Leandro Prevosto

Preserving minimally processed fruits represents a technological challenge. Therefore, non-thermal plasma (NTP) is proposed as one of the preservation methods. The aim of this work was to evaluate the effect of the application of NTP before and after packaging sliced apples in two films: One with high and another with low oxygen barrier features. Different parameters were evaluated during 14 days at 4 °C. Samples treated before packaging showed lower crunchiness and browning development, as indicated by chromatic and textural parameters. NTP reduced mesophiles, psychrotrophs, and yeasts and molds on the slices by 1–2 log units, although it had no effect on the antioxidant content of the apple slices, which were better preserved with high-barrier packaging. Samples treated with NTP, and low barrier packaging showed lower sugar content on day one. When applied after packaging, NTP contributed to better preservation of slice microstructure and tissue viability. Results showed that the combination of NTP applied after packaging and high-barrier film was the most suitable for maintaining fruit quality, mainly by better preserving slice color. In turn, tissue microstructure, texture analysis, and viability tests also supported this conclusion.

Low-temperature plasma treatments were applied to barley seeds using a dielectric barrier-stabilized corona discharge operated in ambient air enriched with oxygen or nitrogen to quantify surface chemical modifications and seed wettability. X-ray photoelectron spectroscopy showed that oxygen-enriched plasma produced the strongest oxidation, increasing surface oxygen from 9 ± 5 at% (control) to 24 ± 5 at%, while reducing carbon from 88 ± 5 at% to 76 ± 5 at%. Nitrogen-enriched plasma induced more moderate changes (O: 13 ± 5 at%, C: 85 ± 5 at%) but resulted in clear nitrogen incorporation, with an enhanced N 1s amine/amide component at ~400.8 eV. The hydroxyl O 1s contribution increased from 70% (control) to 82% (oxygen) and 90% (nitrogen), indicating substantial surface hydroxylation. SEM-EDX showed only minor micrometer-scale composition changes and no detectable morphological damage. Raman and ATR-FTIR spectra confirmed that polysaccharide, protein, and lipid structures remained intact, with intensity variations reflecting increased hydrophilicity. Water imbibition kinetics fitted with the Peleg model demonstrated faster initial hydration after plasma exposure, with 1/k₁ increasing from 20.25 ± 1.90 h⁻¹ (control) to 36.70 ± 6.56 h⁻¹ (oxygen) and 38.87 ± 7.57 h⁻¹ (nitrogen), while 1/k₂ remained nearly unchanged.

Low-temperature plasma treatments are increasingly explored to stimulate seed germination and early plant development. In this study, barley seeds were exposed to dielectric barrier discharge (DBD) plasma generated in air with controlled oxygen or nitrogen admixtures to elucidate surface chemical and structural modifications. X-ray photoelectron spectroscopy (XPS) showed a pronounced increase in oxygen-containing functional groups (C–O, C=O, O–C=O) and the emergence of nitrogen functionalities after plasma exposure, indicating oxidative activation and partial surface amination. SEM-EDX analysis revealed slight oxygen enrichment and nitrogen incorporation at the near-surface region, while backscattered electron images confirmed that the plasma treatments did not induce measurable morphological damage. Raman and ATR-FTIR spectra demonstrated that the molecular backbone of polysaccharides and proteins remained intact, although bands associated with –OH and –NH vibrations intensified, confirming increased surface hydrophilicity. Water absorption kinetics, modeled using the Peleg equation, showed that plasma-treated seeds absorbed water more rapidly than untreated controls, evidencing improved wettability and hydration efficiency. Overall, the combined results indicate that plasma exposure primarily induces surface oxidation and mild nitrogen incorporation without compromising seed integrity, thereby enhancing water uptake.

In this study, plasma-activated water (PAW) was generated using a large-volume (5 L) plasma reactor with a quasi-stationary, water-cathode glow-type discharge in atmospheric pressure air. Tap water was activated up to 75 min. PAW exhibited high concentrations of long-lived reactive nitrogen species (RNSs), reaching 8 mM, which is between 4 and 26 times higher than those reported in previous studies. The reactor reached an RNS synthesis efficiency of 61 nmol/J and an RNS production rate of 526 μmol/min, both among the highest reported. PAW was evaluated on tomato and bell pepper. Seedling emergence was determined in a nutrient-free substrate. To assess plant growth, seedlings were transplanted into pots filled with either nitrogen-free or nutrient-rich substrate. PAW-irrigation significantly promoted seedling emergence and leaf expansion, especially in tomato plants. The plant growth-stimulating effects of PAW were more pronounced in nitrogen-free substrate: fresh weight of tomato and bell pepper increased up to 13.1-fold and 2.6-fold, respectively. In contrast, the effect on the nutrient-rich substrate was negligible. Tomato plants grown in the nitrogen-free substrate and irrigated with 75-min PAW reached a dry weight comparable to those grown in nutrient-rich substrate. PAW irrigation did not induce oxidative stress, as confirmed by malondialdehyde (MDA) levels and antioxidant enzyme activity.

Plasma-activated water (PAW) is a sustainable and innovative alternative for agriculture, especially in controlled environments like greenhouses. Tomato and pepper are key horticultural crops worldwide, with a considerable part of their production in greenhouses. This study examined the effects of PAW irrigation on seed germination, plant growth, and oxidative stress in tomato and bell pepper plants. PAW was activated for up to 15 min using a 1 L capacity plasma reactor based on a glow-type discharge in air with water-cathode. The concentration of nitrogen compounds and the energy efficiency of synthesis obtained with the reactor were moderately high (5.4 mM and 60 nmol/J, respectively). The most notable effects of PAW were observed in bell pepper. The germination percentage in bell pepper increased by up to 26%, while no significant effects were found in tomato seeds. PAW irrigation significantly promoted plant growth, with dry weight increasing by up to 61% in bell pepper and 42% in tomato. Lipid peroxidation results showed no oxidative damage in either crop. The biochemical analysis of antioxidant enzymes (catalase, superoxide dismutase, and guaiacol peroxidase) confirmed that plant defense systems responded adequately to PAW irrigation. These results highlight PAW’s potential as an innovative and eco-friendly alternative in agriculture.