A review of cellulose nanomaterials incorporated fruit coatings with improved barrier property and stability: Principles and applications

A crosslinked and percolation network alginate coating for litchi prevention

The short shelf life of Litchi is due to its rapid metabolism after being harvested. Refrigeration is not a suitable method for preserving litchi, as the browning process of litchi that has been cryogenic will accelerate when it is brought to room temperature. This study introduces an alginate-based coating as a solution to control the post-harvest metabolism of litchi. The coating achieves this by simultaneously establishing crosslink and percolation networks, both of which act as barriers. The percolation network is created using rod-like cellulose nanocrystals, which possess excellent percolation properties. This network effectively reduces moisture loss. Compared to the control group, the coated litchi exhibited a 38.1 % lower browning index and a 62.5 % lower decay rate. Additionally, the soluble solid content increased by 107.1 %. The inclusion of cellulose nanocrystals and the crosslinking of calcium ions enhanced the mechanical properties of the composite membrane. Specifically, the tensile strength and elongation at break increased by 70 % and 366 % respectively. As all the components in the coating are edible, it is environmentally friendly and safe for human consumption.

Development and characterization of cellulose nanofiber reinforced hydroxypropyl methylcellulose films functionalized with propolis-loaded zein nanoparticles and its application for cheddar cheese storage

Cellulose nanofiber (CNF) reinforced hydroxypropyl methylcellulose (HPMC) films were functionalized with propolis-loaded zein nanoparticles (ZNP) to develop active, printable, and heat-sealable films. The films with 0, 0.10, 0.25, 0.50, or 0.75 mg/mL propolis-loaded ZNP, named 0ZNP, 0.10ZNP, 0.25ZNP, 0.50ZNP, and 0.75ZNP, respectively, were characterized for their mechanical, physicochemical, structural, functional and optical properties and antioxidant activity. The addition of propolis-loaded ZNP did not change tensile strength (P > 0.05), but increased elongation at break (from 24.72 to 36.58 %) (P < 0.05) for 0.25ZNP film. A water contact angle increased significantly (P < 0.05) for 0.50ZNP (~45 %) and 0.75ZNP (~137 %) films. The 0.25ZNP and 0.75ZNP films were evaluated for packaging cheddar cheese under refrigerated storage for 30 days, and resulted in comparable water activity, pH, titratable acidity, and lipid oxidation (P > 0.05) with those packaged by LDPE film and vacuum package. The developed films can function as eco-friendly alternatives to single-use plastic food packaging.

Gas barrier coating based on cellulose nanocrystals and its preservation effects on mango

Mango is the "king of tropical fruits" because of its attractive appearance, delicious taste, rich aroma, and high nutritional value. However, mango keeps fast metabolizing after harvest, leading to water loss, starch conversion into sugar, texture softening, and decay. Here, a gas barrier coating based on cellulose nanocrystals (CNCs) is proposed to control the post-harvest metabolism of mango. The results of gas barrier permeability show that CNCs enhance the barrier ability of the chitosan (CS) membrane on mango by 202 % and 63 % for oxygen and water vapor, respectively. The gas-barrier coating reduces the climb in pH and the decrease in firmness by 84.9 % and 45.8 %, respectively, decelerating the conversion process from starch to sugar. Besides, introducing clove essential oil (CEO), the CEO mainly adsorbs and crystalizes on the hydrophobic facets of CNCs, presenting high compatibility, increases the antibacterial rate to nearly 100 %. As a consequence, the preservation period of the mango coated by the CNC-based membrane is at least 7-day longer than the control group. Such a gas-barrier coating based on eco-friendly composites must have excellent potential in the preservation of mango, and even for other tropical fruits.

