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Abstract [Objectives] This study was conducted to discuss the effect of chitin treatment on softening of Actinidia arguta Huanyou No. 1 as the test material. [Methods] Huanyou No. 1 was sprayed with chitin， and the changes of some physiological and biochemical indexes in fruit softening were investigated. [Results] Chitin treatment significantly improved single fruit weight， increased soluble solid content， but decreased titratable acid content and significantly reduced the content of cellulose and hemicellulose； and the chitin treatment significantly inhibited the breakdown of pectin， cellulose and hemicellulose， and inhibited the activities of PG enzyme and β-Gal enzyme. [Conclusions] Chitin spray treatment could increase the yield of A. arguta， and improve its quality and storage property.
Key words Chitin； Actinidia arguta； Cell wall composition； Pectinolytic enzyme
Chitin is a kind of polysaccharide formed from N-acetyl-D-glucosamine by β-1，4-glucoside[1]. It widely exists in cells of lower microbes and alga， shells of arthropods， inner shells and cartilages of mollusc and cell walls of higher plants. The biosynthesis amount of chitin could reach 200 billion tons a year， and its production is only second to plant cellulose in nature， so it is an inexhaustible resource[2]. Chitin and chitosan are widely applied in fields of membrane preparation， water preservation， health care， industrial production and environmental production[3]. Chitin and chitosan effectively promote plant growth， could effectively improve crop yield and quality as well as cold resistance， and have antibacterial property and film-forming property， and therefore， in agricultural field， they are widely used as soil conditioner， disease prevention and fruit and vegetable fresh-keeping agents， plant growth regulator， cold-resistant agent， feed additive and seed coating[4].
Zhou et al.[5] showed that the fruit and vegetable fresh-keeping agent prepared with carboxymethyl chitin （06 CMCH） as a main component has a remarkable fresh-keeping effect on kiwifruit and carambola. Chitin treatment inhibits the respiration of ‘Guichang’ kiwifruit and delays the production of ethylene， thereby improving yield and fruit quality[6]. Actinidia arguta not only has good taste， but also various medical efficacy， and is loved by consumers in general. Fisk et al.[7] performed edible coating treatment on A. arguta fruit， which was then refrigerated at 2 ℃ under a humidity of 88%. The results showed that the treatment could reduce the loss of fruit moisture， and significantly prolonged the storage time of A. arguta. However， there have been no reports about the effects of spraying treatment and soaking treatment on A. arguta fruit. Materials and methods
Experimental materials
The experiment was carried out in A. arguta garden of agricultural college， Yanbian University. Huanyou No. 1 was selected as an experimental material， the trees were five years old with a planting spacing of 3 m×4 m， and horizontal shed frame was adopted. Soil was managed by clean cultivation method， and organic fertilizer was applied at a rate of 2.5-5.0 kg/plant every year. Pollination was performed by bees. Ordinary healthy trees free of diseases and pests were selected for experimental treatment. Single-plant block design was adopted with three replications. From August 20， 2016， chitin spray treatment was started and performed every 10 d. The fruit was harvested on September 29， 2016. The harvested fruit was taken back to lab， and the individuals with uniform size free of diseases and pests and mechanical injury were selected for the investigation of fruit quality at the harvest time. Partial fruit was stored at （3±1）℃， for the determination of quality at hard-ripe stage （the very day of harvest）， softening stage （90% of the fruit is softened）， and too-soft stage （10% of the fruit begin to rot）. Partial fruit was stored frozen， for the determination of cell wall components and activity of pectinolytic enzyme. The used chitin was 200 times dilution produced by Enbio-guard company （Korea）， and 0.05% Tween 20 was used as the speader.
Experimental methods
From each treatment， 60 fruit individuals （three replications） were picked for quality investigation and low-temperature storage， and during each time of investigation， 20 fruit individuals （three replications） were randomly investigated， and partial fruit flesh was stored frozen. Fruit weight was determined with an electronic balance； fruit firmness was determined with a TMS-PRO texture analyzer produced by Beijing Yingsheng Hengtai Science and Technology Co.， Ltd.； soluble solid content in fruit was determined with an ATAGO type hand-held refraction saccharimeter； and titratable acid content was determined by acid-base titration method. The analysis of cell wall components and determination of the activity of pecinolytic enzyme were performed according to the methods of Piao et al.[8-9].
