Triacylglycerol

Triacylglycerol

1. Lecture 8 Triacylglycerol

2. Triacylglycerol are esters of glycerol with fatty acids

3. The fats and oils are chemically triacyglycerol They are insoluble in water and non-polar in character and commonly known as neutral fats

4. Fats as stored fuel Triacyglycerols are the most abundant group of lipids that primarily function as fuel reserves of animals The fat reserve of normal human is sufficient to meet the body’s caloric requirements for 2-3 months

5. Fats primarily occurs in adipose tissues Adipocytes are primarily found in the subcutaneous layer and in the abdominal cavity They are specialized for storage of triacylgycerols The fat is stored in the form of globules dispersed in the entire cytoplasm They are not the structural components of biological membranes

6. Structures of acyglycerols

7. Simple and mixed triacylglycerols Simple: contain the same type of fatty acid residue at all the three crbons e.g. tristearin

8. Mixed are more common They contain 2 or 3 different types of fatty acid residues. In general, F.A attached to C1 is saturated, that attached to C2 is unsaturated while on C3 can be either. Triacylgycerol of plants have higher content of unsaturated fatty acids compared to that of animals

9. Properties of tricacylglycerol Hydrolysis Saponification Rancidity Lipid peroxidation in vivo

10. Hydrolysis Triacylglycerols undergo stepwise enzymatic hydrolysis to finally liberate free F.A and glycerol. The process is catalysed by lipases, important for digestion of fat in the gastrointestinal tract and fat mobilization from the adipose tissues

11. Saponification The hydrolysis of triacylglcerols by alkali to produce glycerol and soaps is known as saponification

12. Rancidity It is a term used to represent the deterioration of fats and oils resulting in an unpleasant taste. Fats containing unsaturated fatty acids are more susceptible to rancidity It occurs when fats and oils are expose to air, moisture, light, bacteria etc Hydrolytic rancidity occurs due to partial hydrolysis of triacylglycerols by bacteral enzymes Oxidative rancidity is due to oxidation of unsaturated fatty acid

13. This reults in the formation of unpleasant products such as dicarboxylic acids, aldehydes , ketones etc They are unsuitable for human consumption

14. Antioxidants The substances which can prevent the occurrence of oxidative rancidity are known as antioxidants Trace amounts of antioxidants such as tocopherols (vitamin E), gallic acid an alpha naphtol are added to the commercial preparations to prevent rancidity Propyl gallate , butylated hydroxyanisole , and butylated hydroxy toluene are the antioxidants used in food preservation

15. Lipid peroxidation in vivo In he living cells lipids undergo oxidation to produce peroxides and free radical which can damage the tissue. The free radical are believed to cause inflammatory diseases, ageing, cancer etc It is fortunate that cells possess antioxidant like vitamin E, urate and superoxide dismutase to prevent in vivo lipid peroxidation

16. Tests to check purity of fats and oils Iodine number: It is defined as the grams (number) of iodine absorbed by 100g of fat or oil Iodine number is useful to know the relative unsaturation of fats and is directly proportional to the content of unsaturated fattt acids Lower is the iodine number less is the degree of unsaturation Determination of iodine number will help to know the degree of adulteration of a given oil

17. Saponification number: it is defined as the mg (number) of KOH required to hydrolyze one gram of fat or oil Saponification number is the measure of the average molecular size of the fatty acids present The value is higher for fats containing short chain fatty acids

18. Acid number: It is defined as the number of mg of KOH required to completely neutralize free fatty acids present in one gram fat or oil In normal circumstances refined oil should be free from any free fatty acids. Oil on decomposition due to chemical or bacterial contamination yield free fatty acids Oil with increased acid number are unsafe for human consumption