Synergistic effects of thyme and oregano essential oil combinations for enhanced functional properties of sericin/pectin film.

This work aimed to assess the synergistic antibacterial effects of thyme and oregano essential oils in various ratios (thyme:oregano; 10:0, 8:2, 6:4, 4:6, 2:8, 10:0). We hypothesized that the synergistic combination of thyme and oregano essential oils can be effectively incorporated into sericin/pectin film to enhance its functional properties. Among the combinations tested, the mixture of thyme/oregano essential oil (TOE) at an 8:2 ratio exhibited the most potent synergistic activity against P. aeruginosa and S. aureus, with fractional inhibitory concentration index (FICindex) of 0.9. In this combination, thymol constituting 51.83 % of TOE (8:2), was the predominant component. TOE at an 8:2 ratio was selected to incorporate into sericin/pectin film. Different concentrations of TOE (0.8 %, 1.2 % and 1.6 %) were applied to evaluate their impact on film properties compared to a film without essential oil (control). It was found that increasing TOE concentration (control; 0 %) to 1.6 % reduced film moisture content (from 21.53 % to 16.91 %), decreased yellowness (from 18.24 to 15.92), diminished gloss (from 63.79 to 11.18), lowered swelling index (from 1.24 to 0.98), and reduced tensile strength (from 9.70 to 4.14 MPa). However, the addition of TOE showed higher film total phenolic content (8.59-31.53 mg gallic acid/g dry sample) and increased antioxidant activity (0.99-3.68 µmol Trolox /g dry sample). Moreover, the film with 1.2 % and 1.6 % of thyme/oregano essential oil exhibited inhibitory effects against all tested bacteria. Therefore, the thyme/oregano essential oil combination can provide the desirable physicochemical properties of the sericin/pectin film, as well as its antibacterial and antioxidant activities, making it a promising alternative for food packaging material applications.

Factors affecting sericin hydrolysis and application of sericin hydrolysate in sericin films.

Sericin is a natural protein and a by-product obtained from silk processing. To enhance the antioxidant properties of sericin, sericin hydrolysis was studied. The solvent effects (distilled water, citric acid and hydrochloric acid) and hydrolysis methods (heat treatment (water bath) and mild ultrasonic treatment at 20%, 40% or 60% amplitude) were investigated on the properties of sericin hydrolysate (SH). Furthermore, solvent effects (distilled water and 15% ethanol) were examined for the properties of the sericin films incorporated with selected SH. The SH samples from acid hydrolysis and the ultrasonic method had a darkened visual appearance. However, the degree of hydrolysis and antioxidant activity of SH increased with ultrasonic-assisted acid hydrolysis. The molecular weight (MW) of sericin was notably reduced. As expected, hydrochloric acid hydrolysis resulted in a lower MW for the SH than from citric acid. Thus, SH from hydrochloric acid and 20% amplitude in the ultrasonic method were selected to produce a sericin film. As revealed, using distilled water as a general solvent provided films with lower solubility and water vapor permeability but higher tensile strength. Furthermore, the addition of SH enhanced the antioxidant properties of its hydrolysate as a novel protein packaging film material for various applications.

Characterization of bioactive film from pectin incorporated with gamma-aminobutyric acid.

Gamma-aminobutyric acid (GABA) is a nutritious bioactive compound that is also an antioxidant. The effect of GABA contents (5-15%) on pectin film properties were investigated and compared to those obtained by adding 10% glycerol, with pure pectin film as the control. The addition of 5% GABA led to similar film tensile strength and elastic modulus with lower film solubility and water vapor permeability compared with film plasticized with 10% glycerol. Additionally, 5% GABA had higher film flexibility compared with the control film. Moreover, GABA content slightly affected the color and moisture content of pectin films with a high antioxidant activity. Furthermore, thermal properties of film plasticized with GABA supported the changes in mechanical properties of pectin film. Therefore, this small amount of GABA provided a desirable film with functional properties similar to those obtained by using the higher amount of glycerol. Thus, GABA not only acted as an alternative plasticizer but also showed antioxidant activity as a bioactive film.

Microwave heating extraction of pectin from lime peel: Characterization and properties compared with the conventional heating method.

Microwave and conventional heating methods were used to extract pectin from lime peel waste using different acid extractants (hydrochloric or citric acid) and peel-to-extractant ratios (1:20 or 1:40). Hydrochloric acid as the extractant resulted in a higher yield of pectin with both methods. The methoxyl content and galacturonic acid content of lime peel pectin were in the range 8.74-10.51% and 79.29-95.93%, respectively. The intense band around 1730 cm-1 corresponded to methyl esterified uronic carboxyl groups and confirmed the higher equivalent weight and degree of esterification for the microwave-extracted pectin than that from conventional extraction. Lime peel pectin could be classified as high methoxyl pectin having a rapid-set gel formation. The viscosity and viscoelastic properties of the pectin solution from both heating methods enhanced with increasing solid concentration. Hence, microwave heating can be a short processing time for pectin extraction from lime peel waste with suitable pectin properties.

Physicochemical and functional properties of protein concentrate from by-product of coconut processing.

Coconut cake, a by-product from milk and oil extractions, contains a high amount of protein. Protein extraction from coconut milk cake and coconut oil cake was investigated. The supernatant and precipitate protein powders from both coconut milk and oil cakes were compared based on their physicochemical and functional properties. Glutelin was the predominant protein fraction in both coconut cakes. Protein powders from milk cake presented higher water and oil absorption capacities than those from oil cake. Both protein powders from oil cake exhibited better foaming capacity and a better emulsifying activity index than those from milk cake. Coconut proteins were mostly solubilized in strong acidic and alkaline solutions. Minimum solubility was observed at pH 4, confirming the isoelectric point of coconut protein. Therefore, the coconut residues after extractions might be a potential alternative renewable plant protein source to use asa food ingredient to enhance food nutrition and quality.

