Introduction Phospholipase A1 PLA1, E.C.3.1.1.32 represents a very diverse subgroup of phospholipase with 1-acyl hydrolytic activity. It is of particular interest in industry for 2-acyl-lysophospholipids production and edible oil degumming, by cleaving sn-1 acyl group of phospholipids 1. PLA1 exhibits broad substrate specificity and harbors some lipase activity as well 2. Similarly to lipases, PLA1 has been described to suffer interfacial activation 3. Lecitase ® Ultra LU is a phospholipase manufactured and marketed by Novozymes, Denmark. It was patented and made commercially available in 2007. LU is a new enzyme with a molecular mass of 35 kDa, it has a single active site which displays both the lipase and phospholipase activities 4. The commercial preparation of this new enzyme is a protein-engineered carboxylic ester hydrolase from the fusion of lipase genes from Thermomyces lanuginosa to obtain good stability and phospholipase genes from Fusarium oxysporum to get the phospholipase activity 5. Commercial applications of LU are mainly focused on the edible oil degumming and phospholipids modifications 6, 7 .

In this study, high-acid soybean oil, with acid values (Av) ranging from 10 to 50, was enzymatically deacidified for diacylglycerol (DAG) production. The effects of glycerol amounts were studied intensively. The glycerol amount could be calculated theoretically based on the Av of the raw oil (1 mol glycerol with 2 mol oleic acid to form 1 mol DAG, and 1 mol glycerol with 2 mol soybean oil to form 3 mol DAG). A total of 60-62% of DAG could be obtained and the free fatty acid (FFA) content was reduced to 0.36-0.66%. Increased glycerol did not lead to DAG content improvement. However, the glycerol amount based on just the deacidification theoretical calculation (1 mol glycerol with 2 mol oleic acid to form 1 mol DAG) was not feasible to reduce the FFA content. Moreover, Novozym 435 was rather stable in the present reaction procedure, no loss of activity was observed after 10 consecutive uses.

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In this study, Candida antarctica lipase B (CALB), Rhizomucor miehei lipase (RML) and Lecitase ® Ultra (LU) were immobilized onto the mesoporous silica SBA-15. The glycerolysis performance of the obtained supported lipases (lipase@SBA-15) in solvent systems was carefully investigated. LU@SBA-15 exhibited good glycerolysis performance in solvent-free system, with diacylglycerols (DAG) content and triacylglycerols (TAG) conversion at 52.4 and 98.6% respectively obtained after 12 h reaction at 60℃. CALB@SBA-15 showed good glycerolysis activity in tert-pentanol and tert-butanol systems, with TAG conversion over 90% obtained. In addition, the present CALB@SBA-15 exhibited selectivity for monoacylglycerols (MAG) production, with glycerol to TAG molar ratio increased to 3:1, MAG content over 80% and TAG conversion over 99% could be obtained from both tert-pentanol and tert-butanol systems. However, RML@SBA-15 showed low glycerolysis activity neither in solvent nor in solvent-free systems. The present results favor the practical enzymatic design for MAG and DAG production.