Effect Of Phospholipids On The Quality Of Edible Oil And Their Removal By Enzymatic Degumming

Modern oil refining is based on the process of degumming. Degumming is the first stepduring the oil refining process, which removes phospholipids, protein and mucilaginous gums.Phospholipids are the main components of the gum, therefore degumming can also be calledas dephosphorization. The relationship between phospholipids and oil quality was studied andthe characteristics of different phospholipases in degummming were observed in this study.Besides, the process of enzymatic degumming was optimized according to the characteristicsof different phospholipases, which would provide theoretical basis for its further applicationin the oil industry.Firstly, the cause of “fishy off odor” in soybean oil was investigated. Based on theanalysis of sensory evaluation and HS SPME GC MS, we identified that trimethylamine(TMA) was responsible for the “fishy off odor” in soybean oil, and the component ofphosphatidylcholine (PC) in phospholipids was a precursor for TMA. When the content of PCin soybean oil reached1450mg/kg, obvious “fishy off odor” could be smelt after18hreaction at110°C. Meanwhile, the formation of TMA was positively related to the content ofPC, the temperature and time of storage. However, the existence of other components inphospholipids (such as PE, PI and PA) could improve the stability of PC and reduce theformation of TMA. The results of accelerated oxidation test revealed that PC would notsignificantly increase oil color, while the other components of phospholipids such as PE coulddeepen the oil color more apparently.Secondly, the effect of phospholipase A1(PLA1) on the degumming efficiency of crudeoil was studied. The optimal conditions for PLA1degumming were: PLA1addition40mg/kg(PLA1activity8670U/g), reaction time4h, reaction temperature50°C, pH5.0, wateraddition33.5%, and the residual phosphorus after PLA1degumming could be reduced below10mg/kg. The application of ultrasound could improve the degumming efficiency of PLA1,and the optimal conditions for ultrasonic assisted PLA1degumming were: pH5.0, reactiontemperature55oC, water addition2.5%, PLA1addition40mg/kg, ultrasonic intensity0.07W/cm3, reaction time2h. The contents of different components in phospholipids weredetected by HPLC during the PLA1degumming process, and the results showed thatglycerol phospholipids were formed by the acyl migration of lyso phospholipids.Thirdly, the effect of phospholipase C (PLC) on the degumming efficiency and yield ofoil was studied. The optimal conditions for PLC degumming were: PLC addition300mg/kg(PLC activity150U/g), reaction time2h, reaction temperature55°C, pH5.45.5, wateraddition3%. The residual phosphorus after PLC degumming could be reduced below15mg/kg, and an increase of0.9%of oil yield was gained under optimum PLC degummingconditions. The contents of different components in phospholipids were detected by HPLCduring the PLC degumming process, and the results showed that most PC and PE could behydrolyzed by PLC within1.52h, but PLC had no activity towards PI or PA. Therefore, theoil after PLC degumming usually could not satisfy the requirement for physical refining.Ultrasound was applied in the oil recovery process from soybean gum by using PLC and the optimal conditions for ultrasonic assisted PLC oil recovery process were: reactiontemperature55oC, PLC addition800mg/kg, ultrasonic intensity1.20W/cm3, gum/oil ratio1/2.0, reaction time5h, and the oil recovery efficiency was145%.Finally, PLA1and PLC were combined used in the degumming process of differentcrude oils. The optimal conditions for the combined enzymatic degumming process were: pH5.5, reaction temperature55°C, water addition3%, PLC addition300mg/kg (PLC activity150U/g), after1h of PLC treatment,40mg/kg PLA1(PLA1activity8670U/g) was added todegum for another hour. The phosphorus could be reduced from697.9mg/kg to8.7mg/kg,and an increase of0.9%of oil yield was gained under the optimal conditions. Meanwhile,combined enzymatic degumming process was applied in eight different kinds of crude oils,and the results showed that an increase of approximately0.31.5%of oil yield was gainedwhen the original phosphorus ranged from203.8to1087.8mg/kg. To the oil sample withhigh content of original phosphorus and low content of non hydratable phospholipids (NHP),PLC degumming with acid pretreatment was the most efficient way. To the oil sample withlow contents of original phosphorus and NHP, PLA1degumming with acid pretreatment couldsatisfy the requirement for physical refining while increase the oil yield.