Oxygen Consumption by Fruits and Vegetables

Abstract

Respiration by fruits and vegetables is vital action to generating the ATP needed for maintenance of cell viability, even after harvesting and as nutrients decompose. Therefore, respiration is strongly associated with qualitative deterioration during transportation and storage. Measurement and mathematical modeling of O 2 uptake and CO 2 production rates have been effective for evaluating the deterioration rate of horticultural products. ATP is produced by F O F 1 -ATP synthase through the transfer of electrons from ubiquinone to cytochrome c oxidase (COX) in plant cells. Although COX consumes a large amount of O 2 taken into cells, oxidizing protons as the terminal enzyme in the classical electron transport chain, an alternative pathway involving an alternative oxidase has been discovered, which performs the same reaction in plant cells without producing ATP. Staining and light sensing have been employed to measure enzymatic activity and O 2 consumption rate, respectively.

Induction of Terminal Oxidases of Electron Transport Chain in Broccoli Heads under Controlled Atmosphere Storage

“…On individual sampling days, there were no significant differences between mean O 2 uptake rates measured in low O 2 and normoxia. Values measured during storage at 1 • C in the present study and those reported by Makhlouf et al [8] were in the range of 0.59-0.80 mmol kg −1 h −1 and 0.26-0.63 mmol kg −1 h −1 , respectively. These are much lower than the values reported elsewhere: 2.5-11 mmol kg −1 h −1 at 25 • C by Wang et al [13]; 7.56 mmol kg −1 h −1 at 20 • C by Makino et al [19]; and 9.99 mmol kg −1 h −1 at 20 • C by Robinson et al [4].…”

“…O 2 molecules taken up by an entire plant are oxidized by AOX and COX. Therefore, oxidation by these enzymes promotes a reduction in stored nutrient concentrations, an effect that is one of the main causes of deterioration in horticultural products such as broccoli [8]. In the present study under CA, mass loss and induction of AOX were indices of deterioration in broccoli heads.…”

“…COX is the crucial terminal oxidase in oxidative phosphorylation, which directly reduces O 2 , and which is coupled with ATP synthesis [8,27]. ATP generated via oxidative phosphorylation is required to maintain the biological activity of plant cells [28].…”

“…Li et al [6] also reported head rot of broccoli caused by bacterial growth. Respiration is a main cause of mass loss [7] and degradation of nutrients [8] after harvest. CA storage at 0 • C with 2-5% O 2 and 10% CO 2 was reported to prolong the shelf life of broccoli heads by 1.5-fold compared to that under normal air [9].…”

“…CA storage extends shelf life by reducing metabolic activity, including respiration [4]. During respiration, stored nutrients are transformed to substrates that drive electron flow through the electron transport chain (ETC) [8]. This suggests that the activities of terminal oxidases of ETC are associated with the shelf life of horticultural products.…”