Lactate Dehydrogenase in Fresh-cut Carrot Shreds Stored under Low Oxygen Atmosphere

Abstract

Carrot (Daucus carota L.) root shreds were stored under a continuous flow of 0.5% and 2% O2 (balance N2) or air at 5 °C to investigate the effect of low O2 atmosphere on respiratory metabolism, particularly on lactate dehydrogenase (LDH) activity and its isozyme composition. Low O2 atmospheres caused a decrease in CO2 production and an increase in lactate concentration and LDH activity compared to air. By day 2, CO2 production rate decreased 0.4- and 0.5-fold, lactate increased 3.5- and 2.2-fold, and LDH activity increased 2.3- and 1.7-fold in carrot shreds stored in 0.5% and 2% O2, respectively, compared to samples in air. Based on nondenaturing electrophoresis, LDH isozyme composition analysis revealed five bands consisting of a tetrameric enzyme with subunits encoded by two different Ldh genes. Changes in staining intensity of the isozymes indicated that the increase in LDH activity in carrots under low O2 atmospheres resulted from increased enzyme synthesis and that there was preferential induction of one Ldh gene. These results suggest that lactic acid fermentation may be accelerated more under 0.5% than 2% O2 atmospheres due to greater expression of the Ldh genes.