Vitexin-loaded poly(ethylene glycol) methyl ether-grafted chitosan/alginate nanoparticles: preparation, physicochemical properties and in vitro release behaviors.

BACKGROUND: Vitexin, a flavonoid in various foods and medicinal plants, has potential clinical, therapeutic and food applications due to its bioactive properties and beneficial health effects. However, its poor water solubility causes low oral bioavailability and poor absorption in the gastrointestinal tract, limiting its practical applications. Encapsulation is an efficient approach to overcome these limitations. This study demonstrates the encapsulation of vitexin into poly(ethylene glycol) methyl ether-grafted chitosan (mPEG-g-CTS)/alginate (ALG) polyelectrolyte complex nanoparticles. RESULTS: The vitexin-loaded mPEG-g-CTS/ALG nanoparticles were characterized by Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy and X-ray diffraction. The vitexin-loaded mPEG-g-CTS/ALG nanoparticles had a spherical shape, 50-200 nm in diameter, and negatively charged surface (-27 to -38 mV). They possessed a loading capacity of 4-60%, encapsulation efficiency of 50-100% and antioxidant activity (30-52% 2,2-diphenyl-1-picrylhydrazyl decoloration) when their initial vitexin content was 0.02-0.64 g g-1 polymers. Successful vitexin loading into mPEG-g-CTS/ALG nanoparticles was also indirectly confirmed by the enhanced thermal stability of both polymers and the residual soybean oil used in the emulsion preparation step and delayed oxidative degradation of the residual soybean oil. Vitexin's in vitro release from the mPEG-g-CTS/ALG nanoparticles was very fast in phosphate buffer at pH 11, followed by pH 7, and very slow in acetate buffer at pH 3. The gastrointestinal digestion of vitexin increased by encapsulating into mPEG-g-CTS/ALG nanoparticles. CONCLUSIONS: Vitexin-loaded mPEG-g-CTS/ALG nanoparticles were successfully fabricated using a two-step process of oil-in-water emulsion and ionic gelation without the use of pungent odor acids and other crosslinkers. The obtained nanoparticles are suitable for oral intestinal-specific delivery systems. © 2023 Society of Chemical Industry.

Property improvement of a thermoplastic starch/poly(butylene adipate-co-terephthalate) blown film by the addition of sodium nitrite.

Recently, global awareness of the adverse environmental impacts of single-use plastics has risen due to their nonbiodegradability and likelihood of ending up in the ocean. Thermoplastic starch (TPS) is an alternative material employed for manufacturing single-use products because of its high biodegradability, nontoxicity, and low cost. However, TPS is moisture sensitive and has poor mechanical properties and processability. Blending TPS with biodegradable polyesters, including poly(butylene adipate-co-terephthalate) (PBAT), can expand its practical applications. This research aims to improve the performance of TPS/PBAT blends by adding sodium nitrite, a food additive, and considering its effect on the morphological characteristics and properties of TPS/PBAT blends. TPS/PBAT/sodium nitrite (TPS/PBAT/N) blends with a TPS:PBAT weight ratio of 40:60 and sodium nitrite concentrations of 0.5, 1, 1.5, and 2 wt% were prepared by extrusion and then blown into films. The acids generated from the sodium nitrite during extrusion led to the molecular weight reduction of starch and PBAT polymers, causing the increased melt flow ability of the TPS/PBAT/N blends. The incorporation of sodium nitrite improved the blends' homogeneity and the compatibility between the TPS and PBAT phases, resulting in the increased tensile strength, extensibility, impact strength, and oxygen barrier properties of the TPS/PBAT blend film.

The effect of polyethylene glycol sorbitan monostearate on the morphological characteristics and performance of thermoplastic starch/biodegradable polyester blend films.