Experimental data were statistically analyzed and used for plotting in Excel， and variance analysis was performed with SPSS.
Results and Analysis
Effect of chitin treatment on fruit quality of A. arguta
Chitin spray treatment was started 40 d before harvest of A. arguta fruit and performed every 10 d. The results showed that chitin treatment significantly improved fruit weight of A. arguta， but had no significant effect on fruit-shape index （Table 1）. Firmness refers to the compressive resistance of fruit， and the change of fruit firmness is an important index reflecting the storage property of fruit for evaluating the storage effect. Soluble solid mainly refers to soluble sugar， and its content directly reflects fruit quality and fruit maturity. Titratable acid as a substrate of respiratory metabolism during storage is consumed continuously. The softening process of A. arguta in the chitin treatment is shown in Fig. 1. The A. arguta fruit in the chitin treatment had a soluble solid content significantly lower than the CK on the very day of harvest， and such difference was kept until the softening stage， and at the too-soft stage， the soluble solid content of the treatment group was significantly higher than that of the CK. Therefore， taste quality was improved. The chitin treatment had no high effect on the content of titratable acid in A. arguta fruit， but there was a rapid decrease process at the too-soft stage. The firmness of the A. arguta fruit in the chitin treatment was significantly higher than that in the CK group， such difference was kept until the softening stage， but waned at the too-soft stage when the firmness was basically the same in the two groups. The difference in firmness was especially more remarkable for fruit firmness than for flesh firmness. It could be seen that chitin treatment could inhibit the increase of soluble solid content， and promote the decrease of titratable acid， so as to keep fruit firmness at a higher level， i.e.， chitin could alleviate the softening speed of fruit， thereby prolonging the storage time of fruit. Effect of chitin treatment on cell wall components of A. arguta fruit
Change of pectin content
Cell wall is manly composed of pectin， cellulose and hemicellulose， and softening of fruit is， in essence， the decomposition of cell wall components. In this study， cell wall components were determined using ethanol-insoluble substance （AIS）. The change of pectin content in A. arguta fruit of the chitin treatment is shown in Fig. 2. The pectin content in A. arguta fruit of the chitin treatment was consistent with that of the CK on the very day of harvest and had no big change during the softening process， while the water pectin content in the fruit of the CK significantly decreased at the softening and too-soft stages， indicating that chitin treatment delayed the decomposition of pectin in A. arguta fruit. The soluble pectin content in the fruit of the chitin treatment was significantly lower than that of the CK on the very day of harvest， and increased rapidly and then slowly during the softening process， but was lower than that of CK all the time. The EDTA soluble pectin content had no big change during the softening process， and was kept lower than the level of the CK all the time. The NaOH soluble pectin content increased slowly at the softening stage， and at the too-soft stage， the NaOH soluble pectin content of the treatment group increased rapidly， while that of the CK group decreased rapidly to the level the same as the NaOH soluble pectin content of the treatment group. It could be seen that chitin treatment inhibited the increase of soluble pectin and delayed the softening process of fruit.
Change of cellulose and hemicellulose
Cellulose， hemicellulose and pectin in cell wall are dissolved by new enzyme system formed in the ripening process of fruit， resulting in local degradation of cell wall， and it is thus believed that the degradation of cell wall is the main reason of fruit ripening and softening. It could be seen from Fig. 3 that the chitin treatment had a cellulose content in A. arguta fruit significantly lower than the CK group， but the experimental and CK groups had the same changing trend of increasing slightly and then decreasing rapidly during the softening process， indicating that cellulose decreased at a lower rate before the softening stage and then was decomposed at a higher rate. The hemicellulose content in A. arguta fruit of the chitin treatment was also significantly lower than that of the CK， and slowly increased at the softening stage， indicating that the decomposition rate of hemicellulose of the treatment group was equivalent to the decomposition rates of other cell wall components. However， the hemicellulose content of the CK group decreased rapidly and then increased rapidly at the softening stage， indicating that hemicellulose was decomposed rapidly before the softening stage and then decomposed slowly. The increases of cellulose content and hemicellulose content were interpreted as slower decomposition relative to other cell wall components， because the unit used here was cellulose or hemicellulose content in unit AIS， i.e.， it was a relative value. Effect of chitin treatment on activity of pectinolytic enzyme in A. arguta fruit
Change of PG activity during the softening process of A. arguta fruit
The main function of PG is to break up cell wall structure by degrading polygalacturonic acid in polysaccharides in fruit cell wall to galacturonic acid， resulting in softening of fruit[10]. The change of PG activity during the softening process of A. arguta fruit is shown in Fig. 4. The PG activity in A. arguta fruit of the chitin treatment was significantly lower than that of the CK group， and decreased slowly during the softening process.
