Effects Of Aqueous Ozone Treatments On Quality Of Fresh-cut Pineapple

Pineapple is nutrient-rich and delicious.It has been widely processed into fresh-cut pineapple for sale since the fruit cannot be peeled easily.However,fruit loses its epidermis after processing,which makes it vulnerable to microbial infection.In addition,mechanical damage caused by processing can induce a series of physiological metabolic changes in tissues,affecting the quality of pineapple and shorten shelf life.In this experiment,aqueous ozone was applied to fresh-cut pineapple.Different concentrations(0.5,1.0,1.5and 2.0 mg·L^-1)and processing time（2,5,8,10 min）of aqueous ozone were evaluated for their effectiveness on microbial load and sensory quality of fresh-cut pineapple.Moreover,physical and chemical properties,enzyme activity and antioxidant activity of fresh-cut pineapple after aqueous ozone treatment(2.0 mg·L^-1,5 min)during storage at room temperature（18±3oC,80%RH）were evaluated.Changes of aroma components of fresh-cut pineapple after aqueous ozone treatment were also studied.The results are as follows:1.Different concentrations and processing time of aqueous ozone significantly reduced the number of microorganisms in fresh-cut pineapple（P<0.05）,and increased ozone concentration and processing time led to decreased number of microorganisms in fresh-cut pineapple.Fresh-cut pineapple treated with 0.5,1.0,1.5 and 2.0 mg·L^-1 aqueous ozone for 5 min,compared with the control,the aerobic plate count reduced by0.17,0.73,0.89,and 1.24 log CFU·g^-1,respectively;when treated with 2.0 mg·L^-1 aqueous ozone for 2,5,8 and 10 min,the aerobic plate count reduced by 0.56,1.03,1.15 and 1.59 log CFU·g^-1,respectively.In addition,aqueous ozone had no effect on the sensory quality of fresh-cut pineapple.2.Aqueous ozone had no significant effect on weight loss,total phenol content,polyphenol oxidase and peroxidase activities（P>0.05）;the firmness,b^*value,total soluble solids content and ascorbic acid content decreased after aqueous ozone treatment,but there was no significant difference（P>0.05）;L^*value and titratable acid content increased after aqueous ozone treatment,but there was also no significant difference（P>0.05）.Aqueous ozone significantly reduced the content of flavonoids in fresh-cut pineapple（P<0.05）.3.Aqueous ozone can delay browning and the decrease in titratable acid,as well as the change of flavonoid content during storage,at the same time,treatment with aqueous ozone had no significant effect on weight loss,firmness,b^*value,total soluble solids content,ascorbic acid content,total phenol content and antioxidant activity during storage（P>0.05）.Aqueous ozone also can decrease the activities of polyphenol oxidase and peroxidase during storage（P<0.05）.4.Aqueous ozone changed the aroma components of fresh-cut pineapple,the total number of aroma components increased by 5 species.Five species esters,one species hydrocarbon,one species alcohol were added after treatment,and two species carbonyl compounds were reduced;the total number of heterocycles and naphthalenes were not changed.Among the characteristic aroma components of fresh-cut pineapple,the contents of ethyl 2-methylbutyrate,ethyl 3-methylthiopropionate and ethyl caproate increased by 0.31%,0.08%and 6.11%respectively after treatment,while the contents of methyl butyrate,methyl2-methylbutyrate,methyl 3-methylthiopropionate and methyl caproate decreased by 0.33%-1.95%,and the total relative contents of characteristic aroma components increased by 1.42%.Ethyl 2-methylbutyrate and ethyl 3-methylthiopropionate were two characteristic aroma components added after treatment.In conclude,aqueous ozone increased the types and total relative content of aroma components in fresh-cut pineapple,and also increased the types and relative contents of characteristic aroma components.