Studies On The Enzymatic Extraction Of Lipids From Egg Yolk

Egg yolk, which has high nutritional value, contains abundant lipids (about 30% of the total egg yolk) and excellent proteins. The lipids contain abundant lecithin and unsaturated fatty acids, which is the important difference to other animal and vegetable oil. So exploitation and utilization of egg yolk component has been paid full attention to by scholars in related realm at home and abroad for a long time. Study on egg yolk lipids positively in order to improve the added value of egg has great benefit in our country, where has the maximum egg production.Based on"Studies on Separation and Extraction of Egg Yolk Oil by Enzymes—Solvent", the technology of enzymolysis and demulsification had been improved in this thesis with fresh egg yolk as raw material, considering energy saving, emission reduction, low consumption, economic benefit and extraction effect. The method of enzymatic hydrolysis to separation and extraction egg yolk lipids from fresh egg yolk has been studied in this thesis.Firstly, different proteinases were used to pre-hydrolyze of fresh egg yolk suspension individually and by two proteinases used in sequence, followed by centrifugation to separate the hydrolyzed fresh egg yolk mixture into three parts-a up layer of oil, a middle layer of colloidal liposome and a bottom layer of hydrolyzed proteins.Secondly, an initial optimal egg yolk lipids separation was obtained by comparison experiments and orthogonal experiments between the hydrolysis condition of acid protease and alkaline protease. The best enzymatic hydrolyzing conditions were as follows: solid-liquid ratio 1:1.5, the optimum pH and temperature of acid protease is 3 and 40℃, the optimum pH and temperature of alkaline protease is 10 and 50℃, the addition of acid protease is 1.5 g/100g egg yolk, the addition of alkaline protease is 1.75 g/100g egg yolk, treatment time is 2 h and 3.5 h respectively. The yield of egg yolk lipids was 93.02% by adjusting the pH of enzyme solution, insulation treatment and centrifugation. Meanwhile the triglyceride and phospholipid could be separated very well.Thirdly, physical-chemical indexes of the obtained products were analyzed. The results indicated that the main component of up layer egg yolk oil by enzymatic extraction was mainly triglyceride, which was golden with good mobility and thick yolk flavor and the content of unsaturated fatty acids was 71.73%. The middle layer of colloidal liposome contained 41.16% lecithin and the content of unsaturated fatty acids was 67.37%.It was yellowish and viscous without mobility. The total recovery of egg yolk protein was 72.25% of the hydrolyzed yolk protein from centrifugation, in which the content of essential amino acid was 23.24 mg/mL, 39% to the total amino acid.Finally, through the influence factor experiment, acid value of the egg yolk oil was effect more by the reaction conditions of acid protease than alkaline protease. Acid value of the egg yolk oil was effect more by insulation treatment time than insulation treatment temperature.