Construction of TiO2/starch nanocomposite cryogel for ethylene removal and banana preservation

Integrated degradation of bacteria, organic pollutants, total phosphorus, and antibiotics in food wastewater through immobilization of Bacillus velezensis on polyethylene glycol-polyvinyl alcohol/sodium alginate/nano-TiO2 microspheres

Food wastewater is characterized by complex composition and a wide range of pollutants. Existing treatment methods are often inefficient for single pollutants and new, environmentally friendly, and integrated treatment methods are needed. This study aimed to construct a novel polyethylene glycol (PEG)-polyvinyl alcohol (PVA)/sodium alginate (SA)/nano-TiO2 hydrogel microsphere-immobilized Bacillus velezensis system for the integrated degradation of complex pollutant components in food wastewater. SEM, FT-IR, XRD, mechanical, rheological, and swelling properties of the microspheres were tested, which confirmed the presence of nano-TiO2 in the microspheres and effectively improved the physical properties of the microspheres. The results showed that the microspheres containing 0.5 g/L nano-TiO2 in the preformed gel solution 1 had the best morphology, mechanical strength, physical stability, and 57.5 % bacterial carrying capacity. The microspheres inhibited Escherichia coli and Staphylococcus aureus and did not affect the growth and reproduction of Bacillus velezensis. The system achieved integrated degradation of chemical oxygen demand (COD), total phosphorus (TP), and antibiotics in food wastewater with degradation rates of 71.85 %, 36.84 %, and 40.52 %, respectively, and remained highly efficient after five times reuse. This method is environmentally friendly, efficient, and economical, which provides a new idea for wastewater treatment by immobilized microbial technology.

Sustainable Active Packaging from On-Demand Degradable PLA/PBAT and Zn-Doped TiO2 Composites

Shelf life extendable packaging and ethylene scavenger technologies for climacteric fruits and vegetables have garnered much attention in recent years. These products effectively enable food quality to be maintained, ensure food safety, and prolong food storage life, which are key to helping reduce food waste. Current technologies - both in terms of academic research and broader commercial application - imply the use of chemicals that are of low activity, of high toxicity, or difficult to handle. Therefore, in this work, we prepared Zn-doped TiO2 photocatalysts, containing 0.1 and 2.0 mol % of Zn dopant (Zn 0.1% -TiO 2 and Zn 2% -TiO 2 ), through a simple sol-gel method, which were then applied to be used as ethylene scavenger fillers in the preparation of on-demand degradable active packaging. TiO2 particles were also prepared under identical conditions for comparison. The active composite film containing Zn 0.1% -TiO 2 was shown to be a better active packaging than the one containing TiO2 and was able to extend the shelf life of bananas for up to 8 days. In addition, the incorporation of Zn-doped TiO2 particles did not significantly compromise either the mechanical properties of the polymer composite film or change its degradation behavior; it slightly improved the thermal stability. Moreover, the active composite film could be degraded on demand by immersing it into a 3 M KOH solution - leading to almost complete polymer film degradation after 4 h at room temperature. The developed active packaging model is a very promising candidate and could serve for future optimization as sustainable active food packaging.

Green fabrication of modified lignin/zeolite/chitosan-based composite membranes for preservation of perishable foods

Chitosan, as a kind of naturally occurring green and degradable material for the preservation of perishable foods, was investigated in this study with the objective of enhancing its preservation performances. Herein, lignin was modified using the solvent fractionation method (modified lignin, ML, including ML1-ML3), while natural clinoptilolite zeolite was modified using the alkali modification method (modified clinoptilolite zeolite, MCZ, including MCZ1-MCZ5). After optimizing the conditions, it was discovered that incorporating both ML3 and MCZ3 into pure chitosan-based membranes might be conducive to fabricate chitosan-based composite membranes for the preservation of perishable foods. As-prepared composite membranes possessed better visible light transmittance, antioxidant activity, and carbon dioxide/oxygen selectivity, resulting in improved preservation effects on the model perishable foods such as bananas, cherry tomatoes, and cheeses. These findings might indicate promising applications for chitosan-based composite membranes with modified lignin and zeolite in the field of eco-friendly degradable materials for the preservation of perishable foods.

Ilmenite-Grafted Graphene Oxide as an Antimicrobial Coating for Fruit Peels

Postharvest loss is a significant global challenge that needs to be urgently addressed to sustain food systems. This study describes a simple microwave-assisted green synthesis method in developing a nanohybrid material combining natural ilmenite (FeTiO3) and graphene oxide (GO) as a promising antimicrobial fruit peel coating to reduce postharvest loss. The natural ilmenite was calcined in an inert environment and was mixed with GO in a microwave reactor to obtain the nanohybrid. The nanohybrid was then incorporated into an alginate biopolymer to form the fruit coating. Microscopic images revealed successful grafting of FeTiO3 nanoparticles onto the GO sheets. Spectroscopic measurements of Raman, X-ray photoemission, and infrared provided insights into the interactions between the two matrices. The optical band gap calculated from Tauc's relation using UV-vis data showed a significant reduction in the band gap of the hybrid compared to that of natural ilmenite. The antimicrobial activity was assessed using Escherichia coli, which showed a substantial decrease in colony counts. Bananas coated with the nanohybrid showed a doubling in the shelf life compared with uncoated fruits. Consistent with this, the electronic nose (E-nose) measurements and freshness indicator tests revealed less deterioration of the physicochemical properties of the coated bananas. Overall, the results show promising applications for the ilmenite-grafted GO nanohybrid as a food coating capable of minimizing food spoilage due to microbial activity.

