Edible Oleogels for Reduction of Saturated Fat

Lead Research Organisation: Heriot-Watt University
Department Name: Sch of Energy, Geosci, Infrast & Society

Abstract

Removing saturated fats from foods is highly desirable because of the health benefits that would be realised, but this is not a trivial exercise because solids fats contribute greatly to the texture of many common foods. They are important in forming the structure in many formulated foods such as baked goods, biscuits, butter, margarine and spreads and confectionery. However, they raise cholesterol levels in the blood and are a risk factor for coronary heart disease. Replacing them with mono-or polyunsaturated oils is not feasible as these are liquid at ambient temperatures and so food where solid fat is replaced by oil would lack the desired solid texture. Even foods that are branded as high in polyunsaturated fats, such as margarines and spreads must contain a relatively high proportion of saturated fat to give the correct texture. The role of the saturated fats in spreads is to provide a network of fat crystals that trap and immobilize the liquid oils in a semi-solid matrix. If food manufacturers are to develop foods with the saturated fat removed they will need to find alternative methods to form the semi-solid structure. One solution that food scientists are developing is the use of edible oleogels. In these, molecules known as gelators are added to liquid oils to mimic the structuring effect of solid fat crystals. The gelators associate with each other to form very long, thin fibres or tubules which crosslink to form a network. This "lattice" of gelator fibres acts in similar way to the network of solid fat crystals and traps the liquid oils in pores in the structure. One group of molecules that can be used to make oleogels are the plant sterols. These also have been found to reduce blood cholesterol levels in their own right, and are added to some functional food spreads for this reason.
In principle, oleogels can have a solid-like texture the same as conventional spreads and margarines. In practice it has proven difficult to develop this technology and to date they have not been used for commercial foods. One reason is that there are few available sterols that form organogels. Since little is known about what makes the ideal gelator it is not possible to make new gelators for a particular food application. In addition the structure and texture of an oleogel is very sensitive to the presence of small amounts of water, and so margarines (which contain small water droplets) have proven difficult to make. To make matters worse, when it does prove possible to make an oleogel, it is often difficult to do so consistently. Again, little is known about how oleogels form, and this makes the control of their texture difficult.
In this project we will address the problems that are holding back the use of edible oleogels in foods. We use a combination of experimental and computer modelling methods to explore the mechanisms of gelator aggregation, tubule formation and gelation. Our aim is to understand how these molecules are able to form tubules, and subsequently how these tubules are able to form a semi-solid texture in liquid oils. Computer modelling allows us to look at the structure of tubules in molecular detail, and to understand the features of a phytosterol molecule that allows it to form an oleogel. Knowing the key structural features of optimum gelator molecules allows new gelators to be synthesised and tested in foods, leading to a wider range of sterol gelators and more widespread application to oily foods. Even with more efficient gelators the formulation of edible oleogels will be difficult. We will also look at the mechanisms of and control of gel formation using a range of experimental techniques, with the ultimate aim that we will use this knowledge to control oleogel structure, and eventually to demonstrate oleogel technology in food products. Successful formulation of edible oleogels will allow healthier oil-based foods that are reduced in saturated fats but maintain a desirable semi-solid or solid texture.

Technical Summary

Oleogels are a form of organogel where the continuous phase is unsaturated triglyceride oil trapped in a network formed by self-associating oleo-gelator molecules. Oleogels are of interest to food companies who manufacture foods such as polyunsaturated margarines and spreads. These contain saturated fat crystals added to give a semi-solid texture. Saturated fats raise blood cholesterol which is a risk factor in cardiovascular disease. Removing saturated fats from these products by using oleo-gelation would lead to a healthier product. Mixtures of sterols and sterol esters as oleogelators are of interest because they have been shown to have blood cholesterol lowering properties in their own right. There are a number of technical difficulties associated with developing oleogel food products from phytosterols. Several sterols are suitable for oleogelation, but only one sterol ester, gamma-oryzanol is available. The mechanism for self-association is not well understood, and it is not possible to predict suitable olegelators for a particular application. Oleogels made from phytosterols are sensitive to oscillatory shear and considerable super-cooling can occur in the gelation process if the shear conditions are not optimised. Finally, the self-association is sensitive to water, and this limits application of oleogelation in water-in-oil emulsion spreads and margarines. We will use a combination of experimental (rheological, AFM, light scattering) and simulation (MD, MC, Lattice-Boltzmann simulation) methodologies to (1) identify other sterol ester structures to broaden the range available; (2) understand and control the effects of shear to optimise oleogel formation and structure; and (3) understand water sensitivity and how to ensure self-association in the presence of water. This will provide information allowing us to identify the optimal routes to processing of oleogel based foods.

