Fat

The fact that so many products have been developed during the past 20 years or so to attempt to replace fat with a less fattening substance underlines the intractability of the problem food technologists have faced. 

Effectively, removing fat results in major structural changes to physical stability, appearance (opacity/colour), texture and viscosity, melting profile and heat transfer, the way food breaks down in the mouth, mouthfeel, flavour release and aftertaste. While much is made of the adverse health effects of fat, fats are also a source of essential fatty acids and fat soluble vitamins.

Indeed, the attempt to find one magic substance that can perform all the functions of fat while contributing fewer calories can be said to have been unsuccessful.

Several synthetic fat substitutes have been developed but have only proved viable in limited applications. At present there are no commercially available and approved synthetic fat substitutes which can be used for all food applications. 

Research has therefore tended to focus on adapting or modifying existing ingredients which can simulate some properties of fat. 

Fat-replacing ingredients break down into three main types: carbohydrate-based (starch and starch hydrolysis products and fibre-based gums, gels, thickeners and bulking agents); protein-based (specially processed proteins or protein/fibre combinations); and lipid-based (synthetic fat substitutes, low-calorie fats and emulsifiers).

Generally, five terms are used to describe the various types of fat replacement:

Fat replacer or fat substitute

A term used to describe any ingredient which replaces fat. 

Synthetic fat substitute

A synthetic compound designed to replace fat on an equivalent weight basis, generally having a similar chemical structure but resistant to hydrolysis by digestive enzymes. 

The best known example is probably Olestra, a sucrose polyester patented by Procter & Gamble in 1971. While it is now used on a limited basis, it has had a controversial history, encountering problems in gaining regulatory approvals and being associated with adverse side-effects. It is currently used in snackfoods but only in the US.

Many other synthetic fat substitutes have also been investigated. Many companies developing such products have waited to see the outcome of the regulatory struggles of Olestra before attempting to bring products to market.

Fat mimetic

A fat replacer requiring a high water content to achieve functionality.

Fat reduction can be achieved with the use of different types of starch-derived fat mimetics. Most of the research activity on starch-derived fat mimetics has centred on maltodextrins, starch hydrolysis products obtained by acid or enzymic hydrolysis of starch materials and characterised by a low dextrose equivalent (DE) value. 

While starch-based mimetics do not require the same regulatory approvals as a product such as Olestra, they are not able to realise the level of fat reduction that tends to be required today, achieving typically reductions of only 25% to 35%. 

Microparticulated processing systems aim to mimic the creamy feel of fat in the mouth, and are considered by many to be a sound general approach for the development of fat mimetics. Such products can for instance be used to add creaminess to low-fat yoghurt while contributing fewer calories than fat. They also have 'clean label' advantages as they only need to be labelled as 'milk protein'. The 'clean label' trend has stemmed from increasing consumer concern about artificial ingredients and highly-processed foods, leading food scientists to place an increasing emphasis on the search for 'natural' ingredients and processes.  

The development of Simplesse, launched by the NutraSweet Company in 1988, was a notable breakthrough product in microparticulated fat mimetics. 

Gums and thickening agents such as pectin and gelatine are also used to mimic the presence of fat, notably in processed meats.

Low-calorie fats 

These are synthetic triglycerides which combine unconventional fatty acids with the glycerol 'backbone' resulting in a reduced caloric value. 

The concept of replacing fat in the product with low-calorie fat was established in the early 1990s, when blends were also becoming more commonplace.  The search for a single synthetic substitute was proving challenging while mimetics did not provide sufficient caloric reduction.

The idea behind low-calorie fats was to use the basic structure of a triglyceride molecule but to change the fatty acid composition in order to reduce the caloric value of the fat. 

Not all fat molecules are metabolised in same way. Most fats present in vegetable oils are triacylglycerides (TAGs). But diacylglycerides (DAGs), which make up around 10% of the fats found in vegetable oils, have been found to induce fat oxidation, suppress fat accumulation and increase satiety. 

Fat extender

A fat replacement system containing a proportion of standard fats or oils combined with other ingredients. 

Emulsifiers function as fat extenders and in recent years there has been an increasing amount of research being conducted into the application of water-in-oil-in-water (WOW) emulsions in various low-fat products. The WOW process, which involves encasing water droplets in fat droplets, potentially offers a highly effective way of reducing fat in products such as mayonnaise, salad dressings, sauces and dips without substantially affecting mouthfeel. 

The advantage is that in a low-fat mayonnaise for example the WOW droplets would behave very much like ordinary fat droplets in the mouth allowing for a creamy texture similar to the full-fat version. Currently, the fat reduction in low-fat mayonnaises is achieved by the addition of thickeners and stabilisers which affect mouthfeel. The use of a WOW emulsion could result in as much as a 40% fat reduction while retaining a creamy texture.

After many years of research it has become increasingly apparent that to achieve a significant fat reduction while maintaining optimal quality will in most cases require the use of other ingredients in combination with the fat replacers. Ingredients companies have come to accept the need to use blended systems, while food manufacturers have increasingly adopted a similarly holistic approach to the development of low- and reduced-fat products. 

In addition to developing new ingredients or blends of ingredients, manufacturers have also made great efforts to improve the quality of existing fat replacers in terms of their functionality, ease of use, susceptibility to processing.  These comprise three main areas of focus: instantisation; alteration in functionality profile; and ease of use during product manufacture. 

Looking ahead

There can be said to have been a shift in the approach to reformulation from the 1980s and 1990s when there was a concerted focus on the search for the magic ingredient to replace fat in all its properties. More recently there has been a greater emphasis on manufacturing products with balanced macronutrients including generally lower levels of fat but importantly cutting down on bad fats, such as trans and saturated.

There has already been a lot of work on reducing trans fats and more recently the focus has shifted towards saturated fat reduction.  

One key objective has been to find a way of producing an unsaturated fat that is solid at room temperature to enable it to be used in cakes and similar products. The drive to reduce saturated fat is likely to continue with the development of technologies such as cryocrystallisation, where a liquid fat is treated with liquid nitrogen to make it solid, which not only meet the need to reduce saturated fat but also have clear 'clean label' advantages. Indeed, as with reformulation in other areas, the clean label trend is increasingly influencing how companies approach fat reduction.

just-food gratefully acknowledges the assistance of Leatherhead Food Research and Alice Pegg in the preparation of this article.

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