Effect of urea and K<sub>2</sub>SO<sub>4</sub> on enzyme activity and biochemical changes of date fruit (<i>Phoenix dactilyfera</i> cv. ‘Zahedi’) during ripening
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This study evaluated the effects of urea and potassium sulfate (K<sub>2</sub>SO<sub>4</sub>) at three concentrations (0, 0.5, and 1%) on the chemical and organoleptic properties of date fruit (<i>Phoenix dactylifera</i> L. cv. ‘Zahedi’) during ripening. A factorial experiment based on a randomized complete block design with three replicates was conducted in 2018 and 2019. Urea at 1% significantly increased antioxidant capacity by 45% in 2018 and 12% in 2019, whereas K<sub>2</sub>SO<sub>4</sub> at 1% reduced it by 9 and 7% in the respective years. Both antioxidant capacity and phenolic content decreased from the Kimri to Tamar stages. Urea and K<sub>2</sub>SO<sub>4</sub> treatments enhanced reducing and non-reducing sugar contents, with 1% K<sub>2</sub>SO<sub>4</sub> increasing reducing sugars by 8 and 1% urea increasing non-reducing sugars by 44% in 2018. Polyphenol oxidase (PPO) and peroxidase (POX) activities increased by 57 and 44% in 2018, and 48 and 42% in 2019, respectively, with 1% urea treatment. K<sub>2</sub>SO<sub>4</sub> at 1% also enhanced POX activity over both years. Sensory attributes showed reduced astringency and crunchiness, with improved sweetness during ripening. These findings suggest that urea and K<sub>2</sub>SO<sub>4</sub> applications significantly influence the biochemical and sensory quality of date fruit. Urea 1% improved antioxidant capacity. Simultaneous spraying of urea and K<sub>2</sub>SO<sub>4</sub> increased sugar significantly. Urea led to improved organoleptic characteristics such as increased sweetness and reduced astringency. The promoted fruit yield in urea and K<sub>2</sub>SO<sub>4</sub>, especially 1% was observed. Minerals, antioxidant capacity, and phenolic contents represented a reducing trend from Kimri to Tamar in date fruits. The activity of PME, PG, cellulase, and invertase exhibited a significant elevation during date fruit ripening, and conversely, POX and PPO activity decreased. By the obvious reduction of crunching and astringency as well as improvement of sweetness followed by ripening process, date fruit became edible.
