsions have compositions and structures specifically designed to increase the bioavailability of nutraceuticals in foods that they are co-ingested with. In this study, olive oil excipient emulsions were shown to significantly increase the bioaccessibility of carotenoids from tomatoes using a simulated gastrointestinal tract (GIT) model (p<0.05): being 8.18±0.93%, 11.85±1.76% for raw tomato-buffer mixture, and cooked tomato-buffer mixture; While being 32.3±2.60%, 55.7±3.28% and 42.6±3.75% for raw tomato-emulsion mixture, cooked tomato-emulsion mixture (boiled together) and cooked tomato- emulsion mixture (tomato boiled alone). These effects were attributed to: (i) the ability of digested olive oil droplets to form mixed micelles in the small intestine that solubilized the carotenoids; and, (ii) the ability of natural antioxidants (phenolics) in the olive oil to protect the carotenoids from oxidation. Thermal treatment (boiling) significantly increased carotenoid bioaccessibility from the tomatoes digested with emulsion, which was attributed to plant tissue disruption at elevated temperatures facilitating carotenoid release (p<0.05). Carotenoid bioaccessibility was higher when the tomatoes were boiled with emulsions (55.7±3.28%) than when they were boiled alone and then added to emulsions (42.6±3.75%). In conclusion, this study indicates that olive oil emulsions boost the bioaccessibility and chemical stability of lipophilic nutraceuticals in tomatoes, which may make an important contribution to the potential health benefits of the Mediterranean diet.

Food Matrix Effects on Nutraceutical Bioavailability: Impact of Protein on Curcumin Bioaccessibility and Transformation in Nanoemulsion Delivery Systems and Excipient Nanoemulsions

Powdered curcumin was either dissolved in the lipid phase of a nanoemulsion delivery system or it was directly mixed with an excipient nanoemulsion. The influence of thermal treatment (30 or 90 °C) and protein addition (caseinate) on the bioaccessibility and transformation of curcumin was then investigated using a simulated gastrointestinal tract (GIT) model: mouth; stomach; small intestine. Curcumin solubility was high in nanoemulsion delivery systems exposed to both thermal treatments because it was already present in the lipid phase. Conversely, curcumin solubility of a powder mixed with an excipient nanoemulsion was appreciably lower when exposed to 30 °C than 90 °C. This effect was attributed to the greater transfer of curcumin to the lipid phase of the excipient nanoemulsions at elevated temperatures. For the heated samples, the bioaccessibility and transformation of curcumin was not greatly affected by original curcumin location or protein addition. However, curcumin bioaccessibility was appreciably higher in the presence of nanoemulsion lipid droplets than in their absence, which was attributed to an increase in the solubilization capacity of the mixed micelle phase. This study provides some useful information for improving the design of functional foods to improve the oral bioavailability profile of lipophilic nutraceuticals.

Effect of Encapsulation on Viability of Pediococcus pentosaceus OZF During Its Passage Through the Gastrointestinal Tract Model.

The main goal of this study was to develop an improved oral delivery system for Pediococcus pentosaceus OZF, a promising probiotic bacterium, and to assess its viability under simulated gastrointestinal (GI) tract model by comparing the efficiency of microbiological and molecular approaches. Encapsulation was carried out using extrusion method and as a result, encapsulation system including 0.75% lactulose, 1.8% sodium alginate, 0.1M CaCl2, and 5min gelling time was shown to have a significantly protective effect against pH 2.0 acid stress over 3h. However, completely loss of viability was exhibited by free OZF cells under similar conditions. To provide an additional barrier for capsules, coating process was investigated using different biopolymers, and the survival rates of free and encapsulated OZF cells upon expose to simulated GI conditions were detected by conventional culture techniques and propidium monoazide-quantitative polymerase chain reaction (PMA-qPCR) method. No significant differences between the biopolymers were detected, except the chitosan which leads totally 85% protection and extra 25% improvement in the survival of OZF cells compared to uncoated capsules. In conclusion, our findings indicated that chitosan-coated capsules provided an important protective effect on the viability of OZF cells against the GI system conditions encountered during the transit of food. In addition, this study was found successful in monitoring the viable OZF cells in capsules using PMA-qPCR method.

