Study On Postharvest Physiology And Preserving-freshness Of Fresh Vegetable Under The Condition Of Simulated Cold Stroage Of Warship

For the first time we studied on the postharvest physiology and preserving-freshness in leafy and fruit vegetable usually used in warship under simulated condition of cold storage of warship and explored fresh vegetable ensuring during warship taking a long voyage by combining preserving-freshness with support. The following is the result.1. The content of chlorophyll, soluble proteins and carotenoid in outer blades decreased more rapidly than that in inner blades during storage. In outer blades there were marked changes in superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) activities and the activities of the these enzymes decreased rapidly after 4 days of storage with a more obvious decrease in CAT activity. Peroxidase (POD) activity and malondialdehyde (MDA) content increased gradually and then rose sharply after 6 days and 4 days of storage, respectively. In inner leaves the activities of both SOD and CAT were at high level and varied very little, APX activity of them kept high and decreased slowly, while POD activity and MDA content didn't increased significantly. These results indicated the postharvest senescence of attached leaves was related to imbalance of activated oxygen metabolism and membrane lipid peroxidation.SOD activity of spinach blade generally increased at 2℃ or 9℃. There was a rapid decrease in chlorophyll content, Hue angle value, activity of CAT, APX and GR, and a rapid accumulation in MDA content in blades of spinach during storage at 9℃. Lower temperature 2℃ effectively reduced the rapid decrease in activity of CAT, APX and GR, inhibited accumulation in MDA content and decreased the decline in chlorophyll content, therefore, delayed spinach senescing postharvest. It can be concluded from the results that spinach blade senescing is related to oxidative stress resulting from reduction in activities of H2O2 scavenging enzymes; lower storage temperature prevents and reduces oxidative stress, therefore, delays spinach senescing by delaying the decrease in H2O2 scavenging enzymes.2. At the simulated conditions of warship cold storage of fresh vegetables, spinaches, leeks, Chinese cabbage and celery packed directly in plastic skepswithout film packaging (CK) lost water very quickly and suffered severe water stress. Preserving-water-treated groups of the vegetables lost water little. Compared to preserving-water-treated ones, water stress accelerated the decline in chlorophyll content in blade of spinach, leek and Chinese cabbage, and leafstalk of celery, increased yellowing index in blade of Chinese cabbage, decrease Hue angle value in blade of leeks, indicating posthavest water stress quicken blade senescing. Compared to preserving-water-treated ones, water stress enhanced the decrease in ascorbic acid content and activities of SOD, CAT, and APX in leek blade and celery leafstalk and accelerated the accumulation in MDA content in blade of leek and Chinese cabbage and in leafstalk of celery. In Chinese cabbage the decline in SOD activity was also accelerated by water stress and it depressed the rise of CAT and advanced the reduction of APX activity. The increase in H2O2 content in leek blade was quickened by water stress. The results suggested that water stress causes and quickens the decrease in ability of leafy vegetables to scavenge activated oxygen, results in and aggravates maladjustment of activated oxygen metabolism and stimulated membrane lipid peroxidation. In spinach, water stress also reduced activities of SOD, CAT, APX and GR, and the activity of CAT and APX was decreased much more than SOD, but didn't enhance accumulation in MDA. Except leek, the POD activity in other leafy vegetables was increased with different degree by water stress, which indicating POD participates in leafy vegetable senescence accelerated by water stress.3.The effects of low temperature storage and film semi-sealed packaging in prolonging storage life of leafy vegetables under the condition of simulated cold storage in warships were studied in celery, spinach, Chinese cabbage and leek using plastic skeps as control of packaging. Control leafy vegetables stored at 2 °C or 9 °C lost water severely manifested by much higher weight-loss, as led to them wilting severely, therefore, the storage lives of them were limited strongly. The vegetables stored at 9°C yellowed or decayed severely with more shorter storage lives. Storage at 2°C reduced markedly them yellowing and the increase in Hue angle of blade in the cabbage, decreased or prevented them rotting. Film semi-sealed packaging of the vegetables could prevented them significantly from losing water. At 9°C the packaging reduced significantly yellowing of celery, but led to decay in Chinese cabbage and caused spinach rotting severely. When the vegetables were stored at 2°Cfilm packaging reduced the yellowing of spinach, Chinese cabbage and leek, had no significant effect on yellowing of celery and didn't lead to decay in these leafy vegetables. The storage lives of the vegetables could only be prolonged 2~4days by film semi-sealed packaging when theywere stored at 9°C. Storage at 2°C combined with film semi-sealed packaging could effectively prolonged storage lives of the leafy vegetables. The storage life of celery, spinach and leeks was prolonged from 9d, 9d and 7d to 42-^4 5 d, 42~55d and 15d respectively and the storage life of Chinese cabbage was prolonged to 25d when stored at 2"C.4. No chilling injury symptom appeared on green pepper fruits and membrane permeability of them changed little during storage at 9°C for 8 weeks. But the fruits stored at 2"C had slight chilling injury symptom only after lweek and suffered severe chilling injury when the storage duration surpassed 4weeks with rapid increase in membrane permeability. Compared to pepper fruits at 9°C, SOD activity of fruits at 2°C was lowered and both CAT and APX activity of them decreased much more than SOD. POD activity of fruits at chilling temperature was much lower than that of fruits at 9"C, but increased abruptly to a climax in 7th week. LOX activity of them changed little during storage at 9°C, but it increased quickly in 2th week, and thereafter kept high level in fruits stored at chilling temperature. Chilling temperature enhanced membrane lipid peroxidation, therefore, the MDA content was higher in fruits stored at 2°C than at 9°C. It is suggested that chilling injury of green pepper fruits during storage at chilling temperature is related to misbalanced metabolisms of activated oxygen caused by decrease in activated oxygen scavenging enzyme activity, especially the decrease in CAT and APX, and membrane lipid peroxidation resulted from increase in LOX activity and accumulation in activated oxygen.50 °C hot water dip 10 minutes or 53 °C 5 minute (prestorage heat treatment) significantly alleviated chilling injury and manifestly hindered increase in membrane permeability of pepper fruits stored at 2°C. Compared to control, 50°Cheat treatment had no obvious effect on SOD activity and 53°C significantly improved SOD activity in week3, week4 and week5. Both heat treatments significantly elevated CAT and APX activity and the effect of them in increasing CAT activity was more obvious than SOD. POD activity of fruits heated changed little without abrupt increase happened in control fruits during storage at 2°C. LOX activity in heated fruits declined fast after 3w during storage. It is suggested that heat treatment maintained balance of activated oxygen metabolism by increasing activated oxygen scavenging enzyme activity, especially the activity of CAT and APX, decreased LOX activity and therefore depressed membrane lipid peroxidation resulting in alleviation of chilling injury in pepper fruits stored at 2°C.After sweet peppers were stored at 0~2"C for 30days, control fruits suffered severe chilling injury and weight-loss and higher decay percent, so...