Relationship between Salmonella enterica attachment and leaf hydrophobicity, roughness, and epicuticular waxes: a focus on 30 baby-leaf salads.

BACKGROUND: The first step in the contamination of leafy vegetables by human pathogens is their attachment to the leaf surface. The success of this is influenced strongly by the physical and chemical characteristics of the surface itself (number and size of stomata, presence of trichomes and veins, epicuticular waxes, hydrophobicity, etc.). This study evaluated the attachment of Salmonella enterica to 30 baby-leaf salads and tested whether the differences found among them were related to the following leaf traits: hydrophobicity, roughness, and epicuticular waxes. RESULTS: Differences in susceptibility to contamination by S. enterica were found between the 30 baby-leaf salads investigated. The lowest attachment was found in wild lettuce (Lactuca serriola L.) and lamb's lettuce 'Trophy F1' (Valerianella locusta [L.] Laterr.), with values of 1.63 ± 0.39 Log(CFU/cm2) and 1.79 ± 0.54 Log(CFU/cm2), respectively. Attachment was correlated with hydrophobicity (measured as contact angle) (r = -0.39) and epicuticular waxes (r = -0.81) but not with roughness (r = 0.24). The most important wax components for attachment were alcohols and, in particular, the three-dimensional (3D) wax crystals of C26 alcohol, but fatty acids probably also had a role. Both these compounds increased hydrophobicity. The presence of thymol, whose antimicrobial properties are well known, was found in lamb's lettuce. CONCLUSIONS: The findings of this study can help to predict and control the attachment and contamination of leafy salads by enterobacteria. They also provide useful information for breeding programs aiming to develop cultivars that are less susceptible to human pathogens, enhancing the food safety of vegetables. © 2024 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Foliar Roughness and Water Content Impact on Escherichia coli Attachment in Baby Leafy Greens.

Understanding the relation between the susceptibility of different leafy greens to human pathogen contamination and leaf traits can contribute to increase the food safety of the fresh vegetable industry. The aim of this research was to evaluate the susceptibility to E. coli ATCC 35218 attachment in 30 accessions of baby leaves, and to identify leaf traits potentially involved in the contamination. The accessions were surface inoculated with a bacterial suspension containing 1 × 107 cells/mL and the attachment was measured 1.5 h after inoculation. Significant differences in attachment were detected between the accessions for p ≤ 0.05. The three most and the three least susceptible accessions were selected and characterized for leaf micro-morphological traits (stomata density and size, surface roughness) and water content. Scanning electron microscopy was used to analyse the stomatal parameters. Roughness was measured by an innovative portable 3D digital microscope. No significant correlation between the attachment of E. coli ATCC 35218 and stomatal parameters was detected, while the attachment was positively correlated with roughness and water content. The E. coli ATCC 35218 population in surface-inoculated leaves was also measured after a UV treatment, which was found to be less effective in reducing bacterial contamination in the rougher leaves. This result suggested that roughness offers UV protection, further highlighting its impact on the microbiological safety of baby leafy greens.

Quantitative Compositional Analyses of Calcareous Rocks for Lime Industry Using LIBS.

Here, the potential of laser-induced breakdown spectroscopy (LIBS) in grading calcareous rocks for the lime industry was investigated. In particular, we developed a system equipped with non-intensified detectors operating in scanning mode, defined a suitable data acquisition protocol, and implemented quantitative data processing using both partial least squares regression (PLS-R) and a multilayer perceptron (MLP) neural network. Tests were carried out on 32 samples collected in various limestone quarries, which were preliminarily analyzed using traditional laboratory X-ray fluorescence (XRF); then, they were divided into two groups for calibration and validation. Particular attention was dedicated to the development of LIBS methodology providing a reliable basis for precise material grading. The congruence of the results achieved demonstrates the capability of the present approach to precisely quantify major and minor geochemical components of calcareous rocks, thus disclosing a concrete application perspective within the lime industry production chain.

Terahertz Time-Domain Reconstruction of Coating Microstratigraphy on Gilded Surfaces.

Here, a systematic study in order to assess the potential of THz time domain reflectometry for measuring the thicknesses of overpaint layers applied on original gilded surfaces was carried out. The work is part of a thorough characterization campaign, which is going on at the Rijksmuseum for addressing the conservation problems of a set of 19th century gilded picture frames on which heavy coatings were applied in previous undocumented restoration interventions. To perform such non-invasive thickness measurements, an analytical protocol based on Gaussian fits of the THz pulse-echo temporal profiles was optimized through the preparation of suitable technical samples and the comparison with direct thickness measurements. Finally, the methodology was validated by characterizing the microstratigraphy of an original sculptural element from a gilded picture frame in the Rijksmuseum collection. The results achieved show the effectiveness of the present approach in revealing multi-layered dielectric microstructures with a spatial resolution of about 30 µm when using a spectral range up to 1.5 THz.

Josephson junctions loaded by transmission lines: a revisited problem.

The problem of evaluating dissipative effects in Josephson junctions loaded by transmission lines is reexamined, for either the symmetric or the asymmetric case, with particular consideration of the time domain in which the interaction between junction and load system occurs.

Reexamination of Josephson junctions coupled to transmission lines.

The effect of dissipation when due to the load of a transmission line coupled to a Josephson junction is reconsidered and evaluated by means of a simple direct procedure that supplies analytical expressions. The results are in good agreement with the ones previously reported in the literature. A simple criterion for testing experimental results is introduced.

Tunneling in frustrated total internal reflection: a comparison of different approaches.

Tunneling processes in frustrated total internal reflection are reexamined in order to compare the results already obtained from adopting a procedure based on a transition-element analysis with those recently reported on the basis of a statistical method applied to a Brownian-like motion. A close agreement between the two approaches can be established, at optical and microwave scales, when suitable values of the involved parameters are adopted.