ReviewEffects of superatmospheric oxygen levels on postharvest physiology and quality of fresh fruits and vegetables
Introduction
Oxygen concentrations greater than 21 kPa (induced through high O2 atmospheres or hyperbaric atmospheres) may influence postharvest physiology and quality maintenance of fresh horticultural perishables either directly or indirectly via altered CO2 and C2H4 production rates. Increased O2 concentrations around and within the commodity result in higher levels of free radicals that can damage plant tissues (Fridovich, 1986). Sensitivity to O2 toxicity varies among species and developmental stages.
Day (1996) discussed the rationale behind, and the potential applications for, the use of novel gas mixtures (i.e. high oxygen, argon, and nitrous oxide) for the modified atmosphere packaging (MAP) of fresh prepared produce. He stated that high O2 levels are effective at inhibiting enzymic discoloration, preventing anaerobic fermentation reactions, and influencing aerobic and anaerobic microbial growth.
Oxygen is colorless, odorless, and tasteless, so O2 enrichment cannot be detected by the human senses. Superatmospheric O2 levels can accelerate combustion of all materials. Thus, special care must be taken in designing and using packaging machines and gas-flushing systems to avoid ignition sources when high O2 concentrations are utilized (British Compressed Gases Association, 1998).
In this report we will review published information and some unpublished data on responses of fresh fruits and vegetables to superatmospheric O2 concentrations alone and in combination with elevated CO2 atmospheres.
Section snippets
Respiratory metabolism
Exposure to superatmospheric O2 levels may stimulate, have no effect, or reduce rates of respiration, depending on the commodity, maturity and ripeness stage, O2 concentration, time and temperature of storage, and the CO2 and C2H4 concentrations. Kidd and West, 1925, Blackman, 1928, Blackman and Parija, 1928 were among the first to describe the intricate relationship between apple ripening, O2 tension and respiratory activity. Kidd and West (1934) found that 100 kPa O2 accelerated the onset of
Ethylene biosynthesis and action
Creech et al. (1973) reported that ‘Russet Burbank’ potato tubers stored in 80 kPa O2+12 kPa CO2 produced ethylene at a much higher rate than those kept in air at 7°C. ‘Bartlett’ pears kept in 100 kPa O2 and 20°C had higher rates of ethylene production, chlorophyll degradation, and softening than those kept in air (Frenkel, 1975). Morris and Kader (1975) reported that 30 and 50 kPa O2 atmospheres accelerated ethylene production and ripening of mature-green and breaker tomatoes stored at 20°C.
Pigments and color
Biale and Young (1947) reported that the change in lemon color from green to yellow was markedly accelerated by high O2 levels. However, exposure to 99.2 kPa O2 also induced rapid peel breakdown. At 18°C, cherries and apricots held in 100 kPa O2 were slightly less ripe (as indicated by color) at the end of 10 days than those held in air (Claypool and Allen, 1948). Oxygen at 30, 50, and 75 kPa hastened ‘Wickson’ plum ripening at 20°C, while 100 kPa O2 delayed color changes associated with
Growth and development
The potential effects of superatmospheric O2 levels on elongation and curvature of asparagus and sprouting of onions and potatoes should be investigated in view of the findings of Abdel-Rahman and Isenberg (1974) that 40 kPa O2 increased sprouting and rooting of 0°C-stored carrots.
Physiological disorders
Kidd and West (1934) showed that storage of ‘Bramley's Seedling’ apples in 100 kPa O2 can be detrimental. After 4 months at 4°C, symptoms included mealy flesh and browning of skin and flesh. Storage of ‘Granny Smith’ apples in 70 kPa O2 at 0°C for 1 month did not accelerate the severity of sunscald (Lurie et al., 1991). Solomos et al. (1997) reported that ‘Gala’ and ‘Granny Smith’ apples exposed to 100 kPa O2 developed extensive injury akin to that which occurs under 1 kPa or lower O2
Responses of microorganisms
Growth rate and growth efficiency as well as the respiration rates of living organisms are dependent on O2 tension (Harrison, 1976). Above the ‘critical level’ in air these parameters are not affected by the O2 concentration, but growth is inhibited below the critical level as well as at toxic high O2 tensions. Obligate anaerobes are injured even by 0.1 kPa O2 concentrations.
Bert (1878) reported that compressed air at 15–44 atmospheres preserved meat and raw eggs for several days at room
Future research needs
It is clear from the limited published information on effects of elevated O2 levels on postharvest physiology and quality of fresh fruits and vegetables that much more research is needed to answer the following questions:
- 1.
What are the mechanisms by which superatmospheric O2 levels influence rates of CO2 and C2H4 production by climacteric fruits, non-climacteric fruits, and non-fruit vegetables?
- 2.
Do high O2 atmospheres ameliorate or aggravate chilling injury and other physiological disorders?
- 3.
Can
Acknowledgements
We thank Beth Mitcham, Mikal Saltviet, and Annette Wszelaki for their critical review of this manuscript.
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