Change of β-galactosidase activity during the softening process of A. arguta fruit
β-Gal is one of the important glycosidases related to the degradation of cell wall polysaccharides. It could make some cell wall components instable by degrading polyuronides with branches， thereby degrading or dissolving pectin[10]. It could be seen from Fig. 5 that the change of β-Gal in the softening process of A. arguta fruit also could be divided into two obvious stages： before the softening stage， the activity of β-Gal increased slowly， and after the softening stage， its activity was kept stable， and the enzyme activity of the treatment group was significantly lower than that of the CK all the time. It was indicated that chitin also had an inhibitory effect on the activity of β-Gal， which was synchronous.
Discussion and Conclusions
Cell wall is mainly composed of pectin and cellulose， which endows fruit with certain shape and elasticity， and when the structure and composition of pectin and cellulose change， the texture of fruit also would change[11-12]. Furthermore， the softening of fruit is caused by cell separation due to the change of middle structure of cell wall， the loss of massive cell wall structure and the degradation of cell wall substances. The destruction of the inner structure of cell wall plus massive degradation of cell wall substances is the primary cause of softening of fruit texture[10]. The chitin treatment significantly improved fruit weight of A. arguta， thereby improving yield. The fruit of the chitin treatment had low soluble solid content and high firmness on the day of harvest， which were beneficial to fruit storage， but after softening， the soluble solid content increased significantly， and the titratable acid content decreased rapidly， which improved the edible quality of A. arguta fruit. The chitin treatment significantly reduced cellulose content and hemicellulose content， thereby improving fruit taste， because higher contents of cellulose and hemicellulose means rough flesh. This result is similar to the research result obtained by Liu et al.[13] on tomato. The slow decrease of total pectin and low content of soluble pectin in A. arguta fruit of the chitin treatment indicated that chitin treatment inhibited the decomposition of pectin. And in addition to the inhibition on degradation of hemicellulose， the degradation of cell wall was delayed， which was the fundamental reason for the improvement of storage property. During the whole softening process， the activity of pectinolytic enzyme in A. arguta fruit of the chitin treatment was significantly lower than that of the CK group， without the appearance of delayed activity peak， and it could be seen that the inhibition of chitin treatment on softening differs from that of MCP[14]. This research result accords with the effect obtained by Fisk et al.[7] by smearing chitin on A. arguta fruit. The chitin treatment improved fruit weight of A. arguta fruit， increased soluble solid content， but decreased titratable acid content and significantly reduced the content of cellulose and hemicellulose， thereby increasing yield of A. arguta and improving quality. The chitin treatment inhibited the decomposition of pectin， cellulose and hemicellulose， and inhibited the activities of PG enzyme and β-Gal enzyme， thereby improving the storage property of A. arguta fruit.
References
[1] JIANG TD. Chitosan[M]. Beijing： Chemical Industry Press， 2001.
[2] HUANG LP， LIU ZM. Application of chitin and chitosan in agriculture[J]. Liaoning Agricultural Sciences， 1999， （6）：18-21
[3] QIN LF， LIU DM. Application of chitin and chitosan[J]. Shanxi Chemical Industry， 2017， 171（5）： 76-78.
[4] JIANG XS， MO HT， SU HJ， et al. The application of chitin and chitosan in agriculture[J]. Chinese Agricultural Science Bulletin 2013， 29（6）： 170-174.
