Starch as a smart, cheap, and green gatekeeper for the controlled release of propyl gallate from antioxidant biodegradable packaging films.

Oxidative rancidity of food products and massive consumption of plastic packaging have put the necessity in manufacturing novel antioxidant biodegradable packaging films. A comprehensive investigation was conducted on starch/poly(butylene adipate-co-terephthalate) (PBAT) antioxidant blown films, in which starch acted as a gatekeeper for the controlled release of propyl gallate (PG). PG was well integrated into the matrices and bound to starch molecules by hydrogen bonding. All films showed strong anti-ultraviolet performance, and higher oxygen barrier than the traditional polyethylene film. Increasing starch proportions promoted the swelling of films and the release of PG, thereby causing higher antioxidant activity at the same contact time to free radical solutions. Similar polarity made PG prone to partition and rapid migration into the food simulants with higher ethanol concentration and the high-fat-content peanut butter. The film with 20:80 w/w starch/PBAT proportion and 3% w/w PG content effectively suppressed the oxidation of peanut butter within 300-day storage. Findings demonstrated this strategy for manufacturing starch/PBAT antioxidant films as a long-term active packaging in food industry.

Effects of co-plasticization of glycerol and small molecular esters on the physicochemical properties of extrusion-blown high-content starch/poly(butylene adipate-co-terephthalate) films.

BACKGROUND: Poor mechanical and water barrier properties of starch-based films severely restrict their applications as packaging materials. In this study, glycerol was combined with various small molecular esters (SMEs) with different molecular structures to plasticize high-content starch/poly(butylene adipate-co-terephthalate) (80/20, w/w) films (SPFs) prepared by extrusion blowing. The effects of co-plasticization on the physicochemical properties and film-forming mechanism of SPFs were investigated. RESULTS: The addition of glycerides to SPFs reduced intermolecular interaction, increased molecular chain mobility, and decreased glass transition, melting temperatures, and crystallinity. Mechanical and water barrier properties of SPFs were improved significantly with the co-plasticization of glycerol and SMEs. The incorporation of triacetate glyceride increased tensile strength of SPFs by 54% and the water contact angle by up to 95°. The SPF with diacetate glyceride exhibited the minimum water vapor permeability, which decreased by 39%. CONCLUSION: The levels of hydrophilic/hydrophobic groups in SMEs and their molecular weights were essential for the plasticizing effects. Glycerides tended to infiltrate into starch for effective plasticization compared with citrates. The combination of glycerol and glycerides had better plasticizing effects on starch. © 2023 Society of Chemical Industry.

Extrusion-blown starch/PBAT biodegradable active films incorporated with high retentions of tea polyphenols and the release kinetics into food simulants.

To reduce thermal degradation of tea polyphenols (TP) in final active packaging materials, poly(butylene adipate-co-terephthalate) (PBAT), starch, plasticizer, and TP were directly synthesized into masterbatches by one-pot method in this study without pre-dispersion, and then blown into active films. TP interacted with starch through hydrogen bonds, with little interaction with PBAT. Barrier properties were improved by incorporating TP into the films, whereas mechanical properties slightly decreased. Blending starch into PBAT greatly accelerated the degradation of the film. And the incorporation of TP slowed down the short-term degradation of the starch/PBAT film, but accelerated the long-term degradation. The initial total polyphenol content in the active film was positively related to the TP loading, whereas the initial retention rate remained above 95 % regardless of TP loadings. The retention rate of TP in active films decreased with storage time, but it was still above 80 % after 12 months, with a favorable stability. TP-loaded films displayed efficient antioxidant and antimicrobial activities with strong dose dependence. The release of TP into food simulants was mainly induced by random diffusion, with little effect from polymer swelling. The short-term release kinetics was well described by Fick's second law. This work has demonstrated the feasibility of TP being incorporated into the active films with high retention through high-throughput fabrication, which provides formula and technical options for the industrial development of active packaging materials.

Effects of natural wax types on the physicochemical properties of starch/gelatin edible films fabricated by extrusion blowing.

