Handbook of Lipids in Human Nutrition

Gene A. Spiller, Gene A. Spiller

• Editore: CRC Press
• Anno: 2020
• ISBN:
  9781000141450
• Edizione: 1
• Argomento: Biological Sciences
• Categoria: Biochemistry

The Handbook of Lipids in Human Nutrition is a concise reference for professionals and students interested in the role of lipids in nutrition. Over 100 tables and illustrations provide quick access to the most current data available.

Section 1: Chemistry, Nomenclature, and Analyses

Chapter 1.1

LIPIDS IN FOODS: CHEMISTRY AND NOMENCLATURE

Irena B. King

INTRODUCTION

Lipids are chemically diverse compounds which can be extracted from animal, plant, and microbial sources with a variety of methods. There is no universal definition of the term lipid. Lipids are usually described, broadly, as those compounds which are insoluble in water and soluble in selected organic solvents such as chloroform, hexane, benzene, diethyl ether, or methanol.¹ Christie² recommends a more constricted definition that closely reflects the origins of the term, i.e., “lipids are fatty acids and their derivatives, and substances related biosynthetically or functionally to these compounds”. In foods, especially those high in fat, lipids are predominantly triesters of fatty acids with glycerol as a main derivative. The purpose of this discussion is to briefly review the nomenclature, structure, and classification of the major lipids normally found in foods.

NOMENCLATURE

The Commission on Biochemical Nomenclature (CBN) formed by the International Union of Pure and Applied Chemistry (IUPAC) and the International Union of Biochemistry (IUB) has established appropriate nomenclature for lipid terminology.³ However, in addition to the systematic names, lipid nomenclature often includes a shorthand notation and a wide range of trivial names which are firmly established in the literature of lipid methodology.

The systematic names of fatty acids are based on the CBN nomenclature and indicate the carbon length, position, and configuration of the double bond (Table 1).

CLASSIFICATION

Lipids are most clearly classified into simple, complex, and derived lipids (Table 2). The simple lipids have a fatty acid ester or ether linkage with alcohols. The complex lipids contain other groups in addition to fatty acids with simple derivatives. The derived lipids include compounds obtained by hydrolysis from simple and complex lipids.

Fatty Acids

Although fatty acids are major building blocks of simple and complex lipids, they occur naturally only in trace amounts in this unesterified form and are usually obtained by hydrolysis of the backbone derivatives (glycerols, sterols, or fatty alcohols). There are more than 1000 different kinds of fatty acids identified; fortunately, only a small fraction of these are important from the perspective of food analysis. All fatty acids have a hydrocarbon chain and a carboxyl terminal. Fatty acids differ from each other primarily in chain length and in the number, position, and configuration of the double bonds (Figure 1).

Fatty acids can be either saturated or unsaturated. The saturated fatty acids do not contain any double bonds, while the unsaturated ones have at least one double bond. Fatty acids that have only one double bond are known as monounsaturated; those that have two or more bonds are polyunsaturated. The double bonds can be designated from carboxyl or methyl ends. The presence of the double bond allows for configurational isomerism in cis or trans position. Naturally occurring fatty acids are mostly in the cis configuration.

TABLE 1
Typical Fatty Acids in Foods

Systematic name	Shorthand notation	Trivial name	Major sources
Saturated
Tetranoic	C4:0	Butyric	Butter
Hexanoic	6:0	Caproic	Butter
Octanoic	8:0	Caprylic	Coconut
Dodecanoic	12:0	Laurie	Palm kernel, coconut
Tetradecanoic	14:0	Myristic	Palm kernel, coconut
Hexadecanoic	16:0	Palmitic	Palm
Octadecanoic	18:0	Stearic	Most animal fats, cocoa
Eicosanoic	20:0	Arachidic	Peanut
Docosanoic	22:0	Behenic	Seeds
Tetracosanoic	24:0	Lignoceric	Peanut
Monounsaturated
Cis
9-Tetradecanoic	14:1n5	Myristoleic	Butter
9-Hexadecanoic	16:1n7	Palmitoleic	Seafood, beef
9-Octadecanoic	18:1n9	Oleic	Olive, canola
11-Octadecanoic	18:1n7	Vaccenic	Seafood
13-Docosenoic	22:1n9	Erucic	Rapeseed
Trans
9-Octadecanoic	t-18:1 n9	Elaidic	Hydrogenated fats
11-Octadecanoic	t-18:1n7	Transvaccenic	Hydrogenated fats, butter
Polyunsaturated
All cis
9,12-Octadecatrienoic	18:3n6	Linolenic	Sunflower, safflower
6,9,12-Octadecatrienoic	18:3n6	γ-Linolenic	Primrose
8,11,14-Eicosatrienoic	20:3n6	Dihomo-γ- linolenic	Shark liver^a
5,8,11,14-Eicosatetraenoic	20:4n6	Arachidonic	Eggs, most animal fats
9,12,15-Octatrienoic	18:3n3	Linolenic	Soybean, canola
5,8,11,14,17-Eicosapentaenoic	20:5n3	Timnodonic	Seafood
7,10,13,16,19-Docosapentaenoic	22:5n3	Clupadonic	Seafood
4,7,10,13,16,19-Docosahexaenoic	22:6n3	Cervonic	Seafood

^a From Perkins.¹

TABLE 2
Lipid Classification

Simple lipids

Acylglycerols

Ether acylglycerols

Sterols and sterol esters

Wax esters

Complex lipids

Glycerophospholipids

Glyceroglycolipids

Sphingolipids

Plasmalogens

Derived lipids

Fatty acids

Alcohols (glycerols, sterols, fatty alcohols)

Acylglycerols

Acylglycerols are esters of fatty acids and glycerol as shown in Figure 2. Although they are often called glycerides or neutral lipids, neither term is recommended by the standard nomenclature rules. One, two, or three fatty acids may be attached to the glycerol backbone, resulting in mono-, di-, or triacylglycerols, respectively. Triacylglycerols are the most abundant in foods. Although the three acyl groups may be identical in nature, the fatty acids are...