Articles
INTERRELATION BETWEEN RESPIRATION RATE, PEEL PERMEABILITY AND INTERNAL ATMOSPHERE FOR SEALED AND WAX-COATED MANDARIN ORANGES
This study explores the relationships of respiration rate, peel permeability and internal atmosphere composition for Satsuma mandarin oranges with a view to improving their storage quality.
Respiration of sealed and wax-coated Satsuma mandarin oranges (Citrus unshiu cv. ‘Miyakawa’ and cv. ‘Hayashi’) was measured at different temperatures (4, 10 and 20°C) and related to internal atmosphere composition.
Oranges were divided into four groups: control, sealed in polyvinyl chloride (PVC) wrap, coated with carnauba wax, and coated with sucrose polyester of fatty acids.
In the wrap treatment, PVC film 13.7 μm thick was used to sheathe the oranges thoroughly.
Coating with carnauba wax was carried out by dipping oranges for 4 – 5 s in a 6.8% solution of Prowax (Coseal Co.
Ltd., Kunsan, Korea), while coating with sucrose polyester used a 1.25% solution of Semperfresh (Inoteck Inc., Mentor, OH, USA).
Sealing or coating treatments reduced apparent respiration rate, peel permeability and weight loss of oranges, and maintained an internal atmosphere of lower O2 and higher CO2 compared with the unsealed and uncoated control.
Respiratory quotient (RQ) increased with sealing/coating and with temperature.
Respiration rate was more sensitive to temperature than peel permeability, which in some cases even decreased with temperature.
Thus high-temperature storage of some coated fruits induced high RQ, very low O2 and high CO2 internal concentrations, anaerobic respiration and accumulation of ethanol in juice.
The recommended modified atmosphere composition for orange storage is reported to be 5–10% O2 and 0–5% CO2; while values far below 5% O2 or above 5% CO2 may be damaging.
In comparison with ‘Hayashi’ fruit (late harvesting variety, thick peel), ‘Miyakawa’ fruit (early harvesting variety, thin peel) showed higher peel permeability, and was less susceptible to anaerobic disorders arising from internal atmosphere compositions of low O2 and high CO2 concentrations outside the tolerance limits.
For both ‘Hayashi’ and ‘Miyakawa’ fruit, PVC wrap was effective in decreasing weight loss during storage without severely altering the internal atmosphere.
At 10°C with ‘Miyakawa’, PVC wrapping and coatings of Prowax and Sempferfresh gave benefits of reduced respiration and an advantageous internal atmosphere.
At 10 and 20°C, ‘Hayashi’ fruit coated with Semperfresh showed high ethanol concentration, off-flavours and some physiological damage due to very low O2 and high CO2 levels, while the coating did not make a good barrier against moisture loss.
For the same cultivar, Prowax coating and PVC wrap may be satisfactory in reducing weight loss and respiration rate at 4 and 10°C. In conclusion, selection of sealing and coating methods should consider simultaneously both peel permeability and fruit respiration rate, which depend on cultivar, temperature and type of coating.