**2.3 Fatty acid profile and distribution intriacylglycerols**

The fatty acid composition of olive oil varies widely depending on the cultivar, maturity of the fruit, altitude, climate, and several other factors(Galtier et al,2008). The major fatty acids in olive oil triacylglycerols are oleic acid (C18:1), a monounsaturated omega-9 fatty acid which makes up 55 to 83% of olive oil. Another fatty acid is linoleic acid (C18:2), a polyunsaturated omega-6 fatty acid that makes up about 3.5 to 21% of olive oil. Palmitic Acid (C16:0), a saturated fatty acid that makes up 7.5 to 20% of olive oil, stearic Acid (C18:0), a saturated fatty acid that makes up 0.5 to 5% of olive oil and linolenic acid (C18:3) (specifically alpha-Linolenic Acid), a polyunsaturated omega-3 fatty acid that makes up 0 to 1.5% of olive oil .Olive oil contains more oleic acid and less linoleic and linolenic acids than other vegetable oils, that is, more monounsaturated than polyunsaturated fatty acids . This renders olive oil more resistant to oxidation. The different fatty acids have stereospecific distribution on the glycerol backbone rather than a completely random or "restricted random" distribution. In most vegetable oils either 18:1 or 18:2 are exclusively at the sn-2 position in the triacylglycerol species like OOO,LLL,POL and LLO. Linolenic acid (C18:3) occurs less commonly,but when present , is at the sn-3 position as seen for OOLn in canola oil. Oleic acid is commonly at the sn-2 position of the olive oil triacylglycerols. (Karupiah & Sundram, 2007).Table 2 shows the fatty acid distribution in the three positions

Biocatalyzed Production of Structured Olive Oil Triacylglycerols 451

In recent years, the use of lipases to modify the properties of triacylglycerols has received considerable interest and has been the subject of extensive research worldwide. Lipases catalyze three types of reactions and the catalytic action of lipases is reversible. They catalyze hydrolysis in an aqueous system, but also esterification (reverse reaction of hydrolysis) in a microaqueous system, where water content is very low. Transesterification is categorized into four subclasses according to the chemical species which react with the ester. Alcoholysis is the reaction with an ester and an alcohol, while acidolysis is the one with an ester and an acid. Interesterification is a reaction between two different esters, where alcohol and acid moiety is swapped. Lipases can be classified according to their positional specificity into two groups: 1,3-positional-specific and non-positional-specific. Usually, pancreatic and fungal lipases are 1,3-positional-specific, while yeast and bacterial ones are non-positional specific or weakly 1,3-positional-specific. It should however be noted that the positional specificity of lipases is not strictly divided into the two categories, but it varies widely in the range of very distinctly 1,3-positional-specific to very weakly specific or completely non-positional-specific By exploitation of the specificity of lipases it is possible to produce acylglycerol mixtures which cannot be obtained by conventional chemical modification processes. Specificity of lipases can be utilized to produce products that cannot be produced otherwise which means that with 1,3 specific lipases, reactions involving triacylglycerol changes are confined to the sn-1 and sn-3 positions and the sn-2 acyl groups remain unaltered. There are several advantages connected to the use of lipases. The relatively mild reaction conditions for lipases reduce the amount of by products formed in a reaction. The use of lipases also renders it possible to process substances such as polyunsaturated fatty acids which cannot be processed by the conventional high temperature/high pressure processes.(Kennedy,1991Adamczack,2004) With the application of new biotechnological techniques ,companies are now able to produce lipases at lower costs. This will make the enzymatic processes far more competitive to the existing processes

Structured triacylglycerols may be prepared by hydrolysis of fatty acyl groups from a mixture of TAGs and random re-esterification follows onto the glycerol backbone. Depending on the desired metabolic effect , a variety of fatty acids are used in this process, including different classes of saturated, monounsaturated, and polyunsaturated fatty acids.Thus, a mixture of fatty acids is incorporated onto the same glycerol molecule. These manufactured lipids are structurally and different metabolically from the more simple, random physical mixtures of medium-chain triacylglycerols (MCTs) and long-chain triacylglycerol (LCT). Six possible fatty acid combinations could result for structured triacylglycerols prepared with an MCT and LCT and these are two MCFAs and one LCFA; one MCFA and two LCFAs; the two positional isomers; and small amounts of the starting MCT and LCT (Fig.2).Based on their high regiospecificity, lipases are effective biocatalysts for the manufacture of structured lipids that have a predetermined composition and distribution of fatty acids on the glycerol backbone. Structured lipids resembling TAGs of human milk have been produced by trans-esterification of tripalmitin, depending on the desired metabolic effect from plant oil, with oleic acid or PUFAs, obtained from plant oils,

**3.1.1 Lipases** 

for the production of structured triacylglycerols.

**3.1.2 Enzymatic processes of modification** 


of the glycerol molecule as reported by Uzzan (1996). In esterified olive oil, the content of saturated acids palmitic and stearic in position 2 is higher, with values of approximately 13- 15% compared to the normal 1.5-2%.

Table 2. Fatty Acid Distribution in the three positions of olive oil triacylglycerol
