Mutton fat has a similar fatty acid profile with Cocoa Butter (CB), except that its degree of unsaturation of Triacylglycerol (TAG) at the Sn-2 position is considerably lower than CB and maybe increased by Sn-2 specific lipase to produce Cocoa Butter Equivalent (CBE), a healthy functional lipid. However, there is no commercially available Sn-2 specific lipase that can be used to convert mutton fat to CBE by improving its Unsaturated Fatty Acids (UFA) at Sn-2 position. Similar to plant, yeast fat contains higher UFAs at the Sn-2 position than animal fat. In this study, we investigated the conversion of mutton fat to CBE by fermentation of oleaginous yeast Yarrowia lipolytica which acts as a "Sn-2 specific lipase". The yeast was able to grow on mutton fat as the sole carbon source yielding a dry cell weight of 14.11 g L −1 and 33.1% lipid content after 3 days of cultivation. At optimal fermentation conditions, the degree of unsaturation of TAGs at the Sn-2 position increased from 61.5 (mutton fat) to 89.3% (cellar lipid, 72 h) while the amount of Saturated Fatty Acids (SFA) of the Total Fatty Acids (TFA) was decreased from 58.9 to 34.5%. In addition, the presence of methyl stearate as the cosubstrate in the medium improved the ratio of SFAs/TFAs. It was found that fatty acid profile of the yeast fat with 24.60% palmitic acid, 31.34% stearic acid, 34.29% oleic acid, 5.57% linoleic acid and degree of unsaturation at Sn-2 position in TAGs (84.66%) resembled that of CB when the yeast was grown on mutton fat/methyl stearate (with a ratio of 60/40) as carbon source. These results suggest that biotransformation or metabolism could be directed by using mixtures of inexpensive animal fats and saturated fatty acid or methyl as co-substrates, to produce functional lipids with predetermined composition, such as CBE.

In order to obtain the optimal control point for single-cell lipid production with fatty acid profile similar to cocoa butter, this study explored the effects of carbon source, nitrogen source, temperature, sterculic acid methyl ester, cobalt on cell growth and lipid accumulation of Yarrowia lipolytica. Glycerol and ammonium tartrate-yeast extract were chosen as carbon source and nitrogen source for production of cocoa butter equivalent. Gradual increase in temperature (20-35°C) resulted in growth reduction, while increased in lipid content per Cell Dry Weight (CDW) (10.13 to 19.7%, w/w) and Saturated Fatty Acids (SFA). Our results suggests that the optimum conditions for Y. lipolytica to synthesize cocoa butter equivalent was 30°C with 0.6 mg L −1 of CoCl 2 ·6H 2 O or 0.03 mL L −1 sterculic acid methyl ester in the medium with glycerol and ammonium tartrate-yeast extract as carbon source and nitrogen source.

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