2. Oil Blend Development

Margarine is a water-in-oil emulsion. An emulsion is a suspension of one liquid within a second, immiscible liquid. In margarine, the fat is the continuous phase. The dispersed phase consists of water and/or water dispersible components. The dispersible aqueous phase typically contains droplets of 1 - 20m m in diameter.

Margarine contains at least 80% fat by weight. The fat in margarine is primarily refined, mixed triglycerides (triacylglycerols) of vegetable or animal carcass origin. Marine oils are also used to formulate margarines in many countries. Tallow and lard is used in some lower-cost margarines. Lauric oils, such as cocunut and palm kernel, were used to make margarines as late as the 1930s. The predominent fat used in the United States for margarine throughout the 1970s and the 1980s has been soybean oil, followed by corn oil. In Europe and elsewhere, palm oil and its fractions are extensively used, as well as some polyunsaturate vegetable and hydrogenated marine oils.

The triacylglycerol mixture which is the main constituent of oils provides structure, lubricity and caloric density to the product. Additional fatty components may be added for their functional performance such as, for instance, lecithin or similar phosphatide which can be used to promote emulsification and retard "spatter" in frying and monoglycerides for textural smoothing and enhanced emulsification, b -carotene as a colour enhancer. The oils are typically refined, bleached, partially hydrogenated and deodorised. Selectively hydrogenated oils are blended by the manufacturer to achieve required composition and physical properties for margarine.

The physical properties of margarine, especially texture, spreadability, colour, appearance and melting properties are derived from the composition of the fat and the processing technique. Margarines and similar spreads are composed of liquid oil, fat crystals and the aqueous phase. The crystals give margarine the required consistency and stabilize the water droplets. Margarines are prepared from edible oils that are chemically modified by hydrogenation and/or interesterification.

Soyabean oil and palm oil are the main alternative constituents of margarine, the US using soyabean and Europe mainly palm. Other oils as such or partially hydrogenated may be blended. These blends are useful to achieve specific ratios of solid fat to liquid fat within a range of temperatures. The standard method of measuring this ratio is the solid fat index (detailed by the American Oil Chemists Society as method Cd 10 - 57). Typical solid fat indices of margarine are shown below.

The fat crystals formed by the solid portion of the margarine fat form a three-dimensional network or lattice. Within this lattice are the liquid oil and aqueous phase of the product. As the ratio of solid-to-liquid fat increases, the texture and consistency become firmer and more rigid. Stick margarines contain 10 -15% more solid fat at 10ºC than soft or tub margarines, which cause the stick product to be more resistant to distortion.

Fats exhibit polymorphic behaviour in that they can solidify in more than one crystal form. The forms, designated a, b‘, b, result from interaction of the component fatty acids of the tryglyceride mixture and from the rate of phase change from liquid form to solid. The a form is the least stable and lowest-melting crystal. The crystals are initially formed by the super cooling, rapid chilling process of margarine manufacture. The a crystals transform with time to an intermediate b‘ crystal that is optimal for margarine. Beta crystals can be formed under certain conditions of storage, typically from inadequate continuous refrigeration. These latter crystals show a tendency to grow and can foreshadow the development of a sandy, coarse textured product. Triacylglycerol polymorphism is not completely understood, but it is generally percieved that b-forming tendencies are proportional to the uniformity of triacylglycerol structure.Margarine formulated for table use rather than for cooking is designed to melt completely slightly below body temperature, which prevents the mouthfeel sensation of waxiness. Puffed pastry needs margarine with the highest transition range so that melting only occurs completely after a reasonable degree of starch gelatinization. In this way the mechanically produced multilayered material initially puffs when heated and only then does lubrication by melted fat occur.