Advances in Colloid and Interface Science (v.165, #1)

Food colloids 2010 - On the road from interfaces to consumers by Reinhard Miller; Miguel Cabrerizo Vílchez (1).

Eric Dickinson—Pioneer of food colloids by Brent S. Murray (2-6).

Trends and past achievements in the field of food colloids are reviewed. Specific mention is made of advances in knowledge and understanding in the areas of (i) structure and rheology of protein gels, (ii) properties of adsorbed protein layers, (iii) functionality derived from protein–polysaccharide interactions, and (iv) oral processing of food colloids. Amongst ongoing experimental developments, the technique of particle tracking for monitoring local dynamics and microrheology of food colloids is highlighted. The future outlook offers exciting challenges with expected continued growth in research into digestion processes, encapsulation, controlled delivery, and nanoscience.
Keywords: Biopolymers; Interactions; Emulsions; Foams; Droplets; Bubbles; Interfaces; Networks; Nanoparticles;

Interfacial & colloidal aspects of lipid digestion by P.J. Wilde; B.S. Chu (14-22).
Amongst the main issues challenging the food manufacturing sector, health and nutrition are becoming increasingly important. Global concerns such as obesity, the ageing population and food security will have to be addressed. Food security is not just about assuring food supply, but is also about optimising nutritional delivery from the food that is available . Therefore one challenge is to optimise the health benefits from the lipids and lipid soluble nutrients.Colloid scientists have an affinity for lipids because they are water insoluble, however this presents a challenge to the digestive system, which has to convert them to structures that are less insoluble so they are available for uptake. Despite this, the human digestive system is remarkably effective at digesting and absorbing most lipids. This is primarily driven through maximising energy intake, as lipids possess the highest calorific value, which was a survival trait to survive times of famine, but is now an underlying cause of obesity in developed countries with high food availability.The critical region here is the lipid-water interface, where the key reactions take place to solubilise lipids and lipid soluble nutrients. Digestive lipases have to adsorb to the oil water interface in order to hydrolyse triacylglycerols into fatty acids and mono glycerides, which accumulate at the interface [2], and inhibit lipase activity. Pancreatic lipase, which is responsible for the majority of lipid hydrolysis, also requires the action of bile salts and colipase to function effectively. Bile salts both aid the adsorption of co-lipase and lipase, and help solubilise the lipolysis products which have accumulated at the interface, into mixed micelles composing bile salts and a range of other lipids, to facilitate transport to the gut mucosal surface prior to uptake and absorption.The process can be affected by the lipid type, as shorter chain, fatty acids are more easily absorbed, whereas the uptake of longer chain fatty acids, particularly the very long chain n-3 fatty acids from fish oils are dependent on source and so may depend on food microstructure for optimal uptake . The uptake of some poorly water soluble nutrients are enhanced by the presence of lipids, but the mechanisms are not clear. In addition, controlling the digestion of lipids can be beneficial as slower release of lipids into the bloodstream can reduce risk of cardiovascular disease, and can promote gut feedback processes that reduce appetite.This presents an opportunity to colloid and interfacial science, as there are many unanswered questions regarding the specific physicochemical mechanisms underlying the process of lipid digestion and uptake. I will review our current knowledge of lipid digestion and present examples of how fundamental research in colloidal and interface science is beginning to address these issues. These include the adsorption behaviour of physiological surfactants such as bile salts; interfacial processes by which different polar lipids can influence lipolysis; and the effect of emulsion based delivery systems on cellular uptake of lipid soluble nutrients.A fundamental understanding of these processes is required if we are to develop intelligent design strategies for foods that will deliver optimal nutrition and improved health benefits in order to address the global challenges facing the food sector in the future.Display OmittedInterfacial processes underpinning lipid digestion► Interfacial mechanisms underlying physiological aspects of lipid digestion. ► Potential contributions of colloid and interface science to diet & health. ► Competitive adsorption of physiological surfactants influences lipid digestion.
Keywords: Food; Colloids; Interfaces; Lipid digestion;

Antihypertensive peptides: Production, bioavailability and incorporation into foods by Blanca Hernández-Ledesma; María del Mar Contreras; Isidra Recio (23-35).
Bioactive food peptides are encrypted within the sequence of food proteins but can be released during food processing (by enzymatic hydrolysis or fermentation) or during gastrointestinal transit. Among bioactive food peptides, those with antihypertensive activity are receiving special attention due to the high prevalence of hypertension in the Western countries and its role in cardiovascular diseases. This paper reviews the current literature on antihypertensive food peptides, focusing on the main methodologies for their production, such as enzymatic hydrolysis, fermentation and the use of recombinant bacteria. This paper also describes the structure/activity relationship of angiotensin-converting enzyme (ACE)-inhibitory peptides, as well as their bioavailability, physiological effects demonstrated by both in vitro and in vivo assays, and the contribution of mechanisms of action other than ACE inhibition. Finally, current reported strategies for incorporation of antihypertensive peptides into foods and their effects on both availability and activity are revised in this manuscript.Display Omitted► Complex interactions between food matrices and bioactive peptides may occur. ► Adequate products formulation is crucial to ensure bioactivity of peptides. ► Processing conditions and storage may affect to antihypertensive peptides in foods. ► Peptides may undergo physiological transformations that determine their bioactivity.
Keywords: Antihypertensive peptides; Angiotensin-converting enzyme inhibitory activity; Enzymatic hydrolysis; Fermentation; Bioavailability; Stability;

