Study On The Effect Of ⁶⁰Co ?-Irradiation On The Blueberry Preservation And Degradation Mechanism Of Polysaccharides In Cell Wall

For unique flavors and nutritional-health functions, blueberry fruits are deeply loved by people, so the blueberry industry is rapidly developing in our country. However, the harvesting time of blueberry fruits are in the summer of high temperature and rainy summer, and, the exuberant respiration and microbial infection will make it quick to rot without timely processing, so eventually produce huge economic losses. Now, some preservation techniques have alleviated these problems, but sensory quality and nutritional quality of blueberry fruit still declined seriously during the storage, especially the late stage of storage. As a "cold" sterilization technology,⁶⁰Co ?-irradiation treament can improve the safety of foods and extend the shelf life of foods through sterilization and antisepsis produced by ionization effects. In order to find a preservation technology of blueberry fruit, which are safe, environmental protection and high efficiency, by using different doses to deal with "Bluecrop" blueberries, this research analyzed the storage effect and physiological mechanism of irradiation treatment, determined the irradiation technique suited for fresh-keeping blueberries, and detailedly studied the laws of regulation and control and the mechanisms of physiology and biochemistry of irradiation treatment on the cell-wall polysaccharide degradation of blueberry fruit during storage. Finally come to the conclusion as follow:?1? Irradiation treatment have very good effects on the killing and inhibition of microorganisms exsiting on the surface of blueberry fruit. The higher irradiation doses, these effects were better. Especially in the later of storage period, the microbes on the surface of blueberry fruit all decreased one order of magnitudes compared with CG at the same period. The sort order of irradiation -doses sensitiveness of microorganisms on the surface of blueberry fruit were following:bacteria> mucedine> yeast.?2? 0.5 kGy irradiation treatment had no effect on the change on decay rate of blueberry fruit during storage time, and 3.0 kGy irradiation treatment can accelerate the decay of blueberry fruit in the later of storage, but, the suitable irradiation treatment ?1.0 kGy-2.5 kGy? can bring down the decay rate of blueberry fruit in the late of storage and effectively delay the decrease of firmness and surface-color of blueberry fruit in the storage.?3? After irradiation treatment, the content of TSS and TA in blueberry fruit remain the same as the CK, but the contents of VC and anthocyanins declined slightly and had a linear-negative correlation with the irradiation doses. During the storage, irradiation treatment can effectively alleviate the degradations of TSS, TA, VC, and anthocyanins in blueberry fruits, so it can well keep its'original quality and flavor.?4? According to the results of the valid storage-period and sensory evaluation, the lowest effective dose and the maximum tolerance dose for irradiation preservation blueberries were respectively sure to be 1.0 kGyand 2.5 kGy. The irradiation treatments of 1.0 kGy?2.5 kGy can make the storage time of blueberry fruit effectively extended to 63 d?71 d and make the decay rate less than 10%.?5? After irradiation treatment, the respiratory intensity, ethylene release quantity, LOX activity, MDA content and membrane permeability were all increased slightly, but but their differences are not obvious ?p> 0.05?, at the same time, respiratory intensity and ethylene release quantity were both positively correlated with radiation doses. During the storage, the irradiation of 1.0 kGy-2.5 kGy can inhibit the respiration action and membrane lipid peroxidation of blueberry fruit, so delay the ageing process, among them,2.5 kGy irradiation dose the best.?6? After irradiation treatment, the active oxygen-ion content ?02-·, H2O2? and protective enzyme system ?SOD, CAT and POD? iin blueberry fruit all increased slightly ?p> 0.05? and all presented direct proportion with irradiation doses. Druing the storage, irradiation treatment of 1.0 kGy-2.5 kGy can make O2-· and H2O2 eliminate constantly at the same time is constantly clearing along with it's continuous production so that the contents of 02-· and H2O2 always stayed at a lower level, consequently can effectively improve the antioxidant capacity of blueberry fruit, among them,2.5 kGy irradiation dose the best.?7? 2.5 kGy irradiation treatment had unconspicuous effects on CWM, ESP and 4KSF in blueberry fruit ?p> 0.05?, but it can delay the rise of WSP content, the decline of SCSP content and 24KSF content, and the degradation of WSP and 24KSF high molecular-weight polymers of, so it can control the solubility and glue-viscosity of polysaccharide in the cell wall of blueberry fruit, and then it can keep the integrity and compactability of cell wall structure, which fruit firmness was 1.06 kg/cm2 and higher than CK. Finally, effectively delay the drop of fruit firmness during storage time.?8? 2.5 kGy irradiation treatment had unconspicuous effects on PE activity and gene expression-level ?p> 0.05?. However, its effects on the gene-expression levels of PG?Cx??-Gal and a-Af are prior to their activities, and it can reducing their demands by regulating and controling gene-expression levels of PG?Cx??-Gal and a-Af, so slow down the degradation and depolymerization of pectin and hemicellulose. Among them, the inhibition effects of PG and Cx are better than that of ?-Gal and ?-Af.Therefore, proper ⁶⁰Co ?-irradiation is an effective method to improve the storage quality of blueberry fruit and prolong its storage time. It can achieve the purposes of sterilization, anti-corrosion, and, keeping fruit hardness and color, by killing microorganisms, restraining postharvest physiology and effecting cell wall degradation, without damaging the quality of the sensory and nutrition during the storage of blueberry fruits.