[5] ZHOU L， WU YG， LIU B. Application of carboxymethyl chitin for the preservation of chinese gooseberry and carambola[J]. Fine Chemicals， 2004， 21（10）： 748-752.
[6] ZHANG C， LI M， LONG YH， et al. Control of soft rot in kiwifruit by pre-harvest application of chitosan composite coating and its effect on preserving and improving kiwifruit quality[J]. Food Science， 2016， 37（22）： 274-281.
[7] CONNIE L. FISK， ALISSA M. SILVER， BERNADINE C. Strik， et al. Postharvest quality of hardy kiwifruit （Actinidia arguta ‘Ananasnaya’） associated with packaging and storage conditions.[J] Postharvest Biology & Technology， 2008， 47（3）： 338-345.
[8] PIAO YL， ZHAO LH， XUE GX. Change in cell wall components during storage of pear fruit[J]. Journal of Fruit Science， 2006， 23（6）： 880-883.
[9] PIAO YL， ZHAO LH， HUANG LZ. Changes in molecular structure of soluble pectin and hemicellulose during storage of pear fruits[J]. Acta Horticulturae Sinica， 2007， 34（6）： 1525-1530.
[10] KAN J， JIN CH， WANG ZJ， et al. The Effect of β-galactosidase and polygalacturonase on peach ripening and softening[J]. Journal of Yangzhou University： Agricultural and Life Science Edition， 2006， 27（3）： 76-80.
[11] ANDREWS PK， LI S. Cell wall hydrolytic enzyme activity during development of nonclimacteric sweet cherry （Prunus avium L.） fruit[J]. Journal of Pomology & Horticultural Science， 1995， 70（4）： 561-567.
[12] ZHOU HW， SONEGO L， BENARIE R， et al. Analysis of cell wall components in juice of ‘Flavortop’ nectarines during normal ripening and woolliness development[J]. Journal of the American Society for Horticultural Science American Society for Horticultural Science， 1999， 124（4）： 424-429.
[13] LIU JF， WANG CY. The effect of chitin on yield and quality of tomato[J]. Science & Technology Vision， 2014（6）： 325-326
[14] ZENG ZX， PIAO YL， JIN DL， et al. Effects of 1-MCP treatment on softening of Actinidia arguta fruit[J]. Northern Horticulture， 2014， 304（1）： 123-126.
Key words Chitin； Actinidia arguta； Cell wall composition； Pectinolytic enzyme
Chitin is a kind of polysaccharide formed from N-acetyl-D-glucosamine by β-1，4-glucoside[1]. It widely exists in cells of lower microbes and alga， shells of arthropods， inner shells and cartilages of mollusc and cell walls of higher plants. The biosynthesis amount of chitin could reach 200 billion tons a year， and its production is only second to plant cellulose in nature， so it is an inexhaustible resource[2]. Chitin and chitosan are widely applied in fields of membrane preparation， water preservation， health care， industrial production and environmental production[3]. Chitin and chitosan effectively promote plant growth， could effectively improve crop yield and quality as well as cold resistance， and have antibacterial property and film-forming property， and therefore， in agricultural field， they are widely used as soil conditioner， disease prevention and fruit and vegetable fresh-keeping agents， plant growth regulator， cold-resistant agent， feed additive and seed coating[4].
