Fat Products Using Fractionation and Hydrogenation

Summary

Fractionation and hydrogenation are two widely used processes which help to alter the melting profile, physical properties and chemical composition of the feed oil or fat and the products so produced are in effect new ingredients suitable for use in applications in which the original oil/fat could never have been used or would have performed poorly.

Fractionation is a thermomechanical process which eventually leads to two new products, an olein and a stearin. The olein can be used in further fractionations. Three types of fractionation systems are available, dry, solvent and detergent. Stages within each process such as nucleation and crystallisation and the conditions under which these are carried out are critical in determining the quality of the fractions. Equally, the separation efficiency of the filters also decides the yield of each fraction. Vacuum filters (e.g. Florentine, Vacuband, Stockdale) are being challenged by positive pressure membrane filters. Recent innovation with respect to the latter is a membrane filter by Krupp used in dry fractionation of fats for cocoa butter replacers. During filtration the pressure can be increased up to an end pressure of more than 50 bar.

Fractionation has enabled the introduction of many fats, particularly milkfat, into new food applications. These fats are now used to better effect in areas such as in the manufacture of stable creams, buttercreams, sauces, infant feed, ice-cream, bakery products and chocolate. The use of fractionated milkfat in yellow fat spreads is increasing, particularly in the production of spreadable butters. Fractionated fats are also used as stable frying oils and salad oils. The fractionated oils or fats can be incorporated directly into some recipes but in others they are used in blends with other oils. Some are also treated in further processes such as texturisation, in this case to make them suitable for use in bakery products.

The measurement of solid fat content at 20°C by pulse NMR is a useful aid for determining suitability of milkfats for specific food applications.

Hydrogeneration decreases the unsaturation of triacylglycerol oils and thereby increases their melting points. The chemical composition of the feed and the conditions under which the reaction is carried out, together with the type of catalyst used, help to determine the physical properties of the fat and the way in which it melts over a temperature range. The choice of the catalyst for the reaction is critical and re-use of catalyst can also generate products with interesting functional benefits.

In a number of applications such as bakery and confectionery products, it is important to have fats which remain firm at ambient temperature but which melt rapidly and are liquid at body temperature. Careful choice of oils and close control of the hydrogenation reactor are important to produce these oils. Equally, it is also sometimes necessary to lightly saturate a liquid oil to improve its oxidative stability, typically for use as a salad oil. Again, similar guidelines apply.

A number of novel processes have been described for the manufacture of stable fats with good taste and colour for use in cooking, as table oils and as base stocks for margarines. Other techniques are available to produce hard butters for bakery coatings and confectionery products. Also, non-conventional oils such as jojoba oil, fish oil, rice bran oil and cottonseed/ coconut oils have been hydrogenated under specified conditions to produce chocolate and confectionery fats. Palm oil and palm kernel oil have also been described and used in several novel processes as feed oils for the manufacture of cocoa butter substitutes.

Hydrogenated milk fat recombined with skimmed milk powder has been shown to result in a whole milk which has a more stable flavour. These fats can also partially substitute for cocoa butter in dark chocolate without loss in product quality. They have also been shown to retard fat bloom in chocolate.