Postharvest treatments of fresh produce.

Postharvest technologies have allowed horticultural industries to meet the global demands of local and large-scale production and intercontinental distribution of fresh produce that have high nutritional and sensory quality. Harvested products are metabolically active, undergoing ripening and senescence processes that must be controlled to prolong postharvest quality. Inadequate management of these processes can result in major losses in nutritional and quality attributes, outbreaks of foodborne pathogens and financial loss for all players along the supply chain, from growers to consumers. Optimal postharvest treatments for fresh produce seek to slow down physiological processes of senescence and maturation, reduce/inhibit development of physiological disorders and minimize the risk of microbial growth and contamination. In addition to basic postharvest technologies of temperature management, an array of others have been developed including various physical (heat, irradiation and edible coatings), chemical (antimicrobials, antioxidants and anti-browning) and gaseous treatments. This article examines the current status on postharvest treatments of fresh produce and emerging technologies, such as plasma and ozone, that can be used to maintain quality, reduce losses and waste of fresh produce. It also highlights further research needed to increase our understanding of the dynamic response of fresh produce to various postharvest treatments.

Fruit quality, antioxidant contents and activity, and antiproliferative activity of strawberry fruit stored in elevated CO2 atmospheres.

The effects of CO2 in the storage atmosphere on color, firmness, ascorbic acid (AA), anthocyanins, flavonoids, phenolics, total antioxidant activity, and antiproliferative activity of strawberry fruit have been investigated. "Northeaster" and "Earliglow" strawberries were stored in air or in 20% CO2 (in air) at 3 degrees C for 20 d. Color changes in Northeaster were delayed more by CO2 treatment than in Earliglow. Firmness of CO2-stored fruit increased slightly compared with those stored in air. The increases in total and reduced AA concentrations during air storage were usually prevented by CO2 storage in both cultivars. Dehydroascorbic acid (DHA) concentrations increased during CO2 storage. Anthocyanins and flavonoids, and total antioxidant activity of both cultivars were higher in air-stored fruit than in CO2-stored fruit. The total phenolic concentration was lower in CO2-stored Earliglow fruit than in air, but storage treatment did not affect that of Northeaster. A 40 mg/mL concentration of Northeaster strawberry extract inhibited about 80% of HepG2 human liver cancer cell proliferation. CO2 treatment did not affect the antiproliferative activity of strawberry fruits, but antiproliferative activity was greater at harvest than after storage.

Release of 1-methylcyclopropene from heat-pressed polymer films.

Gaseous 1-methylcyclopropene (1-MCP) is an inhibitor of ethylene perception that is being used extensively for apples and ornamental products, and under intensive investigation for its potential benefits for other fruits and vegetables. 1-MCP is currently used in closed environments that maintain stable concentrations for several hours in order to be effective. However, food packaging materials that release 1-MCP at a predictable rate into the package headspace might be useful for application in inhibiting the deleterious effects of ethylene in the postharvest packaging and storage of some horticultural products. A 1-MCP/alpha-cyclodextrin (1-MCP-cd) complex was incorporated into several common packaging films by heat-pressing (dry-blend, lamination) and solution-casting methods. The release of 1-MCP from the films was quantified by gas chromatography with respect to time, loading of 1-MCP, temperature, relative humidity (RH), type of film, and film-forming method. Release of 1-MCP was rapid and high in films held at RH >/= 75%. The rate of release was slow during the 1st 12 h and then increased during the next 24 to 36 h. Higher temperatures resulted in higher and faster release. A loading of 8 mg of 1-MCP-cd per 140 mg of polymer was found to be optimal. Pressing 1-MCP-cd containing films above 100 degrees C reduced the amount of 1-MCP remaining in the film. Incorporation into LDPE resulted in a higher and faster release than from PS, PVC, and PP polymers. 1-MCP release from a film matrix appears to be within the acceptable range for produce packaging applications.

Influence of salicylic acid on H2O2 production, oxidative stress, and H2O2-metabolizing enzymes. Salicylic acid-mediated oxidative damage requires H2O2.

We investigated how salicylic acid (SA) enhances H2O2 and the relative significance of SA-enhanced H2O2 in Arabidopsis thaliana. SA treatments enhanced H2O2 production, lipid peroxidation, and oxidative damage to proteins, and resulted in the formation of chlorophyll and carotene isomers. SA-enhanced H2O2 levels were related to increased activities of Cu,Zn-superoxide dismutase and were independent of changes in catalase and ascorbate peroxidase activities. Prolonging SA treatments inactivated catalase and ascorbate peroxidase and resulted in phytotoxic symptoms, suggesting that inactivation of H2O2-degrading enzymes serves as an indicator of hypersensitive cell death. Treatment of leaves with H2O2 alone failed to invoke SA-mediated events. Although leaves treated with H2O2 accumulated in vivo H2O2 by 2-fold compared with leaves treated with SA, the damage to membranes and proteins was significantly less, indicating that SA can cause greater damage than H2O2. However, pretreatment of leaves with dimethylthiourea, a trap for H2O2, reduced SA-induced lipid peroxidation, indicating that SA requires H2O2 to initiate oxidative damage. The relative significance of the interaction among SA, H2O2, and H2O2-metabolizing enzymes with oxidative damage and cell death is discussed.

