chapter  30
Enzymatic Interesterification
Pages 34

I. Introduction ........................................................................................................................ 808 A. Transesterification....................................................................................................... 808 B. Acidolysis ................................................................................................................... 810 C. Alcoholysis ................................................................................................................. 811

II. Lipases ................................................................................................................................ 812 A. Three-Dimensional Structure...................................................................................... 812 B. Active Site .................................................................................................................. 813 C. Activation by Interfaces.............................................................................................. 813 D. Problem of Substrate Concentration........................................................................... 815 E. Kinetics and Mechanism of Action............................................................................ 816 F. Specificity ................................................................................................................... 818

1. Nonspecific Lipases ............................................................................................. 818 2. Positional Specificity ........................................................................................... 819 3. Stereospecificity................................................................................................... 820 4. Fatty Acid Specificity .......................................................................................... 820

III. Reaction Systems................................................................................................................ 820 A. Enzymatic Interesterification in Microaqueous Organic Solvent Systems ................ 820

IV. Immobilization.................................................................................................................... 822 A. Factors Affecting Immobilized Lipase Activity ......................................................... 823

1. Mass Transfer Effects .......................................................................................... 823 2. Nernst Layer and Diffusion Layer ...................................................................... 824

B. Stability of Immobilized Enzymes ............................................................................. 825 C. Immobilized Enzyme Kinetics ................................................................................... 825

V. Enzymatic Interesterification Reactors ............................................................................... 826 A. Fixed Bed Reactor ...................................................................................................... 826 B. Stirred Batch Reactor.................................................................................................. 828 C. Continuous Stirred Tank Reactor ............................................................................... 829 D. Membrane Reactors .................................................................................................... 830 E. Fluidized Bed Reactor ................................................................................................ 830

VI. Factors Affecting Lipase Activity during Interesterification.............................................. 831 A. pH ............................................................................................................................... 831 B. Temperature ................................................................................................................ 831 C. Water Content and Water Activity............................................................................. 832 D. Enzyme Purity and Presence of Other Proteins ......................................................... 832 E. Substrate Composition and Steric Hindrance............................................................. 833 F. Surface-Active Agents................................................................................................ 833 G. Product Accumulation ................................................................................................ 833

VII. Conclusions ........................................................................................................................ 834 References ..................................................................................................................................... 834

The development of methods to improve the nutritional and functional properties of fats and oils is of great interest to food processors. The molecular weight, unsaturation, and positional distribution of fatty acid residues on the glycerol backbone of triacylglycerols are the principal factors determining the physical properties of fats and oils [1,2]. Chemical interesterification produces a complete positional randomization of acyl groups in triacylglycerols. It is used in the manufacture of shortenings, margarines, and spreads to improve their textural properties, modify melting behavior, and enhance stability [3,4]. Interest in interesterification from a nutritional and functional standpoint is increasing since it can be used to produce margarines with no trans unsaturated fatty acids, synthesize cocoa butter substitutes, and improve the nutritional quality of some fats and oils [5]. Recently, research efforts have been directed to substituting some chemical interesterification applications with enzymatic interesterification because of the inherent advantages associated with the enzymatic process. Enzymatic reactions are more specific, require less severe reaction conditions, and produce less waste. In addition, when immobilized, enzymes can be reused, thereby making them economically attractive [6]. Interesterification, whether chemical or enzymatic, is the exchange of acyl groups between an ester and an acid (acidolysis), an ester and an alcohol (alcoholysis), an ester and an ester (transesterification) [7].