Research On Aspartic Acid Inhibiting The Browning Of Fresh-cut Potatoes

Fresh-cut potato is an important kind of fresh-cut vegetables with huge market demand in China.However,fresh-cut potatoes brown easily,which seriously shorten the shelf life.Effective and safe methods to control the browning of fresh-cut potato are needed both domestic and overseas.In this study,aspartic acid was used to inhibit the browning of fresh-cut potato,and its mechanism was studied.The research results are as follows:1.Aspartic acid significantly inhibits the browning of fresh-cut potato chips.By optimizing the concentration and the time of aspartic acid,the best condition was 1.0%of aspartic acid solution with 3 min duration.After treatment in this condition,fresh-cut potato chips still had good quality without browning which was stored at 2-4?C for 5d.However,the control potato chips had been seriously browned with no commodity value.This technology can meet the requirements of fresh-cut potato chips production and market supply.The inhibition effect of aspartic acid on browning of fresh-cut fruits and vegetables was first reported in the world.2.Through the determination of physiological indexes including PPO,POD,total phenol content,DPPH inhibition rate etc.,it was found that aspartic acid could significantly inhibit the PPO activity of potato chips during the whole storage,and significantly reduced the POD activity,total phenol content and antioxidant capacity during the middle and late stage of storage.In addition,the contents of tyrosine and chlorogenic acid in potato pulps treated with aspartic acid were significantly higher than the control,while the changes of protocatechuic acid,gallic acid and caffeic acid were not significant.These results indicate that aspartic acid can inhibit the browning by inhibiting PPO activity,and reducing the oxidation of tyrosine and chlorogenic acid.3.Aspartic acid significantly inhibits the activity of PPO by reducing pH and chelating Cu²⁺.Results showed that the optimum pH of the potato PPO activity is 7.0.Additing 0.1,0.2,0.5,1.0%aspartic acid reduced the pH and PPO activity of potato pulps in different degrees.By recovering the pH of potato pulp treated with aspartic acid to the pH of control,PPO activity were partially recovered.The higher aspartic acid concentration was,the lower PPO activity was.Therefore,aspartic acid can inhibit PPO activity by reducing pH,but pH is not the only factor of aspartic acid to influence the activity.Copper acetate（0.5,1.0,1.5%）was added to potato pulp treated with aspartic acid.The PPO activity of potato pulp increased significantly with the increase of copper acetate⁺concentration,while the PPO activity of water control didn’t change.The results showed that aspartic acid could inhibit PPO activity by chelating Cu²⁺of PPO protein.4.Aspartic acid reduces browning by affecting the transformation of potato browning intermediates.The fresh and non-browning,moderate browning or severe browning potato pulps were treated by aspartic acid respectively.It was found that aspartic acid could significantly inhibit the browning of fresh and non-browning potato pulp,and cause the reddish-brown intermediates of moderate browning potato pulp fading away gradually,but had no effect on potato pulp with severe browning.Browning Inhibition of aspartic acid by pure enzyme of PPO and single phenol were simulated in vitro,and it was found that the browning products of PPO and tyrosine,chlorogenic acid,gallic acid,caffeic acid and protocatechuic acid were different in color,while reddish-brown intermediate of tyrosine wih PPO was the closest to browning intermediates of potato pulps.In addition,aspartic acid can result in the browning intermediate of each phenolic substance fading in different degrees.Therefore,aspartic acid can reduce the browning by inhibiting the transformation of browning intermediatesinto final products,especially browning intermediates of tyrosine,and promoting the transformation of intermediates into colorless substances.In summary,aspartic acid can reduce the browning of fresh-cut potatoes by reducing pH value,chelating Cu²⁺to inhibit PPO activity,and promoting the transformation of potato browning intermediates into colorless substances.