**4. Discussion**

The fungus *Botrytis cinerea*, which causes gray mold, is considered one of the most harmful postharvest pathogens to table grapes, especially during transport and storage. The use of SO2-generating pads is one of the main fungus control methods, especially when grapes are stored in a cold room for prolonged periods [10], which is necessary if the objective is to export 'BRS Vitoria' seedless grape, or even to store it for the domestic market.

It was verified that the SO2 generator pads reduced the incidence of gray mold at 50 days after refrigerated storage, with emphasis on the dual release–fast reduced pads, with no symptoms of the disease, even when the pathogen was inoculated. The grapes treated with dual release pads also presented better results in the presence of the fungus at 7 days at room temperature, and were more promising than the SO2 slow release pad for 'BRS Vitoria' table grapes, which were not efficient in control of the disease. In addition, 'BRS Vitoria' seedless grape was not sensitive to SO2 emitted in the fast phase of the dual release pads tested, nor to other disorders, such as hairline, bleaching, and cracking. The use of clamshells for the refrigerated storage of this grape cultivar has been shown to be suitable for use in combination with the SO2 pads, because it allows a sufficient ventilation area for good circulation of the active ingredient in the package.

In another study, SO2 generator pads contributed to the reduction of gray mold in 'BRS Vitoria' seedless grapes after 30 days of refrigerated storage, with a minimum reduction of 80% [21], but lower than observed in this trial, since the amount of active ingredient was smaller. In addition, the use of SO2 pads in combination with packaging methods using macroperforated liners had high disease control of 'Red Globe' table grapes stored for four months [22]. The use of suitable packaging combined with the conscious and efficient use of SO2 pads and storage at low temperatures (0–2 ◦C, 90–95% RH) may contribute to the maintenance of the postharvest quality of table grapes up to 50 days [23].

The choice of SO2 pads should be judicious to maintain the quality of each table grape cultivar to its final destination, so the level of the active ingredient should be adequate, in order to not injure the fruits or to damage their flavor. The main import markets for fresh grapes, such as the European Community and the United States, have established levels of tolerance to the use of SO2 in postharvest management, aiming at greater protection of the consumers and of the environment [11].

The mechanism used by SO2 pads occurs due to the presence of moisture in the packaging of the grapes, which is absorbed by the sheets and that reacts with the active ingredient, sodium metabisulfite (Na2S2O5), resulting in the release of the gas to the external environment. Slow release SO2 pads have lower permeability and emit low SO2 concentrations over a long period of up to 60 days. The dual release pads contain the Na2S2O5 enclosed between two plastic sheets, a slow release part and a fast release part, which provides different permeabilities, so the gas release takes place in a way specific to the part. The fast part releases SO2, which peaks after 24 h, and then decreases by one week. The slow release of the dual release pads emits SO2 continuously, ensuring the presence of the gas for extended periods [9,10]. The use of the dual release pad in this work proved to be more efficient than the slow release pad, which leads to the belief that the SO2 fast release phase in the first 48 h of the dual release pads is necessary for the conservation of healthy 'BRS Vitoria' grapes, even though the pathogen had been inoculated artificially.

Bleaching and cracking on the surface of berries, and in some cases, stem browning, are unfavorable characteristics that impair the quality of the table grapes preserved in the cold, and can develop through the indiscriminate use of SO2 pads due to the release of excessive levels of the active ingredient [22,24]. In addition to the browning and dehydration of the rachis, the loss of water and the degradation of the berries are factors that also decrease the postharvest life of table grapes during storage and transportation [25,26], and should, therefore, be considered when new techniques or materials for packaging are assessed. In this study, the SO2 pads did not affect the stem browning in the evaluated periods. The stem browning scores indicated that the rachis color was between 'fresh and green' and 'light brown' after 50 days of refrigerated storage. Other authors have observed that SO2 pads maintained a better fresh appearance by preventing browning in 'Thompson Seedless' [27] and

'Red Globe' table grapes [28]. The green and fresh color of the rachis is more attractive to the consumer than when darker [7]; therefore, with a view to commercialization, rachis color is an important parameter to be evaluated.

Shattered and softening berries, and mass loss, are some of the consequences caused by the incidence of *Botrytis cinerea* in table grapes [2,3]. In this trial, the grapes packed and treated with the SO2 pads showed lower shattered berry incidence after the 50-day cold storage period, as well as a lower incidence of gray mold. In the same way, the effectiveness of gray mold control by the dual release and dual release–fast reduced pads, especially when berries were inoculated with *Botrytis*, minimized the mass loss of the grapes at 7 days after room temperature. Therefore, the use of SO2 pads with high efficiency in the control of *Botrytis cinerea* can contribute to the maintenance of these characteristics and, consequently, maintain 'BRS Vitoria' table grapes in long periods of storage, especially when the objective is to preserve grapes over 30 days.

The analysis of the quality profile of the table grapes after the refrigerated storage period, especially in conjunction with techniques such as the use of SO2 pads, is extremely important since any change in the taste or appearance of the fruit may interfere with the commercialization process. The results showed that the effects on the main quality parameters of 'BRS Vitoria' seedless table grapes when treated with SO2 pads were not considerably detrimental. According to international marketing regulations, the minimum SS contents may vary according to the grape cultivar from 14.0 to 17.5◦Brix and the SS/AT ratio must be equal to or higher than 20 [29]; values within what were observed in this work.
