| Gynura bicolor D.C (Gynura), rich in protein and amino acids, edible fiber, minerals, anthocyanin, flavonoid, and essential oil, is concerned as multi-functional plant such as vegetable and medical use. Gynura becomes more and more popular nowdays as a vital force of vegetable market. Like most leaf vegetable, the high levels of transpiration and respiration of Gynura result in the decline of sensory and eating qualities, reduction of nutritious substances and increase of post-harvest loss. The results showed that there was no chilling injury symptom occurred in Gynura stored at 0℃, indicating Gynura is not sensitivie to low temperature and 0℃is appropriate for Gynura storage. This thesis studied the effects of PA,1-MCP and controlled atmosphere (CA) combined nano-packaging on postharvest quality, physiology of Gynura D.C and POD characteristics. The main results are as following:1. Effect of PA on the changes of quality and physiology of Gynura during refrigerated storage0,0.1,0.5 and 1.0 mM phytic acid (PA) was applied to Gynura to investigate the effect of PA on changes of quality and physiology of Gynura during refrigerated storage. Compared with control,0.5 mM PA treatment significantly delayed the decay index, maintained cell membrane integrity, slowed down the loss of anthocyanin, chlorophyll, total carbohydrate, reducing sugar, protein and amino acid, and then better color and quality of Gynura after 20 days storage.0.5 mM PA also inhibited significantly respiration compared with control (P<0.05) (the maximum difference could be as much as 54 mg CO2 kg-1.h-1). On the other hand,0.5 mM PA could maintained total phenolics and free phenol at high level, and higher activities of PPO, SOD and POD (84.5%,110% and 120% respectively of that in control) and then greater ability of removing free radical and retarding O2- accumulation. Among all PA treatments,0.5 mM was most effective, and this treatment could extend the storage life to 15 days. It should mention that 1.0 mM treatment could lead to burning symptom on leaves of Gynura.Correlative analysis reveals significant negative correlation of O2- to POD and SOD, which indicated PA could delay the senscence and therefore prolong the storage period of Gynura.2. Effect of 1-MCP on the changes of quality and physiology of Gynura during refrigerated storage0,0.25 ppm,0.50 ppm,1.00 ppm 1-MCP was use to treat Gynura for 0,6h,12 h, and 24 h respectively to investigate the effect of 1-MCP on changes of quality and physiology of Gynura during refrigerated storage. The results showed that the treating concentration and duration of 1-MCP had a significant influence on decay index of Gynura, and less decay was found in higher concentration or/and longer period of 1-MCP treatment and there was no significant difference between 0.50 ppm and 1.00 ppm 1-MCP treatment. However, both 0.50 ppm and 1.00 ppm 1-MCP treated for 24 h enhanced decay of Gynura. All 1-MCP treatment could inhibit the respiration of Gynura, and the higher concentration or/and longer duration had better result, but treatments with 12 h and 24 h,0.50 ppm and 1.00 ppm 1-MCP were no significant difference.1-MCP could siginificantly inhibit the reduction of anthocyanin, chlorophyll and then maintain the better product color and sensory quality.1-MCP could also maintain total carbohydrate, reducing sugar, protein and amino acid at higher levels; reduce O2- and MDA accumulation, keeping higher enzyme activity for removing free radicals and then cell membrane integrity.Comparisons showed 0.50 ppm 1-MCP was the best among all treated concentrations, and 12 h treatment was the best among all treated duration. Overall, the combination of 0.50 ppm 1-MCP treated 12 h was most suitable treatment for Gynura storage.3. Effect of CA combined with nano-material packaging on the changes of quality and physiology of Gynura during refrigerated storageEffect of NP (nano-material packaging), CA (3% O2, CO2≤5%) and CA+NP (CA combined with nano-material packaging) on the changes of quality and physiology of Gynura during refrigerated storage was investigated. The value of Gynura decay index was in the order of CA>NP>CA+NP at the same storage duration, and significantly smaller for the treatments of NP and CA+NP than that of control (P<0.05) at the end of storage with the smallest for CA+NP (6.97%). Respiratory rate of Gynura showed the same change as the tendency of decay index and CA+NP had the lowest respiratory intensity during storage period (only 56.6% of CA at day 20). Compared with CA and NP, CA+NP was more effective to retard the accumulation of O2- and MDA in Gynura tissue, to maintain cell membrane integrity, and had higher activity of enzymes (SOD, CAT) and then removed free radical. Overall, CA(O23%, CO2≤5%)+NP had the best preservation effect on Gynura among 3 treatments during 20 days storage period.4. Comoarison of harvest time on the quality and physiology of GynuraComparison of different harvested time on the quality and physiology of Gynura was made. According to the analysis of substances composition, Gynura harvested in Jun had the highest contents of anthocyanin, chlorophyll, AAs and soluble protein, compared to that of Gynura harvested in April and May. What is especial is that the content of anthocyanin was respectively 2 times and 3 times in that of May and Apr. Gynura had lower respiration and relative leakage rate, lower content of O2.- and MDA production, higher TSS content, and higher relative activities of POD, CAT and SOD. All these indicate Gynura harvested in June produced not only less oxygen free radical but also had strong scavenging ability. This means that Gynura harvested in Jun had better potential to be stored.According to the analysis of physiological and biochemical changes, Gynura harvested in Jun had the slowest downward trend of chlorophyll, total carbohydrate and protein, and the smallest change of respiratory rate, content of O2.- and MDA. Above results indicated Gynura harvested in Jun had better storage capability.5. Basic investigation on POD characteristics of GynuraThe phenols extracted from fresh Gynura were investigated by ultraviolet scanning and HPLC. The results showed that there were chlorogenic acid and caffeic acid in both leaf and stem of Gynura. Moreover, cinnamic acid was also existed in leaf and (-)-Catechin in stem. The quantity analysis showed that the main phenol in the leaf and stem of Gynura was chlorogenic acid, chlorogenic acid and (-)-Catechin, respectively.Pyrogallic acid was the most suitable substrate of POD both from leaves and stems of Gynura and its optimal pH was 5.0 and 6.0, respectively, and had the highest activity at pH 5.0 from leaves, and 5.4 from stems. The optimal temperature of POD from leaves was 60℃,50～70℃from stem. The inactivation of Gynura POD required more than 3 min at 80℃, indicating the strong heat resistance. The calculated K was 25.5×10-2 min-1 and Z was 14.2℃in leaf of Gynura.1 mmol.L-1 4-HR and 2 mmol.L-1 PA had the best inhibition on POD activity of Gynura; EDTA-2Na, Zn(Ac)2 and Cu2+ could enhance the activity, while Al3+ could significangtly inhibit POD activity.The electrophoresis test showed that the pattern of POD isozymes had 10 bands. Band 1 was catholicity, band 2 was stem specialized, and band 6,7,8 were related to leaves; band 3,4 were closely linked to senescence, band 5 to disease, band 9,10 to decay. Gynura POD band 1 was separated and purified from abstracting liquor of Gynura leaves through salting precipitation, dialysis and DEAE-Sepharose column chromatography. Purfied times of POD were 8.1 and recovery was 26.5%. |
PDF Full Text Request