The Difference Of SO₂ Sensitivity And Physiological Mechanism Of Grape Fruit During Postharvest Storage

Fresh grape is easy to be infected by mould and rotten in the process of storage after harvest.Sulfur dioxide（SO₂）treatment is the most effective and widely used preservative measures for grape.However,the sensitivity of different varieties,maturity and ear compactness of grape fruits to SO₂ is different,which makes SO₂ easy to be excessive in the process of application,causing skin bleaching,juice acidification and other damages,causing great economic losses and restricting the development of grape industry.In order to reduce the excessive injury of SO₂ and reduce the economic loss,this paper uses grapes of different varieties（‘Kyoho’ and ‘Red Globe Grape’）,different maturity（maturity and coloring period）,different ear tightness（compact and loose type）as the experimental materials,treated with SO₂ preservative（0,SO₂ constant,SO₂ excess）,stored at room temperature（20℃）,to explore the post harvest storage process The relationship between SO₂ injury sensitivity and varieties,maturity,ear density of medium and fresh grape.The results show that:1.Excessive SO₂ damage causes bleaching of grape peels and acidifies pulp juice（TA-titrable acid content increases,pH value decreases）,active oxygen（·O₂^-and H₂O₂）and MDA content increases,and membrane lipid increases Increased oxidation also causes the antioxidant enzyme（SOD,POD）activity,PAL activity,and secondary metabolite（total phenol,flavonoid）content to increase significantly and then significantly reduce,resulting in abnormal antioxidant enzyme function and secondary metabolic function abnormal.2.Under SO₂ constant and SO₂ excess treatment,‘Kyoho’ grape did not appear peel bleaching,while ‘Red Globe Grape’ grape appeared peel bleaching on the 8th and 6th day of treatment respectively.The pulp juice of ‘Kyoho’ grape did not acidify under the normal dose of SO₂ treatment,but ‘Red Globe Grape’ grape did acidify on the 8th day;the occurrence time of juice acidification of ‘Kyoho’ grape was later than ‘Red Globe Grape’ on the 10 th day under the excess dose of SO₂ treatment,the increase of TA content（0.02%）and the decrease of pH value（0.02）were smaller than ‘Red Globe Grape’（0.05%,0.07）.Under the SO₂ constant treatment,the juice of ‘Kyoho’ grape pulp was not acidified,while the acidification of "Red Globe" grape occurred on the 8th day;Under SO₂ over-treatment,the acidification time of ‘Kyoho’ grape juice（10th day）is later than ‘Red Globe Grape’（6th day）,the increase of TA content（0.02%）and the decrease of pH value（0.02）are both less than ‘Red Globe Grape’（0.05%,0.07）.Under the treatment of SO₂ constant and SO₂ excess,the rising range of ·O₂^-、H₂O₂、MDA in ‘Kyoho’ grape fruit was smaller than ‘Red Globe Grape’,and the storage end value(constant: 8.73μmol·g^-1·min^-1,18.15μmol·g^-1,11.84nmol·g^-1,excess: 10.48μmol·g^-1·min^-1,19.82μmol·g^-1,12.75 nmol·g^-1)is also less than ‘Red Globe Grape’(constant:10.28μmol·g^-1·min^-1,19.87μmol·g^-1,12.86nmol·g^-1,excess:11.76μmol·g^-1·min^-1,21.27μmol·g^-1,13.53 nmol·g^-1).Under the SO₂ constant and SO₂ over-treatment,the increase of SOD,POD and PAL activity,total phenol and flavonoid content of ‘Kyoho’ grapes are all greater than that of ‘Red Globe Grape’,and the storage termination value(constant: 32.78U·g^-1,11.12 U·g^-1·min^-1,7.74U·mg^-1,27.69 mg GAE·kg^-1,12.69 mg GAE·kg^-1,excess: 24.52 U·g^-1,9.02 U·g^-1·min^-1,6.52 U·mg^-1,23.06 mg GAE·kg^-1,10.87 mg GAE·kg^-1)is also greater than ‘Red Globe Grape’(constant: 19.21U·g^-1,9.28U·g^-1·min^-1,4.28 U·mg^-1,16.81 mg GAE·kg^-1,8.22 mg GAE·kg^-1,excess: 17.46 U·g^-1,8.03 U·g^-1·min^-1,3.72 U·mg^-1,13.88 mg GAE·kg^-1,7.49 mg GAE·kg^-1).In summary,under the same dose of SO₂ treatment,the skin bleaching,acidification of pulp juice and membrane lipid peroxidation of ‘Kyoho’ grapes occurred later than that of ‘Red