Effect of nitric oxide (NO) and associated control treatments on the metabolism of fresh-cut apple slices in relation to development of surface browning

Surface browning is an important cause of deterioration of fresh-cut apples during postharvest handling. ‘Granny Smith’ apple slices treated with NO gas (10 μL/L) and the NO donor compound 2,2′-(hydroxynitrosohydrazino)-bisethanamine (diethylenetriamine nitric oxide (DETANO) (10 mg/L) dissolved in phosphate buffer (pH 6.5) showed delayed development of surface browning during storage at 5 °C and also resulted in a lower level of total phenols, inhibition of PPO activity, reduced ion leakage and reduced rate of respiration but had no significant effect on ethylene production or lipid peroxide level as measured by malondialdehyde (MDA) and hydrogen peroxide levels. The two control treatments of phosphate buffer (pH 6.5) and water dips also had significant effects compared to untreated slices. The relative effectiveness of treatments in extending postharvest life and reducing total phenols, PPO activity, ion leakage and respiration was DETANO > NO gas > phosphate buffer > water > untreated. Apple slices dipped in chlorogenic acid dissolved in water showed surface browning soon after application but dipping in DETANO solution negated the effect of chlorogenic acid whether applied before or after dipping in chlorogenic acid solution while the buffer and NO gas were also effective. It is suggested that an increase in phenols occurs on the apple surface soon after cutting, possibly as a defensive mechanism of the apple to limit damage to surface cells. The effectiveness of the applied treatments to inhibit development of surface browning may relate to their ability to minimize the level of phenols active on the cut surface possibly in conjunction with a reduced PPO activity.

► Browning of apple slices was examined with NO gas, diethylenetriamine nitric oxide (DETANO), and control treatments.
► Increased postharvest life was DETANO > NO gas > phosphate buffer > water > untreated.
► Reduced total phenols, PPO activity, ion leakage and respiration were similarly affected.
► Slices dipped in chlorogenic acid induced browning but it was negated by NO and buffer.
► Inhibition of browning by treatments may relate to the level of phenols on the cut surface.