**1. Introduction**

Table grapes are one of the most consumed fruits in the world, and a valuable source of phytonutrients [1,2].

It is a non-climacteric fruit, and for this reason, unlike many other fruit crops, the ripening process does not continue off the vine. Sugars produced by photosynthesis are translocated from leaves to the grapes only until they are on the vine or until the maximum Brix degree is reached. Also, there is no conversion of starch into sugars, as the amount of starch in berries is very low [3]. Though the concentration of berry solutes can change after harvest, and some other quality-related compounds can evolve or be degraded, in general, grapes should be harvested only when the target quality parameters have been reached.

A common practice used in southern Italy is to appositely cover canopies with plastic film (i.e., low-density polyethylene) during August to delay the harvest times of table grapes from October to the late November or early December [4]. This "late" forcing, conversely to the "early" one, aimed to anticipate the shoot sprouting, is executed to delay the harvest as much as possible, [5] while protecting fruit form autumnal rains. In addition, forced "storage" has the main advantages of maintaining green and hydrated

**Citation:** Piazzolla, F.; Amodio, M.L.; Pati, S.; Colelli, G. Evaluation of Quality and Storability of "Italia" Table Grapes Kept on the Vine in Comparison to Cold Storage Techniques. *Foods* **2021**, *10*, 943. https://doi.org/10.3390/ foods10050943

Academic Editors: Eleni Tsantili and Jinhe Bai

Received: 9 March 2021 Accepted: 21 April 2021 Published: 26 April 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

stalks, and, above all, to allow the use of fungicides, which cannot be applied during storage. Some authors [5,6] reported the benefits of this agronomic technique to meet the demand for high-quality table grapes during Christmas time, resulting in a higher profitability for the producers.

Piazzolla et al. [6], in fact, demonstrated that "late forcing" on the vine is a feasible approach to preserve and even improve table grape quality related to sensorial aspects, even if the authors reported that extreme delay could reduce the quality of the fruit. Nonetheless, nothing is known about quality and storability of "on-vine-stored" grapes and on the potential of this method compared to conventional postharvest storage techniques.

Table grapes are not chilling-sensitive [7]; the respiration rate and the rate of ethylene production for grapes are very low (2 mg CO2·kg−1·h−<sup>1</sup> at 0 ◦C and less than 0.1 <sup>μ</sup>L·kg·h−<sup>1</sup> at 20 ◦C, respectively). Table grape quality is reduced by the occurrence of stem browning and *Botrytis cinerea* infections [8]. Recently, the main physical, chemical and bio-based treatments in postharvest for the control of *Botrytis cinerea* on table grapes have been reviewed by De Simone et al. [9]. Ideally, grapes are stored in cold rooms operating at −1 to 0 ◦C with 95% RH, and a very low airflow; in these conditions, grapes may be stored up to 4 weeks [10], but generally SO2 fumigation are also applied to better control the mold growth [11,12]. Standard commercial practices include initial sulfur dioxide (SO2) fumigation during pre-cooling, followed by weekly fumigations with similar doses during cold storage, or most commonly, SO2 generator pads inside boxes are widely used for table grape storage and transport [13]. As alternative, chitosan, and aloe vera gel treatments have been successfully proposed to maintain table grape quality and extend their shelf-life [14–16].

Other methods used to extend the storability of table grapes include controlled (CA) or modified atmospheres (MA), and active packaging.

As for CA, the addition of CO2 (10 to 15 KPa in air) can be effective in controlling grey mold (*Botrytis cinerea*) for 2 to 4 weeks depending on cultivars [7].

Crisosto et al. [17] concluded that the CA treatment with 10 kPa CO2 combined with O2 levels from 3 to 12 kPa limited grey mold infection on "Red globe" grapes during 12-weeks of cold storage, whereas early harvested "Red globe" could be stored only for 4 weeks in 10 kPa CO2 + 6 kPa O2. In addition, CA treatment [18] and low temperature storage combined with SO2 slow-release generators [19] may be effective as insecticidal control.

As for MAP, Artés-Hernández et al. [20], reported that "Autumn seedless" grapes stored for 2 months in MAP with 15 kPa O2 and 10 kPa CO2 at 0 ◦C followed by 1 week at 15 ◦C in air, helped to prevent rachis browning and flavor losses.

Costa et al. [21] selected the best packaging material to achieve at the equilibrium the desired gas conditions (10–15% O2 and 4% CO2) that could control the respiration, the water loss, and the rachis color changes of the grapes. Among the tested polymeric material, oriented polypropylene (80 μm of thickness) could allow a shelf-life longer than 70 days.

Silva-Sanzana et al. [22] reported that modified-atmosphere packaging controlled the green color losses on stalks of "Red Globe" grapes stored for 90 days at 0 ◦C, compared with a conventional storage even after a shelf-life period, but no comparison is available with grapes "stored on the vine".

Cefola et al. [23] reported that the storage of "Italia" table grapes at high CO2 atmosphere (20 KPa) induced the shift to anaerobic metabolism, reporting an increase in respiration rate, and acetaldehyde and ethanol production, and a lower evaluation at the sensorial test, than grapes stored with lower CO2 concentrations (up to 10%) or in air. Finally, the use of an active packaging based on PET coated with a layered double Hydroxide (LDH) hosting 2-acetoxybenzoic anion (salicylate) as antimicrobial molecule was shown to cause a significant reduction in total mesophilic aerobic count and mold and yeast population with respect to control [24].

This work aimed to assess for the first time the quality and storability of table grapes stored on the vine, also considering quality evolution of grapes from the same plants stored in cold rooms (with or without modified-atmosphere packaging).
