Lipids

 

Study Notes on Lipids

Overview of Lipids

Lipids, along with proteins and carbohydrates, are essential structural components of living cells.

•  They serve as important energy storage compounds, particularly in animals and humans.

• Their role in diet has gained attention due to their connection with blood cholesterol and heart diseases.

• Lipids exhibit unique physical and chemical properties that contribute to their diverse functional roles.

• They encompass a variety of compounds such as oils, fats, waxes, cholesterol, and phospholipids.

• Lipids are insoluble in water and are identified by their solubility in organic solvents like ether, chloroform, and benzene.

• Food lipids are consumed in 2 forms; Visible fats, like vegetable oils and butter, are separated from the original source and are easily seen. Invisible fats are inherent in basic foods like milk, cheese, and meat, consumed without separation.

Fats and Oils 

• Fats are the principal component of diet. Fats are enjoyed in the food due to its characteristics that are its flavor/mouthfeel, perishability, texture, and aroma

• Fats are solids at room temperature while oils are liquids at room temperature.

• They are insoluble in water

• Fats may be processed into monoglycerides and diglycerides by breaking into glycerol units

• Edible oils may use in margarines, spreads, and dressings as retail bottled oils as frying oils and more

• Fats and oils are in many food groups yet they are not part of the composition of fruits and any vegetables.

• Many health recommendations states that fats and oils must be used sparingly in diets

• Fats and oils are diglycerides, an important constituent of lipids.

STRUCTURE OF FATTY ACIDS:

• Fatty acids are long hydrocarbon chains, with a methyl group (CH3) at one end of the chain and a carboxylic acid group (COOH) at the other. 

• Most natural fatty acids contain from 4 to 24 carbon atoms, and most contain an even number of carbon atoms in the chain. For example, butyric acid is the smallest fatty acid, having four carbon atoms, and it is found in butter.

• Fatty acids have the general formula CH3 (CH2 )nCOOH

• There are two types of fatty acids: saturated fatty acids and unsaturated fatty acids.

• Double bonds in fatty acids can be in cis or trans configurations, affecting the molecule's properties.

• In the cis form, hydrogen atoms attached to carbon atoms of the double bond are on the same side, while in the trans form, they are on opposite sides. This affects melting point and shape.

• Trans double bonds have a higher melting point and maintain a linear shape.

• Cis double bonds introduce a kink in the chain, affecting properties like melting points.

STRUCTURE AND COMPOSITION OF FATS 

Glycerides

• Glycerides include monoglycerides, diglycerides, and triglycerides. The first two act as emulsifiers in foods, while the most abundant fatty substance in food—more than 95 %—is the latter, triglycerides. 

• If a triglyceride contains three identical fatty acids, it is called a simple triglyceride; if it contains two or three different fatty acids, it is called a mixed triglyceride. 

FATTY ACIDS:

• Fatty acids are long hydrocarbon chains, with a methyl group (CH3) at one end of the chain and a carboxylic acid group (COOH) at the other.

• Most natural fatty acids contain from 4 to 24 carbon atoms, and most contain an even number of carbon atoms in the chain. For example, butyric acid is the smallest fatty acid, having four carbon atoms, and it is found in butter.

• Fatty acids have the general formula CH3 (CH2 )nCOOH

• There are two types of fatty acids: saturated fatty acids and unsaturated fatty acids.

• The double bonds in fatty acids occur in either the cis or the trans configuration representing different isomeric structures.

• In the cis form, the hydrogen atoms attached to the carbon atoms of the double bond are located on the same side of the double bond.

• In the trans configuration of the isomer, the hydrogen atoms are located on opposite sides of the double bond, across from one another.

• This configuration of the double bonds affects both melting point and shape of a fatty acid molecule.

• The trans double bonds have a higher melting point than the cis configurations, and trans configurations do not significantly change the linear shape of the molecule. However, a cis double bond causes a kink in the chain. (A cis double bond introduces a bend of about 42 deg. into the linear hydrocarbon chain.) Such kinks affect some of the properties of fatty acids, including their melting points as was mentioned.

• The National Cholesterol Education Program (NCEP) has stated that “trans fatty acids are another LDL-raising fat that should be kept to a low intake.

• Specific labeling that includes trans fatty acid content had been desired by some nutrition activists, It became law that Nutrition Facts food labels and advertisements must include data on trans-fatty acids in foods. 

• As a result of this legislation, some food manufacturing companies made an early decision to simply not use trans fats in their products.

• Food manufacturers may only be required to list trans fats if they total more than 0.49 g per serving. Thus, some food content modification may have been necessary for better labeling.

SATURATED FATTY ACIDS	UNSATURATED FATTY ACIDS
They contain single carbon-to-carbon bonds	Fatty acids may be unsaturated, containing one or more carbon-to-carbon double bonds
They have a linear shape, and appear solid at room temperature	unsaturated fats are liquid at room temperature
They have a high melting point.	They have low melting points.
Mostly animal origin	Mostly plant origin
Not too good for health	Good for health
e.g. Palmitic acid, Stearic acid	e.g. oleic acid (mono-saturated) linoleic and linolenic acids (poly-unsaturated)

NOMENCLATURE OF FATTY ACID

• Fatty acids are named in three ways: 

(1) each has a common or trivial name, which has been used for many years, and they also have 

(2) a systematic or Geneva name, which is more recent and has the advantage of describing (3)the structure of the fatty acid to which it belongs. 

