Résumé
Surface properties of apples, and the hydrophobicity of their skin in particular, affect the shelf life and marketability of apples. Surface characteristics of the skin are also of critical importance for securing microbiological safety of this common consumer item. The present work explores how pre-sale waxing in a packaging facility as well as washing and storage by consumers influence the surface energy of apples and assesses the impact of such treatments on pathogen adhesion to the apple surface. Based on contact angle measurements, the surface energy of apples from different geographical regions was quantified and mapped to specific fruit handling scenarios that included extended storage as well as possible waxing and washing. Experimental data were used as to compute the free energy of interfacial interaction between apple skin and two pathogenic viruses of significant relevance for public health - human respiratory syncytial virus (HRSV) and human adenovirus 5 (HAdV5). For the U.S. samples of Fuji apples, washing increased apple skin hydrophobicity for both apples that were waxed (ΔG decrease from –60.3 mJ/m2 to −84.4 mJ/m2) and, even more, for unwaxed apples (ΔG decrease from –53.8 mJ/m2 to −89.5 mJ/m2). Hydrophobicity of waxed apples also increased (steady decrease in ΔG from –58.0 mJ/m2 to –94.7 mJ/m2) over 9 days of shelf storage. A comparative analysis of apples from the U.S., China, and France revealed notable differences in the effects of waxing and washing: waxed but unwashed apples are hydrophobic in both U.S. (–60.3 mJ/m2) and China (–76.5 mJ/m2), while in France, the same treatment results in a hydrophilic surface (34.9 mJ/m2). As sampled (i. e. neither waxed, nor washed), apples from all three countries are moderately hydrophobic, likely due to natural wax. This study provides insights into the interplay between surface treatments, shelf life, and virus-apple interaction, aiming to improve food safety protocols and storage practices for apples.
[Display omitted]
•First study of the impact of waxing and washing on apple skin’s surface energy.•Impacts of waxing, storage time and washing on hydrophobicity are quantified for practically relevant post-harvest scenarios.•A three-country comparison reveals differences in the effects of post-harvest treatment on apple skin hydrophobicity.•Surface energy analysis is used to quantify interactions between Fuji apple skin and two human viruses: HRSV and HAdV5.•Findings can help formulate guidance on post-harvest processing and practices to better protect public health.