Study On Storage Technologies For Crystal Grapes In Guizhou Province At Room Temperature And The Possible Mechanism

Crystal grape is a specialty fruit grown in the Sandu County of Guizhou Province.Crystal grape has a unique aroma,with thin peel,soft flesh,and a high moisture content.Due to the thin skin and high moisture content,crystal grape is easily damaged,rotted and deteriorated during the product circulation.Sandu county is a poverty-stricken mountainous area.The grape preservation technology is less developed,and the cold chain logistics equipment is lacking.At present,the grape usually stored and transportrd at the normal temperature,and the post-harvest losses are serious.Therefore,the research and on new technologies for storage and transportation of crystal grapes at room temperature are important for reducing the post-harvest losses of crystal grapes in Guizhou and improving the economic benefits of the grape industry.This study is part of the scientific and technological counterpart of the Guangzhou Science and Technology Commission counterpart to the Guizhou Science and Technology Assistance Project.This work mainly studied three aspects:Firstly,the effect of pre-harvesting bagging on post-harvest diseases,post-harvest quality and the storability;Secondly,research on the influence of SO₂preservation materials on prevention of postharvest diseases and storability of grapes;Thirdly,screening the packaging materials suitable for storage and transport of crystal grapes,and study the impact of different packaging on grape preservation at room temperature and its physiological and biochemical effects.The main findings are listed as follows:1.The post-harvest storage diseases of crystal grape include Alternaria spp.,Collectotrichum gloeosporioid Penz,Sphaceloma ampelinum de Bary,Botrytis cinerea Pers,Plasmopara viticola and Unecinula necator.2.Pre-harvest bagging for post-harvest storage at room temperature varies depending on the bag types.The white bag bagging had better effect than the yellow bag bagging,but the threshing was more serious in the later period of storage for the yellow bag bagging.The pre-harvest bagging of yellow bags improvedthe color of the crystal grape increased the transparency of the fruit.On the 10th day of storage,the decay rate,threshing rate and weight loss rate of the white bag group were 20.2%,14.1%and 2.9%,respectively,which were lower than that the rotten rate?28.4%?,threshing rate?32.5%?and weight loss rate?3.6%?of the yellow bag group.The commodity rate of white bag group was 73.0%,which higher than the yellow bag group?64.2%?,but lower than the naked group?84.7%?.The pre-harvest bagging of yellow bags significantly reduced the browning of fruit stems.On the 6th day of storage,the fruit stem browning levels of the yellow bags were only at level1²,lower than the white bag group?level 2 to 3?and the naked grapes group?level 2 to 3?.Pre-harvest bagging with white bag increased the content of glucose,fructose and sucrose,which showed 0.3 mg·g^-12.5 mg·g^-1,0.2 mg·g^-13.0 mg·g^-1 and 1.0 mg·g^-1 higher than the naked fruit,respectively.The yellow bag bagging reduced the content of the three kinds of sugar mentioned above,which with less glucose content by 0.9 mg·g^-1 to 2.0mg·g^-1,and less fructose content by 1.0 mg·g^-1 to 2.0 mg·g^-1,but more sucrose content by0.2 mg·g^-1 to 0.5 mg·g^-1 compared to the control.The white bag bagging significantly reduced the amino acid content related to bitterness,while the yellow bag bagging significantly reduced the amino acid content of fruit related to bitterness and sourness,but it also reduced the amino acid content related to sweetness and umami taste.3.All the three SO₂ controlled-release plastic wrap effectively reduced the disease index,weight loss rate and threshing rate of the crystal grapes stored at room temperature,and maintained a high commodity rate of grapes.Among them,the“Cuilv”fresh-keeping paper showed the best effect.At the 14th day of storage,the disease index,weight loss rate,and threshing rate of the"Cuilv"group were 0.13,7.8%,and 47.9%,respectively,which were lower than those of other brand plastic wrap treatments?0.16⁰.19?and weight loss rates?8.7%⁹.2%?and threshing rate?58.6⁵8.7%?,and significantly lower than the disease index?0.26?,weight loss rate?10.3%?and threshing rate?83.2%?.In addition,at 14days storage,the commodity rate of the"Cuilv"Green Group remained about 62.4%,which was higher than that of the other treatment groups?50.3⁶0.8%?and was significantly higher than that of the control group?20.0%?.The“Cuilv”fresh-keeping paper effectively delayed the decrease of fructose and glucose content in the middle?before 8 days?of storage and maintained a high sucrose content during storage.It significantly maintained a high level of the content of Vc in the early storage period?the first 6 days?and decreased the content of malondialdehyde in the late storage period?the 8th to 14th days?.On the 10th day of storage,the“Cuilv”fresh-keeping paper delayed the decline of amino acid content related to sweetness,sourness,bitterness and umami.Three kinds of SO₂ slow-release plastic wraps significantly prevented fruit stem browning and the"Greed Pack."showed he best effect.The SO₂ slow release cling film meets food safety requirements and has been tested by the Ministry of Agriculture's Vegetable and Fruit Quality Supervision,Inspection and Test Center.The SO₂residues in fruit treated with the above-mentioned three kinds of SO₂ controlled release plastic wrap after 10 days storage at room temperature were at the"undetected"levels.4.Appropriate packaging could effectively improve the preservation of crystal grapes.The effect of plastic and non-porous OPP bags was better than that of other packages.The rotting rate was between 17.18%to 17.20%at 10 days storage,which was lower than that of other treatment groups?22.6%to 28.3%?.The effect of plastic box and PE anti-fog bags on reducing grape threshing was better than that of other treatment,and significant difference observed at the 6th day of storage.At the 10th day of storage,the threshing rate was about 17.2%¹9.6%,which was lower than that in other treatment groups?27.8%³7.2%?and the control group?57.4%?.The plastic box and perforated OPP bag had a better effect on preventing fruit weight loss.The weight loss rate was about 2.5%².9%at 10th day of storage,which was lower than that of other packaging?4.6%¹0.8%?and control group?11.2%?.The plastic box package had the best effect on maintaining the commodity rate of grapes.The commodity rate was 78.6%on the 10th day of storage,which was higher than that f other packaged materials?64.4%?and the control group?62.8%?.All packaging methods effectively delayed the browning of fruit stems.Among them,the perforated OPP bag packing had the best effect on controlling fruit stem browning,and significant difference was observed at the late storage period?6 d to 8 d?.The browning of the OPP bagging was about at 2³level and lower than other packaging.Taken together,the plastic box packaging had the best preservation effect on crystal grape,which was better than other packaging and controls.