*3.8. Changes in Catalase, Ascorbate Peroxidase, Monodehydroascorbate Reductase, Dehydroascorbate Reductase, and Glutathione Reductase Activities*

Antioxidant enzymes, such as CAT and AsA-GSH cycle-related enzymes (APX, DHAR, MDHAR, and GR), play important roles to maintain cellular homeostasis by scavenging H2O2 and preventing the accumulation of H2O2 to toxic levels [14].

The activities of CAT indicated a quick decrease in week 1 and steadily declined until the end of the storage duration in all samples. By week 4, the activities of CAT in HWT-1 min fruit remained at a level higher than those of HWT-3 min, HWT-5 min, and control fruits (Figure 10).

**Figure 10.** Effect of hot water treatment (55 ◦C for 1, 3, 5 min) on the activity of catalase (CAT) in red sweet pepper fruit during storage at 10 ◦C. Data represent means ± S.E. (n = 3). Different letters on bars are significantly different (*p* < 0.05).

Ascorbate peroxidase activities in HWT-1 min fruit slightly decreased in the first week of storage but increased in weeks 2 and 3, then declined thereafter, and remained higher than those of HWT-3 min, HWT-5 min, and control fruits throughout the storage period. HWT-3 min and HWT-5 min fruits presented a significant decrease in APX activities until the end of storage time, showing a level lower than those of HWT-1 min and control fruits (Figure 11A).

Monodehydroascorbate reductase activities in HWT-1 min fruit sharply increased and approximately doubled after 2 weeks but decreased afterward. The MDHAR activities in HWT-1 min fruit were higher than those in HWT-3 min, HWT-5 min, and control fruits, except in week 4, when all fruits showed similar levels (Figure 11B).

Dehydroascorbate reductase activities in HWT-1 min fruit tended to increase during cold storage for 3 weeks and decreased thereafter. In HWT-1 min fruits, DHAR activities were higher than those of HWT-3 min, HWT-5 min, and control fruits, except in week 4, when all fruits showed similar levels (Figure 11C).

Glutathione reductase activities in HWT-1 min fruit sharply increased during the storage at 10 ◦C for 4 weeks. The activities of GR in HWT-1 min fruit were higher than those of HWT-3 min, HWT-5 min, and control fruits. There was a gradual increase in GR activities in HWT-3 min and HWT-5 min fruits until the end of storage (Figure 11D).

**Figure 11.** *Cont*.

**Figure 11.** Effect of hot water treatment (55 ◦C for 1, 3, 5 min) on the activity of (**A**) ascorbate peroxidase (APX), (**B**) monodehydroascobate reductase (MDHAR), (**C**) dehydroascorbate reductase (DHAR), and (**D**) glutathione reductase (GR) in red sweet pepper during storage at 10 ◦C. Data represent means ± S.E. (n = 3). Different letters on bars are significantly different (*p* < 0.05).
