Matt Golding

A standardised static in vitro digestion method suitable for food-an international consensus

Simulated gastro-intestinal digestion is widely employed in many fields of food and nutritional sciences, as conducting human trials are often costly, resource intensive, and ethically disputable. As a consequence, in vitro alternatives that determine endpoints such as the bioaccessibility of nutrients and non-nutrients or the digestibility of macronutrients (e.g. lipids, proteins and carbohydrates) are used for screening and building new hypotheses. Various digestion models have been proposed, often impeding the possibility to compare results across research teams. For example, a large variety of enzymes from different sources such as of porcine, rabbit or human origin have been used, differing in their activity and characterization. Differences in pH, mineral type, ionic strength and digestion time, which alter enzyme activity and other phenomena, may also considerably alter results. Other parameters such as the presence of phospholipids, individual enzymes such as gastric lipase and digestive emulsifiers vs. their mixtures (e.g. pancreatin and bile salts), and the ratio of food bolus to digestive fluids, have also been discussed at length. In the present consensus paper, within the COST Infogest network, we propose a general standardised and practical static digestion method based on physiologically relevant conditions that can be applied for various endpoints, which may be amended to accommodate further specific requirements. A frameset of parameters including the oral, gastric and small intestinal digestion are outlined and their relevance discussed in relation to available in vivo data and enzymes. This consensus paper will give a detailed protocol and a line-by-line, guidance, recommendations and justifications but also limitation of the proposed model. This harmonised static, in vitro digestion method for food should aid the production of more comparable data in the future.

Impact of Oil Type on Nanoemulsion Formation and Ostwald Ripening Stability

The formation of stable transparent nanoemulsions poses two challenges: the ability to initially create an emulsion where the entire droplet size distribution is below 80 nm, and the subsequent stabilization of this emulsion against Ostwald ripening. The physical properties of the oil phase and the nature of the surfactant layer were found to have a considerable impact on nanoemulsion formation and stabilization. Nanoemulsions made with high viscosity oils, such as long chain triglycerides (LCT), were considerably larger ( D = 120 nm) than nanoemulsions prepared with low viscosity oils such as hexadecane ( D = 80 nm). The optimization of surfactant architecture, and differential viscosity eta D/eta C, has led to the formation of remarkably small nanoemulsions. With average sizes below 40 nm they are some of the smallest homogenized emulsions ever reported. What is more remarkable is that LCT nanoemulsions do not undergo Ostwald ripening and are physically stable for over 3 months. Ostwald ripening is prevented by the large molar volume of long chain triglyceride oils, which makes them insoluble in water thus providing a kinetic barrier to Ostwald ripening. Examination of the Ostwald ripening of mixed oil nanoemulsions found that the entropy gain associated with oil demixing provided a thermodynamic barrier to Ostwald ripening. Not only are the nanoemulsions created in this work some of the smallest reported, but they are also thermodynamically stable to Ostwald ripening when at least 50% of the oil phase is an insoluble triglyceride.

Oral sensitivity to fatty acids, food consumption and BMI in human subjects

Fatty acids are the chemical moieties that are thought to stimulate oral nutrient sensors, which detect the fat content of foods. In animals, oral hypersensitivity to fatty acids is associated with decreased fat intake and body weight. The aims of the present study were to investigate oral fatty acid sensitivity, food selection and BMI in human subjects. The study included two parts; study 1 established in thirty-one subjects (29 (sem 1.4) years, 22.8 (sem 0.5) kg/m2) taste thresholds using 3-AFC (3-Alternate Forced Choice Methodology) for oleic, linoleic and lauric acids, and quantified oral lipase activity. During study 2, fifty-four subjects (20 (sem 0.3) years, 21.5 (sem 0.4) kg/m2) were screened for oral fatty acid sensitivity using oleic acid (1.4 mm), and they were defined as hypo- or hypersensitive via triplicate triangle tests. Habitual energy and macronutrient intakes were quantified from 2 d diet records, and BMI was calculated from height and weight. Subjects also completed a fat ranking task using custard containing varying amounts (0, 2, 6 and 10 %) of fat. Study 1 reported median lipase activity as 2 mumol fatty acids/min per l, and detection thresholds for oleic, linoleic and lauric acids were 2.2 (sem 0.1), 1.5 (sem 0.1) and 2.6 (sem 0.3) mm. Study 2 identified twelve hypersensitive subjects, and hypersensitivity was associated with lower energy and fat intakes, lower BMI (P < 0.05) and an increased ability to rank custards based on fat content (P < 0.05). Sensitivity to oleic acid was correlated to performance in the fat ranking task (r 0.4, P < 0.05). These data suggest that oral fatty acid hypersensitivity is associated with lower energy and fat intakes and BMI, and it may serve as a factor that influences fat consumption in human subjects.

