The Study On Enzymic Modification Of Egg Yolk Phospholipids With Phopholipase A₂

Phospholipid is a mixture of phosphoru and lipid. Because of its unique physicochemical property, it has been applied in many fields such as food, medicine, stockbreeding. The hydrophily of natural phospholipid isn't so strong that the application has certain restrication. But it could be hydrolysised by phospholipase and be transformed into lysophospholipid which enhances its properties of emulsion and stability. At present many phospholipase A₂ are abstraded from animal's pancreas, snake venom, bee venom, microbe, but the technology of abstraction is complicated and the price is high, which won't benefit the great production and utilization of LPA₂. A lot of phospholipase A₂ that are used in this experiment come from Streptomycs lividans's fermentation (high copy plasmids with PLA₂ gene) . The results are as follows:1.The egg yolk was hydrolyzed by phospholipase A₂. The enzyme reaction was carried in aqueous system. The optimum condition is concentration of substrate 20%, enzyme dosage 0.15 IU/mL, CaCl₂ 30mmol/L, initiatial reaction pH 8.0, 40℃, 180r/min, and 4h of hydrolysis. In this condition the rate of converting lecithin into lysophospholipid was 80%.2.The egg yolk was hydrolyzed in the modified optimum hydrophily condition and then was made into the enzyme-modified egg yolk powder. The result should that in the same concentration, the emulsified layer of enzyme-modified egg yolk powder is higher than that common egg yolk powder's. In different condition of pH the emulsion property is better than commom. On 4℃,20℃,80℃, the stability of enzyme-modified egg yolk powder has lest effect in the emulsion. The enzyme-modified egg yolk powder and common egg yolk powder were not sensitive to salt density when the densities of NaCl and CaCl₂ are 0.5%,1%,2%.The mayonnaise is made from egg yolk powder. The viscosity of enzyme-modified mayonnaise is 1.45 times than common mayonnaise. The stability of enzyme-modified mayonnaise is far better than common mayonnaise on the cold storage or high temperature condition.3.Egg yolk lecithin and enzyme-modified egg yolk lecithin were extracted from egg yolk powder. Their acid value,iodine value,AI ,water content and POV are tested. The data show that every target accords with quality on the whole.