Effect of carrot (Daucus carota) microstructure on carotene bioaccessibility in the upper gastrointestinal tract. 2. In vivo digestions.

Nutrient bioaccessibility and subsequent absorption will be directly influenced by changes in food structure during gastrointestinal processing. The accompanying paper (Tydeman et al. J. Agric. Food Chem. 2010, 58, doi: 10.1021/jf101034a) reported results on the effect of carrot processing on the release of carotene into lipid phases during in vitro gastric and small intestinal digestions. This paper describes results from in vivo digestion of two of the types of processed carrot used previously, raw grated carrot and cooked carrot mashed to a puree. Ileostomy effluents from human volunteers fed meals containing the carrot material were used to study tissue microstructure and carotene release. Raw carrot shreds and intact cells that had survived the pureeing process were identifiable in ileal effluent. The gross tissue structure in the shreds had not changed following digestion. Carotene-containing particles remained encapsulated in intact cells, but were absent from ruptured cells. Microscopy revealed marked changes to the cell walls including swelling and pectin solubilization, which increased in severity with increasing residence time in the upper gut. These observations were entirely consistent with the in vitro observations. It was concluded that a single intact cell wall is sufficient to reduce carotene bioaccessibility from a cell by acting as a physical barrier, which is not broken down during upper gut digestion.

Effect of carrot (Daucus carota) microstructure on carotene bioaccessibilty in the upper gastrointestinal tract. 1. In vitro simulations of carrot digestion.

Studies investigating carotene bioaccessibility (release from the food matrix to a solubilized form) directly from plant material during the process of digestion are scarce, mainly due to the difficulties associated with obtaining such material. Therefore, this paper examines the relationship between tissue microstructure and carotene bioaccessibility using an in vitro digestion model. Dietary oil provides a pool for the initial solubilization. Therefore, carotene partitioning into an emulsified oil phase was assessed using raw carrot tissue and carrot tissue subjected to various degrees of heating and particle size reduction and, in all cases, was found to be greatly reduced compared with juiced carrot. Carotene bioaccessibility was found to be greater from raw tissues than heated tissues of the same size. This is because heating increases the propensity for intact cells to separate, effectively encapsulating the carotene. Although the gross structure of the tissues was found to be relatively unaffected by in vitro digestion, at the cellular level some cell-wall swelling and cell death were observed, particularly close to the surfaces of the tissue. This study suggests that cell-wall rupture prior to digestion is an absolute requirement for carotene bioaccessibility in the upper intestine and that heating does not enhance carotene release from intact cells.

Effect of intragastric acid stability of fat emulsions on gastric emptying, plasma lipid profile and postprandial satiety.

Fat is often included in common foods as an emulsion of dispersed oil droplets to enhance the organoleptic quality and stability. The intragastric acid stability of emulsified fat may impact on gastric emptying, satiety and plasma lipid absorption. The aim of the present study was to investigate whether, compared with an acid-unstable emulsion, an acid-stable fat emulsion would empty from the stomach more slowly, cause more rapid plasma lipid absorption and cause greater satiety. Eleven healthy male volunteers received on two separate occasions 500 ml of 15 % (w/w) [13C]palmitate-enriched olive oil-in-water emulsion meals which were either stable or unstable in the acid gastric environment. MRI was used to measure gastric emptying and the intragastric oil fraction of the meals. Blood sampling was used to measure plasma lipids and visual analogue scales were used to assess satiety. The acid-unstable fat emulsion broke and rapidly layered in the stomach. Gastric emptying of meal volume was slower for the acid-stable fat emulsion (P < 0.0001; two-way ANOVA). The rate of energy delivery of fat from the stomach to the duodenum was not different up to t = 110 min. The acid-stable emulsion induced increased fullness (P < 0.05), decreased hunger (P < 0.0002), decreased appetite (P < 0.0001) and increased the concentration of palmitic acid tracer in the chylomicron fraction (P < 0.04). This shows that it is possible to delay gastric emptying and increase satiety by stabilising the intragastric distribution of fat emulsions against the gastric acid environment. This could have implications for the design of novel foods.

Enhancement of intragastric acid stability of a fat emulsion meal delays gastric emptying and increases cholecystokinin release and gallbladder contraction.

