Hardstock lipids, including trans and saturated fats, have been shown to have serious deleterious health effects. However, it is these ‘heart unhealthy’ lipids which impart the solid elastic properties to foods. It is the intention of this review to examine new technologies which present the first viable alternatives to structuring lipid products without the use of saturated or trans fats.
by Michael A Rogers

Traditional high-fat foods such as ice cream, margarine, butter, lard, and chocolate attain their semi-solid structure from hardstock lipids, which rely on trans and saturated fats to supply their desired elastic properties. Although these ingredients contribute a highly desired physical structure to food products, they are often associated with deleterious health factors such as adverse effects on lipoprotein (cholesterol) profiles, increased incidence of heart disease and metabolic syndrome. It is estimated that around 20-25 percent of the world’s adult population suffers from metabolic syndrome. Sufferers are three times more likely to experience a heart attack or stroke compared with non-sufferers. In addition, patients with metabolic syndrome have a five fold greater risk of developing type 2 diabetes. 230 million people worldwide have been diagnosed with diabetes, one of the most common chronic diseases worldwide and the fourth or fifth leading cause of death in the developed world [1]. The negative health implications associated with diets high in trans and saturated fats may be reversed by reducing the intake of these ‘heart unhealthy’ fats and replacing them with polyunsaturated fats.

In an attempt to curb this new epidemic, governments across the globe including the United States, Denmark and Switzerland have passed aggressive legislation limiting (and in certain cases banning) trans fats in foods. This move has been mirrored by numerous multi-national foodstuff corporations struggling to reduce even further trans and saturated fats in their products. Despite herculean efforts by both governments and corporations, the major challenge is not one of willingness but the lack of suitable ingredient technology.

A look at lipids
Lipids, as an ingredient, supply flavour, mouthfeel, satiety and structure. Lipids that are solid at room temperature have very straight fatty acid backbones the most common being mysteric, palmitic, and stearic acid. However, polyunsaturated fats with the same number of carbons as stearic acid (i.e., oleic acid (18:1), linoleic acid (18:2) and linolenic acid (18:3)) are solid at much colder temperatures. For example stearic acid will crystallise at approximately 65oC, while oleic acid crystallises around 10oC and linoleic acid at -10oC. Hence the inclusion of polyunsaturated lipids into semi-solid food products is constrained by their temperature range. Typically, hardstock lipids are soft, plastic materials with different levels of structure which influences their macroscopic properties. Upon cooling, saturated and trans lipids have limited solubility and, via nucleation, assemble and grow into small spherical crystals interacting via non-covalent forces, thus forming a continuous network of lipid crystals. Lipids, below their melting point exist as a 3-dimensional colloidal fat crystal network, which confers their desirable physical properties. Upon crystallisation, hardstock lipids aggregate to form fat crystals. These in turn interact to form clusters which eventually aggregate into flocs. Weak links develop between flocs to form the final macroscopic network. These hardstock fats have been central in the development of solid-based lipid products. However, given legislative and consumer pressure to reduce saturated fat levels, the food industry is at a cross roads; how to go forward in order to reduce the amount of traditional hardstock fats in foods?

The search for lipid replacers
With this in mind, researchers have been actively researching novel lipid replacements. In order to be effective, these ingredients should provide sufficient elastic properties and a solid appearance. Self-assembled fibrillar networks (SAFiNs) have been central over the past five years to this exhaustive research effort. SAFiNs, as opposed to colloidal fat crystal networks, produce 1-dimensional crystals from low molecular weight compounds (as opposed to spherulitic crystals produced from higher molecular weight compounds (i.e., triacylglycerides)). Numerous new technologies have been developed and studied; however, major complications have presented an obstacle to their introduction into the food industry. Examples of such limitations include; stearic acid gels - due to the unhealthy connotation of saturated lipids; span and tween gels, - due to the high concentrations required; lecithin gels - due to their instability; and hydroxylated fatty acids, - due in part to their laxative effect.
However, three promising new technologies are currently under development and these may have an impact on reducing the amount of trans and saturated fats in complex food products. The first has been developed at the University of Guelph, Canada. Here researchers have exploited the application of Lα liquid-crystalline lamellar phase of monoglycerides in water and oil emulsions [2]. Cooling the emulsion causes the droplet wall previously coated with the Lα liquid-crystalline lamellar phase to crystallise, thereby efficiently entraining the liquid oil. From a nutritional stand-point this fat-like material contains no trans fats and may be designed with as little as 4% saturated fat. The β-gel structure has other positive physiological effects; e.g. blood TAGs, free fatty acids and insulin levels are lower following a concentrated intake of the oil-water-MAG gel compared with an oil-in-water emulsion. The current limitations to this technology are the meticulous balance between the oil, water, emulsifier and salt that is required. Due to the meticulous phase diagram involved some practical limitations prevent this technology from being applied to all lipid-containing foods. Additionally, this technology utilises saturated fatty acids esterified to a glycerol (albeit at greatly reduced concentrations compared to traditional lipid hardstock ingredients).