Zhou et al.[5] showed that the fruit and vegetable fresh-keeping agent prepared with carboxymethyl chitin （06 CMCH） as a main component has a remarkable fresh-keeping effect on kiwifruit and carambola. Chitin treatment inhibits the respiration of ‘Guichang’ kiwifruit and delays the production of ethylene， thereby improving yield and fruit quality[6]. Actinidia arguta not only has good taste， but also various medical efficacy， and is loved by consumers in general. Fisk et al.[7] performed edible coating treatment on A. arguta fruit， which was then refrigerated at 2 ℃ under a humidity of 88%. The results showed that the treatment could reduce the loss of fruit moisture， and significantly prolonged the storage time of A. arguta. However， there have been no reports about the effects of spraying treatment and soaking treatment on A. arguta fruit. Materials and methods
Experimental materials
The experiment was carried out in A. arguta garden of agricultural college， Yanbian University. Huanyou No. 1 was selected as an experimental material， the trees were five years old with a planting spacing of 3 m×4 m， and horizontal shed frame was adopted. Soil was managed by clean cultivation method， and organic fertilizer was applied at a rate of 2.5-5.0 kg/plant every year. Pollination was performed by bees. Ordinary healthy trees free of diseases and pests were selected for experimental treatment. Single-plant block design was adopted with three replications. From August 20， 2016， chitin spray treatment was started and performed every 10 d. The fruit was harvested on September 29， 2016. The harvested fruit was taken back to lab， and the individuals with uniform size free of diseases and pests and mechanical injury were selected for the investigation of fruit quality at the harvest time. Partial fruit was stored at （3±1）℃， for the determination of quality at hard-ripe stage （the very day of harvest）， softening stage （90% of the fruit is softened）， and too-soft stage （10% of the fruit begin to rot）. Partial fruit was stored frozen， for the determination of cell wall components and activity of pectinolytic enzyme. The used chitin was 200 times dilution produced by Enbio-guard company （Korea）， and 0.05% Tween 20 was used as the speader.
Experimental methods
From each treatment， 60 fruit individuals （three replications） were picked for quality investigation and low-temperature storage， and during each time of investigation， 20 fruit individuals （three replications） were randomly investigated， and partial fruit flesh was stored frozen. Fruit weight was determined with an electronic balance； fruit firmness was determined with a TMS-PRO texture analyzer produced by Beijing Yingsheng Hengtai Science and Technology Co.， Ltd.； soluble solid content in fruit was determined with an ATAGO type hand-held refraction saccharimeter； and titratable acid content was determined by acid-base titration method. The analysis of cell wall components and determination of the activity of pecinolytic enzyme were performed according to the methods of Piao et al.[8-9].
Experimental data were statistically analyzed and used for plotting in Excel， and variance analysis was performed with SPSS.
Results and Analysis
Effect of chitin treatment on fruit quality of A. arguta
Chitin spray treatment was started 40 d before harvest of A. arguta fruit and performed every 10 d. The results showed that chitin treatment significantly improved fruit weight of A. arguta， but had no significant effect on fruit-shape index （Table 1）. Firmness refers to the compressive resistance of fruit， and the change of fruit firmness is an important index reflecting the storage property of fruit for evaluating the storage effect. Soluble solid mainly refers to soluble sugar， and its content directly reflects fruit quality and fruit maturity. Titratable acid as a substrate of respiratory metabolism during storage is consumed continuously. The softening process of A. arguta in the chitin treatment is shown in Fig. 1. The A. arguta fruit in the chitin treatment had a soluble solid content significantly lower than the CK on the very day of harvest， and such difference was kept until the softening stage， and at the too-soft stage， the soluble solid content of the treatment group was significantly higher than that of the CK. Therefore， taste quality was improved. The chitin treatment had no high effect on the content of titratable acid in A. arguta fruit， but there was a rapid decrease process at the too-soft stage. The firmness of the A. arguta fruit in the chitin treatment was significantly higher than that in the CK group， such difference was kept until the softening stage， but waned at the too-soft stage when the firmness was basically the same in the two groups. The difference in firmness was especially more remarkable for fruit firmness than for flesh firmness. It could be seen that chitin treatment could inhibit the increase of soluble solid content， and promote the decrease of titratable acid， so as to keep fruit firmness at a higher level， i.e.， chitin could alleviate the softening speed of fruit， thereby prolonging the storage time of fruit. Effect of chitin treatment on cell wall components of A. arguta fruit
Change of pectin content
Cell wall is manly composed of pectin， cellulose and hemicellulose， and softening of fruit is， in essence， the decomposition of cell wall components. In this study， cell wall components were determined using ethanol-insoluble substance （AIS）. The change of pectin content in A. arguta fruit of the chitin treatment is shown in Fig. 2. The pectin content in A. arguta fruit of the chitin treatment was consistent with that of the CK on the very day of harvest and had no big change during the softening process， while the water pectin content in the fruit of the CK significantly decreased at the softening and too-soft stages， indicating that chitin treatment delayed the decomposition of pectin in A. arguta fruit. The soluble pectin content in the fruit of the chitin treatment was significantly lower than that of the CK on the very day of harvest， and increased rapidly and then slowly during the softening process， but was lower than that of CK all the time. The EDTA soluble pectin content had no big change during the softening process， and was kept lower than the level of the CK all the time. The NaOH soluble pectin content increased slowly at the softening stage， and at the too-soft stage， the NaOH soluble pectin content of the treatment group increased rapidly， while that of the CK group decreased rapidly to the level the same as the NaOH soluble pectin content of the treatment group. It could be seen that chitin treatment inhibited the increase of soluble pectin and delayed the softening process of fruit.