Although thermoplastic starch (TPS) has been developed to mitigate greenhouse gas emissions and environmental and health-related impacts from plastics, high moisture sensitivity and poor mechanical properties limited its practical applications. Blending TPS with biodegradable polyesters, i.e., poly(lactic acid) (PLA) and poly(butylene succinate-co-butylene adipate) (PBSA), is an alternative approach; however, the compatibility among polymer phases needs to be improved. Here, polyethylene glycol sorbitan monostearate (Tween 60), an amphiphilic surfactant, was proposed to improve the compatibility and performance of the TPS/PLA/PBSA 40/30/30 blend. The concentration of Tween 60 varied in the range of 0.5-2.5 wt%. The blends were fabricated using an extruder through two different melt-mixing routes, i.e., direct mixing and masterbatch mixing, and then converted to film using a blown film extrusion line. Tween 60 could improve compatibility between TPS dispersed phase and PLA/PBSA matrix, resulting in increased tensile strength, extensibility, impact strength, thermal stability, and water vapor and oxygen barrier properties of the ternary blend. In addition, better performance of the blend was obtained from the direct mixing route. Tween 60 could thus be considered a potential compatibilizer for the TPS/PLA/PBSA blend film, which can be further used as a biodegradable packaging material.

Bio-based thermoplastic natural rubber based on poly(lactic acid)/thermoplastic starch/calcium carbonate nanocomposites.

Bio-based thermoplastic natural rubber (TPNR) has recently received much attention due to its sustainability. TPNR based on natural rubber (NR), poly(lactic acid) (PLA), thermoplastic starch (TPS), and nano-precipitated calcium carbonate (NPCC) was fabricated using a twin-screw extruder with two different mixing sequences: MI (NPCC was first compounded with PLA) and MII (NPCC was initially compounded with TPS), and then converted to a sheet through cast sheet extrusion. A constant weight ratio of NR:PLA:TPS at 30:40:30 and varying concentrations of NPCC at 0.5, 1, 3, and 5 wt% were employed. The effects of NPCC and mixing sequence on the properties of NR/PLA/TPS/NPCC nanocomposites were investigated. The NR and TPS phases were dispersed in the PLA matrix. The nanocomposites loaded with a small amount of NPCC (0.5 and 1 wt%) showed increased tensile strength and Young's modulus. NPCC enhanced melt flowability, slightly improved the water vapor barrier property of the NR/PLA/TPS blend and caused decreased Tg, Tcc, and Tm of PLA in the nanocomposites. The PLA phase of the MI nanocomposites contained a higher amount of NPCC, consequently having greater PLA chain scission and poorer tensile properties than that of the MII nanocomposites.

Poly(lactic acid)/thermoplastic cassava starch blends filled with duckweed biomass.

Duckweed (DW) is a highly small, free-floating aquatic plant. It grows and reproduces rapidly, comprises mainly protein and carbohydrate, and has substantial potential as a feedstock to produce bioplastics due to its renewability and having very little impact on the food chain. The aim of this work was to analyze the effect of DW biomass on the characteristics and properties of bio-based and biodegradable plastics based on a poly(lactic acid)/thermoplastic cassava starch (PLA/TPS) blend. Various amounts of DW biomass were compounded with PLA and TPS in a twin-screw extruder and then converted into dumbbell-shaped specimens using an injection molding machine. The obtained PLA/TPS blends filled with DW biomass exhibited a lower melt flow ability, higher moisture content, and increased surface hydrophilicity than the neat PLA/TPS blend. Incorporation of DW with low concentrations of 2.3 and 4.6 wt% increased the tensile strength, Young's modulus, and hardness of the PLA/TPS blend. Moisture and glycerol from DW and TPS played important roles in reducing the Tg, Tcc, Tm, and Td of PLA in the blends. The current work demonstrated that DW could be used as a biofiller for PLA/TPS blends, and the resulting PLA/TPS blends filled with DW biomass have potential in manufacturing injection-molded articles for sustainable, biodegradable, and short-term use.

Relationship between microstructure and performances of simultaneous biaxially stretched films based on thermoplastic starch and biodegradable polyesters.