In addition, there is the omega system, which classifies fatty acids according to the position of the first double bond, counting from the methyl end of the molecule. 

PROPERTIES OF FATS AND OIL 

1) CRYSTAL FORMATION 

When liquid fat is cooled, the molecular movement slows down as energy is removed, and the molecules are attracted to each other by van der Waals forces. These forces are weak and of minor significance in small molecules. However, their effect is cumulative, and in large or long-chain molecules, the total attractive force is appreciable. Consequently, fat molecules can align and bond to form crystals.

2) POLYMORPHISM:

• Fats can exist in different crystalline forms, and this phenomenon is known as polymorphism. A fat may crystallize in one of four different crystal forms, depending on the conditions during crystallization and on the composition of the fat. 

• The smallest and least stable crystals are called alpha (α) crystals. These are formed if fats are chilled rapidly. 

• The alpha crystals of most fats are unstable and change readily to beta prime (β’) crystals. These are small needlelike crystals, approximately 1 μm long. 

• Fats that can form stable β-crystals are good for use as shortenings, as they can be creamed easily, and give a smooth texture. 

• Unstable β’-crystals change to the intermediate crystal form, about 3–5 μm in size, and finally convert to coarse beta (β) crystals, which can range from 25 to 100 μm in length. Beta crystals have the highest melting point.

3) MELTING POINT:

• The melting point of a fat or oil is an index of the force of attraction between molecules. The greater the attractive forces between molecules, the more easily they will associate to form a solid, and the harder it is to separate them when they are in the crystalline form and convert them to a liquid. A lot of energy in the form of heat must be put in to convert a solid to a liquid; thus, the melting point will be high.

4) EMULSIFICATION: 

Emulsification is the process of mixing two immiscible liquids, such as oil and water, in such a way that they become finely dispersed into each other to form a stable emulsion. 

This is usually achieved by adding an emulsifying agent, such as a surfactant, that can stabilize the interface between the two liquids and prevent them from separating. Emulsions can be either oil-in-water (where the oil is dispersed in the water) or water-in-oil (where the water is dispersed in the oil). 

Emulsification is an important process in many industries, including food, cosmetics, and pharmaceuticals, where it is used to create products with desired physical and chemical properties.

PROCESS AND PRODUCTION 

1) DEODORIZED OIL:

• Deodorized oil is a type of oil that has undergone a process called deodorization, which removes the strong and often unpleasant odors and flavors associated with certain types of oils.

2) RENDERED FAT:

Rendered fat is a type of fat that is obtained by melting and heating animal fat or tissue, such as pork, beef, or poultry, to separate the fat from the protein and other solids. The process of rendering involves simmering the fat or tissue in a pot or oven until the fat melts and the solids are removed.

Rendered fat can be used in cooking and baking, as a substitute for butter or oil, and is also used in the production of processed foods, such as snacks and baked goods.

DETERIORATION OF FATS 

RANCIDITY:

Rancidity is a term used to describe the development of off-flavors and odors in fats and oils when they undergo oxidative spoilage. This can happen due to exposure to air, light, heat, or moisture, causing the fats and oils to break down and become rancid.

1. Oxidative rancidity:

• Oxidative rancidity is a type of rancidity that occurs when fats and oils are exposed to oxygen and undergo oxidation. This can happen when the fats and oils are exposed to air, light, or heat, or when they are stored for long periods of time.

2. Hydrolytic Rancidity: 

• Hydrolytic rancidity is a type of rancidity that occurs when fats and oils are exposed to water and undergo hydrolysis. This can happen when fats and oils are exposed to moisture, or when they are stored in a humid environment.

APPLICATIONS OF FATS AND OIL

Fats and oils are widely used in the food processing industry for a variety of applications, including:

1. Cooking oils: Fats and oils are used as cooking oils for frying, baking, and sautéing. They provide heat transfer and add flavor and texture to food.

2. Margarine and shortening: Margarine and shortening are used as substitutes for butter in many baked goods, such as cakes, cookies, and pastries. They are also used in spreads and as a cooking fat.

3. Salad dressings and mayonnaise: Fats and oils are used in salad dressings and mayonnaise to provide emulsification and to enhance flavor and texture.

4. Confectionery: Fats and oils are used in the production of confectionery, such as chocolate and candy, to provide texture, mouthfeel, and stability

5. Dairy products: Fats and oils are used in the production of dairy products, such as cheese, butter, and ice cream, to enhance flavor, texture, and stability.

6. Meat and poultry processing: Fats and oils are used in meat and poultry processing to improve tenderness, flavor, and moisture retention.

7. Baked goods: Fats and oils are used in baked goods to provide structure, tenderness, and flavor.

Overall, fats and oils are essential ingredients in many food products, providing flavor, texture, and functionality. Their unique chemical properties make them ideal for use in a wide range of food processing applications.