Chemistry of Fats and Oil

Chemistry of Fats and oil

Fats and oil are triglycerides ester of fats. They are made up of glycerol (OH) base and fatty acid (carboxylic group). Fatty acid is not itself fat. After esterification, it becomes fat. Glyceride is the backbone of fat and oil.

Fig: chemical structure of Fat

Monoglyceride contain one combined (esterified) fatty acid and two free hydroxyl group. Diglyceride contains two esterified fatty acid and one free hydroxyl group. Mono and diglyceride results from partial hydrolysis of triglycerides and occur in appreciable amount in spoiled oils. Oils are almost unsaturated fatty acids. Higher the degree of unsaturation, lower the melting point.

Fig: Monoglyceride, Diglyceride and Triglyceride

Fatty acid:

The molecular weight of glycerol protein, C3H5 of triglyceride is 41. The combined molecular weight of triglyceride including fatty acid ranges from 650 – 970. Thus fatty acid contribute 94- 96% of total weight of triglyceride. Because of their predominant weight in the glyceride molecule and also because they contribute to both chemical and physical properties of glycerides. Fatty acid greatly influences both physical and chemical characteristics of glycerides.

Properties of fatty acid:

1. Minimum number of carbon should be 4 (C4) to maximum 24 (C24)

2. For fatty acid, carbon number must be even

3. Presence of only single bond makes it saturated while presence of double bond makes it unsaturated. Triple bond does not exists.

4. In case of only one double bond, double bond exists in 9th

5. Smallest unsaturated chain have ten number of carbon (C10)

6. Mono and diglycerides are emulsifiers

7. All natural fatty acids are monocarboxylic acid.

The smallest no. of carbon in fatty acid is 4, which gives butyric acid C4H8O2. The number of double depends bond in fatty acid depends upon oil type but is usually 0 to 4. Fatty acids are broadly classified as

1. saturated fatty acid

2. unsaturated fatty acid

 

Classification of fatty acid:

Fig: Classification of fatty acid

 

Saturated fatty acid: Those fatty acids in which no double bond is present are called saturated fatty acids. The most common saturated fatty acid in cooking oil are palmitic acid (palm oil) and stearic acid (lard) and lauric acid (in coconut oil). Some common saturated fatty acid are mentioned below.

No. of carbon Fatty acid Melting point (°C)
4 Butyric acid -8
6 Caproic acid -3.4
8 Caprylic acid 16.7
10 Capric acid 31.6
12 Lauric acid 44.2
14 Myristic acid 54.4
16 Palmitic acid 62.9
18 Stearic acid 69.6

Unsaturated fatty acid: Fatty acid that contain double bond are called unsaturated fatty acid. The degree of unsaturation depends upon number of double bond present. Mono-unsaturation fatty acid (MUFAs) have single double bond and poly-unsaturated fatty acids (PUFAs) have two or more double bonds.

Fig: linoleic acid (Example of polyunsaturated fatty acid)

Some common unsaturated fatty acid:

No. of carbon Fatty acid Position of double bond
10 Caproleic acid 9
12 Lauroleic acid 9
14 Myristoleic acid 9
16 Palmitoleic acid 9
18 Oleic acid 9
18 Linoleic acid 9,12
18 Linolenic acid 1, 12, 15
20 Arachidonic acid 5, 8, 11, 14
22 Clupanodonic acid 4, 8, 12, 15,19

PUFAS are of special importance because of their essentiality in human health.  They are important for hormone secretion, skin health and eye health. Although unsaturation up to three double bond are common, fatty acid with four or more double bond also occur in some vegetable oil and animal fat.

Short chain PUFAs (ACPUFAs): These are absolute requirement in in food as they cannot be synthesized because human lacks desaturase enzyme. This includes linoleic acid and α-linoleic acid (ALA).

Long chain PUFAs (LCPUFAs): These includes

1. Ecosapentanoic acid (EPA)

2. Docosahexanoic acid (DHA)

3. γ-Linolenic acid (GLA)

4. Dihomo γ-Linolenic acid (DGLA)

5. Arachidonic acid (AA)

Essential fatty acids: Some PUFAs are called essential fatty acid because they must be necessarily supplied though diet. There are two family of such essential fatty acid, omega- 6 (ω-6) and omega-3 (ω-3). In balanced diet, adequate proportion of ω-3: ω-6 is 1:3 to 1:5. While counting the carbon in PUFAS from methyl group, where the first double bond occurs, that carbon number is the omega (ω) number. Below is the given example.

Non-glyceride component of fat and oil:

Besides glycerol and fatty acids, fat and oil also contains elements like phosphatides, carbohydrates, protein degradation products, sterols, antioxidants etc. these are called non-glyceride component of fat and oil.

Cholesterol: Cholesterol is the characteristic and predominant sterol of animal fat. It is also known as best known and plentiful sterol.

Phytosterol: Sterols of vegetable oil. Example; sitosterol (cotton seed oil), stigma sterol (soybean oil).

Classification of fat and oil on the basis of their food sources:

1. Animal depot fat: These are present in animals as adipose fat and marble fat. Adipose fat is found in adipose tissue below hide and marble fat is the intramuscular fat found especially in sea animal. Example; lard (edible grade, mainly from pig) and tallow (inedible grade, mainly from beef, buff and goat). They contain mainly palmitic acid, oleic acid and stearic acid and are high in saturated fatty acid (up to 60 %).

 

2. Ruminant milk fat: These are the fat extracted from milk of cow and buffalo. These contain saturated fatty acid (C4 – C12) in high amount.

 

3. Marine oil: These are extracted from sea creatures, mainly fish. They are rich source of PUFAs particularly EPA and DHA.

 

4. Fruit coat fat: These contain mainly palmitic acid, oleic acid and linoleic acid. Example; palm oil.

5. Seed oil: These are extracted from seed of mustard, rapeseed, sesame seed etc. They are characterized by large amount of unsaturated fatty acid such as oleic, linoleic and linolenic acid.

6. Microbial fat and oil: Some microorganisms are developed to produce fat and oil with novel properties. Yeast produce fat by using substrate of petroleum products. These fats are mainly used for industrial use such as lubricants, engine oil etc.

7. Lauric oil: These oil have dominant amount of lauric acid (C12) such as in coconut oil and palm kernel oil.

8. Oleic-linoleic oil: These include most seed oils. Soybean, sunflower, safflower, cottonseed etc. These are rich in linoleic acid and contain appreciable amount of oleic acid. Palmolein and olive oil contain large amount of oleic acid.

9, Linolenic oil: These include oil that contain tri-unsaturation as in linolenic acid. Example; linseed oil (> 40% linolenic acid).

10. Drying, semidrying and nondrying oil:

Drying oil Semidrying oil Non-drying oil
Viscosity of oil increases on storage Viscosity of oil partially changes Viscosity of oil does not change on storage.
Example; linseed oil Example; soybean, mustard Example; olive oil

Fat content of some oil bearing fruits.

Fruit Oil content g/100g
Avocado = 20
Palm = 40
Walnut = 64
Pecan = 73

 Fat content of some oil seeds

Oil seed Oil content g/100g
Soybean = 20
Mustard = 22 – 25
Linseed = 24 – 36
Peanut = 43 – 48
Sesame = 50