Effect Of Wounding Intensity And Methyl Jasmonate Pre-treatment On Quality And Antioxidant Capacity Of Fresh-cut Pineapple

Pineapple is a perennial tropical fruit all over the world.Pineapple has unique flavor and not only rich in nutritive properties including vitamin C,carbohydrates and organic acids,but also contains natural antioxidants such as phenolics and flavonoids.The whole pineapple has shortcomings of peeling and eating,while fresh-cut pineapple is convenient for eating.And fresh-cut progress can keep better flavor and taste of pineapple.On the one hand,the fresh-cut treatment can lead to the deterioration on quality and shelf life of products by causing the microbial infection and physiological and biochemical changes.On the other hand,recent studies have shown that wounding can accumulate the synthesis of phenolics,the antioxidant compound,to prevent mechanical damage and increase antioxidant activity after cutting treatment.And some researches have shown that,the methyl jasmonate(MeJA)treatment can maintain the nutritional quality of fresh-cut fruits and vegetables and improve the antioxidant capacity by inducing the synthesis and accumulation of antioxidant ingredient during storage.But the effects of different wounding intensities and MeJA pre-treatment on quality and antioxidant activity of pineapple have not been reported.This dissertation study was designed to analyze and compare the effects of fresh-cut treatment at different wounding intensities on quality and antioxidant activity of pineapple as the basis,and then analyze and compare the effects of MeJA pre-treatments of different concentrations on the changes of quality and antioxidant activity of fresh-cut pineapple.The changes of reactive oxygen species metabolism and phenylpropanoid metabolism were investigated to explore preservation mechanisms involved and supply a gist for the development of the processing and preservation technique of fresh-cut pineapple.The results were as follows:(1)The effects of different wounding intensities(A/W)on quality and antioxidant activity of the pineapples during the storage of 60 hours at 15 ? were investigated.Generated A/W of 0,3.45,4.61 and 6.42 cm2/g,corresponded to whole,half,quarter and eighth.We found that increased wounding intensity could enhance the total plate count,browning degree,MDA content and activity of LOX and the reduction of total soluble solid,titratable acid and vitamin C contents.Different wounding intensities can increase the antioxidant activity significantly by enhancing the activities of PAL,the key enzyme of phenylpropanoid metabolism,inducing the synthesis and accumulation of phenolics,improved the scavenging rate of DPPH and ·OH radical.Whereas different wounding intensities can increase the activities of antioxidant enzymes to enhance the antioxidant activity.By simply increasing wounding stress intensity it is possible to enhance the biosynthesis of phenolic antioxidants,with the treatment cutting into eighth slice being the most effective.(2)The effects of MeJA pre-treatments at different dosage(0,1,10 and 100 pmol/L)on quality and antioxidant activity of fresh-cut pineapple during the storage of 48 hours at 15 ? were investigated.The study found that MeJA pre-treatments at different concentrations could inhibit the decrease of the total soluble solid and titratable acid contents and had no significant effect on the number of bacterial colonies and browning of fresh-cut pineapple with the treatment at 10 ?mol/L being the most effective.Whereas the study found that MeJA pre-treatments at different concentrations could promote the accumulation of secondary metabolites containing phenolics and flavonoids,and increase DPPH radical scavenging activity and enhance the activities of the key enzymes of phenylpropanoid metabolism to induce the synthesis and accumulation of phenolics.And 10 ?mol/L MeJA pre-treatment can the most significantly increase the antioxidant activity of fresh-cut pineapple.(3)The effects of 10 ?mol/L MeJA pre-treatment on phenylpropanoid metabolism and reactive oxygen species of fresh-cut pineapple during the storage of 48 hours at 15 ?were investigated.The results were that 10 ?mol/L MeJA pre-treatment was able to enhance the activities of key enzymes in phenylpropanoid metabolism including PAL and C4H,promote the accumulation of phenolics and flavonoids,and increase the DPPH radical and · OH radical scavenging rate.10 ?mol/L MeJA pre-treatment regulated activities of scavenging enzyme for reactive oxygen species,for example SOD,APX,CAT,POD,etc.and inhibited the accumulation of O2·-,H2O2 and MDA content during the storage.These results indicated that 10 ?mol/L MeJA pre-treatment could increase the antioxidant activity of fresh-cut pineapple by promoting phenylpropanoid metabolism and enhancing the activities of antioxidant enzymes.