Construction of photocatalytic coating for alleviating the shriveling of postharvest fruit cucumber after simulated transportation

The shriveling of fruit cucumber was commonly occurred during supply chain, photocatalyst exposed to UV light can endow the coatings with ethylene removal capacity to reduce the respiration of fruit and water loss. The study developed a novel photodynamic technology responsive photocatalytic coating with exceptional ultraviolet (UV) photocatalytic degradation of ethylene ability to decay the shriveling of postharvest fruit cucumber during supply chain. This coating involved the integration of Carbon dots (CDs)-loaded nano ZnO and the skillful selection of pullulan (Pul) and apple pectin (AP) matrix. The CDs/ZnO coatings boasted an impressive array of photocatalytic degradation of ethylene and adhesion properties, including high ethylene removal rates of 32.04 % in 60 min UV light stimulation. The decrease of cell-wall strength, degradation of the cell wall polysaccharides and water loss resulted in cucumber shriveling. Compared with CK sample, after UV-CDs/ZnO coating treatment, the higher firmness and cell wall polysaccharides were found in cucumbers with lower cell wall degrading enzymes activities, weight loss and water movement, which was associated with the decrease of respiration and ethylene accumulation. The UV-CDs/ZnO coatings possessed promising potential for alleviating the shriveling of postharvest fruit cucumber and applications in fruits preservation in the future.

One-pot co-crystallized hexanal-loaded ZIF-8/quaternized chitosan film for temperature-responsive ethylene inhibition and climacteric fruit preservation

Controlling ethylene production and microbial infection are key factors to prolong the shelf life of climacteric fruit. Herein, a nanocomposite film, hexanal-loaded ZIF-8/CS (HZCF) with "nano-barrier" structure, was developed by a one-pot co-crystallized of ZIF-8 in situ growth on quaternized chitosan (CS) and encapsulation of hexanal into ZIF-8 via microporous adsorption. The resultant film realized the temperature responsive release of hexanal via the steric hindrance and hierarchical pore structure as "nano-barrier", which can inhibit ethylene production in climacteric fruit on demand. Based on this, the maximum ethylene inhibition rate of HZCF was up to 52.6 %. Meanwhile, the film exhibits excellent antibacterial, mechanical, UV resistance and water retention properties, by virtue of the functional synergy between ZIF-8 and CS. Contributed to the multifunctional features, HZCF prolonged the shelf life of banana and mango for at least 16 days, which is 8 days longer than that of control fruit. More strikingly, HZCF is washable and biodegradable, which is expected to replace non-degradable plastic film. Thus, this study provides a convenient novel approach to simplify the encapsulation of active molecule on metal-organic frameworks (MOFs), develops a packaging material for high-efficient freshness preservation, and helps to alleviate the survival crisis caused by food waste.

Photocatalytic chitosan-based bactericidal films incorporated with WO3/AgBr/Ag and activated carbon for ethylene removal and application to banana preservation

Ethylene (C2H4) and pathogenic microorganisms are the two major causes of the deterioration of postharvest fruits and vegetables (F&V). Hence, the development of active packaging with C2H4 scavenging and bactericidal activities is urgently desirable. Herein, a novel photocatalytic active film (CS-PC-AC) is developed for banana preservation by incorporating WO3/AgBr/Ag photocatalyst (PC) and activated carbon (AC) into chitosan (CS). The fabricated PC is a ternary Z-scheme heterojunction and its high photocatalytic activity is achieved by the bridge of Ag between WO3 and AgBr through rapid transfer and separation of photogenerated electrons and holes. AC plays an indispensable role in the photocatalytic reaction through molecule adsorption and transport. PC and AC are hydrogen bonded with chitosan and their incorporation has slight effect on film's thermal stability but decreases the film's mechanical and barrier properties to some extent. CS-PC-AC exhibits strong bactericidal activity (killing ~100 % of Escherichia coli and Staphylococcus aureus within 3 h) and good C2H4 scavenging activity (C2H4 scavenging rate of 49 ± 2 %) under visible light irradiation, which can extend the banana shelf-life by at least 50 % at 25 °C. These results indicate the good perspective of CS-PC-AC in the delay of the deterioration of postharvest F&V.

Eco-friendly food packaging based on paper coated with a bio-based antibacterial coating composed of carbamate starch, calcium lignosulfonate, cellulose nanofibrils, and silver nanoparticles

Traditional paper-based packaging commonly needs to be coated to achieve sufficient mechanical and barrier performances. In this research, a bio-based coating for paper was developed from carbamate starch (Sc), calcium lignosulfonate (CL), and cellulose nanofibrils (CNF). Controlling the electrostatic and hydrogen-bonding interactions among the components of the coating was conducive to tailoring the structure and performance of the coated paper. When the degree of substitution (Ds) of Sc was 0.10, the amount of CL was 1.00 g, and the amount of CNF was 0.65 % of the weight of Sc, the paper coated with the resulting 0.10Sc-1.00CL-0.65CNF coating exhibited increased hydrophobicity and excellent mechanical, air-barrier, and UV-light-barrier properties. After the addition of 0.10 % of silver nano-particles (AgNPs) to the 0.10Sc-1.00CL-0.65CNF coating, the paper coated with the resulting 0.10Sc-1.00CL-0.65CNF-0.10AgNPs coating exhibited good antibacterial activity against Escherichia coli and Staphylococcus aureus. The coated paper was used as the packaging for cherry tomatoes stored under ambient conditions. Due to the synergistic preservation effects of the Sc-CL-CNF coating and AgNPs, the shelf life of the cherry tomatoes was at least 7 days. The coated paper described herein has the potential for applications in the food packaging sector.