ROS-mediated membrane damage and antioxidant imbalance drive apple flesh browning during cold storage

Area of Science:

• Plant Physiology
• Biochemistry
• Postharvest Biology

Background:

• Flesh browning is a significant postharvest issue in apples during cold storage, with unclear physiological underpinnings.
• Understanding the role of reactive oxygen species (ROS) and antioxidant systems is crucial for managing this disorder.

Purpose of the Study:

• To investigate the physiological basis of flesh browning in apples under cold storage.
• To compare ROS metabolism and antioxidant status in browning-susceptible and normal apple tissues.

Main Methods:

• 'Fuji' apples were cold-stored for 120 days.
• Analyzed flesh color, membrane damage, phenolic metabolism, antioxidants (ascorbic acid, glutathione), ROS levels, and antioxidant enzyme activities (SOD, CAT, APX), alongside gene expression.

Main Results:

• Browning tissues exhibited higher polyphenol oxidase (PPO) and peroxidase (POD) activities, increased membrane damage, and elevated ROS.
• Total antioxidant capacity decreased, with significant reductions in ascorbic acid and glutathione, and lower CAT/APX activities.
• Despite upregulated phenylpropanoid pathways, phenolics and flavonoids were insufficient to mitigate ROS, correlating strongly with browning intensity.

Conclusions:

• Prolonged cold storage leads to ROS accumulation and membrane damage in apple flesh.
• Reduced non-enzymatic antioxidants and antioxidant enzymes create an ROS imbalance, triggering enzymatic browning.