## 1 Introduction  
Phospholipids are major constituents of cell membranes and play a critical in the metabolic activity of cells [1]. They have been beneficial used as biocompatible amphiphilic materials for foods, cosmetics and pharmaceutical components. Egg yolks and plant seeds are commonly known as major bioresources of phospholipids [2, 3]. Phospholipase A\({}_{1}\) (PLA\({}_{1}\)) is one subgroup of phospholipases with 1-acyl hydrolytic activity. PLA\({}_{1}\), particularly, hydrolyzes the ester bond at the sn\({}^{-1}\) position of a phospholipid [4, 5], and therefore it is commonly employed to modify the fatty acid ester bond at the sn\({}^{-1}\) position. Fatty acid esters act as excellent biocompatible emulsifiers for the food and pharmaceutical industries such as polyglycerol esters of fatty acids or sugar ester [6, 7]. In the industrial applications for biotransformation, enzyme immobilization is a key technique that ensures the recycling of the biocatalyst [8, 9, 10]. However, the arising challenge is to assess the industrial applications of hydrophobic reactions. Particularly, accurate selection of lipase carrier which has good compatibility with hydrophobic solvent, requiresspecial attention. The enhanced reproducibility and repeatability allow for the continuous easy separation of the product and reduces the cost of the biochemical processing [11; 12; 13]. Hydrophobic enzyme reactions normally contain an antinomy. A fatty acid substrate needs a hydrophobic solvent [14; 15; 16]. However, enzymes dislike hydrophobic surroundings as they require a certain amount of water molecules to form a special molecular structure for reactivity. Therefore, the optimal hydrophobic-hydrophilic condition of the reaction media in a hydrophobic enzyme reaction is critical to realize the maximum yields of lipase-aided biochemical reactions. The optimal water content in water-in-oil (\(W\)/O) microemulsion systems has been the focus of previous investigations [17; 18]. However, the relationship with the water content in the immobilized enzyme reaction system has not been reported in previous study in this field. Therefore, the investigation of the water content under the immobilized enzyme reaction should be considered and optimized. Stable reactivity by repeated use of immobilized lipases is a dominant factor to determine suitable carriers. Previously, hydrophilic gels (such as silica gel) and solid porous carriers have been employed for reactions with hydrophobic substrates. In the case of lipases, hydrolysis, synthesis, and esterification should be considered for industrial applications. Table 1 summarizes previously studied hydrolysis, synthesis and esterification reactions using immobilized lipases and phospholipases. The suitable immobilization of an enzyme allows for its long-term repeated use and higher purity of the product without any by-product separation. The physicochemical characteristics of the surface of the carrier and the morphological structure of the carrier particles determine the lifetime of the immobilized enzymes in the bioreactor. Immobilized enzymes are more tolerant to organic solvents, heat, and shearing forces and are much easier to recover than free lipases. Thus, these enzymes are more suitable for industrial applications. However, although a reaction component can be produced, there is a demand for higher reaction activity and reuse. Therefore, it is important to find the optimized carrier of PLA\({}_{1}\) for immobilization. Among the carriers used for immobilization of enzymes, Accurel has been widely used. This polymer has a highly hydrophobic microporous structure and has been used in this study. Moreover, in the preparation of immobilized enzymes, attention has also been paid to the low inactivation rate of enzymes and the long-term retention rate. However, since there are many types of enzymes, the optimum combination of carrier, enzyme, and reaction conditions should be altered individually.