Polyglutamic Acid Improves The Physiological Mechanism Of Postharvest Refrigeration Preservation Effect Of Strawberry Fruit

Since the application of polyglutamic acid(PGA)in the preservation of strawberry fruit during storage has not been reported,this paper studied the effects of 50 mg/L,100 mg/L and 200 mg/L PGA on the appearance quality,nutritional quality,taste quality,transportation quality,antioxidant properties and storage effect of strawberry fruit under cold storage.After 4 d and 8 d of PGA treatment,the fruit appearance quality(aspect diameter,fruit shape index,color parameters),nutritional quality(protein,soluble sugar,total phenols,total flavonoids,anthocyanin,Vc,free amino acid content),taste quality(soluble solids,tannin content,titratable acid content,sugar-acid ratio),storage quality(hardness,fruit softening-related enzyme activity)and antioxidant properties(SOD,POD,CAT,APX,MDHAR,DHAR,GR,GPX,GST activity,MDA content,GSH content,hydrogen peroxide content,total antioxidant capacity)were measured.Strawberry fruits were photographed on day 0,day 4,day 8 and day 14 of PGA treatment during cold storage period to compare storage preservation effects of different treatments.Through above researches,the aim of this study is to clarify the physiological mechanism of PGA in regulating the preservation effect of strawberry fruit during cold storage,which will provide a theoretical basis for the application of PGA in the preservation of strawberry fruit during cold storage.The results of this study are as follows:1.Different concentrations of PGA significantly improved the values of color parameters L and b and dcreased the values of a and ΔE of strawberry fruits,compared with the control.Among different concentrations of PGA,100 mg/L PGA had the most significant effects on above indexes.Above results indicated that exogenous application of appropriate concentration of PGA can effectively maintain the color quality of strawberry fruit under cold storage.However,different concentrations of PGA had no ignifucant effects on the vertical diameter,horizontal diameter and fruit shape index of strawberry fruit,compared with the control.2.Different concentrations of PGA significantly improved the contents of protein,soluble sugar,total phenol,anthocyanin and Vc in strawberry fruits,compared with the control.Among different concentrations of PGA,100mg/L PGA had the most significant effects on above quality indicators.Above results indicated that exogenous application of appropriate concentration of PGA could effectively maintain the nutritional quality of strawberry fruit under cold storage.However,different concentrations of PGA had no significant effects on the contents of total flavonoids and free amino acids in strawberry fruit.3.Different concentrations of PGA significantly improved the soluble solids content and sugar-acid ratio and deceased the total acid content in strawberry fruits,compared with the control.Among different concentrations of PGA,100mg/L PGA greatly increased soluble solids content and sugar-acid ratio in above taste indicators and decreased total acid content.Above results indicated that exogenous application of appropriate concentration of PGA could effectively maintain the taste quality of strawberry fruit under cold storage.But,different concentrations of PGA had no significant effects on the tannin content of strawberry fruits,compared to the control.4.Different concentrations of PGA significantly improved the hardness of strawberry fruits and decreased the activities of polygalacturonase(PG),pectinlyase(PL),cellulose(CL)and β-galactosidase(β-GAL),compared with the control.Among different concentrations of PGA,100mg/L PGA had the most significant effects on above storage and transportation quality indicators.Above results indicated that exogenous application of appropriate concentration of PGA can delay the decrease of fruit hardness by reducing the softening enzyme activity of strawberry fruit,thereby improving the storage and transportation quality of strawberry fruits.5.Different concentrations of PGA significantly improved the activities of antioxidant enzymes SOD,POD,CAT,APX,MDHAR,DHAR and GR,compared with the control.The contents of MDA and H2O2 in fruits treated by PGA were lower than the control,and the total antioxidant capacity of fruits was higher than the control in strawberry fruits.Among different concentrations of PGA treatment,100mg/L PGA had the most significant effect on above indexes.Above results indicated that the exogenous application of appropriate PGA concentrations can effectively enhance the antioxidant capacity of fruits under cold storage conditions.However,different concentrations of PGA treatment had no significant effects on GSH content,GPX and GST activities in strawberry fruits,compared with the control.6.Different concentrations of PGA significantly decreased the decay rate of fruits,compared with the control.Among different concentrations of PGA treatment,the fruit decay rate of fruits treated by 100mg/L PGA treatment was the lowest.Above results indicated that exogenous application of appropriate concentration of PGA has the best preservation effect and prolongs fruit storage time under cold storage.In summary,PGA treatment can significantly improve the appearance quality,nutritional quality,taste quality,antioxidant capacity in strawberry fruits,and delay the softening of strawberry fruit and reduce the decay rate,prolong the storage time under cold storage.Among different concentrations of PGA,100 mg/L PGA had the most significant effects on above fruit qualities.Therefore,this study not only explained the physiological mechanism of PGA in improving the preservation effect of strawberry fruit,but also provided a theoretical basis for the application of PGA in the preservation of strawberry fruit.