Effectiveness of essential oil extracted from pompia leaves against Penicillium digitatum.

BACKGROUND: In recent years, interest in the use of natural compounds as possible substitutes for chemicals, to prevent microbial food spoilage has grown. The antimicrobial activity of the essential oils (EOs) is well known and nowadays there is renewed interest in their application as natural preservatives in postharvest management. The aims of this study were to characterize the EO extracted from pompia leaves and to evaluate its effectiveness for the control of the postharvest decay agent Penicillium digitatum, when applied as vapor contact in new airtight boxes, supplied with a heating system. RESULTS: Fumigation was performed in vitro and on food using two concentrations of the EO, heated at controlled temperature. The headspace analysis revealed that the heating of the EO favored the evaporation of the volatile compounds, without altering their functionality. The treatments reduced the pathogen growth in vitro and rot on inoculated food by about 50%. CONCLUSION: The chemical analysis of the vapor composition demonstrated that heating the oil did not alter the components and thus the antimicrobial effect of the oil. The treatment by vapor contact with the EO was effective in controlling the pathogen growth in vitro but, above all, it was successful in halving rot in vivo. Due to their bioactivity in the vapor phase, EOs could be delivered as fumigants during postharvest protection; however, the techniques commonly employed are not ideal for simulating real pre-treatment conditions. The new device allows real large-scale conditions to be reproduced. © 2020 Society of Chemical Industry.

Antimicrobial activity of gaseous Citrus limon var pompia leaf essential oil against Listeria monocytogenes on ricotta salata cheese.

Contamination by Listeria monocytogenes is a particularly challenging problem in the food industry due to the ability of the bacterium to develop under conditions normally used for food preservation. Here, we show that the gaseous phase of Citrus limon var pompia leaf essential oil (hereafter PLEO) exerts specific anti-Listeria activity on ricotta salata cheese stored at 5 °C. The synergic effect of gaseous PLEO treatment and refrigeration was first confirmed in vitro on L. monocytogenes strains treated for 3 h with gaseous PLEO and then stored at 5 °C. Ricotta cheese was then inoculated with L. monocytogenes strains and subjected to hurdle technology with different concentrations of gaseous PLEO. Cell counts revealed gaseous PLEO to exert a bactericidal effect on L. monocytogenes 20600 DSMZ and a bacteriostatic effect on a mix of L. monocytogenes strains. Scanning and transmission electron microscopy analyses of L. monocytogenes cells suggested that gaseous PLEO targets the bacterial cell wall and plasma membrane. Chemical analyses of the liquid and vapor phases of PLEO indicated linalyl acetate to be the predominant compound, followed by limonene and the two isomers of citral, whereas EO composition analysis, although generally in line with previous findings, showed the presence of linalyl acetate for the first time. Solid-phase microextraction coupled with gas chromatography confirmed the presence of all crude oil components in the headspace of the box.

Sodium carbonate treatment induces scoparone accumulation, structural changes, and alkalinization in the albedo of wounded citrus fruits.

Following sodium carbonate treatment, accumulation of scoparone (6,7-dimethoxycoumarin) but not scopoletin (6-methoxy-7-hydroxycoumarin) was found in the albedo of wounded fruit from different Citrus sp. and cultivars. Treating wounded mandarin fruit cv. Fairchild with 5% Na(2)CO(3) (SC) lead to a scoparone accumulation in the albedo of 310, 361, and 382 microg g(-1) fresh weight after 7, 10, and 15 days, respectively. Scoparone accumulation was associated with a decrease in decay severity. When oranges cv. Biondo comune wounded and treated with 5% SC were inoculated with Penicillium digitatum or Penicillium italicum conidia 3 days posttreatment, the decay percentage as compared to untreated wounds was reduced by 97.2 and 93.9%, respectively. Observations by scanning electron microscopy of wounded Citrus fruits treated at 20 degrees C with 2, 3, 4, or 5% (w/v) solutions of sodium carbonate showed structural modifications to the albedo as well as damage to 24-48 h old mycelia of P. digitatum, the cause of citrus green mold. Modifications were more evident in orange, lemon, and grapefruit as compared to mandarin fruit. The efficacy of the treatment was strictly related to the SC interaction with the albedo tissue that, in addition to structural changes, significantly increased tissue pH, affecting P. digitatum pathogenicity. The SC remaining as a film on unwounded flavedo had no effect in preventing contact infection by the Penicillia.