Effect of emulsifier hydrophilic-lipophilic balance (HLB) on the release of thyme essential oil from chitosan films

Effect of Chitosan Coatings with Cinnamon Essential Oil on Postharvest Quality of Mangoes

Mango (Mangifera indica Linn.) is a famous climacteric fruit containing abundant flavor and nutrients in the tropics, but it is prone to decay without suitable postharvest preservation measures. In this study, the chitosan (CH)-cinnamon essential oil (CEO) Pickering emulsion (CH-PE) coating was prepared, with cellulose nanocrystals as the emulsifier, and applied to harvested mangoes at the green stage of maturity. It was compared with a pure CH coating and a CH-CEO emulsion (CH-E) coating, prepared with the emulsifier Tween 80. Results showed that the CH-PE coating had a lower water solubility and water vapor permeability than the other coatings, which was mainly due to electrostatic interactions, and had a better sustained-release performance for CEO than the CH-E coating. During mango storage, the CH-PE coating effectively improved the appearance of mangoes at 25 °C for 12 d by reducing yellowing and dark spots, and delayed water loss. Hardness was maintained and membrane lipid peroxidation was reduced by regulating the activities of pectin methyl esterase, polygalacturonase, and peroxidase. In addition, the nutrient quality was improved by the CH-PE coating, with higher contents of total soluble solid, titratable acid, and ascorbic acid. Therefore, the CH-PE coating is promising to comprehensively maintain the postharvest quality of mangoes, due to its enhanced physical and sustained-release properties.

Functional polysaccharide-based film prepared from chitosan and β-acids: Structural, physicochemical, and bioactive properties

β-Acids are natural antibacterial and antioxidant ingredients, obtained from supercritical CO₂ hop extract. In this study, β-acids/chitosan complex films were prepared using the casting method. Complex films were characterized using scanning electron microscopy (SEM), atomic force microscope (AFM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction analysis (XRD). Structure analysis revealed that β-acids can be successfully combined with the chitosan matrix. Mechanical tests demonstrated that the tensile strength of the films showed a significant upward trend (1.9 MPa to 9.6 MPa) with increase in β-acids content (0.1%-0.3%). Interestingly, the chitosan-based films showed excellent UV barrier capability below 400 nm. The release of β-acids from the film followed Fickian diffusion (n < 0.45). In addition, the complex films inhibited the growth of five food-borne pathogens (Escherichia coli, Staphylococcus aureus, Bacillus subtilis, Salmonella enteritidis and Listeria monocytogenes). This study highlights the promising nature of composite film as a desirable alternative for active packaging.

Functional Properties of Biopolymer-Based Films Modified with Surfactants: A Brief Review

An increase of environmental awareness recently has increased the interest of researchers in using of biopolymer-based films. The films have been prepared extensively by utilizing starch, carboxymethyl cellulose, chitosan, protein, gelatin, carrageenan, alginate, pectin, guar gum and pullulan. They are typically modified with surface-active agents (surfactants) such as glycerol monostearate, sucrose ester, sodium stearoyl lactate, sodium dodecyl sulfate, ethyl lauroyl arginate HCl, Span 20 to 80, Tween-20 to 80 and soy lecithin for improving the functional properties of the films. In this brief review, two types of biopolymer-based films that prepared through casting method were categorized, specifically solution- and emulsion-based films. The four types of surfactants, namely non-ionic, anionic, cationic and amphoteric surfactants that are regularly used to modify biopolymer-based films are also described. The functional properties of the films modified with different types of surfactants are briefly reviewed. This study enhances the attraction of researchers in biopolymer-based films and the improvement of new concepts in this niche area.

