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The Physics of Digestion
Alan [email protected]
Introduction
• Digestion is a complex process but the ability to predict digestion kinetics would be helpful for both Food and Pharma applications
• Surprisingly transport phenomena in the gut are still not well-understood processes
• Can multi-scale approaches help us understand gastrointestinal digestion and thus risk factors for non-communicable disease?
Stomach volume changing with time (as highlighted)
Measuring Changes in Stomach Volume
Two isocaloric meals: The impact on Gastric retention
Liquid - - - - , Solid t½ = 70 min. and 100 min.
Gastric Processing
Ferrua et al. Trends in Food Science & Technology. (2011) 22(9) 480–491
• Preparing interfacial scenario for colipase/lipase adsorption– Further emulsification of lipids
– Desorption of surface active agents
• Solubilisation of hydrolysed lipids
Lipid digestion
+ 2H+
Triglyceride (TG)Monoglyceride (MG)
Free fatty acids (FFA)
Stomach
Undispersed oil
Gastric lipase
Oil droplets
Pancreas
Small intestine
Liver
Gall bladder
Lipid
droplet
(TG)
Pancreatic lipaseColipase
BS
Mixed micelle of BS and hydrolysed lipids
Lipid digestion
Products are mixed by intestinal contractions and then must diffuse through the intestinal mucus layer to be absorbed
What factors affect the kinetics of this mixing and diffusion?
Nutrient transport and mixing
27/01/20208
Nutrient transport and mixing
Displacement of a diffusive probe (D =3×10−10 m2 s−1), initially aligned in a horizontal plane, during a contraction and relaxation cycle with finger-like aligned villi with
(a) Newtonian (left)
(b) Shear-thinning (n = 0.4, ˙γc = 0.01) fluids. Colour keys are the concentration. (right)
Diffusion coefficients of sodium alginate in ex vivo mucus or buffer as measured by FRAP
Diffusion of sodium alginate through mucus
Does Alginate stick to intestinal mucus?
QCM measurements of mucin absorption followed by the introduction of alginate above the absorbed layer
Intestinal Mucus permeability
Measuring particle diffusion
Mean square displacement
(MSD) <Δr2(Δt)> = <Δx2 + Δy2>
Deff = MSD/4Δt= kT/6πr
viscosity
The effect of food components on gut mucus permeability
Using pigs as a model system
Increasing dietary oat fibre decreases the permeability of intestinal mucus
100 nm bile salt coated carboxylated polystyrene beads through small intestinal mucus ex vivo from pigs fed Control (open circles) or OM10 diets (closed circles).
Increasing dietary oat fibre decreases intestinal mucus permeability
The data from this study showed that increasing dietary fibre reduced mass transfer of lipid through the intestinal mucus layer. Journal of Functional Foods 26 (2016) 418–427
Fluorescently labelledlipid from the pig diet
Diffusion coefficient of 500nm latex beads plotted as a function of polymer concentration.
Water
DNA
mucin ex vivo mucus
The role of endogenous polymers
Conclusions
• Digestion is a complex process / series of processes.• Kinetics is important for health.• Gastric emptying is a significant controller of digestion kinetics but
what are the factors driving gastric emptying rate?• Mixing and rheological properties are key controllers of digestion
and absorption (fluid dynamics).• Finally, diffusion of nutrients and bioactives through the unstirred
mucus layer can also have a significant impact on absorption and bioavailability.
Acknowledgements
My Staff and Colleagues at Quadram and Leeds
Adam Macierzanka, Balazs Bajka, Neil Rigby, Louise Salt, Pete Wilde, Mike Ridout, and many others
Alan Mackie: [email protected]