**1. Introduction**

Mango fruits (*Mangifera indica* L.) are recognized as one of the most desirable fruits due to their appealing color, delectable flavor, and superior nutritional value. However, mangoes, a climacteric fruit, ripen shortly after harvest and are susceptible to anthracnose

**Citation:** Khalil, H.A.; Abdelkader, M.F.M.; Lo'ay, A.A.; El-Ansary, D.O.; Shaaban, F.K.M.; Osman, S.O.; Shenawy, I.E.; Osman, H.-E.H.; Limam, S.A.; Abdein, M.A.; et al. The Combined Effect of Hot Water Treatment and Chitosan Coating on Mango (*Mangifera indica* L. cv. Kent) Fruits to Control Postharvest Deterioration and Increase Fruit Quality. *Coatings* **2022**, *12*, 83. https://doi.org/10.3390/ coatings12010083

Academic Editors: Lili Ren and Stefano Farris

Received: 6 December 2021 Accepted: 31 December 2021 Published: 12 January 2022

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**Copyright:** © 2022 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/).

caused by *Colletotrichum* species, which results in significant postharvest losses and restrictions on mango fruit storage, handling, and transportation [1]. Mango fruits are currently stored in a controlled (or modified) atmosphere to control postharvest decay and delay the ripening process [2]. In addition, fungicides are widely used to minimize postharvest decay and prolong the shelf life of mango fruits. However, fungicides are being limited as pathogens gain resistance to them, and consumers are concerned about the risks associated with fungicide residue [3]. Therefore, alternative and safe techniques are needed to slow the ripening of mango fruit and reduce postharvest decay.

Hot water (HW) treatment is the oldest and simplest form of heat treatment for controlling postharvest decay that uses a combination of appropriate temperatures (typically over 40 ◦C) and exposure durations to avoid fruit quality loss [4,5]. In a variety of fruits, HW treatment can effectively inhibit many important postharvest pathogens [6]. Treatment with HW at 55 ◦C for 35 min reduced the incidence of anthracnose in mango cultivars 'Tu Shien' [7], 'Kent', 'Keitt', and 'Tommy Atkins' [8]. Likewise, Dessalegn et al. [6], working on mango cv. 'Amba Kurfa', found that HW treatment at 51 ◦C for 3 min decreased the amount of anthracnose disease. Additionally, HW treatment has been identified as an elicitor for the activation of the defensive response in harvested fruits [9].

Although HW treatment helps prevent postharvest decay in mango fruits, there have been reports of detrimental impacts on the quality of the fruit, including accelerated fruit ripening, fruit skin browning, and mango fruit softening [10]. Based on the results presented above, it would be better to develop new treatments that may mitigate the negative effects of HW treatment, prevent postharvest decay, and delay the ripening process of mango fruits.

Several biopolymers, including chitosan, pectin, alginate, starch, carrageenan, zein, soy protein, and gelatin, have been applied in the development of coating formulations for fruit shelf life extension. Edible coating is simple, biodegradable, and ecologically friendly, it is a good alternative for synthetic materials, and it may be consumed by humans [11]. Edible coatings have been highlighted as a potential technology to prevent postharvest infection and the associated fungal degradation of fruits [12–14]. The application of fruit coatings has demonstrated technological advantages such as better appearance, antibacterial and antioxidant properties, and improved taste [15]. Some coatings have already been tested on tropical fruits, including avocados and mangoes, with different degrees of effectiveness. For instance, Daisy et al. [16] found that gum Arabic (15%) preserved ascorbic acid and carotenoids in 'Apple' mango kept at room temperature for 15 days. Likewise, Moalemiyan et al. [17] reported that coating mango with pectin, sorbitol, monoglyceride, and beeswax combinations resulted in an increased shelf life, especially at decreased color development, weight loss, softness, and acid production compared with the control. In addition, a study by Bambalele et al. [15] reported that moringa leaf extract (1%) and carboxymethyl cellulose (1%) maintained the ascorbic acid and membrane integrity and delayed fruit softening in 'Keitt' mango after storage at 10 ◦C for 21 days.

Chitosan is one of the polysaccharide-based coatings. It is a high molecular weight cationic polysaccharide commonly formed by the alkaline deacetylation of chitin found in the crustacean exoskeleton, fungal cell walls, and other biological components [18]. It is composed of poly-1,4-β-D-glucopyranos amine and 2-amino-2-deoxy-(1->4)-β-Dglucopyranan. Chitosan has great potential as a film or a biodegradable edible coating for food packaging [19], with good biocompatibility, nontoxicity [18], and film-forming characteristics [20]. Chitosan has been used on a variety of fruits such as mango as a semipermeable coating to prolong storage life and decrease postharvest decay [21,22]. The application of chitosan in mango [23] has been demonstrated to enhance fruit quality, keep firmness, decrease ethylene production and mold contamination, delay the ripening process and senescence, and decrease color changes.

The combination of edible coating and HW treatment has been examined to maintain fruit quality and minimize unanticipated damage [24,25]. Keeping fruit quality and controlling postharvest decay in fruit cannot be entirely controlled by HW treatment or

chitosan treatment alone. For several reasons, combining HW and chitosan may have a synergistic impact on fruit: (1) The fruit surface may be partly disinfected by the HW treatment; (2) Pathogen resistance may be induced by chitosan; (3) Combining HW with chitosan can improve the effectiveness of postharvest disease control. In the previous studies, researchers used a combination of these two treatments on sweet cherry [26], papaya [27], and dragon fruit [28], and the results indicated that the combination treatment reduced postharvest disease and preserved fresh fruit quality better than HW or chitosan.

Although HW and edible coatings have been intensively investigated in recent years, the combined effect of these treatments has received less attention, especially on mango fruits. To our knowledge, there are no published data about the use of hot water treatment and chitosan coatings for maintaining fruit quality and prolonging the shelf life of "Kent" mangoes. Thus, our research aimed to see if HW treatment, followed by chitosan coating, may help keep mango fruit fresh, maintain quality indices, and extend the shelf life of "Kent" mangoes while also reducing postharvest decay. In addition, HW treatment-induced resistance in mango fruit was also investigated to better understand the defense mechanism of HW treatment against pathogens during storage.