Change of cellulose and hemicellulose
Cellulose， hemicellulose and pectin in cell wall are dissolved by new enzyme system formed in the ripening process of fruit， resulting in local degradation of cell wall， and it is thus believed that the degradation of cell wall is the main reason of fruit ripening and softening. It could be seen from Fig. 3 that the chitin treatment had a cellulose content in A. arguta fruit significantly lower than the CK group， but the experimental and CK groups had the same changing trend of increasing slightly and then decreasing rapidly during the softening process， indicating that cellulose decreased at a lower rate before the softening stage and then was decomposed at a higher rate. The hemicellulose content in A. arguta fruit of the chitin treatment was also significantly lower than that of the CK， and slowly increased at the softening stage， indicating that the decomposition rate of hemicellulose of the treatment group was equivalent to the decomposition rates of other cell wall components. However， the hemicellulose content of the CK group decreased rapidly and then increased rapidly at the softening stage， indicating that hemicellulose was decomposed rapidly before the softening stage and then decomposed slowly. The increases of cellulose content and hemicellulose content were interpreted as slower decomposition relative to other cell wall components， because the unit used here was cellulose or hemicellulose content in unit AIS， i.e.， it was a relative value. Effect of chitin treatment on activity of pectinolytic enzyme in A. arguta fruit
Change of PG activity during the softening process of A. arguta fruit
The main function of PG is to break up cell wall structure by degrading polygalacturonic acid in polysaccharides in fruit cell wall to galacturonic acid， resulting in softening of fruit[10]. The change of PG activity during the softening process of A. arguta fruit is shown in Fig. 4. The PG activity in A. arguta fruit of the chitin treatment was significantly lower than that of the CK group， and decreased slowly during the softening process.
Change of β-galactosidase activity during the softening process of A. arguta fruit
β-Gal is one of the important glycosidases related to the degradation of cell wall polysaccharides. It could make some cell wall components instable by degrading polyuronides with branches， thereby degrading or dissolving pectin[10]. It could be seen from Fig. 5 that the change of β-Gal in the softening process of A. arguta fruit also could be divided into two obvious stages： before the softening stage， the activity of β-Gal increased slowly， and after the softening stage， its activity was kept stable， and the enzyme activity of the treatment group was significantly lower than that of the CK all the time. It was indicated that chitin also had an inhibitory effect on the activity of β-Gal， which was synchronous.
