Classification and composition of food oil and fat

Classification and composition of food oil and fat 1. Classification of vegetable oils Before we talk about composition and characters of vegetable oils and their types, we take a look over classification of vegetable oils and fats and their original sources and fields of various uses in daily lives. We find vegetable or animal oils or fatty acids are widespread in the nature due to basic necessity in composition of all forms of plants and animals life. Every plant or animal produces large amounts of oil or fat during its lifetime. Oils and fats are classified to the following categories.

1. According to natural vegetable or animal source 2. According to chemical composition 3. According to iodine number 1. According to natural vegetable or animal source Vegetable and animal oils are classified according to its natural source to two parts: A. Vegetable B. Animal oils fats and oils

A. Vegetable oils The plants, especially annual plants are considered major source of oil in present time. These plants include in particular field crops group such as soy bean, cottonseed, peanut, flaxseed, sesame, sunflower, safflower, castor bean, rapeseed, pop corn, wheat embryo, tomato, grape seeds and rice husk which we get it as a secondary resulting because basically it is planted other than obtain oil as a main resulting. As plant perennial trees form a second source of vegetable oils where these trees and plants produce oily fruit such as coconut oil, palm and olive trees.

Animal fat and oils: The source of animal oils and fats are animals where they form a second source for oils and fats in nature, which human being need it in his food. These fats are present in animal body, either distributed in its tissue or concentrated in certain regions of body.

1. According to chemical composition Oils and fats are divided according to its chemical composition to three main parts: a. Mineral oils Which are formed of hydrocarbons, which includes distillation of petroleum as kerosene, benzene and others which are material used in fuel, greasing and lubrication. These oils are not inedible.

a. Vegetable and animal oils These oils consist of vegetable or animal origin, and considered alcohol esters for triple hydrate called glycerol with fatty acids. These esters are called glycerides, and are used for nutrition, medical and industrial purpose. This is considered a largest groups of oils and fats used in food and their oils is resulted in from cottonseed, peanut, sesame, sunflower , olive oil and palm consist mainly of unsaturated fatty acids.

a. Volatile oils or aromatic oils: Consist of a number of chemical compounds used in fragrances, cosmetics and a spice in various food items used in the food. These chemical compounds belonging to aldehydes and ketones, alcohols, esters, phenols and carboxylic acids and types of turbines (terpenes).

There are many sources of aromatic oils and most imported are: 1. Natural source in the plant or animal 2. Industrial sources produces by chemical methods or from natural materials after chemical modifications have 3. Material separated from natural source

Classification according to iodine number: Before we divide the oils depending on the iodine number, we have to identify the iodine number and its importance for oils. The Iodine number is the number of grams of iodine absorbed by one hundred grams of oil. It reflects the unsaturated number of double bonds quantity in substance. It is the number of grams of iodine required for saturation of double bonds in 100 gram of fat or oil. The iodine number is a chemical test for drought character in oil and plays an important role in its uses. Oils divided to three parts in terms of their iodine number

1. Non-dying oils A non-drying oil is an oil which does not harden when it is exposed to air and that the iodine number of such oils is less than 100 and such oils are found in seeds of castor bean, peanut , rapeseed, olive oil, palm oil and coconut oil. 1. Semi drying oils That are easily oxidized and polymerized to form a hard, dry film on exposure to air, used in paint and varnish. These oils lose part of their liquidity and become half dry. The figure of iodine for such oils ranges between 100 -140. The most important seeds that contain this type of oil is sesame seed oil, cotton seed oil, sunflower oil, soybean oil and corn oil.

1. Drying oils Are those oils that their iodine number is more than 140. The most important that contain dry oils are flax seed oil, safflower oil and soy bean oil. (dry to semi dry oil)

Oil Production & Process The conventional process for preparation of the oil involves the following steps: 1 - Extraction: A screw press is used to extract about 90 % of the oil from the seed. The rest of the oil remains in the seed cake and is often extracted by a petroleum solvent. After the oil /solvent mixture is mechanically extracted from the crushed seed, the solvent is removed from the oil at a temperature of about 300 F. 2 - Refining: The oil is mixed with sodium hydroxide and the resulting soap, comprising sodium salts of free fatty acids, is separated from oil by centrifugation and washed away. 3 - Bleaching: Absorbent earth is added to oil to remove color bodies which are subsequently removed with cloth filters.

4 - Winterization: The oils is cooled and kept at low temperature for some time in order to form crystals that are large enough to be removed by filtration. 5 - Deodorizing: Deodorizing removes aromatic oils, and any remaining free fatty acids. This process consists of blowing steam though heated oil (464 -518 o. F), held under high vacuum, for 30 -60 minutes to remove volatile components, responsible for tastes and odors.

Three pathways are involved in the deterioration of edible oils. I - Hydrolytic Rancidity: In the presence of moisture the fatty acids are cleaved from triglycerides. The reaction is either enzymatic or chemical. The enzymatic reaction occurs in the presence of an enzyme such as lipase and is called lipolytic rancidity. Liberation of free fatty acids leads to the development of off-flavors. The spontaneous chemical reaction is triggered by heat.

II - Oxidative Rancidity Oxidative rancidity takes place when unsaturated fatty acids, free or bound to triglycerides, are attacked by oxygen. Oil deterioration by oxidative rancidity proceeds through autooxidation, although enzymes, lipoxygenases, can also be involved. The auto-oxidation mechanism includes the following steps: free radicals (R ) are formed from lipid molecules (RH) by their interaction with oxygen in the presence of a catalyst (heat, light, metal ions). Free radicals then react with oxygen to form lipid peroxy radicals (ROO ), which in turn react with lipid molecules to give hydroperoxides (ROOH)

III - Ketonic Rancidity Ketonic rancidity results from fungal attack on oils and leads to liberation of ketones and short-chain saturated fatty acids. Lipids There are three classes of lipids in plants; 1. Triglycerides or fats 2. Membrane lipids 3. Cuticular