ABSTRACT
Lipids are very important cell constituents, which can function either as structural components or as carbon and energy reserves. These “basal” molecules are also well known as precursors of compounds, such as prostaglandins or thromboxanes, which play a very important role in the physiology of animal cells. Although mammals use fat as a storage form of energy, they cannot synthesize the very specific lipid molecules which they need, particularly polyunsaturated fatty acids (PUFAs). Since they are unable to introduce double bonds at carbon atoms between C-9 and the terminal methyl group, in order to synthesize ω-3 as well as ω-6 unsaturated fatty acids, such as linoleic (18:2 ∆9,12), α-linolenic (18:3 ∆9,12,15), or γ-linolenic (18:3 A5,9,12), they have to obtain these from exogenous producers (i.e., plants or micro-organisms) through their food. The idea of supplementing human food, particularly that of infants, with exogenous PUFAs (Certik and Shimizu 1999) or modifying lipids in order to produce reduced calories structured lipids (Fomuso and Akoh 1997) is widely developed. Most of the oils used in animal nutrition are produced by plants but, if these sources do not contain enough of certain essential fatty acids, it is often necessary to modify their fatty acid content (Gunstone 2001). The production of novel plant oils (Murphy 1999) and possible alternative sources Gunstone (1999) have been thoroughly reviewed. Micro-organisms (Certik and Shimizu 1999) are able to accumulate fats (Meesters et al. 1996; Ratledge and Wynn 2000). Among them, fungi, which are metabolically very versatile microorganisms, many of which have been shown to be safe for the production of food ingredients (Streekstra 1997) can be used on several ways:
Direct extraction of high value fat accumulated in the cells, using efficient procedures (Chen and Chi 1994; Certik et al. 1996; Somashekar et al. 2001), which do not induce any alteration of fatty acids (Walker et al. 1999; Certik and Horenitzky 1999).
