**1. Introduction**

Papaya (*Carica papaya* L*.*) is a perennial plant with a rapid growth, and it provides fruits for more than twenty years [1]. Papaya is considered one of the most important fruits worldwide because of its high contents of ascorbic acid, provitamin A, calcium, and carotenoids [2]. Mexico is the third largest producer worldwide of this fruit with 951,922 t in 2016 [3]. It is a climacteric fruit that shows short life after harvest, and it is susceptible to fungi contamination mainly by *Colletotrichum gloeosporioides* responsible for anthracnose disease, which reduces its shelf life, severely depreciating the market value of the fruit [4]. Papaya maturation after harvest involves various metabolic processes; first, papaya is mature, hard and inedible, and after a few days of being harvested, the edible fruit becomes sweet, soft, and aromatic. However, an uncontrolled fruit maturation process can cause pulp softening, changes in skin and pulp color, and strong aroma development; all this is related to increased ethylene production causing postharvest losses [5].

Edible coatings have emerged as a new technology for safe maintenance and the improvement of quality of fresh fruits by their application immediately after harvest to reduce water loss and mechanical and microbial damage, prevent favorable volatiles losses, and delay senescence [6]. Coatings used for fruits preservation must have precisely balanced gas permeability properties for a normal exchange of CO2/O2, limited permeability to water vapor to inhibit the escape of moisture, antimicrobial activity, and good adhesion to product surface [7]. According to their composition, edible coatings may be classified into three groups: polysaccharides, proteins, and lipids as their major compounds. Coatings based on polysaccharides are characterized by providing a minimum moisture barrier, whereas gas barrier properties induce desirable atmosphere modification and increased shelf life without creation of severe anaerobic conditions. Polysaccharides commonly used in edible coatings are starch, dextrin, pectin, cellulose and its derivatives, chitosan, alginate, carrageenan, gellan, etc. [8].

Chitosan is a biopolymer obtained from chitin deacetylation in an alkaline medium, consisting of β-(1–4)-2-acetamido-D-glucose and β-(1–4)-2-amino-D-glucose units [9]. It is biodegradable, biocompatible, and nontoxic, and shows antimicrobial activity and good film-forming properties. Applied as a coating on fruit and vegetable surfaces, it reduces respiration rate by regulating gases permeability [10]. Starch is frequently used in edible coatings preparation due to its chemical, physical, and functional characteristics [11]. It comprises two structures, one linear (amylose) and the other branched (amylopectin), that are assembled naturally in granular form (size of ~1 μm to 100 μm) [12]. Amylose tends to be orientated in parallel due to its linearity, resulting in hydrogen bonds between hydroxyl groups reducing polymer affinity for water and allowing films and gels formation [11]. Other components may be added to edible coatings to extend their applications, such as antimicrobial agents, antioxidants, texture modifiers, dyes, flavorings, nutrients, spices, surfactants, emulsifiers, and plasticizers, among others [13].

Ethyl lauroyl arginate (LAE) is a generally recognized as safe (GRAS) cationic surfactant that is water soluble and provides antimicrobial activity against fungi and Gram-positive and Gram-negative bacteria, due to its cationic surfactant nature. It specifically affects the negatively charged microbial proteins of cell membranes or enzymatic systems, causing their denaturation and leading to microbial inhibition or death [14]. Nisin is a bacteriocin from *Lactococcus lactis* subsp*. lactis* considered as GRAS that is used in the food industry as a preservative and consists of unusual and distinctive amino acids post-translationally modified: lanthionine bound to a thioether, 3-methylanthionine, 2,3-didehydroalanine, and 2,3-didehydrobutirin. Gram-positive bacteria such as *Mycobacterium*, *Staphylococcus* spp., *Clostridium* sp., *Listeria* sp., and *Bacillus* sp. are very sensitive to this antibiotic [15]. The objective of this work was to evaluate the effect of an edible coating based on chitosan and oxidized starch on the shelf life of *Carica papaya* L., and the physicochemical and antimicrobial properties of the active coating.

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

#### *2.1. Materials*

Medium molecular weight chitosan from shrimp shells (375 kDa, >75% deacetylation), glycerol (≥99.5%), and Tween 80 were purchased from Sigma-Aldrich (St. Louis, MO, USA); lactic acid (85%) was obtained from Fermont (León, Mexico). Oxidized starch was supplied by Ingredion (San Juan del Río, Mexico), LAE was a gift from Lamirsa (Barcelona, Spain). Violet red bile agar, papa dextrose agar, plate count agar, and casein peptone were acquired from BD Bioxon (Distrito Federal, México). Papayas (*Carica papaya* L.) were harvested from Tecoman, Colima, Mexico.
