| Blueberry belongs to the genus Vaccinium of Rhododendron family.The harvest of blueberry fruit is at high temperature and rainy season in summer.Due to the vigorous physiological and metabolic activities and the lack of nutritional supply after harvest,blueberry fruit tends to soften its sarcocarp and rot its pedicle at room temperature,which seriously affects the commercial and economic value of blueberry fruit.Low temperature storage is one of the most effective methods to prolong the postharvest life of blueberry,which can effectively delay the ripening and senescence of blueberry fruit and inhibit the occurrence of decay.However,with the prolongation of cold storage time,especially during the room temperature shelf period,blueberry is prone to pitting,greatly affecting its commodity value.The occurrence regularity of pitting,ultrastructure,membrane lipid,unsaturated fatty acids(linolenic acid and linoleic acid),moisture content,cell membrane permeability of blueberry fruit during cold storage and room temperature shelf life were analyzed systematically.The changes of membrane lipid peroxidation product malondialdehyde(MDA),proline content,membrane lipid metabolism key enzyme(Phospholipase D(PLD)and Lipoxygenase(LOX))activity and gene expression were used to analyze the occurrence of pitting in blueberry under low temperature stress from the perspective of membrane lipid metabolism.On this basis,through intermittent warming to explore the regulation technology of pitting in blueberry fruit in cold storage,to provide a theoretical basis for the storage,transportation and fresh-keeping of blueberry fruit.The main findings are as follows:1.Blueberry fruits are prone to pitting during at room temperature after refrigeration.It can be observed from the ultrastructure that compared with fresh blueberry fruit,the cell membrane of blueberry with pitting shrinks and the cells are separated from the plasmalemma.The structure and function of chloroplasts and mitochondria are destroyed.Secondly,we detected two kinds of glycolipids(MGDG and DGDG),six phospholipids(PA,PC,PE,PG,PS)and three lysophosphatides(LPC,LPE,LPG)from blueberry fruit.Among them,the content of DGDG,PA in increased significantly and the content of PC,PE,LPC decreased significantly after cold storage.The contents of linolenic acid and linoleic acid of blueberry fruits stored for 60 days were obviously decreased during the whole shelf period,and the contents of linoleic acid and linoleic acid remained at a significantly lower level(P<0.05).At the sametime,the activities of PLD and LOX,the relative conductivity and the contents of malondialdehyde and proline in blueberry fruits increased significantly after long-term cold storage.Therefore,we concluded that low temperature activated the activities of PLD and LOX and accelerated the process of membrane lipid metabolism,and damage to the structure and function of the membrane,resulting in a pitting in blueberry fruit.2.Intermittent warming treatment can effectively reduce the occurrence of pitting in blueberry during shelf life at room temperature after refrigeration,and keep the blueberry fruit with higher hardness,SSC and lower decay rate.At the same time,intermittent warming treatment can delay the degradation of membrane lipid and fatty acid in blueberry fruit,and keep the cell membrane of blueberry fruit unsaturation,fluidity and stability of fatty acid maintain relatively high level.It also delayed the increase of membrane permeability and MDA,proline content,and significantly inhibited the activity and gene expression of its key enzymes(PLD and LOX)in membrane lipid metabolism.Thus,the degradation of membrane lipid in blueberry fruit was further delayed.In addition,intermittent warming treatment could increase the gene expression of CBF transcription factor,which could increase the low temperature resistance of blueberry fruit,and reduce the occurrence of pitting in blueberry fruit. |
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