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- Author or Editor: Albert C. Purvis x
Abstract
Polyethylene shrink film reduced pitting type chilling injury in ‘Marsh’ grapefruit (Citrus paradisi Macf.) stored at low temperatures. The film did not restrict heat exchange between the fruit and air in the storage room. Chilling injury occurred most rapidly in fruit stored at 5° and 7.5°C, but after 5 weeks the severity of injury was greatest in fruit stored at 2.5°. The pattern of response to temperature was the same for unsealed fruit and sealed fruit. Prestorage conditioning of the fruit for 8 days at 21° prior to storage at 5° reduced chilling injury. Restricting moisture loss with shrink film during the prestorage conditioning treatment did not negate the beneficial effects of conditioning. Restricting moisture loss following chilling had no effect on chilling injury. Thus, although moisture loss is a contributing factor, it does not appear to be the primary factor in chilling injury of grapefruit. In order to minimize chilling injury, moisture loss should be prevented during fruit exposure to chilling temperatures.
Abstract
O2 uptake by tissues of grapefruit (Citrus paradisi Macf.) was measured using manometric Warburg techniques. The highest rate of uptake was by flavedo tissue and the lowest rate was by intact juice vesicles. O2 uptake by flavedo tissue increased exponentially when temperature increased, and the proportion of O2 uptake insensitive to azide (N3), an inhibitor of the cytochrome path, was greater at low temperatures than at high temperatures. Salicylhydroxamic acid (SHAM), an inhibitor of the alternative path, was only marginally inhibitory at all temperatures. Arrhenius-type plots of O2 uptake showed discontinuities at 12°C in the presence and absence of respiratory inhibitors. O2 uptake increased in flavedo tissue of grapefruit during the low temperature hardening of young trees. The increase was primarily in the N3-insensitive component. Low temperatures also induced N3-insensitivity in detached stored fruit, and induction was greater in chilling-resistant interior canopy fruit than in chilling-susceptible exterior fruit. Thus, N3-insensitive O2 uptake may be related to chilling resistance of sensitive fruit.
Mature, unripe peaches were stored at 1°C in air or in 1% O2 plus 2.5%, 5.01, or 10.0% CO2 for 25 days and then ripened in air at 15°C for 3 days. Fruit stored in air or 2.5% CO2 developed browning of the flesh during ripening but fruit stored in 5.0% or 10.0% CO2 turned yellow. Only the fruit stored in 10.0% CO2 softened during ripening, but water soluble pectin content increased and protopectin content decreased in peaches stored in 5.0% or 10.0% CO2. Low temperature storage apparently interferes with the levels and/or activities of the pectin degrading enzymes during subsequent ripening of peaches. High levels of CO2 during low temperature storage appears to reduce chilling injury by protecting the capacity of the fruit to produce adequate levels of the pectolytic enzymes at ripening temperatures.
Diphenylamine has been used to reduce low-temperature-induced storage scald of apples for decades. Its effectiveness in reducing scald has been attributed to its antioxidant properties. Oxidative reactions have also been implicated in chilling injury of other commodities, including green bell peppers (Capsicum annuum L.). Diphenylamine was applied as a dip at rates of 500 to 2000 ppm to green bell peppers prior to storing them for 7 days at 1 °C. The development of sheet pitting, the most common visible symptom of chilling injury in bell peppers, was inhibited almost completely by diphenylamine. Diphenylamine, however, only slightly reduced the chilling-induced decrease in chlorophyll fluorescence ratios. Darkening of the vascular tissues of the calyxes and seed darkening, which are also symptoms of chilling injury, were not prevented by diphenylamine. Thus, diphenylamine either did not get into all of the sites of oxidative reactions or some of the manifestations of chilling injury are initiated by processes other than oxidative ones.
Abstract
This study was initiated to determine if differences exist in the rates at which reducing sugars accumulate in the flavedo tissue of interior and exterior canopy ‘Marsh’ grapefruit (Citrus paradisi Macf.) during low-temperature storage and if intermittent warming treatments alter the conversion of sucrose to reducing sugars. Sucrose concentrations decreased and reducing sugar concentrations increased in the flavedo tissue of grapefruit stored at 5C. Relative changes in sucrose and reducing sugar concentrations were similar in fruit harvested from interior and exterior canopy positions. Thus, differences in chilling sensitivity of interior and exterior canopy fruit were not related to the concentrations of sugars in the peel tissue. Reducing sugars accumulated and sucrose decreased more rapidly in the flavedo tissue of intermittently warmed grapefruit than in similar tissue of grapefruit held constantly at 5C. Exogenous glucose did not stimulate O2 uptake by grapefruit flavedo tissue in air (21% O2) or in 100% O2 at any time during the harvest season. Dinitrophenol stimulated O2 uptake by tissue in 100% O2, but not in air. Thus, sugar substrate appeared to be adequate to support the respiratory rates of grapefruit flavedo tissue and O2 availability limited respiration. Chilling sensitivity of grapefruit is not directly related to the concentration of reducing sugars per se.
The mechanism by which diphenylamine (DPA) controls superficial scald in apples and reduces chilling injury in green bell peppers [Capsicum annuum L. var. annuum (Grossum Group)] has been assumed to be related to its antioxidant activity. In the present study, DPA inhibited the respiratory activity of green bell pepper fruit as well as oxygen uptake by the mitochondria isolated from them. When the alternative oxidase was inhibited with n-propyl gallate or disulfiram during state 4 respiration, DPA did not further inhibit O2 uptake. Treating green bell peppers with DPA before storage did not alter the induction and abundance of the alternative oxidase protein in mitochondria which was maximally induced in peppers stored at 4 °C. Whether added before or after the uncoupler, 2,4-dinitrophenol, DPA negated the enhanced O2 uptake associated with uncoupling of electron transfer in isolated mitochondria. These observations indicate that DPA inhibits the flow of electrons through the cytochrome path, probably somewhere in the cytochrome bc 1 complex. Although the secondary amine function of DPA makes it a powerful antioxidant, the effectiveness of DPA in reducing chilling injury in green bell peppers and superficial scald in apples [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] also may be due, in part, to its inhibition of respiration.