Development and characterization of corn starch/PVA active films incorporated with carvacrol nanoemulsions

An active film was prepared by corn starch (CS), polyvinyl alcohol (PVA) and carvacrol nanoemulsions (CNE). The microstructure and properties of CNE/corn starch/PVA (CNE/CSP) films were characterized and investigated. Scanning electron microscopy (SEM) revealed the uniform distribution of CNE and discontinuity of the film matrix. Fourier transform infrared (FT-IR) and rheological analysis indicated that CNE could weaken molecular interaction of the film matrix. X-ray diffraction (XRD) show that the films are amorphous and CNE has no effect on crystal structure of the films. Incorporation of CNE significantly increased the tensile strength, Young's modulus, elongation at break, barrier (water vapor and ultraviolet), antioxidant and antifungal activity. With the CNE incorporated, the optimal tensile strength, Young's modulus, elongation at break and antioxidant activity of the films can reach 12 MPa, 11 MPa, 133%, 81%, respectively. Minimum water vapor permeability was 3.1 × 10^-12 gd^-1m^-1Pa^-1. Notably, films incorporated with CNE (≥20%) had good DPPH free radical scavenging ability (>50%) when stored up to 6 days. Films with 25% CNE exhibited excellent antifungal activity against Trichoderma sp. and its inhibitory zone was 47 mm. Overall, the CSP films loaded with CNE (>15%) could be used as food packing materials with good antioxidant and antimicrobial activities.

Properties and characterization of thyme essential oil incorporated collagen hydrolysate films extracted from hide fleshing wastes for active packaging

In this investigation, collagen hydrolysate (CH) films extracted from hide fleshing wastes were successfully developed using solvent casting method by incorporating different concentrations of thyme essential oil (TO) (2%, 4%, 6%, and 8%) into the CH. Depending on the concentration of TO, thickness, tensile strength (TS), elongation at break (EAB), film solubility (FS), color, opacity, light transmittance, and thermal properties varied. Addition of TO resulted in the increases in the thickness, EAB (%), and light barrier performance of CH-TO films while there was a significant decrease in TS and FS of the CH films (p ≤ 0.05). According to our findings, the increment of TO content induced higher lightness and yellowness but lower redness values compared to CH film. Fourier-transform infrared spectroscopy was conducted to determine the molecular changes and interactions between CH extracted from hide fleshing wastes and TO. In order to analyze the thermal behavior of the films, differential scanning calorimetry analysis was conducted. Moreover, the structure-property relationships of CH and TO were examined by scanning electron microscopy and a reduction in the compact and homogenous structures of the films containing TO was observed. Promising results have been obtained showing that CH-based films can be used for active packaging purposes, thereby contributing to a significant reduction in the environmental impact of both leather solid waste and plastic packaging materials.

Formulation of black pepper (Piper nigrum L.) essential oil nano-emulsion via phase inversion temperature method

Recent trends in preservation of processed foods involve the use of natural compounds, rather than chemically synthesized additives, to simultaneously confer antimicrobial properties and prevent fat oxidation. In this regard, black pepper essential oils, due to its diversity in biological activities, have been increasingly popular. The compounds are often used in relatively low amounts and in the form of nanoparticles to permit well blending into foods or uniform dispersion on the surface of fresh meat. The purpose of this study is to determine experimental parameters of a nano-emulsion formation process from black pepper essential oil via the phase inversion temperature (PIT) technique. The study results showed that the system achieved the optimal nano-emulsion under following condition: the ratio by weight of water: Tween-80: oil = 86:9.7:4.3, the stirring speed of nano-emulsions at 500 rpm for 45 min (heating at 75°C for 30 min and then rapidly cooling at 5°C for 15 min).

Enhancement of UV absorbance and mechanical properties of chitosan films by the incorporation of solvolytically fractionated lignins

In this work, an effective sequential organic solvent extraction of kraft and organosolv lignins was carried out to separate lignin into more homogeneous fractions with specific properties. The selected solvents were ethyl acetate, ethanol, methanol, and acetone in that order. Fractions were analysed in terms of their yield, molecular weight, S/G ratio, and phenolic hydroxyl groups content. The incorporation of lignin fractions into the chitosan was aimed to increase the UV absorbance and the mechanical resistance of the chitosan films, which would provide good properties for applications in the packaging field. Films were analysed in terms of UV-vis absorption spectra, tensile strength, as well as colour changes. Results showed a significant increase in the absorbance of UV-A and UV-B with the addition of lignin fractions, mechanical properties showed an increase in the ultimate tensile strength in case of kraft fractions, while organosolv fractions do not affect tensile strength significantly.