Hydrogenation is the process by which hydrogen is added directly to points of unsaturation in the fatty acids. The purpose of hydrogenation is to obtain oils and fats with specific melting profiles or oxidative stability by reducing unsaturated double bonds in the oil system. Since hydrogenation converts unsaturated triglycerides into saturated ones, thus it converts liquid oils to the semi-solid form for greater utility in certain food uses.
Once hydrogenated, vegetable oils have better functionalities in the food systems, e.g. as bakery shortenings, confectionery fats, and stable frying oils. Hydrogenation is accomplished by reacting oil with hydrogen gas and in the presence of heat and metal catalysts, e.g. nickel. The input oil quality into a hydrogenation step must be clean, since impurities may interfere with catalysts during process. The minimum quality requirement of oils used in the hydrogenation process is neutralised and bleached oil, but some processors even utilise fully refined oils as input oil.
A better melting profile of oil/fat system can also be achieved via interesterification, which is defined as the interchange of fatty acids from different fats/oils on the glycerol backbone. There are two types of interesterification processes: chemical and enzymatic. Chemical interesterification in the presence of basic catalysts, e.g. sodium methoxide, results in non-selective or random rearrangements of fatty acids. Interesterification using immobilised lipases is more commonly done in the industry due to its selective modification of fatty acids.
After hydrogenation or interesterification, the output product is bleached (if necessary) and (re-) deodorised.
The predominant commercial application for interesterification in the EU is the production of shortenings and speciality fats for the confectionery and vegetable dairy industries. This process permits the production of high-stability margarine blends that have highly desirable melting qualities, such as cocoa butter substitutes.
The fractionation process consists on the removal of solids by controlled crystallization and separation techniques involving the use of solvents or dry processing. Dry fractionation encompasses both winterization and pressing techniques and is the most widely practiced form of fractionation. It relies upon the differences in melting points and triglyceride solubility to separate the oil fractions.
Pressing is a fractionation process sometimes used to separate liquid oils from solid fat. This process presses the liquid oil from the solid fraction by hydraulic pressure or vacuum filtration. This process is used commercially to produce hard butters and specialty fats from oils such as palm and palm kernel.
Solvent fractionation is the term used to describe a process for the crystallization of a desired fraction from a mixture of triglycerides dissolved in a suitable solvent. Fractions may be selectively crystallized at different temperatures after which the fractions are separated and the solvent removed. Solvent fractionation is practiced commercially to produce hard butters.