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In our previous study (Mustan et al. 2021) we showed that foams formed from two oil-soluble nonionic surfactants (Span 60 and Brij 72) can remain stable for more than 10 days at room temperature at high sugar concentration. The major aim of the current study is to reveal the interrelation between the surfactant structure and foam stability by investigating 6 polyoxyethelene alkyl ethers and 12 fatty acid esters with a wide variety of hydrophobic chain lengths (C12; C16; C18 and C18:1) and hydrophilic head-groups (sorbitol, glycerol, sucrose). Foams stable for more than 100 days at room temperature are obtained when sucrose palmitate or stearate (P1670 or S1670) are used as surfactants. This exceptional foam stability is related to the gelation of the aqueous phase and to the formation of solid adsorption layer with zero surface tension upon compression, thus preventing water drainage and decelerating the bubble Ostwald ripening. The foam stability decreases with (i) increasing the number of EO groups in polyoxyethylene alkyl ethers and in fatty acid sorbitan esters; (ii) decreasing the number of C-atoms in the surfactant tail for all studied surfactants; (iii) addition of double bond in the surfactant tail. The lower foam stability in all three cases is related to the worse packing of the surfactant molecules within the adsorption layer, leading to faster Ostwald ripening and subsequent bubble coalescence. The diesters present as admixture in the fatty acid esters play an important role in the foam stabilization by further compacting the adsorption layers and lowering the rate of Ostwald ripening. These conclusions can be used as a predictive tool for surfactant selection in the development of food or pharmaceutical foam concentrates that can be diluted before final use.

The surface and foam properties of two oil-soluble surfactants, Span 60 and Brij 72, and two water-soluble surfactants, Tween 60 and Brij S20, are compared. Aqueous surfactant solutions containing sugar at high concentration (63 wt %) are also studied in the context of sweet food-related foams. The experimental results show that foams with very small bubbles of ca. 5 µm are formed and remain stable for more than 10 days at room temperature when oil-soluble surfactants are dispersed in the sugar-rich solutions. The excellent stability of these foams is related to (1) The multilamellar vesicles present in the respective surfactant dispersions which increase the viscosity and decrease the rate of water drainage from the foam; (2) The very slow exchange of surfactant molecules between the interface and the adjacent aqueous solution that leads to very significant difference in the surface tension of shrinking and expanding bubbles, which in turn decreases the rate of bubble Ostwald ripening. The foams formed from Span 60 are more stable as compared to the foams formed from Brij 72, due to the higher viscosity and the slower interface-solution exchange. The foams formed from Brij S20 solutions are least stable - they are completely destroyed after 1 day at room temperature, even in the presence of sugar. The main conclusion of this study is that oil soluble surfactants can form condense adsorption layers on the bubble surfaces after adsorption from aqueous solutions with and without sugar in it. The formed layers, which present a better molecular packing, reduce the gas permeability and decelerate the Ostwald ripening disproportionation of the foam This is obtained by a relatively low interfacial tension imparted by continuous shrinkage and expansion of bubbles during foam generation, ultimately ensuring long-term stabilization of formed foams.

Whilst aeration is ubiquitous in the food industry, little work has been done on foams generated from viscous non-Newtonian liquids. We study the production of foams from viscous shear-thinning liquids containing a non-ionic food grade surfactant (PGE 55), Xanthan gum and caster sugar, using a continuous pilot-scale device having twelve rotor-stator pairs. The effects of process parameters (rotor speed, gas-liquid volumetric flowrate ratio (G/L)) and liquid composition (surfactant concentration, Xanthan gum concentration) on foam gas volume fraction and bubble size distribution are elucidated. X-ray micro-Computed Tomography is employed to characterise the 3D microstructure of the foams. Rotor speed and G/L ratio are the dominant factors in determining the gas volume fraction and bubble size distribution. The foams produced exhibit a rich fine texture with high static stability. For a given energy input in turbulent flow, a higher G/L ratio results in a higher gas fraction and a smaller bubble size. Industrial relevance Aeration is ubiquitous in the food industry and innovative ways to generate stable foams with fine texture from viscous non-Newtonian media are needed to satisfy the increasing demand for better quality, healthier and cheaper products. The use of continuous multi rotor-stator devices operating in turbulent flow and under atmospheric pressure achieves optimum aeration efficiency and prevents foam expansion. The use of an effective surfactant such as PGE 55 and a thickener such as Xanthan gum help provide the desired fine texture and stability for longer shelf-life. Operating at high gas-liquid ratios in turbulent flow achieves the production of finer more uniform foams with less energy input.