Preprocessed fatty foods often contain calories added as a fat emulsion stabilized by emulsifiers. Emulsion stability in the acidic gastric environment can readily be manipulated by altering emulsifier chemistry. We tested the hypothesis that it would be possible to control gastric emptying, CCK release, and satiety by varying intragastric fat emulsion stability. Nine healthy volunteers received a test meal on two occasions, comprising a 500-ml 15% oil emulsion with 2.5% of one of two emulsifiers that produced emulsions that were either stable (meal A) or unstable (meal B) in the acid gastric environment. Gastric emptying and gallbladder volume changes were assessed by MRI. CCK plasma levels were measured and satiety scores were recorded. Meal B layered rapidly owing to fat emulsion breakdown. The gastric half-emptying time of the aqueous phase was faster for meal B (72 +/- 13 min) than for meal A (171 +/- 35 min, P < 0.008). Meal A released more CCK than meal B (integrated areas, respectively 1,095 +/- 244 and 531 +/- 111 pmol.min.l(-1), P < 0.02), induced a greater gallbladder contraction (P < 0.02), and decreased postprandial appetite (P < 0.05), although no significant differences were observed in fullness and hunger. We conclude that acid-stable emulsions delayed gastric emptying and increased postprandial CCK levels and gallbladder contraction, whereas acid-instability led to rapid layering of fat in the gastric lumen with accelerated gastric emptying, lower CCK levels, and reduced gallbladder contraction. Manipulation of the acid stability of fat emulsion added to preprocessed foods could maximize satiety signaling and, in turn, help to reduce overconsumption of calories.

Magnetic resonance imaging of the behaviour of oil-in-water emulsions in the gastric lumen of man.

Pre-processed foods often contain a high percentage of lipid, present as emulsions stabilised with various surface-active agents. The acidic gastric environment can affect the behaviour of such emulsions, modifying the lipid spatial distribution and, in turn, the rate of gastric emptying and nutrient delivery to the gut. The aim of the present study was to use echo-planar magnetic resonance imaging (EPI) to determine the behaviour of model olive oil emulsions during gastric processing. Six healthy male volunteers were intubated nasogastrically on two separate occasions and fed 500 ml 15 % (w/w) olive oil-in-water, surfactant-stabilised emulsions designed to have identical droplet size distribution and which were either stable or unstable under gastric acid conditions. EPI was used to assess the oil fraction of the intragastric emulsions, gastric emptying and to visualise the spatial distribution of the oil at 10, 30 and 50 min postprandially. The in vivo imaging measurements of the oil volume fraction of the emulsions correlated well (r 0.66, acid-stable; r 0.52, acid-unstable) with that assayed in the gastric aspirates. Compared with the acid-stable emulsion, the acid-unstable emulsion in the gastric lumen rapidly separated into lipid-depleted 'aqueous' and lipid layers. Phase separation in the acid-unstable meal allowed the oil-depleted component to empty first and more rapidly than the stable emulsion as determined by the gastric emptying curves. These pilot data suggest that gastric processing and emptying of high-fat foods could be manipulated by careful choice of emulsifier.

Monitoring of gallbladder and gastric coordination by EPI.

PURPOSE: To assess for the first time the potential of echo-planar magnetic resonance imaging (EPI) for measuring simultaneously both gallbladder and gastric emptying. MATERIALS AND METHODS: Eight healthy subjects ingested 500 mL of an acid-stable liquid test meal containing 15% olive oil and flavoring. Every 20 minutes for three hours thereafter, a rapid EPI multislice set was acquired across the whole abdomen, using a dedicated whole-body 0.5-T EPI scanner. RESULTS: The bile in the gallbladder and the test meal in the stomach appeared bright in the EPI images, aiding localization and region of interest analysis. We measured the gallbladder emptying curve and fitted the data to a simple analytical model. The mean fasted gallbladder volume was 25 +/- 4 mL, comparable to previously published MRI and ultrasound values. Gastric emptying data fitted well to a linear model linear (R2 = 0.99), and we observed an exponential (R2 = 0.98) relationship between gallbladder and gastric volumes for the first 90 minutes. CONCLUSION: This study shows the potential of EPI to monitor simultaneously and noninvasively the emptying of the gallbladder and of the gastric lumen. No contrast enhancing agents are needed. This method could overcome the limitations of previous gamma scintigraphy and ultrasound techniques.

Solubilization of carotenoids from carrot juice and spinach in lipid phases: I. Modeling the gastric lumen.

