Application of Hormetic UV‐C for Delayed Ripening and Reduction of Rhizopus Soft Rot in Tomatoes: the Effect of Tomatine on Storage Rot Development

Abstract

The application of ultraviolet-light C (UV-C, 254 nm) hormesis on tomato fruits to stimulate beneficial responses is a new method of inducing host resistance to Rhizopus soft rot, with maximum protection at 72 h following artificial inoculation with Rhizopus stolonifer and delay fruit ripening. In the tomato-Rhizopus soft rot pathosystem, UV-C induced resistance of tomatoes to soft rot was reversed by fluorescent light, and not by storage under dark condition. The present study was aimed at finding a possible fungal toxic mechanism that was involved in the control of Rhizopus soft rot. The development of carotenoids, loss of chlorophyll and ethylene production were significantly retarded during storage after treatment with hormetic doses of UV-C. The delayed ripening of UV-C treated fruits was attributed in part to the high level of putrescine and spermine polyamines. In a time-control study, it was found that the resistance of UV-C-treated tomatoes artificially inoculated with R. stolonifer correlated with a high concentration of tomatine which accumulated up to 72 h after UV-C treatment. However, there was a higher tomatine content in UV-C-treated fruits compared to untreated fruits where it was transitory at 96 h after treatment in the time-course study. ZusammenfassungAnwendiing von homietischen UV-C fur das verzogerte Reifewerden von Tomaten sowie die Reduzierung der Rhizopus Weichfaule: EinfluB des Tomatins auf die Lagerfauleentwicklung Die Anwendung von ultraviolettem Licht C (UV-C, 254 nm)-Honnesis bei Tomatenfrtichten, um vorteilhafte Reaktionen hervorzurufen, ist eine neue Methode, bei der eine wirtspezifische Resistenz gegen die RizopusWeichfaule induziert wird, der maximale Schutz ist 72 Std. nach einer Inokulation mit Rhizopus stolonifer vorhanden, und das Reifwerden der Fruchte wird verlangsamt. Im Tomaten-i?/!Jzo/)ai-Weichfaulesystem wird die UV-C-induzierte Resistenz der FrUchte zur Weichfaule durch fluoreszierendes Licht aufgehoben, aber nicht durch eine dunkle Lagerung. Die vorhegende Arbeit hatte als Ziel, einen moglichen pilztoxischen Mechanismus nachzuweisen, welcher an der KontroUe der RhizopusWeichfaule beteiligt ist. Die Entwicklung von Karotinoiden, der Chlorophyllverlust sowie die Ethylenproduktion wurden wahrend der Lagerung nach einer Behandlung mit hormetischen UV-C-Dosen signifikant gehemmt. Die gehemmte Reifung der UV-C-behandelten FrQchte wurde zum Teil dem hohen Grad von Putrescin und Sperminpolyaminen zugeschrieben. In einer Zeitstudie wurde festgestellt, daB die Resistenz von UV-Cbehandleten Fruchten, die mit R. stolonifer inokuliert worden waren, mit einer hohen Konzentration von der Verbindung Tomatin korrelierte, welche bis zu 72 Std. nach der UV-C-Behandlung akkumuherte. 96 Std. nach der Behandlung war eine vorubergehende hohere Tomatinkonzentration in UV-C-behandelten als in nicht behandelten Fruchten nachzuweisen.

Effect of postharvest ultraviolet-C treatment on the proteome changes in fresh cut mango (Mangifera indicaL. cv. Chokanan)

“…The UV‐C treatments have been used for maintaining the quality as well as reducing postharvest losses in fruits . Fruits that were exposed to UV‐C were found to exhibit delayed ripening, delayed senescence as well as reduced spoilage . Several researchers have reported on the immediate effects of UV‐C treatment on the quality of fruits while the underlying changes at a proteomic level that occurs as a result of UV‐C irradiation remains unclear .…”

“…8,9 Fruits that were exposed to UV-C were found to exhibit delayed ripening, 10 delayed senescence 11,12 as well as reduced spoilage. 13,14 Several researchers have reported on the immediate effects of UV-C treatment on the quality of fruits while the underlying changes at a proteomic level that occurs as a result of UV-C irradiation remains unclear. 15 -20 UV-C irradiation has been known to cause either generation of reactive species, which results in protein thiol oxidation, or protein damage through photolysis.…”

Photo-Induced Modification of Food Protein Structure and Functionality

“…These positive effects were attributed to the photo-induced modulation of enzymatic activity in the cell [29,31]. For instance, light exposure often increases the activity of phenylalanine ammonia-lyase, which enhances the biosynthesis of phenols toxic to pathogens [64,88]. However, Charles et al [9] reported that PL treatment at higher fluence (80 kJ m -2 ) did not affect the activity of this enzyme in fresh-cut mangoes and activated polyphenoloxidase.…”

Rhizopus stolonifer (Soft Rot)

“…the retarded degradation of tomatine (a compound which is toxic to some fungi). Likewise, it has been demonstrated that UV-C treated tomatoes are resistant to polygalacturonase activity secreted by R. stolonifer (Stevens et al, 1997(Stevens et al, , 1998. Another alternative that has been explored is the application of microwave energy, which provides rapid heating and is already widely used in the food industry.…”