Depletion flocculation of emulsions containing unadsorbed sodium caseinate

Abstract The influence of unadsorbed protein on the stability of fine oil-in-water emulsions containing sodium caseinate has been investigated. Time-dependent creaming profiles were determined at 30°C using the ultrasound velocity scanning technique. The results show that, at a protein concentration (2% w/w) around that required for nearly saturation coverage of droplets, emulsion stability with respect to creaming is good (30 days), with no indication of flocculation or coalescence. At a higher protein concentration (4% w/w), corresponding to considerably more protein than required for saturation coverage, creaming stability is reduced, with rapid development of a serum layer within 20 h of emulsion preparation. Further increase in protein concentration (e.g. to 6% w/w) results in partial restabilization of the emulsion through the formation of a weak particle network gel. Complementary rheological studies have shown that increasing protein concentration results in pseudoplastic emulsions with significantly higher low-shear viscosities. This behaviour, directly confirmed by light microscopy, is attributed to reversible depletion flocculation of the emulsions by protein remaining unadsorbed in the aqueous phase. It is suggested that aggregation of caseinate to form sub-micelles causes depletion by small particles in a manner similar to that observed previously for micelle-containing small-molecule surfactant-stabilized systems.

Impact of gastric structuring on the lipolysis of emulsified lipids

Understanding and manipulating how emulsion structure impacts on fat digestion is an important step towards understanding the role of fat in our diet. This article reports on the nature of emulsion structuring within the digestive tract and how it affects the dynamics of fat digestion. Emulsions were designed a priori to have specific structuring behaviours (stable, coalesced, partially coalesced and fully broken) under gastrointestinal conditions, through careful emulsifier selection and control of solid fat composition. The impact these structures had on lipolysis was then assessed in vitro using a digestion model and in vivo by measuring the postprandial change in blood triglyceride concentration as a marker of fat absorption. The major factor controlling the rate of fat digestion in vitro was the droplet surface area available for lipase adsorption, which was governed by emulsion instability. The rate of fat absorption in vivo was only affected by large changes in the droplet surface area, and only if these changes remained until the droplets reached the small intestine. This was most evident in emulsions that had undergone extensive partial coalescence under gastric conditions. Partial coalescence resulted in a dramatic reduction in triglyceride absorption, in part because the network of fat crystals provided the agglomerates with an internal scaffold to resist re-dispersion as they passed through the pylorus. The differences in fat absorption profile achieved by controlling emulsion structural stability during digestion provide a basis for examining the physiological effects of food structure on lipid metabolism, which will be the subject of a follow-up clinical paper.

The droplet size of intraduodenal fat emulsions influences antropyloroduodenal motility, hormone release, and appetite in healthy males

