Table grapes were irradiated with laser pulses at two different wavelengths: one selected at 302.1？nm, that is, resonant with the transresveratrol biphoton absorption band, and another selected at 300？nm, that is a nonresonant wavelength where trans-resveratrol two-photon absorption is negligible. Attenuated total reflectance Fourier transformed infrared spectroscopic analyses of the irradiated grapes' skin showed an enhancement of polyphenols' content when the resonant wavelength was employed. Furthermore, microbiological analysis performed with nontreated (control), nonresonant, and resonantly irradiated grapes demonstrated how the last samples developed a significantly lower number of colony forming units. Since the only difference between the two (resonant and nonresonant) irradiation conditions was just a couple of nanometres in the employed UV-B laser wavelengths, the germicidal effect should be considered very similar. As a result, the observed difference in the table grape resistance to microbial infection was attributed to a wavelength-dependent-induced photochemistry. Finally, the potentiality of this method to enhance the postharvest health status of table grapes is remarked. 1. Introduction Over the past two decades the employment of UV light to improve the quality of fresh fruits and vegetables has received an increased attention [1], and nowadays, it is considered an alternative to chemical approaches because its potential application to control postharvest diseases [1–4]. Typically, the most widely used UV light is the short-wave UV-C radiation which comprises from 200 nm to 280 nm. Such an UV-C light when employed at high doses is harmful to living systems, but, however, at low doses, it may induce fruit disease resistance, in many cases due to the elicitation of the so-called defence compounds, naturally present in fruits and vegetables [1]. Table grape is perhaps one of the fruits where UV-C irradiation has been extensively applied. It is well accepted that its resistance to postharvest decay, and specifically to Botrytis cinerea, and other pathogens can be enhanced by UV-C induction of phenolic compounds, that is, phytoalexins like resveratrol, -viniferin, and -viniferin [5, 6]. In addition, the consumption of vegetables and fruits rich in phenolic compounds is an important claim in human dietary habits as these compounds have shown to be beneficial for the human health. An example of such phenolic compound is transresveratrol (3,5,4′-trihidroxistilbene), hereafter denoted as tr, a well-known antioxidant naturally produced by grapes,
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