Effects Of Different Treatments On Physicochemical Properties And Softening Of Persimmon Fruit

Persimmon fruit has the characteristics of thick and juicy flesh,sweet and fragrant,and rich in nutrients,which is favored by consumers.However,persimmon fruit belongs to the typical respiratory jump type,which is easy to soften during post-harvest storage and transportation,and has poor storage resistance.At present,low temperature storage is commonly used to extend the shelf life,but low temperature can cause cold damage to fruit,induce decline in disease resistance and resistance of stored fruit,leading to brown and decay of meat and making it lose its commercial value.Therefore,the study of the persimmon fruit softening mechanism as storage and preservation methods is particularly necessary.In this project,the differences between six different persimmon fruit cell wall pectins were compared,and on this basis,the effects of ultrasonic and calcium chloride treatment on persimmon fruit cell wall pectin were discussed,and the biochemical mechanism of the two treatment methods regulating persimmon fruit softening was revealed.The main findings were as follows:1.Through the study on the differences in physicochemical indexes and cell wall pectin of six different persimmons,it was found that the hardness of"Xingjin 20"and"Youhou"was higher,while the hardness of"Fuyu","Jiro"and"Guiqiu"was lower,the three kinds of persimmons with low hardness had higher WSP content,and the correlation analysis shows that there was a very significant negative correlation between hardness and water-soluble pectin(WSP)with a negative correlation coefficient of 0.921.Different persimmon fruit WSP have the same characteristic peaks,and the intensity of characteristic peaks was slightly different with the strongest"Xinqiu"and the weakest"Youhou".There was no significant difference in the molecular weight distribution of WSP,and the molecular weight varied from 100 to 150 KDa.The polygalacturonase(PG)activity of"Fuyu","Jiro"and"Guiqiu"was higher,while the pectin methylesterase(PME)activity of"Guiqiu"was the highest.Meanwhile,the PME and pectin lyase(PL)activity of"Xingjin 20"was significantly lower than that of other varieties(P<0.05).Moreover,WSP was highly significantly positively correlated with PG,PME and PL(P<0.01)and hardness was negatively correlated with PG,PME and PL(P<0.01).2.Through the determination of physical and chemical indexes of persimmon fruit during storage,the results showed that the decrease in persimmon fruit hardness was significantly inhibited after ultrasound and calcium treatment(P<0.05).At 15 d,the fruit hardness after ultrasound and calcium treatment was 3.74 kg/cm² and 5.17 kg/cm² higher than that of the control group.Ultrasonic and calcium treatment during storage has little effect on soluble solids and titrable acid content.Ultrasound and calcium treatment inhibited the elevation of?E and a*(redness).There was no significant difference in total Ca²⁺content between the sonicated group and the control group(P>0.05).The total Ca²⁺content of the calcium treatment group gradually increased during storage,and at 15 d,the total Ca²⁺content increased by 31.66%compared to the control group.Compared with ultrasonic treatment,calcium treatment was more effective in stabilizing the migration between water and inhibiting the increase in bubble water content,thus maintaining the high hardness of persimmon.3.Through the study of cell wall pectin composition,structure and cell wall pectin degradation enzyme activity of persimmon fruit during storage,it was found that after ultrasound and calcium treatment,the rise of persimmon fruit WSP was significantly inhibited(P<0.05),particularly calcium treatment.WSPs had characteristic absorption peaks of pectin,and different treatment methods had no effect on their structure.The monosaccharides of WSP consist of glucose(Glu),galactose(Gal),rhamnose(Rha),fucose(Fuc),and arabinose(Ara).Ultrasound and calcium treatment maintained WSP higher Gal/Rha,(Ara+Gal)/Rha and molecular weight,and the main side chain of WSP had better integrity than the control.At the same time,ultrasound and calcium treatment can significantly inhibit the PG,PME and PL activities of persimmon fruit.Therefore,ultrasound and calcium treatment delayed the degradation of pectin structure and the migration of water by inhibiting the activity of pectin degradation enzymes,such as PG,PME and PL,so as to maintain high hardness of persimmon fruits and reduce the softening rate.