Determination of Respiratory Parameters of Onion Bulbs (Allium cepa L.) under Total Anoxia

This work aimed to investigate the effect of total anoxia (100 N-2) on the respiratory parameters of onion bulbs. Freshly harvested onion bulbs (Allium cepa L. 'Rouge Amposta' obtained from organic farming) were used for this experiment. Under total anoxia, Fermentative Index (FI) values were 0.048, 0.072 and 0.14 mmol CO2 kg(-1) h(-1) at 4, 10 and 20 degrees C, respectively. The fermentative process was temperature dependent and followed an Arrhenius-like equation (R-2=0.992). The Q(10) of onion bulbs under anoxia was 1.93 and FI0 (fermentative index at 0 degrees C) was estimated at 0.037 mmol CO2 kg(-1) h(-1) with an activation energy (Ec) of 44 578 J mol(-1). Moreover, the FI of the bulbs (in mmol CO2 kg(-1) h(-1)) was measured within 6h after closing the vessels (jars). Beyond 24h at 20 degrees C, high CO2 production was observed and was likely due to anaerobic or aero/anaerobic microorganisms such as yeast and lactic acid bacteria. Furthermore, ethanol production under anoxia was also estimated and averaged <0.001, 0.55 and 0.79 pmol kg(-1) h(-1) at 4, 10 and 20 degrees C, respectively. These results indicated that onion bulbs are less sensitive to anoxia and tolerated total anoxia for at least 24 h.