Nanoencapsulation application to prolong postharvest shelf life

This review offers our opinion on current and future trends regarding nanoencapsulation interventions to extend postharvest shelf life of stored grains, fruits, and vegetables. Herein, we considered two major factors influencing postharvest shelf life for comments: aerobic food spoilage microorganisms and stored pests. Nanoemulsions, edible/active coatings, and nanopackaging loading essential oils as antimicrobial, antioxidant, or pesticide showed promising results in prolonged shelf life at room/cold storage without compromising quality, organoleptic properties, and postharvest physiology. Trends with nanoencapsulation using plant-based pesticides as agrochemical-free methods to keep produce fresh longer were commented as potential candidates for prolonging the shelf life of stored grains and fruits at the postharvest stage. Research with potential large-scale feasibility is intensive, but safety assessment is required and remains little explored.

Impact of Bacterial Cellulose Nanocrystals-Gelatin/Cinnamon Essential Oil Emulsion Coatings on the Quality Attributes of ‘Red Delicious’ Apples

This study aimed to assess the effectiveness of bacterial cellulose nanocrystals (BCNCs)-gelatin (GelA)/cinnamon essential oil (CEO) emulsion coatings containing various CEO concentrations (1200, 1800, and 2400 μL/L) in retarding ripening and senescence of ‘Red Delicious’ apples during cold storage (60 days at 4 °C). Coatings decreased the weight loss (WL) (~3.6%), as compared to uncoated fruit (~4.8%). A direct relationship between CEO concentration and respiration rate/ethylene production was also disclosed. Flesh firmness was higher for coated samples, with better results detected especially when the highest amount of CEO was applied (36.48 N for the 2400 μL/L delivered dose vs. 32.60 N for the 1200 μL/L one). These findings were corroborated by additional tests on the surface color, total acidity, soluble solids content, pH, ascorbic acid, and activities of polyphenol oxidase (PPO) and peroxidase (POD). This study demonstrated the capability of BCNCs-GelA/CEO systems to dramatically enhance the storability and quality of apples during refrigerated storage, thus avoiding undesired losses and increasing the economic performance of fresh fruit industries.

Single-Step Application of Polyelectrolyte Complex Films as Oxygen Barrier Coatings

Polyelectrolyte complex (PEC) films such as polyelectrolyte multilayers have demonstrated excellent oxygen barrier properties, but unfortunately, the established layer-by-layer approaches are laborious and difficult to scale up. Here, we demonstrate a novel single-step approach to produce a PEC film, based on the use of a volatile base. Ammonia was used to adjust the pH of poly(acrylic acid) (PAA) so that direct complexation was avoided when it was mixed with polyethylenimine (PEI). Different charge ratios of homogeneous PEI/PAA solutions were successfully prepared and phase diagrams varying the concentration of ammonia or polyelectrolyte were made to study the phase behavior of PEI, PAA, and ammonia in water. Transparent ∼1 μm thick films were successfully deposited on biaxially orientated polypropylene (BOPP) sheets using a Meyer rod. After casting the films, the decrease in pH, caused by the evaporation of ammonia, triggered the complexation during drying. The oxygen permeation properties of films with different ratios and single polyelectrolytes were tested. All films displayed excellent oxygen barrier properties, with an oxygen permeation below 4 cm³·m^-2·day^-1·atm^-1 (<0.002 barrer) at the optimum ratio of 2:1 PEI/PAA. This ammonia evaporation-induced complexation approach creates a new pathway to prepare PEC films in one simple step while allowing the possibility of recycling.

Fabrication of novel self-healing edible coating for fruits preservation and its performance maintenance mechanism

Coating damage destroys the integrity features critical for maintaining the modified atmosphere inside the fruit. In this study, we developed a self-healing edible coating that maintains its barrier properties for extending the shelf life of strawberries. The coating was fabricated via the layer-by-layer assembly of chitosan (CS) and sodium alginate (SA). (SA/CS)₃ formed by three assembly cycles could completely heal the visibly damaged area by treating water. The mechanical properties and the water and oxygen rates of the healed coating were 97%, 63%, and 95%, respectively, of the intact coating. (SA/CS)₃ coating effectively delayed strawberry deterioration. Moreover, the coating reduced the impact of coating damage on strawberries by restoring the coating barrier properties. The present findings have important implications for solving the reduction in freshness caused by coating damage.