Planned Impact

A number of benefits, both societal and economic, have been identified that could occur as a consequence of this project. Consumption of saturated fats has been linked to an increased risk of coronary heart disease, since saturated fats increase the levels of blood cholesterol. However, solid fats are also important in the formation of structure and texture in oily foods. Replacing saturated fats with structured, polyunsaturated oil based oleogels has the potential to lead to a revolutionary change in saturated fat levels in the diet, reduction in blood cholesterol and an associated increase in health benefits. In addition to these highly significant societal benefits, the potential economic benefits are also significant. Products that contain saturated fats include spreads, chocolate, cream and ice cream. However, far greater impact on health could be realised by incorporation of oleogel technology into staple foods such as bread. As part of the follow up of this project we would look to engage with food manufacturers who would test the oleogel technology in a range of prototype food products.
Further societal benefits can be accrued through public engagement. The area of food and health is of great interest to the general public. The opportunity exists for us to connect with the public through the Edinburgh Beltane Beacon for Public Engagement in Science an organisation (www.edinburghbeltane.net). The annual Edinburgh International Science Festival offers huge scope for promoting the results of this project to a wider general audience. Both HWU and UoE are members of the Edinburgh Beltane. To reach members of the public who would not normally attend science fairs, but nonetheless have an interest in the health implications of what they eat, we would explore using other events such as the Royal Highland Agricultural show as a showcase for food and health related research.
Dissemination of research on organogels that may be interest to other academics and industrial sectors will be achieved through publication (with the prior permission of DRINC) in high impact peer-reviewed journals and presentation at international conferences. The researchers in this proposal have a track record of publication across a wide range of journal subject areas (food chemistry, physical chemistry, colloid chemistry and soft-matter physics) with this breadth of coverage ensuring outreach to a wide range of secondary beneficiaries.

The academics have the ideal fit in terms of their complementary scientific expertise, and excellent track record of engaging with industry, thus ensuring the success of the project. Euston and Clegg have a joint translational research project with industry funded by the EPSRC (EP/J501682/1 and EP/J501712/1) on novel food proteins. Euston is PI or CoI on government and industry funded projects for the food industry (TS/L002426/1, TS/L004542/1, KTP009473 & KTP009478). Clegg has been a Royal Society Industry Research Fellow with Syngenta and has contributed as PI/CoI to a number of industry related projects. He is Director of the Edinburgh Complex Fluid Partnership (ECFP, www.edinburghcomplexfluids.com): the industrial collaboration vehicle of the Edinburgh University Soft Condensed Matter Group. Existing or recent collaborations of ECFP are with AkzoNobel, Mentholatum, Johnson Matthey, Macphie of Glenbervie and Rowett Institute for Nutrition and Health. He led the Edinburgh University half of a recent DRINC collaboration with the Institute of Food Research (PI Wilde, BB/I006133/1) on the mouth feel of emulsions. Stewart has a wide portfolio of grants related to the links between food and health funded by the EU (FP7 KBBE/ 613513, KBBE/ 613793), KTP and the Scottish Government.Westacott has been or is PI or CoI on EPSRC (GR/S12005/1, EP/D003679/1, EP/G029601/1) grants based completely or partly in molecular simulation of interfaces and on KTP projects funded by the TSB (KTP000058 and KTP009119).