γ-oryzanol and phytosterols are both capable of acting as hardstock lipid replacers at concentrations of between 2-4% in vegetable oil [3]. γ-oryzanol and phytosterol mixtures form fibrillar hollow tubes that are 7.2±0.1 nm in diameter [4]. The ability of these compounds to act as a hardstock lipid replacer is dependent on several structural features of phytosterols. These include; the position and presence of the hydroxyl group, the presences of unconjugated rings, and the number of double bonds present in the ring structure. Constraints acting on phytosterols’ gelling systems include the narrow melting ranges and the difficulties experienced in significantly manipulating their structure. The most intriguing aspect of this novel system, however, is that plant phytosterols are capable of lowering blood cholesterol levels. This charasteristic imparts a healthy aspect to this potential food ingredient.

Each of the aforementioned systems has at least one significant limitation. These include  health implications, a lack of crystal network flexibility and practical limitations. The final system, which may overcome these practical limitations, is the application of ceramides to replace traditional fat crystal networks.

The role of ceramides
Ceramides are a class of polar lipids found everywhere in nature. It has been demonstrated that sphingolipids and ceramides reduce total serum cholesterol by 30%, improve the chemical composition of serum lipoproteins and can also induce apoptosis (cell death) in cancer cell lines. The crystal network of ceramides can be modified by adjusting their chemical composition. Ceramides, like triacylglycerides exhibit variability in the fatty acid chain length, degree of saturation and chemical substitution. For example, ceramides with short carbon side chains form long thin fibres several hundred microns in length [5]. Conversely, mixed ceramide systems extracted from milk or eggs have long carbon chains (i.e., C16-C24) and produce small maltese-cross crystals, which are capable of immobilising the oil efficiently. The only limitation to this technology is the lack of an industrial supplier who can extract these compounds from a food grade source, in a food grade fashion, and at a reasonable price. Current research in this field is examining the feasibility of extracting these compounds from by-products of the biodiesel and bio-ethanol industries, which concentrate ceramides during the processing of these commodities.

With metabolic syndrome quickly becoming a worldwide epidemic there is an urgent need to reduce or eliminate trans and saturated lipid consumption from manufactured foods. Research must be implemented quickly to reduce the amount of unhealthy fats, sugar and sodium in our food. If action is not taken, serious health consequences will follow. Ceramides are a promising group of compounds able to solidify liquid vegetable oils. These compounds confer desirable health benefits and are also able to closely mimic the structure of colloidal fat crystal networks. This technology is the first viable alternative to structuring lipid products without the use of saturated or trans fats.

References
1. IDF Communications. The IDF consensus worldwide definition of the metabolic syndrome. International Diabetes Federation, 2006.
2. Marangoni A G et al.  Encapsulation-stucturing of edible oil attenuates acute elevation of blood lipids and insulin in humans. Soft Matter 2007; 3: 183-187.
3. Bot A and Agterof WGM. Structuring of edible oils by mixtures of γ-oryzanol with γ-sitosterol or related phytosterols. Journal of American Oil Chemists Society. 2006; 83: 513-521.
4. Bot A et al. Fibrils of γ-oryzanol + γ-sitorsterol in edible oil organogels. Journal of the American Oil Chemists Society. 2008; 85: 1127-1134.
5. Rogers MA, Wright AJ, Maranoni AG. Oil Organogels: The Fat of the Future? Soft
Matter 2009; 5:1594 - 1596.

The author
Michael A Rogers
Assistant Professor
University of Saskatchewan
Saskatoon, Canada
Email: michael.rogers@usask.ca