Lipases are widely used in the reactions such as esterification of various carboxylic acids such as fatty acids with alcohols such as mono-alcohol and polyalcohol, and trans-esterification between plural carboxylates. In these, the trans-esterification method is an important technology not only as reforming animal and plant fatty oils but also as methods for producing various fatty esters, sugar esters and steroids. When a lipase, which is a fatty acid hydrolytic enzyme, is used as a catalyst of the above reactions, esterification can be conducted under the mild condition such as at room temperature to about 70° C. Therefore, the lipase can better inhibit side reactions and reduce energy costs compared with the existing chemical reactions. Besides those, a lipase as a catalyst is a natural product and, therefore, safe and secure. Further, the lipase can effectively produce the intended compounds through its substrate specificity and site specificity. However, even if lipase powder is used in esterification as itself, activity does not fully express. Further, it is difficult to uniformly disperse a lipase, which is basically a water-soluble product, into oily raw materials, and recover thereof is also difficult. Therefore, in the conventional methods, it is common to immobilize a lipase to some carriers, such as anion-exchange resin (Patent Literature 1), phenol adsorption resin (Patent Literature 2), a hydrophobic carrier (Patent Literature 3), cation-exchange resin (Patent Literature 4) and chelate resin (Patent Literature 5) and to use it in the reactions such as esterification and trans-esterification.
As mentioned above, a lipase has been conventionally immobilized and used in the esterification. However, the immobilized lipase loses an original lipase activity through the immobilization. In addition, when a porous carrier was used, the raw materials and products have gotten stuck in fine pores and, as a result, decreased the ester exchange ratio. Further, in the trans-esterification wherein the conventional immobilized lipase is used, water which a carrier retains is brought into the reaction system, and therefore, it has been difficult to prevent the side reactions such as production of diglyceride and monoglyceride in the trans-esterification of fatty oils.
In light of the situations mentioned above, various technologies have been developed wherein lipase powder is used. For example, a trans-esterification method is proposed wherein in the presence or absence of an inactive organic solvent(s), lipase powder is dispersed into a raw material(s) containing ester in the trans-esterification in such a manner that 90% or more of the particles of the dispersed lipase powder can keep particle size of 1 to 100 μm in the reaction (Patent Literature 6). It is also proposed that enzyme powder is used, which is obtained by drying an enzyme solution(s) containing phospholipid and lipid-soluble vitamins (Patent Literature 7).
However, there has been desired a lipase powder wherein the lipase activity and stability are further improved.    [Patent Literature 1] Japanese Patent Publication No. Sho 60-98984    [Patent Literature 2] Japanese Patent Publication No. Sho 61-202688    [Patent Literature 3] Japanese Patent Publication No. Hei 2-138986    [Patent Literature 4] Japanese Patent Publication No. Hei 3-61485    [Patent Literature 5] Japanese Patent Publication No. Hei 1-262795    [Patent Literature 6] Japanese Patent No. 2668187    [Patent Literature 7] Japanese Patent Publication No. 2000-106873
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