Nitric Oxide-Induced Enhancement of Banana Fruit Attributes and Keeping Quality

The effect of nitric oxide (NO) on quality attributes such as texture, colour,
respiration, total soluble proteins, sugars, and activities of phenylalanine ammonia
lyase (PAL) and polyphenol oxidase (PPO) were studied in ripening banana fruit.
Freshly harvested banana fingers, ‘Cavendish’, were soaked in water containing
different concentrations (0.1, 0.2, 0.5, 1, 2, 3, 4 and 5 mM) of NO donors (sodium
nitroprusside (SNP), nitroso-1-naphthol, nitroso-R-salt, S-nitrosoglutathione (SNG),
S-nitroso-N-acetyl D-L-penicillamine (SNAP) and spermine-NO complex) for 3, 4
and 5 h separately. Among treatments, SNP, SNG and SNAP were relatively slowed
ripening with colour deviation of 44, 52 and 47%; firmness loss of 49, 48 and 50%
and storage period of 27, 29 and 28 days respectively, whilst, control recorded higher
colour deviation (62%) and firmness loss (69%) with storage period of only 17 days.
A structural analogue of NO donor, potassium ferricyanide having no NO donor
effect did not show similar positive effects imparted by NO donor indicating the
factual effects of NO. Among the NO-donors, treatment with SNP at 1 mM showed
delayed respiratory peak coinciding with delay in the accumulation of total soluble
as well as reducing sugars and significantly lower activities of PAL and PPO during
ripening. Early and high expression of PAL may serve as a biochemical marker for
studying climacteric stage of ‘Cavendish’ banana fruit.