Margarine was originally developed in 1869 as an alternative to butter which was in short supply and was also expensive [1
]. Margarine is a water-in-oil emulsion. The aqueous phase consists of water, salt and preservatives. The fatty phase, which contributes to the polymorphic behaviour of margarine, is a blend of oils and fats, antioxidants and emulsifiers. Traditionally, the solid fat content of margarine is obtained by hydrogenation of liquid oils. Hydrogenation results in the formation of trans fatty acids where some cis double bonds are rearranged to trans bonds [2
]. Several studies have suggested a direct relationship between trans fatty acids and increased risk for coronary heart diseases as well as raise of plasmatic lipid levels [3
]. Different processes are currently available for the production of zero-trans solid fats in the food industry including chemical [8
] or enzymatic transesterification [9
]. Chemical transesterification usually needs cleaning process to remove the residual catalyst besides the formation of undesirable products. It is being successfully replaced by enzymatic processes of modifying fats and oils by utilizing lipases from various origins [11
]. Enzymatic conversion of fats has been reported by various researchers [12
]. Ghazali et al. [14
] have conducted in hexane media the enzymatic transesterification of palm olein with nonspecific and 1,3-specific lipases immobilized on Celite. The effects of transesterification of palm olein by the various lipases resulted in changes in the triglycerides mixture and no clear correlation between the enzyme positional specificity and the products formed was found.
Palm oil is extracted from the fruit of oil palm, Elaeis guineensis
. It is one of the traditional fats that have been widely used throughout the world in the human diet. Global palm oil production was estimated to 45.9 millions of tons during 2009–2010, accounting for 40
% of the worldwide production of total dietary oils [15
]. Palm oil contains a mixture of high and low melting points triacylglycerols. Using a simple dry fractionation process under controlled conditions, palm oil can be resolved into two fractions, namely olein (liquid fraction) and stearin (solid fraction) [16
]. Palm olein is rich in low melting point triacylglycerols and is the mostly used fraction [8
]. However, the high melting point fraction (palm stearin, melting point ranging from 45 to 55°C) is hardly used in manufacturing edible fats due to its low plasticity [16
]. Nevertheless, palm stearin deserves attention as a potential hard fat of vegetable origin to replace hydrogenated lipids. It might be appropriately blended and interesterified with liquid oils in order to modify the physical characteristics of the mixture to meet the functional properties and the quality required for margarine preparation.
Lai et al. [17
] have used nonspecific and 1,3-specific lipases to transesterify mixtures of palm stearin and sunflower oil at a 40:60 mass ratio in a solvent-free medium. The authors have found that the palm stearin and sunflower oil mixtures were converted to a more fluid product. In the same context, Lai et al. [10
] have also transesterified a mixture of palm stearin and palm kernel olein using the same lipases. They reported that the enzymatic transesterification was able to produce fat mixtures with substantially lower melting points by repositioning the fatty acids of triglycerides in the higher melting range to form lower-or middle-melting components.
In the same context, this work reports the synthesis of a fatty phase by transesterification of palm stearin and palm olein using an immobilized Rhizopus oryzae
lipase as a biocatalyst. The maximal rate of palm stearin that is usually added to a standard table margarine formulation is 10% [16
]. The purpose of this work was to maximise the palm stearin proportion in the fatty phase (higher than 35%). A margarine was prepared out of the palm stearin/palm olein interesterified (40/60; w/w) mixture used as fatty phase. Slip melting point and rheological properties of the margarine were studied. In order to improve the colour, powder of dry bark orange was added to one margarine sample which rheological properties were studied.