Globe Grape’ grapes,and were less damaged than ‘Red Globe Grape’ grapes.It is believed that the ‘Kyoho’ grape is less sensitive to SO₂ than the ‘Red Globe Grape’ grape.The physiological mechanism is: under SO₂ stress,the increase in antioxidant enzyme activity,PAL activity,secondary metabolite content and storage end value of ‘Kyoho’ grapes are greater than that of ‘Red Globe Grape’ grapes.3.Under the treatment of SO₂ constant and SO₂ excess,the peel bleaching of ‘Kyoho’ grape did not appear at the ripening stage,but at the coloring stage,the peel bleaching appeared at the 10 th and 6th day,respectively.Under the constant SO₂ treatment,the juice did not acidify at maturity,but acidified at the 10 th day of coloration;under the excessive SO₂ treatment,the acidification time of juice at maturity（10d）was later than that at coloration（6d）,the increase of TA content（0.02%）and the decrease of pH value（0.02）were less than that at coloration（0.05% and 0.06）.The increase of O₂^-,H₂O₂,MDA content of fruits in mature stage is smaller than that in fruits of coloring stage,and the storage end value(constant: 8.73μmol·g^-1·min^-1,18.03μmol·g^-1,11.84nmol·g^-1,Excess: 10.48μmol·g^-1·min^-1,19.82μmol·g^-1,12.75nmol·g^-1)less than the coloring period(constant: 13.22μmol·g^-1·min^-1,22.37μmol·g^-1,13.75nmol·g^-1,excess: 13.86μmol·g^-1·min^-1,23.21μmol·g^-1,14.07 nmol·g^-1).The SOD,POD and PAL activities,total phenols and flavonoids of fruits in the mature period increased more than the coloring period,and the storage end value(constant: 32.78 U·g^-1,11.12 U·g^-1·min^-1,7.74 U·mg^-1,27.69 mg GAE·kg^-1,12.69 mg GAE·kg^-1,excess: 24.52U·g^-1,9.22U·g^-1·min^-1,6.52 U·mg^-1,23.06 mg GAE·kg^-1,10.87 mg GAE·kg^-1)is also greater than the coloring period(constant: 18.27 U·g^-1,7.84 U·g^-1·min^-1,3.62 U·mg^-1,11.68 mg GAE·kg^-1,6.34 mg GAE·kg^-1,excess: 16.23 U·g^-1,7.21U·g^-1·min^-1,2.87U·mg^-1,9.76 mg GAE·kg^-1,5.89 mg GAE·kg^-1).Under the treatment of SO₂ constant and SO₂ excess,the bleaching time（constant: Day 8,excess: Day 6）of ‘Red Globe Grape’ grape was later than that of the fruit（constant: Day 6,excess: Day 4）,and the bleaching index（constant: 25.66%,excess: 39.76%）was less than that of the color stage（constant: 33.73%,excess: 50.60%）.The appearance time of pulp acidification in the mature period（constant: Day 8,excess: Day 6）is later than the coloring period（constant: Day 6,excess: Day 4）,the TA content increases（constant: 0.03%,excess: 0.05%）And pH drop（constant: 0.03,excess: 0.07）is less than the coloring period（constant: 0.05%,0.06,excess: 0.1%,0.11）.The increase of O₂^-,H₂O₂,MDA content of fruits in the mature stage is less than that in the coloring stage,and the storage termination value(constant: 10.28μmol·g^-1·min^-1,19.21μmol·g^-1,12.86nmol·g^-1,excess:11.76μmol·g^-1·min^-1,21.27μmol·g^-1,13.53nmol·g^-1)less than the coloring period(constant: 11.55 μmol·g^-1·min^-1,20.82μmol·g^-1,14.03nmol·g^-1,excess:13.47μmol·g^-1·min^-1,23.04μmol·g^-1,14.76nmol·g^-1).The increase of SOD,POD and PAL activity,total phenol and flavonoid content of the fruit is greater than the coloring period,storage end value(constant: 19.21 U·g^-1,9.28 U·g^-1·min^-1,4.28U·mg^-1,16.81 mg GAE·kg^-1,8.22 mg GAE·kg^-1,excess: 17.46U·g^-1,8.03 U·g^-1·min^-1,3.72 U·mg^-1,13.88 mg GAE·kg^-1,7.49 mg GAE·kg^-1)greater than the coloring period(constant: 13.86 U·g^-1,6.57 U·g^-1·min^-1,2.36 U·mg^-1,7.28 mg GAE·kg^-1,3.44 mg GAE·kg^-1,excess:11.56U·g^-1,5.54U·g^-1·min^-1,1.84U·mg^-1,5.07 mg GAE·kg^-1,2.05 mg GAE·kg^-1.In summary,under the same dose of SO₂ treatment,the bleaching,pulp acidification,and membrane lipid peroxidation of ripening period（‘Kyoho’ and ‘Red Globe Grape’）occurred later than the coloring period,and the degree of damage was less than the coloring period.From this,it is believed that the sensitivity of fruits to SO₂ in the mature stage is less than that in the coloring