BACKGROUND The presence of fat in the small intestine modulates gastrointestinal motility, stimulates plasma cholecystokinin and peptide YY release, and suppresses appetite and energy intake. These effects are dependent on the lipolysis of fat. OBJECTIVE Our aim was to evaluate the hypothesis that increasing the droplet size of a fat emulsion would attenuate these effects. DESIGN Ten healthy, lean males were studied on 4 separate occasions in single-blind randomized order. Antropyloroduodenal pressures, plasma triglycerides, cholecystokinin, peptide YY, and appetite were measured during 120-min intraduodenal infusions of fat emulsions comprising 3 different droplet sizes: 1) 0.26 microm (LE-0.26), 2) 30 microm (LE-30), and 3) 170 microm (LE-170) in addition to saline (control). Energy intake at a buffet lunch was quantified immediately after the infusions. RESULTS Increasing the droplet size of the lipid emulsion was associated with diminished suppression of antral (r = 0.75, P < 0.01) and duodenal (r = 0.80, P < 0.01) pressure waves and with stimulation of isolated (r = -0.72, P < 0.01) and basal (r = -0.83, P < 0.01) pyloric pressures. Increasing the droplet size was also associated with attenuation of the stimulation of plasma triglycerides (r = -0.73, P < 0.001), cholecystokinin (r = -0.73, P < 0.001), and peptide YY (r = -0.83, P < 0.001) as well as with reductions in the suppression of hunger (r = 0.75, P < 0.01) and energy intake (r = 0.66, P < 0.001). CONCLUSIONS The acute effects of intraduodenal fat emulsions on gastrointestinal function and appetite are dependent on fat droplet size. These observations have implications for the design of functional foods to maximize effects on those gut functions that are involved in the suppression of appetite.

Development of a standardized low-dose double-blind placebo-controlled challenge vehicle for the EuroPrevall project

To cite this article: Cochrane SA, Salt LJ, Wantling E, Rogers A, Coutts J, Ballmer‐Weber BK, Fritsche P, Fernández‐Rivas M, Reig I, Knulst A, Le T‐M, Asero R, Beyer K, Golding M, Crevel R, Clare Mills EN, Mackie AR. Development of a standardized low‐dose double‐blind placebo‐controlled challenge vehicle for the EuroPrevall Project. Allergy 2012; 67: 107–113.

Slowly and Rapidly Digested Fat Emulsions Are Equally Satiating but Their Triglycerides Are Differentially Absorbed and Metabolized in Humans

Little is known about the effect of dietary fat emulsion microstructure on plasma TG concentrations, satiety hormones, and food intake. The aim of this study was to structure dietary fat to slow digestion and flatten postprandial plasma TG concentrations but not increase food intake. Emulsions were stabilized by egg lecithin (control), sodium sterol lactylate, or sodium caseinate/monoglyceride (CasMag) with either liquid oil or a liquid oil/solid fat mixture. In a randomized, double-blind, crossover design, 4 emulsions containing 30 g of fat in a 350-mL preload were consumed by 10 men and 10 women (BMI = 25.1 ± 2.8 kg/m(2); age = 58.8 ± 4.8 y). Pre- and postprandial plasma TG, cholecystokinin (CCK), glucagon-like peptide-1 (GLP-1), and peptide YY (PYY) concentrations and food intake were measured. In a second experiment in a subset of the participants (n = 8, 4 men and 4 women), (13)C-labeled mixed TG was incorporated into 2 different emulsions and breath (13)C was measured over 6 h. In the first experiment, the postprandial rise in plasma TG concentrations following the CasMag-stabilized emulsion containing 30% solid fat was lower than all other emulsions at 90 and 120 min (P < 0.05). Plasma CCK (P < 0.0001), GLP-1 (P < 0.01), and PYY (P < 0.001) concentrations were also reduced following this emulsion compared with control. Food intake at a test meal, eaten 3 h after the preload, did not differ among the emulsions. In the second experiment, when measured by the (13)C breath test, 25% of the TG in the CasMag emulsion was absorbed and metabolized compared with control. In conclusion, fat can be structured to decrease its effect on plasma TG concentrations without increasing food intake.

A comparison of the organization of longitudinal and circular contractions during pendular and segmental activity in the duodenum of the rat and guinea pig

Background  Little is known of the spatiotemporal organization of pendular duodenal contractions.

Ultrasonic spectroscopy studies of casein in water

A new ultrasound spectroscopy apparatus is described and the theory underlying its use is outlined. Application of the technique to sodium caseinate solutions reveals a trimodal size distribution with the largest particles disappearing slowly with time. The results indicate that ultrasound spectroscopy is sensitive to the degree of hydration of caseinate and therefore would be potentially useful in measuring dissolution kinetics.