Optimizing Gas Composition and Moisture Content for Preservation of Specific Metabolites of Cultivated Stinging Nettle (Urtica dioica L.) Leaves.

The objective of this study was to evaluate the influence of modified atmosphere and moisture absorbers on specific metabolites (SMs) content in packaged stinging nettle leaves (Urtica dioica L.). Hydroponically cultivated fresh nettle leaves were packaged in two experiments: 1. packaging in ambient or modified atmosphere (MAP) and 2. packaging in MAP without or with moisture absorbers. The results demonstrated that both modified atmosphere and moisture absorbers statistically significantly affected (at p ≤ 0.05) the SM content of nettle leaves, but with opposing effects. Specifically, leaves packed in modified atmosphere had significantly higher values of phenolic compounds, ascorbic acid, total chlorophylls, and antioxidant capacity compared to ambient packaging. In contrast, the inclusion of moisture absorbers in packages was associated with a general decline in metabolite content. The highest levels of caffeoylmalic acid (405.73 mg/100 g fm), total phenolic compounds (627.35 mg GAE/100 g fm), total chlorophylls (0.87 mg/g fm), and antioxidant capacity (ABTS: 24.5 µmol TE/g, DPPH: 6.98 µmol TE/g, FRAP: 43.85 µmol TE/g fm) were observed in samples stored for 17 days under modified atmosphere without the addition of absorbers. Based on these findings, for optimal preservation of SMs during extended storage (up to 20 days), packaging stinging nettle leaves in a modified atmosphere without moisture absorbers is recommended.