Cell Wall Changes in Nectarines (Prunus persica) : Solubilization and Depolymerization of Pectic and Neutral Polymers during Ripening and in Mealy Fruit.

Nectarine fruit (Prunus persica L. Batsch var nectarina [Ait] maxim) cultivar Fantasia were either ripened immediately after harvest at 20 degrees C or stored for 5 weeks at 2 degrees C prior to ripening. Fruit ripened after 5 weeks of storage did not soften to the same extent as normally ripened fruit, they lacked juice, and had a dry, mealy texture. Pectic and hemicellulosic polysaccharides were solubilized from the mesocarp of the fruit using phenol:acetic acid:water (PAW) treatment to yield PAW-soluble material and cell wall material (CWM). The carbohydrate composition and relative molecular weight (M(r)) of polysaccharide fractions released from the CWM by sequential treatment with cyclohexane-trans-1,2-diamine tetra-acetate, 0.05 m Na(2)CO(3), 6 m guanidinium thiocyanate, and 4 m KOH were determined. Normal ripening of nectarines resulted in solubilization of pectic polymers of high M(r) from CWM during the first 2 d at ripening temperatures. Concurrently, galactan side chains were removed from pectic polymers. Solubilized pectic polymers were depolymerized to lower M(r) species during the latter stages of ripening. Upon removal from cool storage, fruit had undergone some pectic polymer solubilization, and after ripening, pectins were not depolymerized and were of high M(r). Side chains did not appear to be removed from insoluble pectic polymers and branched pectins accumulated in the CWM. The molecular weight profiles obtained by gel filtration of the hemicellulosic fractions from normally ripening and mealy fruit were similar. The results suggest that mealiness results as a consequence of altered pectic polymer breakdown, including that associated with neutral side chains.

Inhibition of pear fruit ripening by mannose.

Softening of the flesh and the rise in ethylene evolution and respiration associated with ripening in pear (Pyrus communis L.) fruit was delayed when mannose was vacuum infiltrated into intact fruit. The extent of delay could be modified by altering the concentration or the volume of mannose applied to the fruit. Inhibition of ripening was associated with phosphorylation of mannose to mannose 6-phosphate (M6P), and accumulation of M6P was associated with lowered levels of inorganic phosphate (Pi), glucose 6-phosphate (G6P), and ATP in the fruit tissue. Subsequently, however, as the M6P was metabolized, the levels of Pi, G6P, and ATP increased and ripening processes were concomitantly released from inhibition. Hence, the degree of inhibition by mannose or the release from inhibition was related to the level of M6P in the fruit and its rate of metabolism. The data provide correlative evidence to support a view that one inhibitory effect of mannose is depletion of Pi in the cell as a result of phosphorylation of mannose to M6P. Inhibition of ripening by mannose was not alleviated by co-application of glucose as a competitive substrate for the hexokinase(s), or by Pi, presumably the depleted metabolite. Also, incubation of tissue disks with M6P resulted in inhibition of ethylene production and respiration. The structural analogs of mannose, glucosamine, and 2-deoxyglucose, which have been shown to mimic mannose action in several plant tissues, did not cause inhibition of ripening of pear fruit comparable with that associated with mannose. Both analogs stimulated respiration, and glucosamine caused only a small inhibition of softening and ethylene evolution. Another mannose analog, alpha-methylmannoside, did inhibit fruit ripening though to a lesser extent than mannose. Its influence was also associated with accumulation of M6P and a decrease of Pi levels. We conclude that the mannose effect may, in part, be due to M6P toxicity, as well as by depletion of Pi.

Computation of steady flow in a two-dimensional arterial model.

The Navier-Stokes equations are solved numerically for steady flow through a double-branched two-dimensional section of a three-dimensional model of a canine aorta for which experimental data is available. The numerical scheme involves transforming the physical coordinates to a curvilinear boundary-fitted coordinate system and performing finite-difference computations in the transformed system. Shear stress at the wall is calculated for a Reynolds number of a 1,000 with branch-to-main aortic flow rate ratios as a parameter. The results are compared with the aforementioned experimental data and show reasonable qualitative agreement.

Inhibition by calcium of senescence of detached cucumber cotyledons: effect on ethylene and hydroperoxide production.

The effect of Ca on senescence was followed in detached cucumber (Cucumis sativus L.) cotyledons floating on various solutions in the dark. Compared with those in water, cotyledons in 10(-4) molar CaCl(2) exhibited reduced chlorophyll loss and H(2)O(2) production, reduced and delayed ethylene production, and did not undergo a burst in CO(2) production. In contrast, Mg had little effect on cotyledon senescence, whereas K stimulated chlorophyll loss but did not increase H(2)O(2) accumulation of ethylene and CO(2) production. This reduction in the rate of senescence by Ca could also be achieved by increasing the endogenous levels of Ca in the cotyledons before excision, although the reduction was less than that with Ca in the external solution. The addition of H(2)O(2) to the solutions on which cotyledons were floated stimulated chlorophyll breakdown, but effects on ethylene and CO(2) were not consistent.