Lactic Fermentation of Carrot Root Shred under Low Oxygen

Abstract

Glycolysis has been shown to accelerate in many plant species, and the glycolytic pathway was considered to replace the Krebs cycle as the main source of energy when O2 becomes limiting. The increase in glycolytic flux is accompanied by the accumulation of glycolytic end products, including ethanol and lactate. Lactate dehydrogenase (LDH) has been isolated from several plant sources; however, there is very little work reported on LDH induction during anaerobiosis and no information is available on the long-term effect of low O2 atmosphere on lactic fermentation in carrot (Daucus carota L.) roots. To understand the regulation of metabolism of lactic fermentation, carrot root shreds were stored under a continuous flow of 0.5% and 2% O2 (balance N2), or air at 5°C and 15°C. The concentration of lactate and the activity of LDH increased rapidly, reached peaks after 2 days, and then gradually decreased. The maximum increase level of LDH was 2.8-, 2.1-, 2.0-, and 1.6-fold; that of lactate was 5.6-, 3.8-, 2.9-, and 2.6-fold for 0.5% O2 at 15°C and 5°C, and 2% O2 AT 15°C and 5°C, respectively, compared with corresponding air control. These results indicate that the lactic fermentation was more accelerated in 0.5% O2 than 2% O2 atmosphere, and more accelerated at the higher storage temperature than the lower one. However, ethanol accumulation, which was found in the carrots under the same low-O2 atmosphere, was much more than lactate accumulation. Thus, carrot roots possess LDH, which appears under low-O2 atmosphere, but lactic fermentation may be a minor carbon flux compared to ethanolic fermentation.