Publications


10 25 50
 
Description Computational methods have been employed with the aim to gain structural information and thorough understanding of the physico-chemical energy balances involved and the structure-function relations of the oleogelling compounds. We have used docking methods and molecular dynamics (MD) to investigate the self-association of ß-sitosterol and ?-oryzanol in order to understand better the mechanism of self-association at a molecular level. The top-ranked cluster of ß-sitosterol and ?-oryzanol docking model reveal a favourable hydrogen bond between the the hydroxyl group of the sitosterol and the carbonyl group of the oryzanol. In such conformation, the binding of ß-sitosterol and ?-oryzanol is stabilized by extensive p-p contacts between the sterane cores. The top-ranked cluster is among the two highest populated comprising 13 out of 100 conformations with the lowest-energy model estimated to have free energy of binding ?G = -5.17 Kcal?mol-1. Based on the above experimental studies, we have built a model of ß-sitosterol/?-oryzanol tubule (15 nm length) compised of 230 molecules (50:50 mixture), and MD simulations were applied. The intermolecular hydrogen bonding between the hydroxyl group of the sitosterol and the carbonyl group of the oryzanol is observed for over 85% of the simulation time. In addition, favorable p-p contacts were observed between the ferulic acid aromatic groups of the ?-oryzanol.
Rheology and atomic force microscopy (AFM) have been employed to examine the microstructure of ß-sitosterol : ?-oryzanol organogels in sunflower oil. Using time resolved rheology we obtained information on the structure and growth kinetics of the system. Using AFM we observed gel structures directly, and observed that fibrils aggregate into bundles which fuse and bifurcate. Quantitative analysis suggests that though gels are formed by the self-assembly and aggregation of one-dimensional fibrils, the manner in which these fibrils aggregate results in complex structures of higher dimensionality. Comparing AFM images of 10 % w/w and 20 % w/w gelator systems, we observed differences in the degree of branching which are consistent with the rheology. We also observed the individual self-assembled fibrils which make up these gels with much greater clarity than in previous microscopy studies, and the fibril diameters of ~ 9.8 nm we measured agree excellently with those obtained from existing small angle neutron scattering data. These results provide insight into the structure and formation kinetics of this important organogel system.
We have submitted our combined AFM and rheology results as a manuscript to Langmuir.
Exploitation Route The project is funded by the BBSRC Diet and Health Research Industry Club (DRINC) partly funded by the food industry. We have established contact with one of the funders, Unilever and continue to discuss the progress of this project with them.
Computational studies will be applied to investigate the alternative candidate derivatives of oryzanol and sitosterol, and these will be synthesized for comparative studies. This will enable us to probe experimentally the roles of different chemical groups, and to identify potential gelators with improved functionality. Additionally, we are just beginning to explore the role of changing the host solvent. By this route we should be able to systematically weaken and destroy the oleogel - while observing the changes to the molecules using spectroscopic studies. This should provide some insight into how the oleogel "works". We are also beginning to investigate alternative gelator systems which can incorporate ?-oryzanol. There is an outside chance that these might prove useful for gels which need to be robust to the presence of water.
Sectors Agriculture, Food and Drink,Chemicals,Healthcare,Manufacturing, including Industrial Biotechology,Pharmaceuticals and Medical Biotechnology
URL http://www.foodproteins.org
 
Description Organic synthesis of alternative gelator molecules 
Organisation Heriot-Watt University
Department Mathematics Department Heriot-Watt
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Academic/University 
PI Contribution Shared information on olegelation. Invited collaborator to project meetings. Eventual joint publications.
Collaborator Contribution The partner will synthesize a range of alternative olegelator molecules that are derivatives of gamma oryzanol that either have the ferullic acid side chain substituted for another group, or have a hydroxyl group substituted. The hydroxyl group is believed to be important in dimerization of the sterols prior to their subsequent self-association into tubules, and also stabilizes the tubules through cooperative H-bonding. The ferrulic acid group is believed to allow inter-tubule interaction (it sticks out from the surface of the tubule) via pi-pi stacking interactions, thus leading to gel formation. By creating and testing oleogelators where one or both of these groups has been substituted will allow us to understand the role they play in the self-association and gelation process.
Impact Too early in project/collaboration.
Start Year 2017
 
Description Attendance at Diet and Health Research industry Club Industry engagement meetings 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact Mandatory DRINC dissemination event to inform industry sponsors of the DRINC program of the progress and outcomes of DRINC funded research project. Three have been attended (1 per year) so far.
Year(s) Of Engagement Activity 2015,2016,2017
 
Description Food Colloids Conference, Wageningen The Netherlands 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Results presented at a major food colloids conference (sponsored by the Royal Society of Chemistry) held in Wageningen, The Netherlands in April 2016.
A poster was given on the computer simulation of olegelation by sterols and sterol esters, and on the functional properties of novel fungal proteins.
Year(s) Of Engagement Activity 2016