To address the limitation of strong hydrophilicity of edible films, starch/gelatin (S/G) films incorporated with natural waxes (beeswax (BW), candelilla wax (CL), and carnauba wax (CB)) were fabricated by extrusion blowing. Rheological analysis demonstrated that the incorporation of natural waxes reduced storage modulus and complex viscosity of S/G blends. BW and CL weakened molecular interactions among film components, whereas CB did not. CB exhibited the strongest crystalline behavior after film formation. The degree of starch gelatinization and water vapor barrier property of films depended on wax type. The presence of waxes increased the water resistance and surface hydrophobicity of the films. However, CL and BW addition decreased the tensile strength of films. The highest water contact angle (102.6°), strongest thermal stability, and lowest water vapor permeability were found in S/G-BW film, which could be the optimal choice to produce highly hydrophobic edible films.

Relationship between phase morphologies and mechanical properties of thermoplastic starch/poly(butylene adipate-co-terephthalate) composite films prepared by extrusion blowing.

Biodegradable films with various weight proportions of thermoplastic starch (TPS) and poly(butylene adipate-co-terephthalate) (PBAT) were prepared by extrusion blowing. Relationship between phase morphologies and mechanical properties of TPS/PBAT composite films was investigated and discussed. Iodine dyeing technique was used to clearly identify TPS and PBAT phases in the composite films. Such blending systems proved to be immiscible and the phase morphology evolution with changes in TPS/PBAT proportions was elucidated. Two phase transition points were found near PBAT content of 30 and 70 wt%, respectively, where mechanical properties of the composite films leaped. Significant correlations were established between mechanical properties and continuity indices of the two phases, namely a positive correlation with continuity index of PBAT and a negative correlation with that of TPS. Inducing the formation and enhancement of continuous structure of PBAT phase is proposed as a practical approach to improve mechanical properties of TPS/PBAT composite films.

Effects of beeswax emulsified by octenyl succinate starch on the structure and physicochemical properties of acid-modified starchfilms.

This work aimed to develop a novel strategy to modulate the distribution of beeswax in acid-modified starch films via tuning octenyl succinate starch (OSS) ratios and to elucidate their structure-property relationships. The apparent viscosity and storage modulus of the film-forming solution decreased with the increase of OSS ratio. Attenuated total reflectance-fourier transform infrared (ATR-FTIR) spectroscopy revealed that the hydrogen bond in the film-forming network was cleaved with the presence of OSS. Scanning electron microscope (SEM), atomic force microscope (AFM), and X-ray diffraction (XRD) demonstrated that OSS ratio had an obvious effect on the formation and distribution of beeswax crystal particles. Uniform distribution of beeswax effectively enhanced the hydrophobicity and water barrier properties of films and performed preferable elongation at break but at the expense of tensile strength and optical properties. The films with higher OSS ratio (>12 %) presented higher thermal stability. This study provides new information on the rational design of emulsified films to obtain desirable physicochemical properties by tuning the distribution of beeswax.

Preparation and evaluation of agar/maltodextrin-beeswax emulsion films with various hydrophilic-lipophilic balance emulsifiers.

The structural and physicochemical properties of agar/maltodextrin-beeswax films in the presence of three emulsifiers, including glycerol monostearate, sodium stearoyl lactylate, and polysorbate 80 were investigated. Scanning electron microscopy revealed that addition of lower hydrophilic-lipophilic balance value emulsifiers produced smaller size and more uniform distribution of beeswax in the film matrix. X-ray diffraction and differential scanning calorimetry indicated that the emulsifiers with lower hydrophilic-lipophilic balance values promoted the compatibility between agar/maltodextrin and beeswax more effectively. The incorporation of different emulsifiers showed diverse impacts on the film network structure and physicochemical properties. Agar/maltodextrin-beeswax-polysorbate 80 film showed maximum stiffness (861.99 MPa). Agar/maltodextrin-beeswax-glycerol monostearate film exhibited the highest tensile strength (26.79 MPa), elongation at break (31.83%), water vapor barrier (7.64 × 10-13 g·m-1·s-1·Pa-1) and oxygen barrier properties (3.82 × 10-17 cm2·s-1·Pa-1), which could be more effective for packaging foods that are prone to oxidize.

Antimicrobial starch/poly(butylene adipate-co-terephthalate) nanocomposite films loaded with a combination of silver and zinc oxide nanoparticles for food packaging.