Although thermoplastic starch (TPS) is a good candidate to overcome the limitations of poly(lactic acid) (PLA) due to its relatively low cost and high flexibility, the toughness and barrier properties of PLA/TPS blends are still insufficient for film applications. Therefore, the present work aims to improve the performance of PLA/TPS blend by simultaneous biaxial stretching and partially replacing PLA with poly(butylene adipate-co-terephthalate) (PBAT) for packaging film applications. PLA/TPS and PLA/PBAT/TPS sheets were prepared by melt cast extrusion and simultaneously biaxially stretched to form films. The mechanical, morphological, thermal, and water vapor and oxygen barrier properties and crystallinity of both intermediate sheets and their corresponding stretched films were examined. After stretching, PLA/TPS and PLA/PBAT/TPS blends showed markedly improved extensibility, impact strength, crystallinity, water vapor and oxygen barrier properties, and surface hydrophobicity. The stretched films demonstrated stacked-layer planar morphology, in which their outermost layers were a biodegradable polyester-rich phase. The synergistic effects of simultaneous biaxial stretching and partial replacing PLA with PBAT were extremely impressive for toughness improvement. The stretched films have the potential to replace non-biodegradable plastic packaging films, particularly where good mechanical and barrier properties are required.

Thermoplastic starch blown films with improved mechanical and barrier properties.

The development and production of thermoplastic starch (TPS) films based on blown film extrusion have been spurred by increasing interest in renewable resources and an alternative solution to meet industrial-scale demand. The chemical structure of the plasticizer and its proportion have a significant effect on the mechanical and barrier properties of TPS films. Therefore, this research aims to evaluate the influence of plasticizer type and content on the performance of TPS blown films. TPS films were prepared by mixing cassava starch with three types of plasticizer, i.e. glycerol, glycerol/xylitol, and glycerol/sorbitol with a weight ratio of 1:1. The quantity of plasticizer varied among 38, 40, and 42 parts per hundred parts of starch. Although TPS films plasticized with the small-sized plasticizer glycerol were easily processed and extensible, the surface stickiness leading to single-wall films, low tensile strength, and poor water vapor barrier properties would limit their use. By replacing glycerol with larger-sized plasticizers such as xylitol or sorbitol, the films exhibited reduced stickiness and separable double walls and showed improved tensile strength, stiffness, and water vapor and oxygen barrier properties. The obtained TPS blown films offer potential applications as edible films for food and pharmaceutical products.

Structure and properties of in situ reactive blend of polylactide and thermoplastic starch.

In this study, in situ reactive extrusion of polylactide and thermoplastic starch modified with chloropropyl trimethoxysilane coupling agent (PLA/mTPS) is proposed. The success of covalent bond formation between PLA matrix and mTPS phase is clarified by two-dimensional nuclear magnetic resonance (2D-NMR) spectroscopy with 1H1H TOCSY mode. This chemically bound PLA with starch gives the remarkable compatibility in the PLA/mTPS film, with not only a decreased glass transition temperature (47 °C) but also an increased crystallinity of PLA (Χc of 50%). It consequently increases oxygen barrier significantly and also enhances the film flexibility as observed from the drastic increase of elongation at break (from 3% to 50%). Moreover, the PLA/mTPS 60/40 (w/w) film exhibits the accelerated degradation as compared with pure PLA film.

Water-soluble poly(ethylene glycol) methyl ether-grafted chitosan/alginate polyelectrolyte complex hydrogels.

This study aimed to fabricate polyelectrolyte complexes from water-soluble poly(ethylene glycol) methyl ether-grafted chitosan (mPEG-g-CTS) and alginate (ALG) in the absence of acetic acid. The complexes formed fibrous network macrogels when mPEG-g-CTS with short mPEG chains (mPEG750-g-CTS and mPEG2000-g-CTS) and mPEG-g-CTS:ALG weight ratios in the range from 1:0.14 to 1:1 were used. The macrogels at a weight ratio of mPEG-g-CTS:ALG of 1:1 possessed the highest elasticity with electrophoretic mobility close to 0 m2·V-1·s-1. Water uptake of the sponge-like lyophilized macrogels decreased with increasing ALG content, mPEG chain length, and degree of substitution of mPEG-g-CTS. In contrast, the polyelectrolyte complexes prepared using long mPEG chains of mPEG-g-CTS (mPEG5000-g-CTS) formed spherical nanoparticles (70-90 nm) and showed highly negative electrophoretic mobility (< -3.20 × 108 m2·V-1·s-1). The obtained mPEG-g-CTS/ALG polyelectrolyte complex hydrogels and nanoparticles have the potential to be applied as carriers for functional food additives, drugs, and bioactive compounds.

Morphology and properties of thermoplastic starch blended with biodegradable polyester and filled with halloysite nanoclay.

