Oil Structuring: Concepts, Overview and Future Perspectives

ASHOK R. PATEL

Sci Five Consulting Services, Coupure 164F, 9000 Gent, Belgium

Introduction

Emerging evidence related to the negative cardiovascular effects of increased fat consumption has resulted in increased regulation of trans fats in food products by regulatory authorities the world over. Starting from the mandatory labelling of the amount of trans fats in food products in the mid-2000s, to concrete steps taken towards complete removal in recent times, there has been a consistent decline in the use of trans fats in food products over the last few years.' Accordingly, the food manufacturing industry has been under pressure to innovate and find alternative solutions to formulate products with the complete absence of trans fats. The solution currently used by the food industry is replacing trans fats with saturated fats from natural sources, such as palm oil. Although quite effective in terms of replicating the functionality of trans fats, the use of saturated fats is criticized for two main reasons: (a) negative image of palm oil owing to the ecological damage that is often linked to palm plantations, and (b) possible negative cardiovascular effects of the long-term consumption of saturated fats. The latter point has seen its share of debate in recent times where some authors have argued the scientific validity of such claims based on empirical evidence. However, it is widely accepted that consumption of polyunsaturated fats over saturated fats is beneficial for cardiovascular health. The current dietary guideline with respect to saturated fat consumption is to restrict the daily consumption to less than 10% of total calories and this is unlikely to change in the near future. As the food industry is currently phasing out trans fats in formulations after the ban imposed by the US FDA in 2015, the demand for palm oil has increased. In order to shed the negative image linked to palm oil, many food manufacturers have publicly shared information about their engagement with sustainable palm oil product suppliers (Roundtable on Sustainable Palm Oil or RSPO) to minimize environmental damage done by palm plantations. However, recent scientific opinion from the EFSA panel on Contaminants in the Food Chain (CONTAM) regarding the negative health effects of 3- and 2-monochloropropanediol, as well as their fatty acid esters and glycidyl fatty acid esters, has somewhat tarnished the image of palm oil in the eyes of consumers. Hence, there is a great deal of interest in finding ways to formulate products with a better nutritional profile (i.e. trans fat-free and high in unsaturated fats), and preferably without the use of palm oil.

In recent years, oleogelation has gained popularity as an approach for formulating food products where the functionality provided by saturated fats (i.e. texturing, oil binding, rheological characteristics, organoleptics and stabilizing properties) can be replicated by non-fat components used as structuring agents. The possibility of gelling >90 wt% of liquid oil at a relatively lower mass fraction of gelator molecules makes oleogelation a very efficient approach for oil structuring. This efficient structuring in oleogels is usually achieved by supramolecular assemblies (building blocks) of gelator molecules that organize into a three-dimensional network that can physically imprison a large volume of mobile liquid oil into an 'arrested' gel-like structure. In the following sections, a general concept and an overview of the field of oleogelation is presented with special emphasis on the research done in the recent years.

1.2 Oleogelation: Concepts

By definition, oleogels are a sub-class of a broader class of colloidal structures called organogels and are defined as a gel system where an oil continuous liquid phase is immobilized in a network of self-assembled molecules of an oleogelator or a combination of gelators. In the last few years, oleogelation has changed from a relatively unknown term into a heavily investigated research domain. Academic research in this area has progressed rapidly as researchers from a wide range of backgrounds (such as applied chemistry, colloid science, material science and process engineering) have taken up the challenge of identifying novel ingredients and innovative processing methods to create oleogels. At the same time, industrial scientists have shown increased interest in investigating edible applications of these oleogels in a range of food products, including chocolates, baking fats and meat fat replacements. Fundamentally, it is fascinating to fabricate and characterize this new class of edible soft matter systems as there is still a lot to be learnt about their structuring mechanisms and the 'tunability' of their bulk properties through microstructural alterations. From an application point-of-view, the oleogelation approach has the potential to cater to a number of generalized and 'niche' applications. Such applications include: (a) reduction of saturated fat levels in food products, (b) stabilization of surfactant-free emulsions, (c) decreasing oil mobility and migration in chocolate products (controlling fat bloom in filled chocolates), (d) improving temperature stability in certain food products (heat-resistant chocolates), (e) developing controlled-release systems for delivery of low molecular weight bioactives, and (f) transforming liquid oils...