stage.The physiological mechanism is: under SO₂ stress,the antioxidant enzymes and PAL activities,the increase of secondary metabolite content and the storage termination value of fruits in the mature period（‘Kyoho’ and ‘Red Globe Grape’）are greater than those in the coloring period.4.Under the constant SO₂ treatment,the skin bleaching and flesh acidification did not occur in the compact and loose type grapes,and there was no significant difference in the contents of O₂^-,H₂O₂,MDA,SOD,POD,PAL,total phenol and flavonoids between the two types of grapes.In the case of SO₂ excess treatment,the skin bleaching did not occur in compact fruit,but occurred in loose fruit on the 10 th day of storage,with a bleaching index of 13.7%,The content of O₂^-,H₂O₂,and MDA in compact fruit was less than that in loose fruit,and the storage end values(9.36μmol·g^-1·min^-1,18.86μmol·g^-1,12.66 nmol·g^-1)were also less than those in loose fruit(10.88μmol·g^-1·min^-1,21.33μmol·g^-1,13.90nmol·g^-1).The compact fruit did not acidify,but the loose fruit acidified on the 8th day.At the end of storage,TA content increased 0.04%,pH value decreased 0.04,The increase of SOD,POD,PAL activity,total phenol and flavonoid content in compact fruit was smaller than that in loose fruit,and the storage termination values(26.72 U·g^-1,10.41 U·g^-1·min^-1,7.04 U·mg^-1,25.37 mg GAE·kg^-1,12.28 mg GAE·kg^-1)were larger than that in loose fruit(21.89 U·g^-1,8.57 U·g^-1·min^-1,5.26 U·mg^-1,19.24 mg GAE·kg^-1,10.02 mg GAE·kg^-1).At the end of SO₂ constant and SO₂ excess treatment,the skin bleaching index of compact grape（constant: 22.86%,excess: 34.94%）was lower than that of loose grape（constant: 28.92%,excess: 40.96%）.Under the treatment of SO₂ constant and SO₂ excess,the juice acidification time（constant: Day 8,excess: Day 6）of compact fruit was later than that of loose fruit（constant: Day 6,excess: Day 4）,the TA content increased（constant: 0.02%,excess: 0.03%）and the pH value decreased（constant: 0.03;excess: 0.04）less than that of loose fruit（constant: 0.06%,0.07,excess: 0.08%,0.1）.The content of O₂^-,H₂O₂ and MDA in compact fruit was less than that in loose fruit,and the storage termination values(constant: 10.22 μmol·g^-1·min^-1,18.15 μmol·g^-1,12.78nmol·g^-1,excess: 11.76μmol·g^-1·min^-1,18.15μmol·g^-1,12.78nmol·g^-1)were also smaller than loose type(constant: 11.65 μmol·g^-1·min^-1,19.87μmol·g^-1,13.79nmol·g^-1,excess: 13.32μmol·g^-1·min^-1,22.84μmol·g^-1,14.36nmol·g^-1);The increase of SOD,POD,PAL activity,total phenol and flavonoid content in compact fruit was less than that in loose fruit,and the storage termination value(constant:19.75U·g^-1,8.81U·g^-1·min^-1,4.97U·mg^-1,17.94 mg GAE·kg^-1,8.54 mg GAE·kg^-1,excess :18.52U·g^-1,8.35U·g^-1·min^-1,4.28U·mg^-1,15.91 mg GAE·kg^-1,7.85 mg GAE·kg^-1)was greater than that in loose fruit(constant: 15.23U·g^-1,7.03U·g^-1·min^-1,3.35 U·mg^-1,13.06 mg GAE·kg^-1,6.29 mg GAE·kg^-1,excess: 13.2U·g^-1,6.28 U·g^-1·min^-1,2.36U·mg^-1,11.37 mg GAE·kg^-1,5.43 mg GAE·kg^-1)To sum up,under the constant SO₂ treatment,the skin bleaching and juice acidification did not occur in the compact and loose ‘Kyoho’ grape fruits,and there was no significant difference in O₂^-,H₂O₂,MDA content,antioxidant enzyme activity,PAL activity and secondary metabolite content.Under the constant SO₂ treatment,the skin bleaching,juice acidification and membrane lipid peroxidation of compact and loose Red Globe grapes were later than those of loose grapes,and the damage degree was less than that of loose grapes.Therefore,the SO₂ sensitivity of compact grapes was less than that of loose grapes.The physiological mechanism is that the increase of antioxidant enzyme activity,PAL activity and the content of secondary metabolites in compact type（‘Kyoho’,‘Red Globe Grape’）grape is less than that in coloring period,and the storage end value is greater than that in coloring period.