Study On Degradation Process Of Lignin By Laccase And Its Antioxidant Property

With the rapid development of human society,the world's energy consumption is also growing increasingly.After all,the three major energy resources?coal,oil,natural gas?were limited,they already can't satisfy the need of human society.On the other hand,the potential harmfulness of synthetic materials also made scientists to intensify research progress in the field of natural renewable products.Lignin is a kind of renewable organic matter content in nature after cellulose,it has a rich source and chemical structure is complex,as well as has certain antioxidant capability.But its antioxidant capability is much lower than synthetic antioxidants.This paper,by means of laccase degrade lignin to improve its antioxidant capability,to provide theory support for lignin can be used as a natural antioxidant,which increases the added value of comprehensive utilization of lignin.The main research contents and results are as follows:?1?Alkali lignin?AL?was degraded by laccase,and the effects of pH value,reaction temperature?T?,reaction time?t?and laccase dosage?Venzyme?on the antioxidant capacity were investigated.The optimum degradation conditions were as follows:pH = 5.0,T= 25 ?,T= 6 h,Venzyme =1.2 mL·g-1?AL?.?2?Taking DPPH method to characterized antioxidant capacity of alkali lignin,the experimental result showed that:the antioxidant capacity of degraded alkali lignin?DAL?(IC50 = 56.75 ?g·mL^-1)was significantly higher than that of AL(IC50 = 396.2 ?g·mL^-1).FTIR,SEM,particle size and GPC analysis showed that:after degradation,the main functional groups of alkali lignin did not change,the molecular size became smaller and looser,and the molecular weight also decreased.It could be found that in the main functional group content determination experiment:the content of phenolic hydroxyl groups of DAL?1.39 mmol·g-1?was significantly higher than that of AL?0.512 mmol·g-1?,and the methoxyl content?1.06 mmol·g-1?was also lower than that of AL?4.06 mmol·g-1?.After degradation,the increasing of phenolic hydroxyl group content and the change of molecular morphology of degradation products make DAL's antioxidant capability stronger than AL.?3?Hydrolytic lignin?HL?was degraded by laccase,and the effects of pH value,reaction temperature?T?,reaction time?t?and laccase dosage?Venzyme?on the antioxidant capacity were investigated.The optimum degradation conditions were as follows:pH = 5.6,T = 35?,t = 4 h,Venzyme =1.0 mL·g-1?HL?.?4?Taking DPPH method to characterized antioxidant capacity of hydrolytic lignin,the experimental result showed that:the antioxidant capacity of defrauded hydrolytic lignin?DHL?(IC50 = 28.78 ?g·mL^-1)was significantly higher than that of HL(IC50 = 31.25 ?g·mL^-1).FTIR,SEM,particle size and GPC analysis showed that:after degradation,the main functional groups of hydrolytic lignin did not change,the molecular size became smaller and looser,and the molecular weight also decreased.It could be funded that in the main functional group content determination experiment:the content of phenolic hydroxyl group of DHL?1.96 mmol·g-1?was significantly higher than that of HL?1.81 mmol·g-1?,and the methoxyl content?7.53 mmol·g-1?was also higher than that of HL?4.22 mmol·g-1?.After degradation,even if phenolic hydroxyl group was only increased slightly,but methoxyl group content was improved greatly,coupled with changed in molecular morphology,DHL's antioxidant capability was still stronger than HL.?5?Phenolic hydroxyl is the most important functional group to determine the antioxidant capacity,the higher the content,the stronger the antioxidant capacity;methoxyl can promote the antioxidant capacity,the higher the content,the more obvious the effect.