Development of active packaging films based on chitosan and nano-encapsulated luteolin.

Luteolin is a flavone with potent antioxidant and antimicrobial activities. In this study, luteolin was encapsulated in oil-in-water nanoemulsions that were emulsified by glycerol monooleate and Tween 20. Results showed 68 mg luteolin-loaded nanoemulsions had the highest stability (zeta potential of -39.8 mV) and encapsulation efficiency (89.52%). Then, active packaging films were developed by incorporating free or nano-encapsulated luteolin into chitosan-based matrix. The microstructure, physical and functional properties of CS film containing free luteolin (CS-LL) or nano-encapsulated luteolin (CS-LLNEs) were compared. Different from CS film, CS-LL and CS-LLNEs films had compact inner microstructure and strengthened intermolecular interactions. Moreover, CS-LLNEs film was more homogenous and compact than CS-LL film. As a result, CS-LLNEs film presented higher water vapor and oxygen barrier abilities and mechanical properties in comparison with CS-LL film. In addition, CS-LLNEs film showed slower release rate of luteolin in 95% ethanol (fatty food stimulant) as compared with CS-LL film. The controlled release of luteolin from film matrix could guarantee CS-LLNEs film to exert antioxidant activity up to 10 days. Our results suggest CS-LLNEs film can be developed as an emerging active packaging material that has potential applications in food industry.

Preparation and characterization of antioxidant packaging by chitosan, D-α-tocopheryl polyethylene glycol 1000 succinate and baicalein.

Baicalein (BN) is a kind of flavonoid with strong antioxidant ability. In this study, antioxidant packaging was developed by incorporating BN and D-α-tocopheryl polyethylene glycol 1000 succinate (TPGS) into chitosan (CS) film matrix for the first time. Effect of BN content (0.5 wt%, 1 wt% and 2 wt% on CS basis) on the structure, physical, release and antioxidant properties of CS-TPGS-BN films was investigated. Micro-structural observation showed 0.5 wt% of BN was compatible with film matrix, whereas 1 wt% and 2 wt% of BN reduced the homogeneity of the film. Fourier transform infrared spectroscopy revealed hydrogen bonds formed between BN and film matrix. X-ray diffraction showed the crystallinity of CS-TPGS film was increased by BN incorporation. The addition of BN remarkably increased the yellowness, water vapor and light barrier properties, opacity and antioxidant activity of the film. The release of BN from CS-TPGS-BN films to fatty food stimulant was demonstrated to fit second-order, Ritger-Peppas, and first-order models. Notably, CS-TPGS-BN films could effectively inhibit the oxidation of soybean oil during 28 days of storage. Thus, CS-TPGS-BN films could be used as novel antioxidant packaging for fatty foods.

Synthesis, characterization, antioxidant and antimicrobial activities of starch aldehyde-quercetin conjugate.

In this study, corn starch was functionalized with quercetin. Starch was first oxidized by sodium periodate to produce starch aldehyde, and then starch aldehyde was conjugated with quercetin through acid catalyzed condensation reaction. The structure, antioxidant and antimicrobial activities of starch aldehyde-quercetin conjugate were evaluated. Thin layer chromatography confirmed the conjugate did not contain free quercetin. The UV-vis spectrum of the conjugate exhibited an absorption band at 320 nm. Fourier-transform infrared and proton nuclear magnetic resonance spectra of the conjugate confirmed the aldehyde groups of starch aldehyde were involved in the conjugation reaction. X-ray diffraction pattern revealed the conjugate was in the amorphous state. Scanning electron microscopy observation showed the conjugate had sheet-like, virgate and round shapes. The structure of starch aldehyde-quercetin conjugate was different from that of native starch and starch aldehyde. As compared with native starch and starch aldehyde, starch aldehyde-quercetin conjugate exhibited higher reducing power, free radical scavenging activity and antimicrobial activity against Escherichia coli, Staphylococcus aureus, Salmonella and Listeria monocytogenes. Our results suggested starch aldehyde-quercetin conjugate could be developed as an antioxidant and antimicrobial agent in food industry.

Structure and functional properties of active packaging films prepared by incorporating different flavonols into chitosan based matrix.

Kaempferol, quercetin and myricetin are typical flavonols that feature different number of hydroxyl substituents at B-ring. In this study, kaempferol, quercetin and myricetin were individually mixed with chitosan (CS) based film matrix to develop active packaging films. Results showed the incorporation of flavonols produced dense inner microstructure by establishing intermolecular hydrogen bonding interactions with film matrix. The addition of flavonols reduced the water vapor permeability, oxygen permeability and UV-vis light transmittance of the films, whereas elevated the tensile strength, elongation at break, 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity and antimicrobial activity of the films. Among all the films, the film containing myricetin showed the highest water vapor and oxygen barrier abilities and mechanical properties. Notably, different films presented distinct flavonol release behaviors in fatty and aqueous food stimulants. Kaempferol was easily released into fatty food stimulant, while myricetin was easily released into aqueous food stimulant. The release behavior of flavonols in different food stimulants greatly affected the antioxidant activity of the films. Our results suggest the structure and functional properties of the films are closely related to the number of hydroxyl substituents at B-ring of flavonols.

Preparation and characterization of antioxidant and antimicrobial packaging films based on chitosan and proanthocyanidins.

The antioxidant and antimicrobial food packaging films were prepared by using chitosan (CS) and proanthocyanidins (PA). Effect of PA content (0, 5, 10, 15 and 20 wt% of PA on CS basis) on the physical, antioxidant and antimicrobial properties of CS-based films were determined. The prepared CS-PA films showed a brown color. PA incorporation remarkably increased the thickness, water solubility, water vapor permeability, opacity, tensile strength and thermal stability of CS film; whereas significantly reduced the moisture content, oxygen permeability, UV-vis light transmittance, elongation at break and crystallinity of CS film. Scanning electron microscopy showed PA was evenly distributed in the CS film matrix, making the films more compact. Some spontaneous agglomeration of PA was observed in the films when PA contents exceeded 5 wt%. Infrared spectra indicated the intermolecular interactions between PA and CS were through hydrogen bonds. Notably, CS-PA films exhibited improved antioxidant and antimicrobial activity in comparison with plain CS film. Our results suggested CS-PA films could be applied as active packaging materials in food industry.