Effects of coating and heat treatments on energy levels and physiological indexes and qualities of grape fruits during storage

Abstract: Harvested grape fruit tissues are still alive. Grape fruit tissues still have metabolism including physiological and biochemical reactions. They are prone to physiological deterioration, such as texture softening, browning, decay and mildew. More and more studies have indicated that senescence and cell membrane permeability of horticultural crops may be related to energy deficit caused by the decline of energy synthesis. Changes of energy levels in grape fruit tissues during storage have not been reported. Effects of energy level on physiological quality of grape fruit tissues after coating and heat treatment with Ca2+ are not clear. In this paper, the effects of coating and heat treatments with Ca2+ on post-harvest energy levels and physiological deterioration of "Victoria" grape fruit during cold storage were explored through determining energy levels and physiological indices. Coating and heat treatments with Ca2+ were applied to post-harvest grape fruits (compared with untreated grape fruits, i.e. the CK treatment). Grape fruits after coating and heat treatments with Ca2+ were stored at (4±0.5) ℃. Respiratory rate, browning index, decay rate, hardness, contents of malondialdehyde (MDA), adenosine triphosphate (ATP), adenosine diphosphate (ADP) and adenosine monophosphate (AMP), energy charge (EC), and enzyme activities of polyphenol oxidase (PPO), peroxidase (POD), lipoxygenase (LOX) and soperoxide dismutase (SOD) of grape fruits were tested every 10 days. Results showed that with the extension of storage time, energy levels were in a loss state for grape fruit tissue under the CK. Respiratory rate decreased, but cell membrane oxidation and permeability increased. Browning index and decay rate increased, and enzyme activities of POD, PPO and LOX increased too, but enzyme activities of SOD were decreased. Physiological qualities of grape fruits decreased, and fruits were softened. Calcium combined with heat and coating treatment reduced the loss of grape fruits by rotting during storage. In addition, treatment of heat and coating with Ca2+ could maintain higher energy status, energy charge, hardness and enzyme activities of SOD to keep qualities of grape fruit, delay grape fruit softening, inhibit respiratory intensity and accumulation of membrane lipid peroxidation, slow down growth of cell membrane permeability, decrease MDA content, inhibit enzyme activities of POD, PPO and LOX, and delay browning and rotting, aging process and physiological quality deterioration of grape fruits. But coating treatment was better than heat treatment. ATP was significantly positive correlation with hardness and SOD enzyme activity (r=0.938，0.930, P<0.01), but negative correlation with MDA membrane permeability and LOX enzyme activity (r=-0.896，-0.932，-0.940, P<0.01). EC was negative correlation with membrane permeability and LOX enzyme activity (P<0.05), but positive correlation with respiration intensity and SOD enzyme activity (P<0.05). Browning of grape fruits was closely related to membrane lipid peroxidation and membrane structure (the integrity of membrane structure was destroyed). PPO and POD were reacted with phenolic substrates to form brown pigment. Results showed that with the extension of storage time, energy levels of grape fruits were in a loss state. Fall of energy level significantly affected oxidation and integrity of cell membrane. Coating and heat treatments with Ca2+ could maintain higher energy levels of ATP and ADP, and EC, which could slow down aging and physiological quality deterioration of grape fruit tissues. Coating and heat treatments with Ca2+ may maintain high energy status and physiological qualities, and slow down aging and physiological quality deterioration of grape fruits tissues. Effects of coating treatment with Ca2+ were better than heat treatment with Ca2+. Slowing down physiological deterioration of grape fruits can be realized by maintaining high energy status and preventing development of physiological deterioration.