Microencapsulation of Thai rice grass (O. Sativa cv. Khao Dawk Mali 105) extract incorporated to form bioactive carboxymethyl cellulose edible film.

Microencapsulation was investigated to enhance the stability of Thai rice grass extract. Microencapsulated powder (MP) was formed using total solid of extract solution and maltodextrin ratios of 1:4 (MP 1:4) and 1:9 (MP 1:9). The absence of an endothermic peak for both MPs confirmed all extract solutions were coated with maltodextrin. MP 1:9 had a lower total phenolic content (TPC) but was higher in antioxidant capacity than MP 1:4. Moreover, the TPC of the MPs slightly decreased (70.02-93.04%) during storage at 10, 30 and 70°C for 30d. Comparatively, the TPC of the extract solution significantly decreased from 100% down to 20.8%, 11.2% and 8.6% at 10, 30 and 70°C, respectively. Therefore, MP 1:9 incorporated with blended carboxymethyl cellulose film increased the water barrier and the TPC. This film can serve as a bioactive biodegradable packaging material to reduce plastic packaging in the food industry.

Development and characterization of banana flour film incorporated with montmorillonite and banana starch nanoparticles.

Banana flour film is an alternative biopolymer material but still needs improvement of its mechanical properties and water vapor permeability. Banana starch nanoparticles (BSNs), prepared using miniemulsion cross-linking, make an interesting reinforcing agent. The properties of plasticized banana flour film (PBF) were characterized incorporated with 5% (w/w) of either montmorillonite; MMT-Na+ (PBF-M) or BSN (PBF-B), including a mixture of nanoparticles at 1:1 for 5% (PBF-MB5) and 10% (PBF-MB10). PBF-MB5 provided better improvement in the film mechanical and water barrier properties compared with PBF-B. Moreover, PBF-MB5 exhibited an intercalated structure as confirmed by the shift peak of pristine MMT-Na+ from 2θ=7.3 to 3.9° and the increase in the d-spacing from 1.21 to 2.26nm in X-ray diffraction. Fourier transform-infrared spectra confirmed the intercalated structure. Therefore, the mixture of BSN and nanoclay at 5% was sufficient to reinforce the biopolymer films as a biomaterial packaging for food and pharmaceutical applications.

Rice stubble as a new biopolymer source to produce carboxymethyl cellulose-blended films.

Rice stubble is agricultural waste consisting of cellulose which can be converted to carboxymethyl cellulose from rice stubble (CMCr) as a potential biomaterial. Plasticizer types (glycerol and olive oil) and their contents were investigated to provide flexibility for use as food packaging material. Glycerol content enhanced extensibility, while olive oil content improved the moisture barrier of films. Additionally, CMCr showed potential as a replacement for up to 50% of commercial CMC without any changes in mechanical and permeability properties. A mixture of plasticizers (10% glycerol and 10% olive oil) provided blended film with good water barrier and mechanical properties comparable with 20% individual plasticizer. Principle component (PC) analysis with 2 PCs explained approximately 81% of the total variance, was a useful tool to select a suitable plasticizer ratio for blended film production. Therefore, CMCr can be used to form edible film and coating as a renewable environmentally friendly packaging material.

One-step preparation of banana powder/silver nanoparticles composite films.

Silver nanoparticles (Ag-NPs) were synthesized using banana powder as a reducing and stabilizing agent, and banana/Ag-NPs composite films with different concentration of Ag-NPs were prepared simultaneously. The composite films were yellowish brown and exhibited characteristic plasmon resonance peak of Ag-NPs at 430 nm. The optical, mechanical, water vapor barrier, thermal stability, and antimicrobial properties of the composite films were greatly influenced by the concentration of Ag-NPs. The composite film with a silver concentration of 1.0 mM demonstrated the highest tensile strength, thermal stability, transparency, and water contact angle with the lowest water vapor permeability (1.36 ± 0.10 × 10-9 g m/m2 Pa s). Also, the composite films incorporated with 1.0 mM of Ag-NPs exhibited a strong antibacterial activity against both Gram-positive (Listeria monocytogenes) and Gram-negative (Escherichia coli) food-borne pathogenic bacteria.

Effect of plasticizer type and amount on hydroxypropyl methylcellulose-beeswax edible film properties and postharvest quality of coated plums (cv. Angeleno).

The effect of the composition of hydroxypropyl methylcellulose (HPMC)-beeswax (BW) edible coatings on stand-alone film properties and on postharvest quality of coated 'Angeleno' plums was studied. Glycerol (G) and mannitol (M) were tested as plasticizers at two different plasticizer/HPMC ratios (100:1 and 300:1 molar basis). BW content was 20 or 40% (dry basis). An increase in G content increased film flexibility and vapor permeability (WVP), whereas an increase in M content enhanced film brittleness without affecting WVP. An increase in BW content reduced film flexibility and reduced WVP of only G-plasticized films. Coatings reduced plum softening and bleeding, but were not effective in reducing plum weight loss. At low plasticizer content, coatings reduced texture loss effectively. Low BW also lowered plum bleeding. Plasticizer type affected only ethanol and acetaldehyde contents without affecting the remaining quality parameters. Therefore, HPMC-BW coatings have the potential to extend the shelf life of plums. However, this effect depends on coating composition. Differences between coating and film performance indicate that data from stand-alone films may be used as a preliminary screening, but coating performance should be analyzed on coated fruit.