**1. Introduction**

Guava (*Psidium guajava* L.) is a popular fruit with a climacteric nature feature. It has a relatively short shelf life (3–4 days) at tropical ambient temperature (28 ± 2 ◦C), due to its

**Citation:** El-Gioushy, S.F.; Abdelkader, M.F.M.; Mahmoud, M.H.; Abou El Ghit, H.M.; Fikry, M.; Bahloul, A.M.E.; Morsy, A.R.; A., L.A.; Abdelaziz, A.M.R.A.; Alhaithloul, H.A.S.; et al. The Effects of a Gum Arabic-Based Edible Coating on Guava Fruit Characteristics during Storage. *Coatings* **2022**, *12*, 90. https:// doi.org/10.3390/coatings12010090

Academic Editor: Lili Ren

Received: 2 December 2021 Accepted: 7 January 2022 Published: 13 January 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**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/).

physiology, disorder, postharvest infection, and aging [1,2]. The stability of guava could be influenced by numerous factors, such as storage temperatures, relative humidity, packaging materials, and coating nature [3,4]. Producers of guava fruits store them in traditional packs, such as paper and/or plastic materials. Although these packaging materials present some merits, they could cause severe environmental difficulties because they are non-recyclable and nonedible resources [4–6].

Physiologically, guava is a climacteric fruit with high inhalation and transpiration degrees that are analogous to different products such as bananas [5] and mushrooms [7]. This creates the need to develop novel technologies for extending its shelf life [8], providing better storage conditions, and enhancing its visual features.

The edible coatings are applied directly on the surface of the fruit, consisting of thin membranes, invisible to the naked eye. They can carry natural additives and are important in extending the shelf life of foods, as they enhance the protective action of the fruit epidermis in preventing water loss, color changes, mechanical lesions and even microbial deterioration, and generally give surface glossy appearance [3,9]. Such technology has exposed a great possibility with low cost and proper features for related usage in food plants.

Previously, edible coatings were fabricated from biomaterials—namely polysaccharides, proteins and lipids—and their results were utilized to formulate edible coatings [10]. Formerly, coating materials efficiently prolonged a fruit's shelf-life, and increased the consumers' health and environment. Numerous studies have reported the efficiency of edible coatings in expanding the shelf-life of different kinds of fruits by decreasing their weight loss [10,11], respiration [12,13], oxidative reaction rates [14], and physiological disorders [15]. Edible coatings are an excellent alternative to chemical preservation [16].

Among the natural polymers used to formulate edible coatings, gum Arabic (GA) and cactus pear extract have been deemed the most promising materials, mostly because their high accessibility, low price, and good performance. However, their high hydrophilicity permits H2O to easily form. GA is one of the ecological biopolymers acquired from the branches and stems of Acacia trees (*Acacia* spp.). It is comprised of rhamnose, galactose, arabinose, and glucuronic acid with Ca, Mg, and K ions [17,18]. In addition, GA is commercially and securely utilized as a food additive, due to its film shaping, emulsification, and encapsulation attributes [18,19].

Numerous studies have been conducted on the application of GA for nullity purposes, such as its ability to postpone the physicochemical alterations of bananas during cold storage [20], and minimize the fungal infection of anthracnose on banana and papaya fruits [20]. GA coatings have efficiently kept the antioxidative polyphenols of tomatoes [21] and papayas [22], and lowered browning, vitamin C, and the polyphenols of cold-stored mangos [23]. Moreover, GA-coating significantly decreases weight loss, chilling damage, membrane leakage, and decay prevalence, with slight increases in total soluble solids, pH, and sugar [24,25].

*M. oleifera* is widely in demand for its nutritional and medicinal properties, due to its content of vitamins B and C, amino acids, crude protein, and its low anti-nutritional and antimicrobial agents with film organic and shelf-life-boosting properties [26–28]. Moreover, its extracts have been utilized to formulate the coating that effectively preserves the postharvest quality of citrus fruit [29]. Moringa extract maintains postharvest quality, keeping and elongating the shelf life of avocado fruit by lowering respiration, ethylene production rates and higher firmness during storage [28,30,31]. It also significantly inhibits (30–33%) radial mycelial growth of the pathogen with a combination of GA edible coatings with moringa leaf extract. There is evidence for the incorporation of moringa leaf extract with edible coatings improving antimicrobial activity [32,33].

The mucilage films from the cactus pear plant prolong shelf life and maintain guava quality attributes. Further research is wanted to realize whether mucilage is possible for use as an edible film under cold storage [28]. In guava and cactus pear, the film prolonged the fruit's skin color and retained superior total soluble solids concentration (TSSC), firmness (F), and dry matter concentration (DMC), lowered the fruit's weight loss and prolonged its skin color. Firmness, TSSC, and DMC of fruit were comparable among treatments [34].

Henna (*Lawsonia inermis*) leaf extracts are a natural plant product with a projecting function against pathogens. Their expansion and propagation inhibit toxic activity [35].

There were no experiments undertaken to estimate the impact of combining the GA with each of the leaf extracts of Moringa, cactus pear, and Henna plants, in prior ediblecoating investigations. Therefore, this study aimed to investigate the effects of edible coatings based on GA with cactus pear, moringa, and Henna leaf extract on the storability and shelf life of guava.