The incorporation of halloysite clay nanotubes (HNTs) into thermoplastic starch/poly(butylene adipate-co-terephthalate) (TPS/PBAT) blends has been investigated with the aim of improving the compatibility and properties of the matrix. TPS/PBAT/HNTs nano-biocomposites with different TPS/PBAT weight fractions and HNTs contents were elaborated using a melt blending process, and their morphology and properties were investigated. The TPS80/PBAT20 and TPS20/PBAT80 blends exhibited dispersed phases of small droplets of PBAT or TPS, respectively, whereas the TPS50/PBAT50 blend presented a more homogeneous structure. Elongation at break of the TPS/PBAT/HNTs biocomposites with 5 wt% of HNTs significantly increased with increasing PBAT proportion, i.e., 6.5 %, 41.3 %, and 351.5 % for the composites based on TPS80/PBAT20, TPS50/PBAT50, and TPS20/PBAT80, respectively. The incorporation of 5 wt% of HNTs improved compatibility and increased Young's modulus of the TPS80/PBAT20, TPS50/PBAT50, and TPS20/PBAT80 blends approx. 350 %, 142 %, and 18 %, respectively. These results demonstrate that HNTs are promising nanofillers to improve properties of TPS-based blends.

Oligo(lactic acid)-grafted starch: A compatibilizer for poly(lactic acid)/thermoplastic starch blend.

The objective of this study was to improve the compatibility between poly(lactic acid) (PLA) and thermoplastic starch (TPS) in PLA/TPS blown films by incorporating oligo(lactic acid)-grafted starch (OLA-g-starch) as a compatibilizer. OLA-g-starch with a degree of substitution of 1.2 and degree of polymerization of 2.0 was synthesized via a ring-opening polymerization of lactide initiated by hydroxyl groups of starch. The PLA/TPS blends containing OLA-g-starch were prepared using a twin-screw extruder with a constant weight proportion of PLA to TPS of 50:50 and various concentrations of OLA-g-starch, i.e., 1, 2, 3, and 5%. The obtained blends were blown into thin films using a blown film extruder. SEM confirmed the droplet/matrix morphology of the PLA/TPS blends both with and without OLA-g-starch. Incorporating OLA-g-starch improved the compatibility between the TPS dispersed phase and PLA matrix, as evidenced by the smaller size and better distribution of the TPS phase. As a result, the blends containing OLA-g-starch exhibited up to 280% greater extensibility as well as enhanced water vapor and oxygen barrier properties, water resistance, melt flowability, and thermal stability. The Tg, Tcc, and Tm of PLA in the blends shifted to higher temperatures when OLA-g-starch was incorporated. The obtained PLA/TPS blown film containing OLA-g-starch has the potential to be used as flexible packaging.

Thermoplastic cassava starch/poly(lactic acid) blend reinforced with coir fibres.

One way to obtain more benefit from coconut waste is to utilise coir fibre (CF) as reinforcement in biodegradable plastics. The current work aims to study the effect of CF on the performance of a thermoplastic starch (TPS)/poly(lactic acid) (PLA) blend. TPS/PLA/CF biocomposites with a constant TPS: PLA ratio of 60:40 by weight and various concentrations of CF (2.7, 5.5, 8.2, and 10.9 wt%) were fabricated using a twin-screw extruder and then injection moulded into dumbbell-shaped specimens for property testing. The obtained TPS/PLA/CF biocomposites exhibited improved stiffness and hardness, corresponding to the stronger hydrogen bond interaction between starch and PLA and/or starch and CF and the increased PLA crystallinity. Due to the reinforcing effect, the biocomposites also exhibited lower extensibility, tensile strength and impact strength compared to the TPS/PLA blend. Incorporating CF enhanced compatibility between the TPS and PLA phases; however, it also caused reduced melt flow ability, increased shear viscosity, and a decreased shear thinning effect of the blend. The resulting TPS/PLA/CF biocomposites could potentially be used to produce bio-based and biodegradable injection-moulded products.

Morphological characteristics and barrier properties of thermoplastic starch/chitosan blown film.

