**1. Introduction**

Fresh produce is considered to be an important source of vitamins (i.e., A, C, niacin, riboflavin, thiamine), minerals (i.e., potassium, calcium, iron) and dietary fibers. Increase consumption of vegetables has been associated with a healthy lifestyle, reducing the risk of vitamin and mineral deficiencies, cancer and other chronic diseases [1]. These benefits derive from the previously mentioned phytonutrients that possess antioxidant, anti-inflammatory, and anti-cancer properties, among others [2].

Vegetables are perishable products and their quality might be affected by various environmental factors throughout the food supply chain [2]. The factors that can influence the quality and storability of vegetables include pre-harvest (i.e., growing temperature and light conditions, irrigation, maturity, pest management, harvesting, cultivation practice) and postharvest (i.e., poor handling, processing, storage temperature, marketing, pathogens) parameters [3–6]. During postharvest handling (including processing, storage, transport and retailing) and under unfavorable conditions (i.e., high temperature, low relative humidity, improper hygiene), vegetables' quality gradually deteriorates resulting in great losses for the food industry [1,7,8].

During storage, fresh produce might exhibit water loss (wilting), degradation of pigments (discoloration, i.e., loss of chlorophylls, carotenoids), and increased susceptibility

**Citation:** Xylia, P.; Ioannou, I.; Chrysargyris, A.; Stavrinides, M.C.; Tzortzakis, N. Quality Attributes and Storage of Tomato Fruits as Affected by an Eco-Friendly, Essential Oil-Based Product. *Plants* **2021**, *10*, 1125. https://doi.org/10.3390/ plants10061125

Academic Editors: Hazem Salaheldin Elshafie, Laura De Martino, Adriano Sofo and Petko Denev

Received: 12 May 2021 Accepted: 28 May 2021 Published: 1 June 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/).

to diseases and all these result in a less acceptable product by the consumer [2,3]. The main factors that affect vegetables' quality include exposure to undesirable temperature, relative humidity and light [2]. It has been shown that storage at low temperatures and high humidity suppresses the respiration rate of fresh produce, extending their shelf life [9]. Furthermore, the use of sanitizing agents including chlorine and chlorine-based means for fresh produce decontamination, might not be able to sufficiently reduce the microbial load, while at the same time, these products have been associated with the production of harmful, carcinogenic compounds [9,10].

Nowadays there is a turn towards the investigation of natural products in an attempt to reduce the use of chemical sanitizing agents in the food industry and meet consumers' demands for fresh, high nutritional and safe fresh produce [11,12]. Chlorine, the most commonly used sanitizing agent, has been linked with the formation of carcinogenic compounds that can adversely affect human health [10] and its application is of concern. Among the natural products investigated, the essential oils (EOs) from medicinal and aromatic plants gained more attention by researchers due to their antioxidant, antiinflammatory, antifungal and antibacterial activities, among others [4,11,13–19]. Various EOs have been used in the food industry (as food preservatives) in a variety of foods including meat and meat products, fruits and vegetables, minimally processed products and dairy products [8,19–21].

The application of EOs for the postharvest preservation of fresh produce and the utilization of their properties have been previously reported and the results are promising since they are able to preserve/improve product quality and ensure its safety for consumption [4,8,22]. The use of EOs alone or in combination with other compounds, i.e., chitosan, on fresh and/or minimally processed vegetables (including tomato and cucumber) has been previously studied and the results are encouraging [4,17,23–25]. For instance, EOs from eucalyptus lemon, helichrysum, sage, nutmeg, cinnamon and clove inhibited the growth of *Escherichia coli* in cucumber fruit, preserving fruit's quality and flavor [18]. The use of dittany EO in eggplant fruits decreased gray mold (*Botrytis cinerea*) development and at the same time did not negatively affect fruit's quality attributes [15]. The use of natural products (including sage EO) in vapor phase resulted in suppressed gray mold growth when inoculated on pepper fruits, while sage EO incorporated in *Aloe vera* gel improved (via dipping application) tomato fruit quality attributes alongside with decreased fruit decay throughout storage [4,23]. Moreover, Santoro et al. [26] reported that vapor application of thyme and savory EOs on peaches and nectarines was found to improve fruit's quality attributes (i.e., less weight loss and no significant losses of ascorbic acid and carotenoid content), but at the same time they showed conflicting results on postharvest diseases (brown rot and gray mold). Among EOs, rosemary and eucalyptus have been studied for their many beneficial properties and many uses have been proposed [27,28].

Even though EOs are classified as generally recognized as safe (GRAS) food additives, it is noteworthy that their application might result in phytotoxicity, allergies and undesired alterations in product quality (i.e., appearance, aroma, flavor) if used with inappropriate (high) concentrations and/or food combinations [18,19,29]. Thus, the aim of this study was to evaluate the effects of an eco-product (EP—based on rosemary and eucalyptus essential oils) by two different application methods (vapor and dipping) on the quality attributes of tomato fruits throughout storage at 11 ◦C and 90% relative humidity for 14 days.

#### **2. Results**

#### *2.1. Preliminary Test*

The effects of the EP on tomato during the preliminary screening are shown in Figure 1. Both application methods (vapor and dipping) at the highest concentration (0.8% EP) resulted in decreased weight loss compared to the other concentrations tested (Figure 1A,B). Vapor application led to lower scoring on the marketability scale with 0.1%, 0.2% and 0.8% EP, whilst dipping application with 0.4% EP also presented lower scores after two days of storage (Figure 1C,D). Furthermore, all applied concentrations (for both application

methods) showed lower scoring values on the aroma scale compare with the control. However, all tested concentrations showed higher scores as compared to the higher applied concentrations (i.e., for vapor: 0.8% and for dipping: 0.4% and 0.8%) (Figure 1E,F).

**Figure 1.** Effects of vapor (**A**,**C**,**E**) or dipping (**B**,**D**,**F**) application with eco-product (EP) at different concentrations (0%, 0.05%, 0.1%, 0.2%, 0.4% and 0.8%) or control (application of water) on weight loss (%), marketability (scale 1–10) and aroma (scale 1–10) of tomato fruits stored for two days at 11 ◦C. In each day, means (±SE) followed by different Latin letters significantly differ according to Duncan's MRT (*p* = 0.05).