Our understanding of the factors determining the bioavailability of carotenoids from fruits and vegetables is poor. The apolar nature of carotenoids precludes their simple diffusion from the food structure to the absorption site at the enterocyte. Therefore, there is interest in the potential pathways for solubilization in the gut before absorption. We have studied the transfer of carotenoids from carrot juice and homogenized spinach into lipid phases that mimic the intestinal lumen at the start of digestion. In this paper we report on their transfer into olive oil under conditions pertaining to the gastric environment. A comparison between preparations of raw spinach and of carrot, in which the intact cells have been largely broken, suggests that the membrane-bound carotenoids of spinach are more resistant to transfer than the crystalline carotenoids of carrot. Lowering the pH and pepsin treatment enhance the transfer from raw vegetables. The process of blanching and freezing spinach destroys the chloroplast ultrastructure and leads to (i) a substantial increase in transfer of the carotenoids to oil and (ii) an attenuation or reversal of the enhancement of transfer seen with reduced pH or with pepsin treatment. Similar effects are seen after blanching carrot juice. Our results show that removal of soluble protein and denaturation of membrane proteins enhances the partition of carotenoids into oil. For both vegetables there is no evidence of preference in the extent of transfer of one carotenoid over another. This suggests that partitioning into oil under gastric conditions is not the stage of digestion that could lead to differences in carotenoid bioavailability.

Solubilization of carotenoids from carrot juice and spinach in lipid phases: II. Modeling the duodenal environment.

We have been investigating the factors determining the bioavailability of carotenoids from vegetables. The previous paper [Rich, G.T., Bailey, A.L., Faulks, R.M., Parker, M.L., Wickham, M.S.J., and Fillery-Travis, A. (2003) Solubilization of Carotenoids from Carrot Juice and Spinach in Lipid Phases: I. Modeling the Gastric Lumen, Lipids 38, 933-945] modeled the gastric lumen and studied the solubilization pathway of carotenes and lutein from carrot juice and homogenized spinach to oil. Using the same vegetable preparations, we have extended our investigations to solubilization pathways potentially available in the duodenum and looked at the ease of solubilization of carotenes and lutein within simplified lipid micellar and oil phases present within the duodenum during digestion. Micellar solubility of raw spinach carotenoids was low and was enhanced by freezing, which involved a blanching step. The efficiency of solubilization of carotenoids in glycodeoxycholate micelles decreased in the order lutein(carrot) > lutein(blanched-frozen spinach) > carotene(blanched-frozen spinach) > carotene(carrot). Frozen spinach carotenoids were less soluble in simple micelles of taurocholate than of glycodeoxycholate. The results comparing the solubility of the carotenoids in mixed micelles (bile salt with lecithin) with simple bile salt micelles are explained by the relative stability of the carotenoid in the organelle compared to that in the micelle. The latter is largely determined by the polarity of the micelle. Below their critical micelle concentration (CMC), bile salts inhibit transfer of carotenoids from tissue to a lipid oil phase. Above their CMC, the bile salts that solubilize a carotenoid can provide an additional route to the oil from the tissue for that carotenoid by virtue of the equilibrium between micellar phases and the interfacial pathway. Mixed micellar phases inhibit transfer of both carotenoids from the tissue to the oil phase, thereby minimizing this futile pathway.

A physicochemical investigation of two phosphatidylcholine/bile salt interfaces: implications for lipase activation.

Within the gastrointestinal tract ingested lipids are broken down into their constituent mono-acylglycerides and fatty acids by the enzyme family of lipases. In this study we have investigated the interfacial composition and structure of two phospholipid/bile salt (BS) systems that display significant differences in the duration of the lag phase of porcine pancreatic lipase kinetics. The interfacial tension of the single BSs, and their binary mixtures with phospholipid is reported at an n-tetradecane/water interface as a function of phospholipid mole fraction and total surfactant concentration. The structuring of the interface was probed by characterisation of the thin liquid film formation, thickness and stability. Lateral interactions were quantified by measurement of the diffusion coefficient of a probe fluorophore. We conclude that interfacial tension was not a factor in lag time duration as there was no significant difference in the minimum interfacial tension for the phosphatidylcholine (PC)/sodium taurocholate and the PC/sodium taurodeoxycholate system. No correlation was found between lag phase duration and the physiochemical properties of the interface, i.e. lateral diffusion, thin liquid film formation or interfacial tension. This is in agreement with our previous study that the lag time duration was directly related to the phospholipid content of the interface.