Removal of trans-fats without increasing saturated fats
In the 1990s evidence emerged showing deleterious effects of TFA on blood cholesterol concentrations. TFA and SFA have similar effects in raising blood TC and LDL-cholesterol but TFA also lower HDL-cholesterol. Thus, CHD risk with TFA appears to be at least as bad as that with SFA (Willett et al. 1993). As a reaction to these new scientific findings, Unilever decided in 1995 to take the initiative and eliminate TFA from the fat-phase composition of margarine, and most European margarine manufacturers have now followed this decision.
In foods TFA originate from three major sources: bacterial transformation of unsaturated fatty acids in the rumen of ruminant animals (milk, butter and other dairy products, beef); hydrogenation (the process for increasing the solid fat crystals in unsaturated fats) and deodorization (the process for refining unsaturated vegetable and fish oils); when oils are heated to a high temperature (Food Standards Agency, 2004). Data from the TRANSFAIR study has shown that TFA levels in soft margarine in 1995–6 ranged between 1 and 17% in a survey of fourteen European countries (Food Standards Agency, 2004). Follow-up data from this study has shown the levels have dropped to Food Standards Agency, 2004). Presently, the effects of TFA on a g per g basis are considered to be worse than those of SFA, but usually the level of SFA in the diet is many-fold higher than that of TFA.
Unilever decided to eliminate TFA, but under the condition that SFA levels would not increase. The challenge for technologists was to increase the solids in unsaturated fats without using partial hydrogenation. Thus, other methods of modifying the solid-phase characteristics required development, such as fractionation, interesterification and hydrogenation. Fractionation is the controlled crystallisation of the ‘solid’ TG in a fat mixture followed by the separation of the solid and liquid fractions. The main oil that is fractionated worldwide is palm oil, mainly because of the demand for clear liquid oil (olein). More recently, there has been an interest in the solid product of fractionation of cocoa butter (stearin). Fractionation alone will produce a relatively soft stearin component that is not optimal for structuring margarine. However, fractionation followed by interesterification (see Fig. 4) is used to produce a fat phase suitable for margarine that does not contain hydrogenated components. Interesterification involves the rearrangement or redistribution of the fatty acid chains on the glycerol fragment of the TG molecule. This rearrangement can reduce the solids level at high temperature while maintaining the solids level at low temperature, making the solid-phase line steeper and the product better suited as a fat-phase component for margarine (see Fig. 4). Interesterification can be promoted by an alkaline catalyst or by lipase enzymes. Alkaline-catalysed reactions produce a mixture of TG in which the fatty acids are distributed randomly among the fat molecules and randomly among the three available positions within each molecule. In contrast, lipase is more specific as it catalyses the rearrangement of the glycerol at the sn-1 and sn-3 position but leaves the ester link at the sn-2 position intact. The modification of the fatty acid distribution leads to an alteration in the solid-phase characteristics and the crystallisation behaviour. The actual change in solid-phase characteristics depends on the composition of the fatty acids included in the interesterified mixture. When interesterification is combined with fractionation a TFA-free margarine can be produced. Alternatively, liquid seed oils may be fully hydrogenated and while the TFA level remains very low (Fig. 5). Thus, the elimination of TFA has been achieved without increasing the level of blood-cholesterol-raising SFA, while maintaining the margarine properties.
The transfer to TFA-free margarine production has been one of Unilever's major technical projects in the past decade, as it has involved the development of new fat-phase compositions for >600 margarine blends while safeguarding the typical margarine characteristics.
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