Fabrication of starch-based edible film using blown film extrusion is challenging and interesting because this process provides continuous operation with shorter production time and lower energy consumption, is less labor intensive, and results in higher productivity than the conventional solution casting technique. Previously, we reported on the preparation and some properties of thermoplastic starch/chitosan (TPS/CTS) blown films; however, their morphological characteristics and barrier properties had not yet been elucidated. The present work thus aims to investigate the effect of chitosan (0.37-1.45%) on morphological characteristics, water vapor and oxygen barrier properties as well as hydrophilicity of the TPS and TPS/CTS films. The relationship between morphological characteristics and properties of the films was also discussed. Scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM) and X-ray photoelectron spectroscopy (XPS) confirmed the distribution and deposition of chitosan on the film surface. The existence of chitosan on the surface imparted the improved water vapor and oxygen barrier properties and the reduced surface hydrophilicity to the film. The results suggest that this biodegradable bio-based TPS/CTS film could potentially be used as an edible film for food and pharmaceutical applications.

Effect of stearic acid-grafted starch compatibilizer on properties of linear low density polyethylene/thermoplastic starch blown film.

The present work aims to investigate the effect of stearic acid-grafted starch (ST-SA) on the rheological, thermal, optical, dynamic mechanical thermal, and tensile properties of linear low density polyethylene/thermoplastic starch (LLDPE/TPS) blends, as well as on their water vapor and oxygen barrier properties. Blends consisting of LLDPE and TPS in a weight ratio of 60:40 and ST-SA at different concentrations, i.e. 1, 3 and 5%, were prepared using a twin-screw extruder. The obtained resins were subsequently converted into films via blown film extrusion. Incorporation of ST-SA resulted in a decreased degree of shear thinning, reduced ambient temperature elasticity, and improved tensile strength, secant modulus, extensibility, and UV absorption, as well as diminished water vapor and oxygen permeabilities of the LLDPE/TPS blend. These effects are attributed to the enhanced interfacial adhesion between LLDPE and TPS phases through the compatibilizing effect induced by ST-SA, and the good dispersion of the TPS phase in the LLDPE matrix. The results confirmed that ST-SA could potentially be used as a compatibilizer for the LLDPE/TPS blend system.

Development of thermoplastic starch blown film by incorporating plasticized chitosan.

The objective of the present work was to improve blown film extrusion processability and properties of thermoplastic starch (TPS) film by incorporating plasticized chitosan, with a content of 0.37-1.45%. The effects of chitosan on extrusion processability and melt flow ability of TPS, as well as that on appearance, optical properties, thermal properties, viscoelastic properties and tensile properties of the films were investigated. The possible interactions between chitosan and starch molecules were evaluated by FTIR and XRD techniques. Chitosan and starch molecules could interact via hydrogen bonds, as confirmed from the blue shift of OH bands and the reduction of V-type crystal formation. Although the incorporation of chitosan caused decreased extensibility and melt flow ability, as well as increased yellowness and opacity, the films possessed better extrusion processability, increased tensile strength, rigidity, thermal stability and UV absorption, as well as reduced water absorption and surface stickiness. The obtained TPS/chitosan-based films offer real potential application in the food industry, e.g. as edible films.

Ferulic acid-coupled chitosan: thermal stability and utilization as an antioxidant for biodegradable active packaging film.

The aim of the present research was to study the thermal stability of ferulic acid after coupling onto chitosan, and the possibility of using ferulic acid-coupled chitosan (FA-CTS) as an antioxidant for biodegradable active packaging film. FA-CTS was incorporated into biodegradable film via a two-step process, i.e. compounding extrusion at temperatures up to 150°C followed by blown film extrusion at temperatures up to 175°C. Although incorporation of FA-CTS with a content of 0.02-0.16% (w/w) caused decreased water vapor barrier property and reduced extensibility, the biodegradable films possessed improved oxygen barrier property and antioxidant activity. Radical scavenging activity and reducing power of film containing FA-CTS were higher than those of film containing naked ferulic acid, by about 254% and 94%, respectively. Tensile strength and rigidity of the films were not significantly affected by the addition of FA-CTS with a content of 0.02-0.08% (w/w). The above results suggested that FA-CTS could potentially be used as an antioxidant for active packaging film.

Hydrophobically modified chitosan: a bio-based material for antimicrobial active film.

