**1. Introduction**

The strawberry is among the most popular fruits worldwide, and is thus referred to as the "fruit queen". Strawberries possess high levels of antioxidant activity and vitamin E, vitamin C, β-carotene, and phenolic compounds such as anthocyanins, which benefit consumer health [1]. However, strawberries are perishable and have very short postharvest lives (around five days at 4 ◦C) because of their susceptibility to mechanical damage, physiological deterioration, and lack protective rinds, which can exhibit symptoms of pathogens [2]. Previous research has reported that Botrytis cinerea determines strawberry shelf lives, so the inhibition of microbial growth can prolong sellable periods [3]. Some researchers have used fungicides to prevent postharvest rot by spraying them on the strawberries several times. However, the presence of residues limits the broad use of fungicides [4]. Controlling CO2 and O2 levels can also reduce the incidence of strawberry decay. Modified atmospheres with low O2 and high CO2 concentrations are very effective at inhibiting microbial growth and reducing the decay of fresh produce, including strawberries [5]. However, some experiments have shown that prolonged exposure of strawberries to high CO2 concentrations can cause the development of unwanted flavors [6]. To slow metabolic processes and reduce deterioration prior to transport, low temperatures are widely used to reduce spoilage and extend the lives of fresh fruits and vegetables. However, it is inconvenient and expensive to use transportable freezers or ice to control strawberry temperatures.

Biologically active packaging has become an effective method of controlling fungal decay, and several studies have investigated the potential of natural polymers for food protection. Most of these types of macromolecules can be processed into films or coated onto fruit surfaces. Owing to their high (CO2/O2) permselectivities and ability to act as partial moisture barriers, these films can reduce fruit respiration and transpiration rates [7]. Biologically active packages include polysaccharides such as chitosan (CH). CH is a linear polysaccharide that consists of a low acetyl substituted form of chitin and a natural carbohydrate copolymer. CH offers several advantages such as biodegradability, broad availability, and non-toxicity [8]. CH also has good anti-fungal activity against several postharvest pathogens, particularly the grey mold that is one of the main causes of strawberry deterioration and postharvest decay [9]. Moreover, studies have demonstrated that CH can be mixed with other polymers to increase the shelf lives of fresh strawberries [10]. The use of liquid CH with strawberries would be effective, but would require high proportions, which would result in bad flavors, oily textures, and the potential for allergic reactions after consuming large amounts [11].

Unfortunately, pure CH films have high water vapor permeabilities and poor mechanical properties, and so cannot act as inert barriers between the product and the environment. In order to fulfill all necessary fruit packaging requirements, several methods of mixing CH with other polymers such as polylactic acid, poly(lactic-co-glycolic acid), polyethylene, etc. in composites have been developed. Poly(vinylalcohol) (PVA) is a hydroxyl-rich, semi-crystalline polymer. It can be processed using aqueous methods, and has several interesting physical properties that arise from the presence of hydroxyl groups and hydrogen bond formation. It is non-toxic, biocompatible and biodegradable, and offers good mechanical properties and chemical stability. Moreover, PVA/CH blends have good physical and antibacterial properties because of specific intermolecular interactions between PVA and CH. PVA/CH blend films represent a better choice for strawberry packaging than coating CH on the fruit surface or refrigeration. These blends are especially appropriate for transportation due to their good mechanical and oxygen barrier properties [12].

In order to prolong the shelf life of strawberries and reduce the hazard of ingesting chemical reagents, edible coating materials have been widely studied. PVA/CH blend films with various CH contents on fresh strawberries were determined in this study. The films were characterized based on scanning electron microscopy (SEM), mechanical tests, oxygen permeability (OP) and water vapor permeability (WVP). Non-packaged strawberries and strawberries packaged with four different films were compared and analyzed in terms of color, weight loss, decay percentage (% decay), firmness, soluble solid content (SSC), titratable acidity (TA), and sensory characteristics.

#### **2. Results and Discussion**

#### *2.1. SEM Analysis*

The weight ratios of PVA:CH of 80:20, 75:25, and 70:30 were denoted as PVA/CH-2, PVA/CH-2.5, and PVA/CH-3, respectively [13]. The morphologies of the PVA film, PVA/CH-2, PVA/CH-2.5, and PVA/CH-3 are seen clearly in the SEM images (Figure 1). PVA film presents good structural integrity, smoothness, flatness, and crack-free states. CH shows even distributions in PVA/CH-2, and PVA/CH-2.5 films, demonstrating the high compatibility of the two polymers and a compact structure lacking phase separation [14]. No air bubbles, pores, cracks, or droplets are observed, further confirming the high compatibility of the two polymers, similar to that observed by Tripathi et al. [15]. However, when the CH content is increased, it appears visibly as rough areas. The rough areas of the PVA/CH-3 show scaly structures. The roughness is because the CH molecules disrupt the compact structure of the PVA matrix. The incorporation of CH minimizes the free volume of the matrix, condensing the microstructure of the film [16]. These structural properties of the dried CH matrices may offer a larger surface area, and therefore, better matrix–solvent interactions, allowing for faster solvent uptake. This leads to dissociation, with the most obvious result of scaly structures [15].

**Figure 1.** Scanning electron microscopy (SEM) morphologies of pure Poly(vinylalcohol) (PVA) film and different PVA/CH films.

#### *2.2. FT-IR Analysis*

Figure 2 presents the characteristic attenuated total reflectance–Fourier transform infrared (ATR–FTIR) spectra corresponding to CH, PVA, and PVA/CH-2.5. For PVA film, the bands at approximately 3455 cm−<sup>1</sup> and 1630 cm−<sup>1</sup> are assigned to the stretching and bending vibrations of the hydroxyl group, respectively [17]. The band corresponding to asymmetric stretching vibrations of the methylene group occurs at approximately 2933 cm−1. The band at approximately 1096 cm−<sup>1</sup> corresponds to C–O stretching in the acetyl groups present on the PVA backbone [18]. Notably, the bands of CH are assigned to the saccharide structure at 1166 cm−1, 1077 cm−1, and 1018 cm−1. The strong amino characteristic bands at 3430 cm<sup>−</sup>1, 1660 cm−1, and 1290 cm−<sup>1</sup> are assigned to hydroxyl stretching, amide I, and amide II, respectively [19]. The spectra of PVA/CH-2.5 indicates clear increases in the intensity of the band at 3380 cm−1, attributed to hydroxyl group stretching vibrations of PVA, with a secondary amide group of CH. The band at approximately 1077 cm−<sup>1</sup> indicates the presence of a hydroxyl group with polymeric association and a secondary amide. The band at 1450 cm−1, appearing for weight fractions of 25% CH, is assigned to C=N pyridine ring vibrations. This confirmed the complexation between the PVA and CH [19]. For all PVA/CH films, the characteristic bands are similar to those of PVA; strong amorphous carbonyl stretching vibrations of PVA remain constant in all films. The peak intensity increases with increased CH contents. The characteristic shape of the CH spectrum is changed, and the peak shifts to a lower frequency range because of hydrogen bonding between the hydroxyl groups of PVA and hydroxyl, or amine groups of CH in the blended films [20]. Kim et al. also reported that the crystallization-sensitive band of PVA at 1140 cm−<sup>1</sup> was observed with a similar intensity without significant changes in frequency for PVA and blended films [21].

**Figure 2.** Attenuated total reflectance–Fourier transform infrared (ATR–FTIR) spectra of PVA, CH, and PVA/CH-2.5 films.