Discussion and Conclusions
Cell wall is mainly composed of pectin and cellulose， which endows fruit with certain shape and elasticity， and when the structure and composition of pectin and cellulose change， the texture of fruit also would change[11-12]. Furthermore， the softening of fruit is caused by cell separation due to the change of middle structure of cell wall， the loss of massive cell wall structure and the degradation of cell wall substances. The destruction of the inner structure of cell wall plus massive degradation of cell wall substances is the primary cause of softening of fruit texture[10]. The chitin treatment significantly improved fruit weight of A. arguta， thereby improving yield. The fruit of the chitin treatment had low soluble solid content and high firmness on the day of harvest， which were beneficial to fruit storage， but after softening， the soluble solid content increased significantly， and the titratable acid content decreased rapidly， which improved the edible quality of A. arguta fruit. The chitin treatment significantly reduced cellulose content and hemicellulose content， thereby improving fruit taste， because higher contents of cellulose and hemicellulose means rough flesh. This result is similar to the research result obtained by Liu et al.[13] on tomato. The slow decrease of total pectin and low content of soluble pectin in A. arguta fruit of the chitin treatment indicated that chitin treatment inhibited the decomposition of pectin. And in addition to the inhibition on degradation of hemicellulose， the degradation of cell wall was delayed， which was the fundamental reason for the improvement of storage property. During the whole softening process， the activity of pectinolytic enzyme in A. arguta fruit of the chitin treatment was significantly lower than that of the CK group， without the appearance of delayed activity peak， and it could be seen that the inhibition of chitin treatment on softening differs from that of MCP[14]. This research result accords with the effect obtained by Fisk et al.[7] by smearing chitin on A. arguta fruit. The chitin treatment improved fruit weight of A. arguta fruit， increased soluble solid content， but decreased titratable acid content and significantly reduced the content of cellulose and hemicellulose， thereby increasing yield of A. arguta and improving quality. The chitin treatment inhibited the decomposition of pectin， cellulose and hemicellulose， and inhibited the activities of PG enzyme and β-Gal enzyme， thereby improving the storage property of A. arguta fruit.
References
[1] JIANG TD. Chitosan[M]. Beijing： Chemical Industry Press， 2001.
[2] HUANG LP， LIU ZM. Application of chitin and chitosan in agriculture[J]. Liaoning Agricultural Sciences， 1999， （6）：18-21
[3] QIN LF， LIU DM. Application of chitin and chitosan[J]. Shanxi Chemical Industry， 2017， 171（5）： 76-78.
[4] JIANG XS， MO HT， SU HJ， et al. The application of chitin and chitosan in agriculture[J]. Chinese Agricultural Science Bulletin 2013， 29（6）： 170-174.
[5] ZHOU L， WU YG， LIU B. Application of carboxymethyl chitin for the preservation of chinese gooseberry and carambola[J]. Fine Chemicals， 2004， 21（10）： 748-752.
[6] ZHANG C， LI M， LONG YH， et al. Control of soft rot in kiwifruit by pre-harvest application of chitosan composite coating and its effect on preserving and improving kiwifruit quality[J]. Food Science， 2016， 37（22）： 274-281.
[7] CONNIE L. FISK， ALISSA M. SILVER， BERNADINE C. Strik， et al. Postharvest quality of hardy kiwifruit （Actinidia arguta ‘Ananasnaya’） associated with packaging and storage conditions.[J] Postharvest Biology & Technology， 2008， 47（3）： 338-345.
[8] PIAO YL， ZHAO LH， XUE GX. Change in cell wall components during storage of pear fruit[J]. Journal of Fruit Science， 2006， 23（6）： 880-883.
[9] PIAO YL， ZHAO LH， HUANG LZ. Changes in molecular structure of soluble pectin and hemicellulose during storage of pear fruits[J]. Acta Horticulturae Sinica， 2007， 34（6）： 1525-1530.
[10] KAN J， JIN CH， WANG ZJ， et al. The Effect of β-galactosidase and polygalacturonase on peach ripening and softening[J]. Journal of Yangzhou University： Agricultural and Life Science Edition， 2006， 27（3）： 76-80.
[11] ANDREWS PK， LI S. Cell wall hydrolytic enzyme activity during development of nonclimacteric sweet cherry （Prunus avium L.） fruit[J]. Journal of Pomology & Horticultural Science， 1995， 70（4）： 561-567.
[12] ZHOU HW， SONEGO L， BENARIE R， et al. Analysis of cell wall components in juice of ‘Flavortop’ nectarines during normal ripening and woolliness development[J]. Journal of the American Society for Horticultural Science American Society for Horticultural Science， 1999， 124（4）： 424-429.
[13] LIU JF， WANG CY. The effect of chitin on yield and quality of tomato[J]. Science & Technology Vision， 2014（6）： 325-326
[14] ZENG ZX， PIAO YL， JIN DL， et al. Effects of 1-MCP treatment on softening of Actinidia arguta fruit[J]. Northern Horticulture， 2014， 304（1）： 123-126.