Ultraviolet-C and Induced Stilbenes Control Ochratoxigenic Aspergillus in Grapes

Abstract

This study investigated the efficacy of ultraviolet-C (254 nm) and induced stilbenes to inhibit Aspergillus carbonarius and Aspergillus tubingensis and control ochratoxin A production in grapes. In addition, the stilbene synthesis as a response to UV-C treatment and to infection of ochratoxigenic Aspergillus was compared. The initial microbial inactivation by a previously optimized UV-C illumination protocol for increasing trans-resveratrol content in grapes (50 W/m (2), 40 cm, 60 s) was similar on undamaged and damaged grapes, achieving 1.2 and 1.3 log conidia/100 g reductions, respectively. After 5 days of storage at 22 degrees C, UV-C treatment and the stilbenes induced by UV-C inhibited ochratoxigenic Aspergillus growth in undamaged grapes. UV-C elicited the biosynthesis of trans-resveratrol, while microbial infection and tissue damage triggered the biosynthesis of trans-piceid. trans-Resveratrol was not synthesized as a consequence of ochratoxigenic Aspergillus contamination. However, when trans-resveratrol was synthesized by UV-C, it contributed to inhibiting the development of ochratoxin A producing aspergilli. Furthermore, UV-C treatment also contributed to decrease ochratoxin A production by ochratoxigenic aspergilli. Therefore, UV-C is a promising emerging technology either for reducing the potential ochratoxigenic risk in grapes, which is of particular interest to the wine industry, and also for increasing trans-resveratrol content of grapes, which would provide an added value to the wine.

Postharvest treatment of table grapes with ultraviolet-C and chitosan coating preserves quality and increases stilbene content

“…Grapes were placed in a single layer on the illumination vessel for the treatment, and the selected UV-C dose (6.0 AE 0.1 kJ/ m 2 ) was applied by establishing a specific exposure time (two illumination steps of 1 min) at a fixed distance (60 cm). The selection of the UV-C dose was based on previous studies (Allende et al, 2007;Selma et al, 2008). Grapes were turned over after the first illumination step to ensure the total surface exposure to UV-C light.…”

Antioxidant activity and phenolics content of selected Brazilian wines

“…Among climatic factors shown to influence the levels of resveratrol in grapes, one of the most studied is UV irradiation. This has been shown to increase the levels of resveratrol (Selma et al, 2003), especially prior to the period of maturation of the fruit. Indeed, post-harvest UV irradiation of grapes has been demonstrated to significantly increase the levels of resveratrol (Cantos et al, 2002).…”

Phytoestrogens in foods on the Nordic market

“…A genotypedependent enhancement of stilbene production by post-harvest UV-C treatment in grapes has also been demonstrated by Guerrero et al (2010). Selma et al (2008) investigated the efficacy of UV-C treatment (resulting in increased concentrations of stilbenes) in inhibiting Aspergillus carbonarius and A. tubingensis infection and controlling ochratoxin A production in grapes. UV-C exposure elicited the biosynthesis of trans-resveratrol while microbial infection and tissue damage triggered the biosynthesis of trans-piceid.…”