There is considerable interest in manipulating the behavior of dietary emulsions in the human stomach as a means of altering satiating properties of fatty foods. However assessing this using intubation markedly disturbs normal gastric motility so a non-invasive imaging approach has a strong rationale. Two 20% sunflower oil-in-water fat emulsions test meals with different droplet sizes (termed Fine and Coarse) and intragastric behaviors were used to demonstrate, for the first time, the feasibility of carrying out magnetic resonance spectroscopy (MRS) measurements of fat emulsions fat fraction, in vivo, in the gastric lumen of six healthy volunteers. Magnetic resonance imaging (MRI) confirmed that as expected the fine emulsion remained mostly homogeneously distributed inside the stomach over the course of 3 h but the Coarse quickly creamed showing an upper layer much richer in fat. The MRS measurements showed that the Coarse emulsion had an upper layer of high lipid/water ratio compared to the lower layer. The fine emulsion fat fraction values remained stable throughout the study with no difference between upper and lower layers. It is therefore possible to quantify in vivo, in the gastric lumen, the intragastric fat fraction of oil-in-water fat emulsions using non invasive MRS techniques. Practical applications: This study shows that it is possible to quantify in vivo, in the gastric lumen, the intragastric fat fraction of oil-in-water fat emulsions using non invasive magnetic resonance spectroscopy techniques. These measurements can help improve understanding of intragastric distribution of fat, its relation to satiety, can improve the relevance of in vitro/in vivo models of fat digestion, and will ultimately aid the design of foods with desired health promoting characteristics and check their performance in vivo. Two 20% sunflower oil-in-water fat emulsions test meals with different droplet sizes and intragastric behaviours are used to demonstrate, for the first time, the feasibility of carrying out magnetic resonance spectroscopy (MRS) measurements of fat emulsions fat fraction, in vivo, in the gastric lumen of six healthy volunteers.

Unexplained nausea and vomiting is often associated with delayed gastric emptying in patients with functional dyspepsia. We hypothesized that the experience of an unpleasant, nauseating taste could lead to a delay in gastric emptying.Sixteen healthy women consumed a bland liquid test meal on three separate study days. On two of the study days subjects sham fed either a bitter tasting, modified Slim-Fast bar or one with a pleasant strawberry flavour. The time for 50% gastric emptying (GE(50)) was non-invasively assessed by electrical impedance tomography and antral motility by electrogastrography (EGG).Gastric emptying was significantly delayed by sham feeding the bitter compared with the pleasant bar, GE(50) 24.7+/-3.9 versus 17.2+/-1.8 min, P0.05. EGG power rose significantly during both the pleasant (basal 1.46+/-0.07 to 2.33+/-0.14 log(10) microV(2)/min, P=0.000) and the bitter sham feed (basal 1.64+/-0.09 to 2.35+/-0.11 log(10) microV(2)/min, P=0.000).An unpleasant bitter taste delays gastric emptying but does not significantly impair antral motility.

Background: Intragastric creaming and droplet size of fat emulsions may affect intragastric behavior and gastrointestinal and satiety responses. Objectives: We tested the hypotheses that gastrointestinal physiologic responses and satiety will be increased by an increase in intragastric stability and by a decrease in fat droplet size of a fat emulsion. Methods: This was a double-blind, randomized crossover study in 11 healthy persons [8 men and 3 women, aged 24 ± 1 y; body mass index (in kg/m2): 24.4 ± 0.9] who consumed meals containing 300-g 20% oil and water emulsion (2220 kJ) with 1) larger, 6-μm mean droplet size (Coarse treatment) expected to cream in the stomach; 2) larger, 6-μm mean droplet size with 0.5% locust bean gum (LBG; Coarse+LBG treatment) to prevent creaming; or 3) smaller, 0.4-μm mean droplet size with LBG (Fine+LBG treatment). The participants were imaged hourly by using MRI and food intake was assessed by using a meal that participants consumed ad libitum. Results: The Coarse+LBG treatment (preventing creaming in the stomach) slowed gastric emptying, resulting in 12% higher gastric volume over time (P < 0.001), increased small bowel water content (SBWC) by 11% (P < 0.01), slowed appearance of the 13C label in the breath by 17% (P < 0.01), and reduced food intake by 9% (P < 0.05) compared with the Coarse treatment. The Fine+LBG treatment (smaller droplet size) slowed gastric emptying, resulting in 18% higher gastric volume (P < 0.001), increased SBWC content by 15% (P < 0.01), and significantly reduced food intake by 11% (P < 0.05, equivalent to an average of 411 kJ less energy consumed) compared with the Coarse+LBG treatment. These high-fat meals stimulated substantial increases in SBWC, which increased to a peak at 4 h at 568 mL (range: 150–854 mL; P < 0.01) for the Fine+LBG treatment. Conclusion: Manipulating intragastric stability and fat emulsion droplet size can influence human gastrointestinal physiology and food intake.

Viscosity, taste and aroma are key attributes of food. Functional magnetic resonance imaging (fMRI) is increasingly used to investigate the cortical brain response to taste and aroma; however hitherto, the response to food viscosity has been the subject of only one fMRI study. This study aims to investigate the cortical response to oral viscosity in humans using wide brain coverage and multi-echo acquisition techniques to improve sensitivity across a range of brain regions to confirm and extend previous findings. The stimulus used was an alginate gel compared to a water control. Activation was detected by group analysis in the right postcentral gyrus/somatosensory cortex, in the right rolandic operculum/parietal operculum cortex and in a more anterior part of the left insula. No activation was detected in the orbitofrontal cortex. PRACTICAL APPLICATIONS Recent neuroimaging studies have begun to unravel the cortical representation of taste and aroma stimuli, detecting brain activation in primary sensory and secondary association areas, as well as those cortical areas associated with reward and emotional behavior. Functional magnetic resonance imaging techniques, as shown here, can be easily extended to the study of the cortical response to oral viscosity, thus adding a unique tool to the field of texture studies.