PAL activities in asparagus spears during storage after ammonium sulfate treatments

Lignification reduces the edible part of asparagus spears resulting in quality loss. Postharvest conditions such as low temperatures induce lignin accumulation. The aim of this study was to inhibit the lignification in asparagus spears by affecting activity of phenylalanine ammonia-lyase (PAL), a key enzyme of the phenylpropanoids pathway. Spears were pulse treated with 0.5, 2 or 4 mmol L-1 ammonium sulfate, 2 mmol L-1 aminooxy acetic acid (AOA), and distilled water (control). PAL enzyme activity, total phenolic content, lignin content, antioxidant capacity, spear firmness, weight loss, and elongation were measured. PAL activity was reduced by ammonium sulfate, with 2 mmol L-1 being the most effective concentration. Total phenolic content was lower in spears treated with the higher concentrations of ammonium sulfate. Elongation was higher in AOA treated spears. Spear tip firmness was not affected by ammonium sulfate treatment, while it increased in the AOA treatment. Total antioxidant capacity was higher in all treatments until nine days of storage, but thereafter only 0.5 mmol L-1 ammonium sulfate was higher than the control. Ammonium sulfate showed promising results as a postharvest treatment for controlling PAL activities during storage.