Nanoemulsion delivery systems for oil-soluble vitamins: Influence of carrier oil type on lipid digestion and vitamin D3 bioaccessibility

The influence of carrier oil type on the bioaccessibility of vitamin D3 encapsulated within oil-in-water nanoemulsions prepared using a natural surfactant (quillaja saponin) was studied using a simulated gastrointestinal tract (GIT) model: mouth; stomach; small intestine. The rate of free fatty acid release during lipid digestion decreased in the following order: medium chain triglycerides (MCT)>corn oil≈fish oil>orange oil>mineral oil. Conversely, the measured bioaccessibility of vitamin D3 decreased in the following order: corn oil≈fish oil>orange oil>mineral oil>MCT. These results show that carrier oil type has a considerable impact on lipid digestion and vitamin bioaccessibility, which was attributed to differences in the release of bioactives from lipid droplets, and their solubilization in mixed micelles. Nanoemulsions prepared using long chain triglycerides (corn or fish oil) were most effective at increasing vitamin bioaccessibility.

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.

Antioxidant and sensory properties of protein hydrolysate derived from Nile tilapia (Oreochromis niloticus) by one- and two-step hydrolysis

Antioxidant and sensory properties of Nile tilapia protein hydrolysates prepared by one- and two-step hydrolysis using commercial proteases were investigated. Hydrolysates prepared using single protease including Alcalase (HA), Flavourzyme (HF), Protamex (HPr) and papain (HPa) had increases in antioxidant activities as the degree of hydrolysis (DH) increased up to 40% (P < 0.05). Amongst all hydrolysates, HA having 40% DH showed the highest antioxidant activities. When HA was further hydrolysed by papain, the resulting hydrolysate (HAPa) exhibited the highest antioxidant activities for all assays tested (P < 0.05). ABTS radical scavenging activity and metal chelating of HAPa generally remained constant in a wide pH range (1-11) and during heating at 30-100°C. Both activities increased in the simulated gastrointestinal tract model system, especially in intestine condition. HAPa (100-1,000ppm) could retard lipid oxidation in β-carotene-linoleate and lecithin-liposome model systems in a dose dependent manner. Peptides in both HA and HAPa with molecular weight of 513Da and 1,484Da possessed the strongest ABTS radical scavenging activity and metal chelating activity, respectively. The amino acid profile of both HA and HAPa contained a high amount of hydrophobic amino acids (38.26-38.85%) and had glutamic acid/glutamine, lysine and aspartic acid/asparagine as the dominant amino acids. However, HAPa showed a higher acceptability than did HA, owing to the lower bitterness. Therefore, the use of Alcalase in combination with papain for hydrolysis of protein isolate rendered the hydrolysate with antioxidant properties and reduced bitterness, which could serve as the functional supplement.

Nutraceutical nanoemulsions: influence of physical states of β‐carotene (crystalized versus dissolved) on bioaccessibility (645.13)

β‐Carotene has a poor oral bioaccessibility in the gastrointestinal tract (GIT) because of its high hydrophobicity and melting point. We investigated the bioaccessibilities of solubilized and crystalline forms of β‐carotene using a simulated GIT model. Three systems were compared: (1) soluble β‐carotene in digestible nanoemulsion (d&lt; 200nm); (2) crystalline β‐carotene added to digestible nanoemulsion (d&lt; 200nm); (3) crystalline β‐carotene added to phosphate buffer saline (pH=7.0). Oil‐in‐water nanoemulsions were formed by high‐pressure homogenization using Tween 20 as emulsifier and corn oil as digestible carrier oil. They were then subject to simulated mouth, stomach and small intestine digestion. The rate and extent of free fatty acid production in the small intestine decreased in the order (2)&gt;(1)&gt;(3); whereas the β‐carotene bioaccessibility decreased in the order (1)&gt;&gt;(2)&gt;(3). The low bioaccessibility (1.3%) of system (3) was attributed to the fact that there were few free fatty acids produced to form mixed micelles to solubilize β‐carotene. The bioaccessibility of system (2) was also relatively low (3.6%) compared to system (1) (42%), which suggests that crystalline β‐carotene is less bioaccessible than soluble β‐carotene. This study provides important information for choosing a better delivery condition for lipophilic bioactive components to achieve higher bioaccessibility.Grant Funding Source: Supported by USDA

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

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

Gelatin hydrolysate from blacktip shark skin prepared using papaya latex enzyme: Antioxidant activity and its potential in model systems