### **2. Materials and Methods**

### *2.1. Fruit Materials*

The guava trees were grown in a commercial orchard in El-Qalubia Governorate, Egypt (latitude, 30◦17" N and longitude, 31◦20" E). The trees were about 12 years of age and planted at a space of 5 × 5 M apart in loamy clay soil under an immersion irrigation system and subjected to all ideal agriculture traditions. The maturity stage (yellowishgreen), was the second week of August based on Mercado-Silva et al. [36], the trees and guavas were similar in size and free of obvious signs of infection.

## *2.2. Postharvest Treatments and Storage*

The current study was performed during two seasons, 2020 and 2021, at the laboratory of the Department of Horticultural Crops Technology, National Research center, Giza, Egypt. Fine-feature guava fruits of the "Maamoura" cultivar, that were deep green color, uniform size, firm, and free from blemishes and mechanical damage, were harvested.

### *2.3. Preparation of Plant Extracts*

Cactus pear stems were skinned and chopped. Samples were steamed with H2O in the ratio of 1:10 in an autoclave at 160 ◦C for 1 h. The boiled pulp was filtered and cooled. The slurry was centrifuged for 10 min and the supernatant gained was utilized as a coating substance (cactus pear mucilage). The filtrate (pulping liquor) was also utilized as a coating solution. Polyethylene glycol of molecular weight 2000 as plasticizer was mixed to the coating solution 5% *w*/*v*. The pH value of this solution was modified at 7, using small drops of ammonia solution.

Moringa leaf extract was made by soaking 100 g of air-dried moringa leaves in 1 L of dH2O for 24 h. Then, it was diluted after being filtered with H2O. Concentrations of 20% were prepared by dispersing 20 mL of filtered solution and 3 mL glycerol in 100 mL dH2O in a beaker.

GA powder of food-grade was acquired from Sigma Co., Cairo, Egypt. GA solution at 10% (*w*/*v*) was arranged by dissolving 500 g of GA powder in 5 L of dH2O. The solution of GA was agitated with low heat at 40 ◦C for 60 min, using a hot plate with a magnetic stirrer (Model: 502P-2 USA), then filtered using a muslin cloth to eliminate impurities and any nameless materials. After cooling the solution to 20 ◦C, glycerol monostearate at 1% was mixed as a plasticizer to increase the intensity and elasticity of the coating solution. The pH of the solution was altered to 5.6 with 1 N NaOH using a digital pH-meter (Model: AD1000, Bucharest, Romania). Then, 3% Henna was formulated; we soaked 100 g of air-dried henna leaves in 1 L of dH2O for 24 h. Then, it was diluted after being filtered with dH2O. A concentration of 3% was prepared by dispersing 3 mL of filtered solution and 3 mL glycerol in 100 mL dH2O in a beaker.

### *2.4. Treatment of Guava Fruit*

A total of 600 clean complete fruits were chosen and haphazardly allocated into 5 treatments with 3 replicates (40 fruits/replicate) and expressed as control: 10% of GA; 10% of GA + 10% of moringa leaves extract; 10% of GA + 10% of cactus pear stems extract; and 10% of GA + 3% of Henna leaves extract. All guava fruits were dipped in the different

extract solutions for 2.5 min. Then, these fruits were dropped in 10% GA solutions for another 2.5 min. After dropping treatments, the fruits were allowed to dry for 60 min at RT by an electric fan. After that, the fruits in each treatment were wrapped in foam sheets enclosed with punched polyethylene layers with a thickness of 0.04 mm and then boxed in cardboard boxes with measurements of 35 × 25 × 10 cm. All untried boxes were kept at 7 ± 1 ◦C and 90 ± 5% RH for 24 days. the physical measurements were analyzed at harvest time and then every 7 days they had breaks from the cold-storage time.

### *2.5. Determination of Fruit Physical Properties*

Fruit weight loss (%) was estimated by the next formula:

$$\frac{\text{Fruit weight before storage} - \text{fruit weight after each period of cold storage}}{\text{Fruit weight before storage}} \times 100 \quad \text{(1)}$$

Fruit decay (%) was documented every 8 days of cold storage by calculating the number of rotten fruits owing to fungus, or any microorganism's infection, and expressed as a percentage of the original number of kept fruits using the next equation:

$$\frac{\text{Number of decayed fruit at specific storage period}}{\text{Initial number of stored fruit}} \times 100\tag{2}$$

Marketable fruit (%) was calculated by the next formula:

$$\frac{\text{Number of sound fruit at specific storage period}}{\text{Initial number of stored fruit}} \times 100\tag{3}$$

Fruit firmness was determined in three guava fruits per replicate at two equatorials at differing sites, to measure the penetration force using a hand-held fruit firmness tester (FT-327, Valencia, Italy) fortified with an 8 mm cylindrical stainless steel plunger tip (Watkins and Harman, 1981). Two senses were shown on each fruit flesh after peeling. The firmness value was calculated in terms of kilogram-force (kgf) and data was assessed as Newton (N).

### *2.6. Fruit Chemical Characteristics*
