Study On Physio-biochemical Metabolism And Its Regulation Of Postharvest Blueberry Fruits

The highbush cultivars of blueberry(Vaccinium corymbosum L.), such as'Bluegold', 'Northland','Berkeley' and 'Sunrise' were studied their postharvest physio-biochemical metabolism, quality and storability during the storage periods, in order to determine the suitable high CO2 shock treatment, the sound concentrations of O2 and CO2 in controlled atmosphere and the storage time for the blueberry fruits. Moreover, the physiological regulation substances, including ethylene and salicylic acid, were used as signal substances properly to induce the generation of resistance. In this experiment, polyphenol oxidase (PPO), peroxidase (POD), lipoxygenase (LOX) and phenylalnine ammonialyase (PAL) were analyzed during different storage conditions, and the relativity between fruit surface color changes and sensory evaluation were studied, and senescence mechanism, occurrence and control of decay were revealed. Meanwhile, the content of biological active substances and antioxidant capacity in various cultivars of blueberry fruits were examined, as well as the main diseases of postharvest blueberry and its control methods were also evaluated in storage. The results will be beneficial to provide integrative technologies for commercial storage of blueberry fruits.This experiments included following contents:(1) Study on the biological active substances and antioxidant capacity in various cultivars of northern highbush blueberry fruits; (2) Effects of Natamycin treatments on the control of blueberry gray mold that caused Botrytis cinerea; (3) Effects of high CO2 shock treatments on physiological metabolism and quality of postharvest blueberry fruits; (4) Effects of plastic box modified atmosphere storage on the physiological and biochemical changes of postharvest blueberry fruits; (5) Effects of exogenous ethylene treatments on sensory properties and metabolism of postharvest blueberry fruits; (6) Effects of exogenous salicylic acid treatment on phenylproanoid metabolic system of postharvest blueberry fruits. The results showed as following:1. There were certain differences in biological active substances and antioxidant capacity between various cultivars of northerm highbush blueberry fruits:Four northern highbush blueberry cultivars, including Bluegold, Sunrise, Sierra and Willow, were used as experimental materials. The content of antioxidant substances such as total anthocyanin. soluble polysaccharide, vitamin C and reduced glutathione were analyzed in the four northern highbush blueberry cultivars. Moreover, DPPH free radical scavenging ability and superoxide dismutase (SOD) activity which behalf of antioxidant ability were investigated. The correlative relationship between DPPH free radical scavenging ability and four kinds of antioxidant substances were researched. The results indicated that DPPH free radical scavenging ability was significantly related with total anthocyanin content, vitamin C content and reduced glutathione content (P<0.05). The total anthocyanin content, vitamin C content, reduced glutathione content and DPPH free radical scavenging ability in Willow cultivar were significantly higher than that of other three cultivars (P<0.05), it is for this reason that Willow cultivar has the highest antioxidant ability.2. The main diseases of postharvest blueberry fruits and its controll:Green mold (Botrytis cinerea) is the main pathogenic microorganism. Low concentrations of Natamycin treatment (200-600mg/L) had a good control effect of Botrytis cinerea. Natamycin induced the increase of PPO, POD, PAL that realted to the disease resistance, reduced the loss of anthocyanins and resisted the invasion of pathogens. The same concentration (600mg/L) of three fruit and vegetable preservatives, including Natamycin, Iprodione and Mildothane, played different roles in controlling the disease of blueberry fruits. Although the control efficiency of Natamycin ranged between Iprodione and Mildothane, as natural food preservation, Natamycin had a good perspective in inhibiting the disease of blueberry.3. Blueberry fruits had good torlerance to high CO2 shock treatment:High CO2 shock treatment (99.9% CO2, v/v) that less than 96 h had no injury on blueberry fruits. The pH value in pulp and fruit rot rate were significantly decreased, fruit firmness was well maintained, the storage period was effectively extended to 50 days, POD activity was increased and the LOX activity was decreased after the high CO2 shock treatments for 48 h and 96 h. The results indicated that the treatments slowed down the rate of metabolism and maintained the fruit quality of blueberry fruits. In contrast,144 h high CO2 shock treatment caused irreversible damage, resulting in anaerobic respiration, off-flavor and fruit rot. As a shock-impact method, high CO2 shock treatment may be used before the storage of blueberry fruits to inhibit the physio-biochemical metabolism, maintain the fruits quality and control the happiness of fruit decay.4. Plastic box modified atmosphere storage CA with high-CO2 concentrations was beneficial for blueberry fruits:Compared with CK (air condition), three kinds of plastic box modified atmosphere with high CO2, including 5%O2+10%CO2; 5%O2+20% CO2和5%O2+30%CO2, stimulated the defense system. Therefore, not only the activities of POD. CAT, SOD, PAL and PPO were increased, but also Vc and reduced glutathione (GSH) contents were kept in a higher lever. Moreover, the plastic box modified atmosphere storage with high CO2 effectively slowed down the respiration rate, inhibited the occurrence of decay and increased the lignin content and fruit firmness, especially 5%O2+30%CO2 was more conducive to delaying the senescence process and effectively extending the storage period to 95 days. It is suggested that blueberry fruits have a strong endurance to high CO2 and the plastic box modified atmosphere storage with high CO2 is perfect at blueberry fruits storage.5. The proper concentration of exogenous ethylene treatments induced the disease resistance of blueberry fruits:Compared with control (air condition), three kinds of ethylene treatments increased the activities of PPO, POD and PAL. Nevertheless, 10ml/L ethylene treatment increased the biosynthesis of endogenous ethylene and accelerated the metabolism rate and senescence process, while 0.1 and 1.0ml/L ethylene treatments promoted the disease resistance ability and storability of blueberry fruits. The lightness discrepancy between before and after removal of wax was significantly related with the result of sensory evaluation (P<0.01).6. Exogenous salicylic acid treatments accelerated the process of phenylproanoid metabolism of postharvest blueberry fruits:0.5mmol/L and 1.0mmol/L salicylic acid treatment promoted the process of phenylpropanoid metabolism. Therefore, the end product of phenylpropanoid metabolism, lignin content increased and it increased the fruit firmness...