Antioxidant activities of gelatin hydrolysates from blacktip shark skin prepared using papaya latex enzyme with different degrees of hydrolysis (DHs: 10%, 20%, 30% and 40%) were evaluated. All antioxidant activity indices of hydrolysates increased with increasing DH (P<0.05). When gelatin hydrolysate with 40%DH was determined for its pH and thermal stability, ORAC and chelating activity remained constant or slightly increased in a wide pH range (1–9) and during heating (100°C) for 240min. It was also stable in simulated gastrointestinal tract model system. Moreover, gelatin hydrolysate at a level of 500 and 1000ppm could inhibit lipid oxidation in both β-carotene linoleate and cooked comminuted pork model systems. Therefore, gelatin hydrolysate from blacktip shark skin (40%DH) can potentially be used as an alternative source of natural antioxidants.

An Investigation into the Utility of a Multi-compartmental, Dynamic, System of the Upper Gastrointestinal Tract to Support Formulation Development and Establish Bioequivalence of Poorly Soluble Drugs

In recent years mechanical systems have been developed that more closely mimic the full dynamic, physical and biochemical complexity of the GI Tract. The development of these complex systems raises the possibility that they could be used to support formulation development of poorly soluble compounds and importantly may be able to replace clinical BE studies in certain circumstances. The ability of the TNO Simulated Gastro-Intestinal Tract Model 1 (TIM-1) Dynamic Artificial Gastrointestinal System in the 'lipid membrane' configuration to support the development of Biopharmaceutics Classification System Class 2 compounds was investigated by assessing the performance of various AZD8055 drug forms and formulations in the TIM-1 system under standard fasting and achlorhydric physiological conditions. The performance data were compared with exposure data from the phase 1 clinical study. Analysis of the AZD8055 plasma concentrations after tablet administration supported the conclusions drawn from the TIM-1 experiments and confirmed that these complex systems can effectively support the product development of poorly soluble drugs. Particularly, the TIM-1 system was able to show that AZD8055 exposure would increase in an approximately dose proportional manner and not be limited by the solubility or dissolution. Additionally, the investigations also showed that the exposure produced by a solution and a tablet would be the same. Specific instances when the TIM-1 system may not be predictive of clinical product performance have also been identified.

Optimization of a cryoprotective medium for infant formula probiotic applications using response surface methodology

The paper focuses on the development of a cryoprotective drying medium suitable for the application of probiotics in infant formulae. Response surface methodology was used to optimize the concentrations of skim milk and prebiotics for maximizing the survival of the probiotic Bifidobacterium lactis DSM 10140 during freeze-drying. The optimal combination was found to be 15.0% skim milk blended with 3.4% prebiotics, which protected viability in 62.16% of cells. There was no significant difference (p > 0.05) between the experimental and predicted values, thereby verifying the model adequacy. The stability of the freeze-dried cells in the optimal combination of drying medium was examined under different conditions of rehydration and storage and in a simulated gastrointestinal tract model. The results showed that optimized drying medium could increase the viability of freeze-dried stationary phase cells by 1.34 log (CFU/ml) as compared to phosphate buffer after 120 days of storage at 4°C. However, with increasing temperature to 25°C, the protective effect of the optimized medium was more obvious. The optimized drying medium was also able to reduce the mortality rate of cells after sequential incubation under simulated infantile gastrointestinal conditions, including gastric conditions (pH 3.0 and 4.0, 90 min) and intestinal conditions (pH 7.5, 5 h) by 1.24 and 0.57 log (CFU/ml), respectively, compared to the control.

Probiotic lactobacilli in a semi-soft cheese survive in the simulated human gastrointestinal tract

In this study, probiotics Lactobacillus acidophilus NCFM and Lactobacillus rhamnosus HN001 in cheese were studied using models simulating the human gastrointestinal tract with the aim of investigating whether the cheese matrix affected the survival and metabolic properties of these probiotic strains. Probiotics in cheese survived in the simulated upper gastrointestinal tract model, and numbers of L. acidophilus, L. rhamnosus and total lactobacilli were increased in the colonic fermentation simulations of the probiotic cheese when compared with the non-probiotic cheese used as a control. The cheese matrix also beneficially affected cyclooxygenase-gene expression of colonocytes in a cell culture model. Freeze-dried probiotics, which were also analysed in the colonic simulator, showed similar changes in Lactobacillus numbers, although gave a stronger increase and also affected other microbial groups. These results indicate that the probiotic microbes in cheese survive in the gastrointestinal tract and that the cheese matrix does not seem to affect the probiotic survival.