Antimicrobial starch/PBAT films with the combination of silver nanoparticles (AgNPs) and zinc oxide nanoparticles (ZnONPs) were prepared by extrusion blowing. SEM demonstrated the relatively homogeneous distribution of nanoparticles on the fracture surfaces of the nanocomposite films. The incorporation of nanoparticles improved mechanical and barrier properties of the film. The UV-vis spectroscopy revealed that the SP-ZnO(1) film had the highest UV-absorbance. The inhibition effects of the nanocomposite films against both Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria were observed. The antimicrobial efficiency of SP-Ag(0.8)-ZnO(0.2) and SP-Ag(0.6)-ZnO(0.4) films reached more than 95% within 3 h of contact. The combination of AgNPs and ZnONPs into starch/PBAT blends showed synergistic effects on improving material properties and antimicrobial efficiency of the films. Furthermore, preliminary packaging studies on peaches and nectarines revealed that the antimicrobial films inhibited spoilage of fresh produce and extended their shelf life compared with commercial LDPE packaging films.

Starch/PBAT blown antimicrobial films based on the synergistic effects of two commercial antimicrobial peptides.

In this study, starch/PBAT antimicrobial film, based on the synergistic effects of two commercial antimicrobial peptides, was fabricated by blown extrusion. The blends with nisin exhibited higher storage modulus and complex viscosity than those with ε-polylysine hydrochloride (ε-PL) alone. ATR-FTIR spectra revealed that new intermolecular hydrogen bonds were formed among starch, nisin, and ε-PL. XRD results indicated that antimicrobial peptides facilitated the destruction of the original crystalline structure of starch. Combination of ε-PL and nisin enhanced tensile strength, flexibility, moisture permeability, and oxygen barrier property of the films with more homogeneous morphology. SP-PN1/2 film (1% ε-PL + 2% nisin) exhibited over 90% inhibition rates against Staphylococcus aureus and Escherichia coli, and prolonged the shelf life of fresh peaches. The antimicrobial film with nisin and ε-PL showed high safety, cost-effectiveness, consumer acceptability, and thus it had a good application prospect in the food packaging field.

Cationized high amylose maize starch films reinforced with borax cross-linked nanocellulose.

In this study, a novel strategy for modifying nanocellulose (NC) by borax cross-linking was developed, and the obtained borax modified nanocellulose (BNC) was incorporated into cationized high amylose maize starch (CS) films to evaluate the applicability. Cellulose molecules were successfully cross-linked by boron ester bonds, and the original crystal type and basic chemical structure were not changed. Compared with NC, the relative crystallinity of BNC was slightly increased, and the thermal stability was obviously enhanced. Addition of NC and BNC to CS films significantly improved their tensile strength and water resistance. The dispersion of nanocellulose in CS films was effectively improved by borax cross-linking modification. CS/BNC films showed higher mechanical and water resistance properties compared with CS/NC films. Compared with pure CS film, tensile strength of the composite film with 6 wt% BNC increased about 4.0 times, and its water-vapor permeability decreased about 37%. The novel strategy for preparing BNC by using boron ester bonds will provide a potential approach for the development of starch films with desirable properties.

High-Throughput Fabrication of Antibacterial Starch/PBAT/AgNPs@SiO2 Films for Food Packaging.

In this current work, antimicrobial films based on starch, poly(butylene adipate-co-terephthalate) (PBAT), and a commercially available AgNPs@SiO2 antibacterial composite particle product were produced by using a melt blending and blowing technique. The effects of AgNPs@SiO2 at various loadings (0, 1, 2, 3, and 4 wt%) on the physicochemical properties and antibacterial activities of starch/PBAT composite films were investigated. AgNPs@SiO2 particles were more compatible with starch than PBAT, resulting in preferential distribution of AgNPs@SiO2 in the starch phase. Infusion of starch/PBAT composite films with AgNPs@SiO2 marginally improved mechanical and water vapor barrier properties, while surface hydrophobicity increased as compared with films without AgNPs@SiO2. The composite films displayed superior antibacterial activities against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. The sample loaded with 1 wt% AgNPs@SiO2 (SPA-1) showed nearly 90% inhibition efficiency on the tested microorganisms. Furthermore, a preliminary study on peach and nectarine at 53% RH and 24 °C revealed that SPA-1 film inhibited microbial spoilage and extended the product shelf life as compared with SPA-0 and commercial LDPE packaging materials. The high-throughput production method and strong antibacterial activities of the starch/PBAT/AgNPs@SiO2 composite films make them promising as antimicrobial packaging materials for commercial application.

