Abstract
Raspberry (Rubus spp.) is an economically important crop with a restricted growing season and very limited fruit shelf-life due to its extreme tenderness. In order to prolong its shelf life, an aqueous composition containing hexanal as the key active ingredient (HC) was applied as a preharvest spray during fruit development. The effects of HC were assessed using physiological, biochemical and anatomical parameters on the treated fruits and compared with the effects of mock inoculation which lacked hexanal. Sugars and acidity did not show a significant change in response to HC treatment, while the pulling force (the tension required to detach the berry from the receptacle) significantly improved in the HC-treated fruits, compared to control. Scanning electron microscope (SEM) analysis revealed a high correlation between the presence of rigid epidermal hairs and a stronger degree of attachment between berries and their receptacle in the HC treated fruits. Further, electron micrographs also showed abnormal crystalline depositions on the epidermal drupelets of the treated berries. Energy Dispersive X-ray Spectroscopy (EDS) analysis showed those crystals to be largely composed of calcium. HC treatment also resulted in the reduction of transcript level of three phospholipase D genes, as well as altered expression pattern of five members of the annexin gene family, and four calmodulin-binding transcription activators. Quantification of PLD activity showed that hexanal inhibited PLD activity in treated berries. The potential crosstalk between hexanal, phospholipase D activity and calcium and this crosstalk’s role in delaying fruit softening and in prolonging storage life of fruits shelf life is discussed.
Highlights
Raspberry (Rubus ideaus L.) is a tender fruit with an extremely short shelf-life
Phospholipase D (PLD), a phospholipiddegrading enzyme is the key enzyme involved in initiating a cascade of catabolic events that leads to the eventual deterioration of the membrane, and is highly active in the fruits of other berry species such as strawberry.[2,3]
During the 6 days storage period, the amount of weight loss was significantly lower in the treated fruit after second and third day postharvest returned to similar rate in both treated and control fruits for the remaining storage period (Table 1)
Summary
Raspberry (Rubus ideaus L.) is a tender fruit with an extremely short shelf-life. It is a rich source of health-promoting compounds such as anthocyanins. Suitable technologies and methods to enhance the postharvest shelf life of tender fruits are in high demand. The application of hexanal as a formulation, either pre- or postharvest, has shown promising results in enhancing the shelf-life of several fruits, vegetables and flowers.[4,5,6] Biochemical and genetic studies of fruit softening have indicated that cell-wall processing is the result of coordinated expression of several gene families encoding proteins associated with cell-wall metabolism, including expansins, pectin methylesterases, polygalacturonases, pectate lyases, β-galactosidases, α-L-arabinofuranosidases, endo-(1,4)-β-D-glucanases, β-xylosidases, xyloglucanases, endotransglucosidases, endomannanases.[7,8,9,10,11] efforts to suppress expression of cell wall-degrading enzymes by genetic engineering did not provide satisfactory results to efficiently prevent softening of fruits.[12,13]
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