| Crystal grape(Vitis vinifera,cv."Guizhou Crystalgrape")is a characteristic fruit of Sandu County in the south of Guizhou Province.Ripe fruit is translucent and translucent,with crystal clear and sweet texture.The peel of crystal grape is quite thin,which are easily fall off and subjected to rot.The fruit stems are easily dehydrated,brown and dry,and the post-harvest quality deterioration is rapid.It is difficult to store and transport crystal grape at normal temperature.Low-temperature storage and transportation are the most used preservation technologies which can effectively reduce post-harvest losses of fruits and vegetables around the world.This study is a scientific and technological assistance project for the counterpart of Guizhou Province supported by Guangzhou city.The present work mainly focuses on the key preservation technologies such as cold storage of crystal grapes,pre-cooling technology,packaging materials,and SO2 fresh-keeping paper,as well as the physiological and biochemical mechanisms of low-temperature on delaying the deterioration of fruit quality.The main results are listed as follows:1.The effects of fresh-keeping grapes for three groups of refrigerated storage temperature of 1°C,4°C and 8°C were compared(combined with polyethylene anti-fog film packaging and Greed's membrane sterilization fresh-keeping paper).The results showed that the grapes stored at 1°C and 4°C were stored for 30 days and the commodity rate was still over 90%.However,the grapes stored at 8°C lost their commodity value after being stored for 30 days.Among them,the best preservation temperature is 1°C,which could effectively keep the grape fruit surface smooth and the fruit stems green,significantly reduced the shedding of fruits and fruit rot,and the preservation period was about 50 days,which was 17% higher than that of the 4°C storage.After cold storage for 50 days,fruits were transferred to the normal temperature and fruit shedding was observed.2.1°C storage maintained grape quality much better than 4°C and 8°C storage.Moreover,when the fruit stored at 1°C,the amino acid content increased,and the characteristic flavor of the fruit were improved.The quality of grapes stored at 8°C declined rapidly.Storage at 1°C effectively delayed decline of the content of sugar,acid and Vc and other nutrients.In the main sugar of the crystal grape,the glucose and fructose content is equivalent,and is 6-9 times that of sucrose and maltose.Tartaric acid is the most abundant organic acid in crystal grapes,followed by malic acid and citric acid,and the least content is oxalic acid.Under the condition of refrigerating at 1°C,the main sweet and umami amino acids content in crystal grape increased with the prolonged storage time,which is consistent with the result of sensory evaluation.3.The lower storage temperature delays the quality deterioration of crystal grape during storage,which is closely related to the changes of antioxidant enzyme activity.1°C and 4°C storage inhibited the activities of SOD,CAT and POD enzymes.However,the change of APX enzyme activity showed the opposite trends.The lower the temperature was,the higher the enzyme activities observed.The 1 °C storage temperature effectively delayed the decrease of the relative content of unsaturated fatty acids.There was no correlation between the change of relative content of unsaturated fatty acids and browning.Browning was positively correlated with high MDA content..4.The preservation effect of four types of packaging materials,OPP,OPP and paper bags,paper bags and plastic boxes(fruit without packaging as the control),was compared.Under the storage condition of 1°C,the control fruit lost the commercial value when stored for 30 days.The OPP packaged grape had a shelf life of up to 50 days,and still maintained fruit plump,green stems,green fruit,little shedding,decay rate.The storage of paper bag pakaging was about 40 days,and then the fruit rot index increased significantly.The storage period of OPP combined with paper bag was about 30 days,and then the shedding rate of fruit significantly increased.The advantages of plastic box packaging are beautiful,easy to carry,but the water loss rate was high,and the storage period was only about 20 days.Plastic box packaging issuitable for short-term sales and storage.5.Three types of SO2 slow-release plastic wrap(Emerald Film,Greed Film,and Gridd Pack)were used for fruit preservation in a polyethylene anti-fog film at 1°C.The rate of fruit decay was significantly reduced compared to the control group,and the grapes were stored for 40 days.The commodity rate could still keep atout 80%,while the control has no commodity value.The best way to prevent crystal grape rot is the Gride drug package,followed by the Greed film,and then the emerald green film.SO2 controlled release plastic wrap meets the requirements of food safety.The SO2 residue of these three kinds of SO2 controlled release plastic wraps in fruit that have been preserved for 30 days was "undetected" by the Ministry of Agriculture's Fruit and Vegetable Quality Supervision,Inspection and Test Center.6.Three different temperatures(1°C,4°C and 8°C)were used to pre-cool the crystal grapes.The lower the precooling temperature was,the shorter the semi-precooling time used and the higher the precooling efficiency was.The minimum pre-cooling time at the precooling temperature of 1°C was about 4 h,and the longest duration at 8°C is about 12 h,and the pre-cooling time was about 7 h at4°C.Pre-cooling can reduce the rate of grape rot,but the grapes pre-cooled at 1°C showed higher fruit shedding rate during shelf life than those at 4°C and 8°C.The pre-cooling temperature of 4°C is recommended. |
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