Effect of lipids with different physical state on the physicochemical properties of starch/gelatin edible films prepared by extrusion blowing.

The effects of various physical state lipids (rapeseed oil (RO), shortening (ST), beeswax (BW)), on the physicochemical properties of starch (S) (hydroxypropyl distarch phosphate (HP), oxidized hydroxypropyl starch (OS))/gelatin (G) blown films were studied. S/G-lipid blends showed decreased storage modulus and complex viscosity. The formation of hydrogen bonds was inhibited by the ST and BW, but facilitated by the RO. Compared with BW and ST, RO was more effective to promote the melted and fractured of starch. Lipids addition promoted the compatibility of starch and gelatin. The presence of the lipids significantly improved the surface hydrophobicity, mechanical, water vapor barrier and water resistance properties of S/G films. S/G-RO films exhibited the strongest surface hydrophobicity and tensile strength, while HP/G-BW film showed the strongest water resistance and water vapor barrier properties. These results revealed that the appropriate lipids could be used to produce S/G-lipid films with desirable physicochemical properties.

Preparation and characterization of biodegradable trilayer films based on starch and polyester.

The trilayer films of polyester/starch/polyester with different starch/polyester layer thickness ratios were prepared by co-extrusion blowing. FTIR and SEM results showed the successful fabrication of trilayer films. The crystallinity of trilayer films gradually increased as the thickness of polyester layer increased. Dynamic mechanical analysis was used to investigate the compatibility between starch and polyester. The presence of polyester layer significantly increased the tensile strength and water contact angle of starch film. All trilayer films had lower water vapor permeability than the starch film, and lower oxygen permeability than the polyester film. The trilayer films were degraded to a much greater extent compared with the polyester film. The weight loss of P10 trilayer film in 120 days is about 80% through degradation test. These results suggested that the polyester/starch/polyester films with excellent mechanical and hydrophobic properties could serve as packaging material for wider applications.

Effects of High-Intensity Ultrasound Pretreatment on Structure, Properties, and Enzymolysis of Walnut Protein Isolate.

The purpose of this paper was to investigate the effect of high-intensity ultrasonication (HIU) pretreatment before enzymolysis on structural conformations of walnut protein isolate (WPI) and antioxidant activity of its hydrolysates. Aqueous WPI suspensions were subjected to ultrasonic processing at different power levels (600-2000 W) and times (5-30 min), and then changes in the particle size, zeta (ζ) potential, and structure of WPI were investigated, and antioxidant activity of its hydrolysates was determined. The particle size of the particles of aqueous WPI suspensions was decreased after ultrasound, indicating that sonication destroyed protein aggregates. The ζ-potential values of a protein solution significantly changed after sonication, demonstrating that the original dense structure of the protein was destroyed. Fourier transform infrared spectroscopy indicated a change in the secondary structure of WPI after sonication, with a decrease in ß-turn and an increase in α-helix, ß-sheet, and random coil content. Two absorption peaks of WPI were generated, and the fluorescence emission intensity of the proteins decreased after ultrasonic treatment, indicating that the changes in protein tertiary structure occurred. Moreover, the degree of hydrolysis and the antioxidant activity of the WPI hydrolysates increased after sonication. These results suggest that HIU pretreatment is a potential tool for improving the functional properties of walnut proteins.

Effects of high starch content on the physicochemical properties of starch/PBAT nanocomposite films prepared by extrusion blowing.

Starch/PBAT nanocomposite films with high starch content were prepared using one-step compounding and subsequent extrusion blowing. The effects of the starch/PBAT weight proportions on the physicochemical properties of the films were investigated. The X-ray diffraction results demonstrated that the extent of intercalation of the starch/PBAT nanocomposite films increased with the increasing PBAT content. The dynamic mechanical analysis revealed that the compatibility of starch and PBAT improved with increasing PBAT content from 10 wt% to 50 wt%. The strength and flexibility of the films were greatly improved by blending with PBAT. The maximum tensile strength and elongation at break of the starch/PBAT nanocomposite films were 7.4 MPa and 614 %, respectively. The water-vapor barrier properties and hydrophobicity of the films were significantly improved with the increase in the PBAT content. The blown starch/PBAT nanocomposite films incurred low cost and demonstrated excellent mechanical and hydrophobic properties, which are suitable for the food-packaging field.