**1. Introduction**

Different methods have been used to reduce food losses and extend the shelf life of fresh fruits and vegetables including conventional refrigerated storage, modified atmosphere packaging (MAP), and controlled atmosphere storage [1]. Active packaging is also a method that has been used to reduce post-harvest losses, and it consists of using synthetic packages with variable active functions such as oxygen scavengers, carbon dioxide absorbents, and ethylene absorbents. Moreover, edible film and coating is a preservation method that has become very popular in the last few decades due its effectiveness in the extension of the post-harvest shelf life of the fresh produce [2].

An edible coating is a thin layer of adhesive material that must be applied on the surface of the food product in a liquid form by brushing, spraying, or complete immersion, forming a protective coating that can be consumed together with the food product, while an edible film is a self-standing material that can be used to wrap the food products or cover them. Edible films and coatings extend the shelf life of fresh produce and protect them from the external environmental damages in addition to the physical, chemical, and biological changes [3]. Research studies have shown that edible films can act as natural barriers against moisture loss, gas exchange, lipids, and flavor compounds losses [4]. Additionally, edible coatings create an internal atmosphere when applied on the surface of the fresh produce, which reduces the respiration and transpiration rates and delays quality deterioration and ripening [5].

Research is focused today on developing eco-friendly and biodegradable food packaging to replace synthetic packaging materials [6]. In the past several decades, scientists have been able to identify different types of natural polymers that can be used in the production of edible films and coatings. These polymers can be derived from multiple sources such as plants, animals, and microorganisms and are divided into three different categories. The hydrocolloid category including proteins and polysaccharides; the lipid category; and composites [3]. Composites are made of a combination of hydrocolloids and lipids to produce edible films and coatings with shared advantages from two different categories [5]. The thermo-physical and mechanical spectral properties of these special composite materials have also been extensively studied to determine their suitability for different applications with the desired adhesive, water vapor and gas permeability control respiration, and transpiration rates of perishable produce [7,8].

Polysaccharides are polymers of monosaccharides connected to each other by glycocidic bonds and used in the production of edible films and coatings. Polysaccharides are suitable for use in the coating of fruits and vegetables due to their effective gas barriers. Their selective permeability to O2 and CO2 gases allows for the creation of a modified atmosphere. Other advantages are their low cost and their high availability since they are mainly found in plants and seaweeds. However, polysaccharides are hydrophilic with a high-water vapor permeability [9]. Cellulose derivatives, starches, alginates, pectin, chitosan, pullulan, and carrageenan are the most commonly used polysaccharides in the production of edible films and coatings [3].

Pullulan is a water soluble microbial exopolysaccharide obtained from the yeast-like fungus *Aureobasidium pullulans* and can be used in the production of thin, colorless, odorless, and tasteless edible films [6]. Moreover, alginates are polysaccharides naturally produced by brown marine algae or seaweeds such as *Laminaria hyperborean* and *Macrocystis pyrifera*. Alginates can also be produced by some bacteria such as *Azotobacter vinelandii,* which were first discovered in 1881. Alginates are considered as generally recognized as safe (GRAS) by the U.S. Food and Drug Administration (FDA) and were used as thickening agents and stabilizers. In addition, they are an approved food additive by the European Commission (EC). Water soluble sodium alginate is commonly used in the making of edible films and coatings and should be mixed with divalent ions to reduce its water solubility. The addition of divalent ions such as calcium allows for the formation of divalent salt bridges due to the binding of calcium ions between two chains, which provides rigid and dense gels [10].

According to the Food and Agriculture Organization report (FAO, 2011), over 4.5 million tons of strawberries were harvested each year around the world, mainly in Spain, Egypt, the USA, and Mexico [11]. Several studies have focused on strawberry fruits due to their high perishability. The effect of a chitosan-based edible coating on the shelf life extension of strawberry cut fruits was reported [12]. Additionally, the effect of a gellan-based edible coating on the quality parameters of strawberry cut fruits was studied. Their soft texture makes them more susceptible to mechanical damage and quality loss during post-harvest storage [13].

With the increased interest in ready to eat and nutritious snacks, cut fruits have become more popular and widely available in supermarkets, cafeterias, airline catering, universities, and schools [10]. Cut fruits and vegetables are wounded tissues with a shorter shelf life than the intact fruits due to the induced mechanical damages. The internal tissues in cut fruits are exposed to the external environment, which increases respiration and transpiration rates, oxidative browning, and microbial growth [14].

Minimally processed fruits and vegetables usually show uneven responses to edible coatings due to the differences in their tissue structures, surface texture, turgidity, and metabolic activity. However, a successful adhesion of the coating solution on the fruit surfaces can extend their shelf life and provide a fresh-like appearance [15].

Several studies have been carried out to evaluate the best coating composition to extend the shelf life of cut fruits. A whey protein-calcium caseinate-based edible coating has been credited with a beneficial effect in preventing oxidative browning in apple and potato cuts. However, whey proteins have low mechanical properties, which makes them not very suitable for use on the surfaces of fresh fruit and vegetables [14]. It has also been reported that a methyl cellulose and sodium alginate-based edible coating extended the shelf life of peaches stored at 15 ◦C, up to 21 and 24 days compared with 15 days in the control samples. This edible coating reduced the respiration and transpiration rates and delayed the increase in total soluble solids content [7,8]. It was also reported that the chitosan-based edible coating significantly reduced the weight loss of fresh strawberries and red raspberries during storage at 2 ◦C and 88% relative humidity (RH) compared to the control [16]. The sodium alginate composites provide some additional advantages because of their ability to complex with calcium chloride [17]. Calcium chloride has been widely used as a texture firming agent for fruits and vegetables for a long time since it can form complexes with low methoxyl pectin present in the produce tissue, thereby facilitating texture firming [18,19]. A similar benefit can potentially be realized with the combination of sodium alginate-calcium chloride combinations [17].

The objective of this study was to evaluate the effect of a sodium alginate-calcium chloride-based edible coating on the quality parameters and the shelf life extension of cut strawberry fruits stored for two weeks at 4 ◦C was evaluated. The available information of edible coating for cut fruits is very scanty.