The objective of the present research was to improve the hydrophobicity of chitosan, while retaining its antibacterial activity, through the grafting of dodecenyl succinyl chains onto phthaloyl chitosan, mainly at the C-6 position. Dodecenyl succinylated phthaloyl chitosan (DS-g-PHCTS) was synthesized via phthaloylation-dodecenyl succinylation-hydrazinolysis. The obtained derivatives were characterized by FTIR, (1)H NMR and XRD. Hydrazinolysis time was found to be a key factor in controlling the substitution of dodecenyl succinyl chains and phthalimido groups of the final product. DS-g-PHCTS - with a grafting degree of dodecenyl succinyl chains and a substitution degree of phthalimido groups of 0.73 and 0.39, respectively - exhibited an anhydrous crystal structure and the same solubility behavior as native chitosan. The introduction of hydrophobic alkyl chains provided DS-g-PHCTS with enhanced antibacterial activity against Gram-positive bacteria. In addition, DS-g-PHCTS film showed more effective bacterial growth inhibition and better water vapor barrier property under neutral pH condition than chitosan film. The results suggested that DS-g-PHCTS film could be potentially used as antibacterial active film.

Water-based oligochitosan and nanowhisker chitosan as potential food preservatives for shelf-life extension of minced pork.

Water-based chitosans in the forms of oligochitosan (OligoCS) and nanowhisker chitosan (CSWK) are proposed as a novel food preservative based on a minced pork model study. The high surface area with a positive charge over the neutral pH range (pH 5-8) of OligoCS and CSWK lead to an inhibition against Gram-positive (Staphylococcus aureus, Listeria monocytogenes, and Bacillus cereus) and Gram-negative microbes (Salmonella enteritidis and Escherichia coli O157:H7). In the minced pork model, OligoCS effectively performs a food preservative for shelf-life extension as clarified from the retardation of microbial growth, biogenic amine formation and lipid oxidation during the storage. OligoCS maintains almost all myosin heavy chain protein degradation as observed in the electrophoresis. The present work points out that water-based chitosan with its unique morphology not only significantly inhibits antimicrobial activity but also maintains the meat quality with an extension of shelf-life, and thus has the potential to be used as a food preservative.

Preparation, characterization and antioxidant property of water-soluble ferulic acid grafted chitosan.

The objective of the present work was to improve the antioxidant activity and water solubility of chitosan by grafting with ferulic acid through a carbodiimide-mediated coupling reaction. UV-vis spectrophotometry, FTIR, (1)H NMR and ninhydrin assay confirmed the grafting of ferulic acid onto chitosan at the C-2 position. Ferulic acid grafted chitosan - prepared using a mole ratio of chitosan to ferulic acid of 1:1, reaction temperature of 60°C, and reaction time of 3h - possessed the highest ferulic acid substitution degree, i.e. 0.37. Although ferulic acid grafted chitosan showed reduced crystallinity (∼10%) and decreased decomposition temperature (∼55°C) as compared to chitosan, it exhibited greater radical scavenging activity (∼55%) and was soluble in water (up to 1.3mg/mL). The improved antioxidant property and water solubility of this chitosan derivative could open a wide range of applications, particularly its use as an antioxidant in food, food packaging, biomedical, pharmaceutical and cosmetics industries.

Eugenol-loaded chitosan nanoparticles: I. Thermal stability improvement of eugenol through encapsulation.

The objective of the present work was to improve the thermal stability of eugenol by encapsulating into chitosan nanoparticles via an emulsion-ionic gelation crosslinking method. The influences of the initial eugenol content and tripolyphosphate (TPP) concentration on the loading capacity (LC), encapsulation efficiency (EE), morphology and surface charge of the eugenol-loaded chitosan nanoparticles were also investigated. LC and EE tended to increase with increasing initial eugenol content and decreasing TPP concentration. Particles with LC of 12% and EE of 20% exhibited a spherical shape with an average size of less than 100 nm. Thermal stability of the encapsulated eugenol was verified through its extrusion at 155°C with a model plastic, i.e. thermoplastic flour (TPF). TPF containing encapsulated eugenol showed 8-fold higher remaining eugenol content and 2.7-fold greater radical scavenging activity than that containing naked eugenol. The results suggest the possible use of eugenol-loaded chitosan nanoparticles as antioxidants in bioactive plastics for food packaging.