Structured Lipids

I. Introduction......................................................................................................................... 841 A. What Are Structured Lipids? ...................................................................................... 841 B. Rationale for Structured Lipid Development.............................................................. 842

II. Production of Structured Lipids ......................................................................................... 843 A. Sources of Fatty Acids for Structured Lipid Synthesis .............................................. 843

1. Short-Chain Fatty Acids....................................................................................... 844 2. Medium-Chain Fatty Acids and Triacylglycerols................................................ 844 3. Omega-6 Fatty Acids ........................................................................................... 846 4. Omega-3 Fatty Acids ........................................................................................... 846 5. Omega-9 Fatty Acids ........................................................................................... 848 6. Long-Chain Saturated Fatty Acids....................................................................... 848

B. Synthesis of Structured Lipids.................................................................................... 848 1. Chemical Synthesis .............................................................................................. 848 2. Examples of Commercial Products...................................................................... 849 3. Enzymatic Synthesis ............................................................................................ 850 4. Analysis of Structured Lipids .............................................................................. 857

III. Absorption, Transport, and Metabolism of Structured Lipids ........................................... 859 IV. Nutritional and Medical Applications ................................................................................ 860 V. Safety and Regulatory Issues ............................................................................................. 862 VI. Diacylglycerol Oils............................................................................................................. 862

A. What Are DAG Oils?.................................................................................................. 862 B. Enzymatic Synthesis of DAG Oils ............................................................................. 862 C. Metabolic Characteristics and Physiological Benefits of DAG Oils .......................... 863

1. Hypotriglyceridemic Effect .................................................................................. 863 2. Antiobesity Effect ................................................................................................ 864

VII. Perspectives ........................................................................................................................ 864 References ..................................................................................................................................... 865

In a broad sense, structured lipids (SLs) are lipids that have been chemically or enzymatically modified from their natural biosynthetic form. In this definition of SLs, the scope of lipids includes triacylglycerols (TAGs) (the most common types of food lipids) as well as other types of acylglycerols, such as diacylglycerols, monoacylglycerols, and glycerophospholipids (phospholipids). The term modified means any alteration in the structure of the naturally occurring lipids. This definition includes the topics covered in Chapters 26-28 and 32. In a narrower sense and in many cases, SLs are specifically defined as TAGs that have been modified by incorporation of new fatty acids, restructured to change the positions of fatty acids, or the fatty acid profile, from the natural state, or

synthesized to yield novel TAGs. The fatty acid profiles of conventional TAGs are genetically defined and unique to each plant or animal species. In this chapter, SLs preferentially refer to TAGs containing mixtures of fatty acids (short chain and=or medium chain, plus long chain) esterified to the glycerol moiety, preferably in the same glycerol molecule. Figure 31.1 shows the general structure of SLs; their potency increases if each glycerol moiety contains both short-(SCFAs) or medium-chain fatty acids (MCFAs) and long-chain fatty acids (LCFAs). SLs combine the unique characteristics of component fatty acids such as melting behavior, digestion, absorption, and metabolism to enhance their use in foods, nutrition, and therapeutics. Individuals unable to metabolize certain dietary fats or with pancreatic insufficiency may benefit from the consumption of SLs.