Short-term high oxygen pre-stimulation inhibits browning of fresh-cut watercored Fuji apples

In this study, short-term high oxygen pre-stimulation (SHOP) was used to prevent the browning of fresh-cut watercored Fuji apples. Browning index (BI), relative electrical conductivity, malondialdehyde (MDA), total phenol content (TPC), soluble quinone content (SQC), as well as the multiple enzymes (namely polyphenol oxidase (PPO), peroxidase (POD), catalase (CAT), and phenylalanine ammonia-lyase (PAL)) were successively investigated to evaluate the anti-browning capacity of SHOP (with oxygen at 21%, 55%, 75%, or 95% as normal, medium, high, and ultra-high levels) for fresh-cut apple. Furthermore, ratio1 and ratio2 between POD or CAT and PPO respectively were developed as a potential new parameter to consider the effect of SHOP on the browning-related enzymes. The cellular damage was evaluated by a new cell membrane damage rate approach based on the Transmission Electron Microscope (TEM) images. As a result, the SHOP at 75% and 95% effectively delayed the browning of apple slices, but not at 55%. The POD, CAT, PAL, TPC, ratio1, and ratio2 increased after SHOP at 75% and 95%, whereas the PPO and SQC were inhibited. Stored at 4 °C for 10 days, the cell membrane damage rates in non-watercored tissues of SHOP at 75% and 95% were 37.41% and 31.28%, lower than that of SHOP at 21%. The influence of SHOP on active oxygen metabolism of apples, the antioxidant system, and sensory attributes (especially flavor) will be further explored.