Effects Of Different Fresh-Keeping Methods On Quality In Daylily

Daylily(Hemerocalisfulva L.)is a perennial herb of the family Liliaceae.It is a specialty vegetable in China and is cultivated throught the country of China.During the picking period of the daylily,the high-temperature and rainy summer induces strong post-harvest respiration and active metabolism,which makes the storage performance extremely poor.Quick-frozen technology and modified atmosphere storage are effective measures to solve the problem of daylily preservation.These two methods do not contain any additives and preservatives,so they can retain the flavor,color and nutrients of the daylily to the maximum extent.Therefore,it is of great practical significance to improve the quality of daylily.In this experiment,Suqian Dawuzui’ was used as plant material.Firstly,the quality of frozen daylily and the membrane lipid peroxidation of postharvest were studied by adopting quick-frozen preservation technology and Controlled Atmosphere(CA)modified storage,then these changes were related to aging during CA atmosphere storage.The expression levels of genes related to the quality of daylily were studied,and bioinformatics analysis was further performed on these genes.The main results are as follows:1.According to the freezing and storage temperature,a total of 8 combinations were designed and coded as P1,P2,P3,P4,P5,P6,P7,P8(PI:-20℃+-20℃;P2:-40℃+-20℃;P3:-60℃+-20℃;P4:-80℃+-20℃;P5:-20℃+-80℃;P6:-40℃+-80℃;P7:-60℃+-80℃;P8:-80℃+-80℃).After storage for 8 months,the thawing treatment was carried out by four kinds of thawing methods:normal temperature,warm water,microwave and citric acid.The best results were obtained in the treatments of P7 and P8 freezing method combined with using microwave thawing method,which possessed the following adventages,i.e.,maintaining the content of soluble solids after freezing thawing,effectively inhibiting water loss,chlorophyll degradation,and increase of malondialdehyde(MDA)content,and significantly reducing lipoxygenase(LOX)activity.Therefore,P7 and P8 freeze treatments combined with microwave thawing could maintain the quality of postharvest daylily.It is a suitable method for freezing and thawing of daylily.2.The following treatments were carried out for the fresh-keeping of daylily(CK:21%O2;A:3%O2+20%CO2;B:10%O2+20%CO2;C:3%O2+25%CO2;D:10%O2+25%CO2;E:3%O2+30%CO2;F:10%O2+30%CO2;G:3%O2+35%CO2;H:10%O2+35%CO2,N2 supplement),the most suitable CA for daylily in the sensory evaluation and physiological indicators screened was 3%O2+35%CO2.After storage for 30 days,compared with the air treatment group,the quality of the daylily treated with CA(3%O2+35%CO2)was relatively good and still had commercial value,the respiratory intensity is significantly higher than that of the control,and can significantly delay the decrease of pH and the degradation of chlorophyll,resulting in that MDA content,LOX,polyphenol oxidase(PPO)and peroxidase(POD)activities are maintained at a low level,thereby inhibiting the decay process of daylily and prolonging its preservation time.3.The relative expression levels of the genes related to the quality of the daylily in CA(3%O2+35%CO2)treatment were measured during the whole storage period.The results showed that two peaks were observed in the relative expression level of DSA3(daylily senescence-associated 3)gene of CA treatment at the storage time of 10 d and 25 d,respectively,and the relative expression level of CA treatment was lower than that of air treatment.The relative expression level of DSA4(daylily senescence-associated 4)gene was decreased first then elevated.Compared with the air treatment group,the expression level of DSA6(daylily senescence-associated 6)gene was low throughout the storage period,its level was increased only in the late storage stage,indicating that CA atmosphere(3%O2+35%CO2)treatment had significant effects on the inhibition of the senescence of the daylily,and it was up-regulated in the later stage.SEN1 02(senescence 102)gene was up-regulated throughout the storage period.Bioinformatics analysis showed that the DSA3,DSA4,DSA6,and SEN1 02 genes secondary structures are composed of α-helix,extended chain,and irregular curl.DSA4 has a transmembrane structure,while DSA3,DSA6,SEN1 02 do not have transmembrane structure.DSA3,DSA4,SEN1 02 gene encoded a protein which is a hydrophilic stable protein,DSA6 encoded protein is a hydrophilic unstable protein.