The role of bile salts in digestion by Julia Maldonado-Valderrama; Pete Wilde; Adam Macierzanka; Alan Mackie (36-46).
Bile salts (BS) are bio-surfactants present in the gastrointestinal tract (GIT) that play a crucial role in the digestion and absorption of nutrients. The importance of BS for controlled release and transport of lipid soluble nutrients and drugs has recently stimulated scientific interest in these physiological compounds. BS are so-called facial amphiphiles showing a molecular structure that is very distinct from classical surfactants. This peculiar molecular structure facilitates the formation of dynamic aggregates able to solubilise and transport lipid soluble compounds. The detergent nature of BS has been studied in the literature, mostly concentrating on the self-assembly behaviour of BS in solution but also in relation to protein denaturation and its effect on improving proteolysis. In contrast, the affinity of BS for hydrophobic phases has received less attention and studies dealing directly with the interfacial behaviour of BS are very limited in the literature. This is despite the fact that the interfacial activity of BS plays a vital role in fat digestion since it is closely involved with lypolisis. BS adsorb onto fat droplets and can remove other materials such as proteins, emulsifiers and lipolysis products from the lipid surface. The unusual surface behaviour of BS is directly related to their intriguing molecular structure and further knowledge could provide an improved understanding of lipid digestion. This review aims to combine the new insights gained into the surface properties of BS and their role in digestion. A better understanding of surface activity of BS would allow manipulation of physico-chemical and interfacial properties to modulate lipid digestion, improve bioavailability of lipid soluble nutrients and reduce absorption of saturated fats, cholesterol and trans fats.Display Omitted► The facial amphipathic structure of bile salts engenders unique surface properties. ► The interactions with phospholipids helps lipases gain access to lipid substrate. ► Bile salts can help to denature proteins for improved proteolysis. ► The charged nature of these amphiphiles is important for diffusion in the GI tract.
Keywords: Bile salt; Surface tension; Lipolysis; Digestion; GI tract;

Emulsion forms a major part of many processed food formulations. During the past few decades, the physico-chemical properties of oil-in-water emulsions under various food processing conditions have been extensively studied. However, over the recent years, interest has turned to understanding the behaviour of emulsions during consumption, i.e. physiological processing. In general, on ingestion, an emulsion is exposed to a relatively narrow range of physical (e.g. shear and temperature) and biochemical (e.g. dilution, pH, pepsin, pancreatin, mucins and bile salts) environments as it passes through the mouth into the stomach and then the intestines. There is currently limited knowledge of the physico-chemical and structural changes, which an emulsion may undergo when it passes through the physiologically active regime. A better understanding of the gastro-intestinal processing of emulsions would allow manipulation of physico-chemical and interfacial properties to modulate lipid ingestion, improve bioavailability of lipid soluble nutrients and reduce absorption of saturated fats, cholesterol and trans fats.Food emulsions are commonly stabilised by proteins, as they are not only excellent emulsifiers but also provide nutritional benefits to the product. The effects of digestion conditions on interfacial protein structures are complicated because of potential breakdown of these structures by proteolytic enzymes of the gastrointestinal tract. Studies dealing directly with the behaviour of protein-based emulsions under digestion conditions are very limited. This paper provides an overview of the behaviour of oil-in-water emulsions stabilised with globular proteins, namely lactoferrin and β-lactoglobulin. Recent advances in understanding the interactions between interfacial proteins on oil droplets and various physiological materials (e.g. enzymes and bile salts) in in vitro digestion systems are considered. Major emphasis is placed on the recent work carried out in our laboratory at Massey University on the behaviour of milk protein based emulsions (lactoferrin or β-lactoglobulin) during their passage through the gastro-intestinal tract.Schematic illustration of the possible changes in emulsions as they pass through the in vitro physiological model (reproduced with the permission of Elsevier Inc. [2]).Display Omitted► The behaviour of protein-stabilised emulsions under oral conditions depends largely on initial charge on the emulsion droplets, and salivary mucins play a crucial role in droplet flocculation. ► Under gastric conditions, rather than the droplet charge, it is the nature of the protein interfacial layer and its susceptibility to pepsin that drives the emulsion destabilisation process. Globular proteins after adsorption onto the droplet surface appear to be more susceptible to pepsin than in their native state. ► Under the intestinal conditions, initial droplet charge and composition of protein adsorbed layers play an insignificant role, as most of the adsorbed protein/peptide layer is further hydrolysed by trypsin and chymotrypsin. Emulsions appear to be stabilised by the adsorption of bile salts under these conditions. ► Pancreatic lipase cleaves triglycerides to form 2-monglycerides and fatty acids; some of these digestion products are surface active and complete with bile salts and peptides for the droplet surface.
Keywords: Emulsion; Protein; Digestion; Enzyme; Gastro-intestinal tract; Lipid digestion;