| Kiwifruit which is rich in vitamin C originated in China's Yangtze River Basin,known as the “king of fruits”.Due to easy softening and rot of kiwifruit,storage and sales were affected.Breaking through the traditional methods of preservation,exploring the new ways and principles of preservation is a new task in the research of fruits and vegetables.This experiment based on the principle of non thermal biological effect of microwave,the use of low power microwave radiate the kiwifruit controlled the temperature below20 ? for a long time,excluding the role of thermal effect.“Wancui” and “Hayward” two kinds of kiwifruit as test materials,with the output power of 32.5W,respectively 3,5,7,9,and 11min;with the output power was 65 W,respectively 2,3,4,5,and 6min,the non irradiated kiwifruit was used as control.Fruits were placed 1 + 0.5c,RH 92~95% freezer storage,regular sampling,the effects of different microwave intensities on the respiratory physiology,quality,flesh firmness,cell wall composition,cell wall degradation enzyme activity and gene expression intensity were studied,which investigated the effect of low power microwave treatment on the fresh keeping of the fruits and the mechanism of delaying the softening of the fruit,in order to provide the theoretical basis for the microwave preservation technology of the kiwi fruit.The main results of the study are as follows:1.The relationship between different microwave treatment intensity and the temperature of kiwifruit was studied,the longest time of 32.5W and 65 W low power microwave treatment were respectively 11 min and 6min to ensure the treatment of fruit temperature < 20?.2.The effects of different microwave treatments on the respiratory physiology of kiwifruit were studied.The results showed that the respiration intensity of the fruit after harvest showed the trend of first rising and then falling,which belongs to the respiration climacteric fruit;certain intensity of microwave treatment can inhibit the respiratory intensity of kiwifruit,in a variety of “Wancui” and “Hayward” by using a treatment for respectively 5min and 7min,65 W processing 3min and 4min inhibitory effect of respiration was the best,the average respiration than the control low 8~10CO2mg/kg.h.Microwave32.5W/3min and 65W/6min treatment,no inhibitory effect,on the contrary,instead promoting respiration.3.The effects of different microwave treatments on the storage quality of kiwi fruit were studied.The results showed that the low power microwave treatment can delay thefruit of titration acid and Vc contents decreased and remained higher firmness,soluble solids content and soluble sugar content,decay index is relatively low,so as to prolong the storage period of fruits.After 90 days of storage,“Wancui” microwave 32.5W/5min and“Hayward” microwave 65W/4min flesh hardness was respectively 3.98 N and 5.55 N,compared with the control respectively high 1.60 N and1.54N;the content of soluble solids and total soluble sugar increased with the increasing of starch degradation,the content of titration acid and vitamin C decreased more slowly than that of the control group.Using32.5W/5min~7min and 65W/3~4min maintain the best quality of kiwifruit.4.There was a close correlation between the degradation of cell wall and the hardness of fruit.Research shows,with 32.5w/5min~7min and 65w/3~4min microwave treating kiwifruit can be a very good inhibition of cell wall,water soluble pectin,covalent pectin,cellulose,hemi cellulose content decreased,delaying increase in ionic pectin content and significantly inhibiting the fruit cell wall degradation,reducing fruit softening degree.Therefore,appropriate microwave processing can inhibit cell wall degradation.5.The softening of the fruit was mainly related to the changes of PG,PME,Cx and-Gal,and the enzyme activity was negatively correlated with fruit firmness.The results showed that a certain intensity range of microwave treatment of kiwi fruit,which can delay the increase of the activity of the enzyme and inhibit the process of fruit softening.The 4kinds of softeniing ralated enzyme activities show an upward trend,4 kinds of enzyme activity about “Wancui” kiwifruit decreased before 15 d,after rising,the PG and PME activity of “Hayward” in the kiwifruit increased before 60 d,and then decreased slowly,PG and PME activity “Wancui” kiwifruit is higher than that of “Hayward” from the change of enzyme activity,on the contrary,the other two kinds of enzyme activity is lower than“Hayward”.It was found that the softening of the kiwifruit is the result of PG,PME,Cx and ?-Gal,which may play a leading role in PG and Cx.The inhibition effect of32.5W/5min~7min and 65W/3~4min treatment on fruit softening enzyme activity was the best,but the fruit of microwave 32.5w/11 min treatment promoted the increase of enzyme activity.6.At the same time,the expression intensity of 4 kinds of softening related enzyme genes in the fruit of the fruit of the low microwave treatment were studied,the test showed that the PG,PME,Cx and ?-Gal gene expression intensity trend and the trend of the change of the enzyme activity is basically the same,the overall upward trend.The PME and Cx the expression intensity of genes of “Wancui” kiwifruit decreased 15 d before,after rising trend,the expression intensity of PG and ?-Gal was higher than the enzyme activitybefore 15 d in the fruit,which was consistent with the later stage of storage,the changes of gene expression intensity and enzyme activities of the “Hayward” are the same.The expression intensity of the 4 enzymes was relatively high in control group,with32.5w/11 min treatment of fruit,but enhanced the fruit of the gene expression intensity.The results showed that the gene expression intensity of the fruit was significantly inhibited by the appropriate treatment of the microwave,the effect of 32.5w/5min~7min and65w/3~4min treatment was especially higher than other treatment groups.7.The softening of fruit caused the hydrolysis of cell wall components by the action of degrading enzymes,which showed that the flesh firmness decreased continuously.The study showed that the changes of the gene expression of 4 cell wall degrading enzymes were significantly positively correlated with the enzyme activity under different microwave intensities,and the flesh hardness was negatively correlated,and the correlation coefficient reached more than 0.9.In summary,the microwave non heat treatment of a certain intensity range of Kiwifruit has the effect of inhibiting fruit respiration rate and softening process,maintaining a high degree of hardness and quality of flesh,and prolonging the period of fresh keeping;the total effect of 32.5w/5min~7min and 65w/3~4min microwave treatment was the best,which significantly reduced the gene expression intensity of the 4 enzymes and the activity of the related enzymes. |
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