Respiratory parameters of onion bulbs (Allium cepa) during storage. Effects of ionising radiation and temperature

The O2 and CO2 respiration rates of untreated and irradiated onion bulbs (Allium cepa) at 0.15 and 0.30kGy were measured at 4, 10 and 20°C. The O2 respiration rate increased for 24h after treatment from 0.19mmole kg-1 h-1 at 20°C for control samples up to 0.26 and 0.39mmole kg-1 h-1 for 0.15 and 0.3kGy irradiated onions respectively. Respiratory quotient (RQ) increased with temperature. The Q10 of the respiration of the control samples (1.61) was lower than that of any other plant tissue, but it increased with storage duration and irradiation dose. The respiration rate of control onions increased steadily over 25 weeks of storage at 4°C, while that of the irradiated samples decreased during the same period after a peak observed after irradiation treatment. The apparent K(m) for the Menten-Michaelis equation was determined on a new respirometer and averaged 1.6kPa at 10°C and 6.3kPa at 20°C. However, at this higher temperature (20°C) apparent K(m) varied with O2 partial pressure, proving that the respiration of onion bulbs does not follow a Menten-Michaelis-like process. The Fermentative Index (FI) of onions was measured under anoxic conditions as CO2 production rates in mmole kg-1 h-1 at 4, 10 and 20°C. (C) 2000 Society of Chemical Industry.