Encapsulation of Volatile Compounds in Silk Microparticles

Recent advances of silk fibroin materials: From molecular modification and matrix enhancement to possible encapsulation-related functional food applications

Silk fibroin materials are emergingly explored for food applications due to their inherent properties including safe oral consumption, biocompatibility, gelatinization, antioxidant performance, and mechanical properties. However, silk fibroin possesses drawbacks like brittleness owing to its inherent specific composition and structure, which limit their applications in this field. This review discusses current progress about molecular modification methods on silk fibroin such as extraction, blending, self-assembly, enzymatic catalysis, etc., to address these limitations and improve their physical/chemical properties. It also summarizes matrix enhancement strategies including freeze drying, spray drying, electrospinning/electrospraying, microfluidic spinning/wheel spinning, desolvation and supercritical fluid, to generate nano-, submicron-, micron-, or bulk-scale materials. It finally highlights the food applications of silk fibroin materials, including nutraceutical improvement, emulsions, enzyme immobilization and 3D/4D printing. This review also provides insights on potential opportunities (like safe modification, toxicity risk evaluation, and digestion conditions) and possibilities (like digital additive manufacturing) in functional food industry.

Stabilization and Sustained Release of Fragrances Using Silk-PEG Microspheres

Fragrances, which are commonly used in food, textiles, consumer products, and medical supplies, are volatile compounds that require stabilization and controlled release due to their sensitivity to environmental conditions such as light, oxygen, temperature, and humidity. Encapsulation in various material matrices is a desired technique for these purposes, and there is a growing interest in using sustainable natural materials to reduce environmental impact. In this study, fragrance encapsulation in microspheres made from silk fibroin (SF) was investigated. Fragrance-loaded silk fibroin microspheres (Fr-SFMSs) were prepared by adding fragrance/surfactant emulsions to silk solutions, followed by mixing them with polyethylene glycol under ambient conditions. The study investigated eight different fragrances, where citral, beta-ionone, and eugenol showed higher binding affinities to silk than the other five fragrances, resulting in better microsphere formation with uniform sizes and higher fragrance loading (10-30%). Citral-SFMSs showed characteristic crystalline β-sheet structures of SF, high thermal stability (initial weight loss at 255 °C), long shelf life at 37 °C (>60 days), and sustained release (∼30% of citral remained after incubation at 60 °C for 24 h). When citral-SFMSs with different sizes were used to treat cotton fabrics, about 80% of the fragrance remained on the fabrics after one wash, and the duration of release from the treated fabrics was significantly longer than that of control samples treated with citral alone (no microspheres). This method of preparing Fr-SFMSs has potential applications in textile finishing, cosmetics, and the food industry.

Controlled-Release Wedelia trilobata L. Flower Extract Loaded Fibroin Microparticles as Potential Anti-Aging Preparations for Cosmetic Trade Commercialization

Background

Wedelia trilobata L. (WT), a common herbal plant in Vietnam, is popularly used as a strong antioxidant in Vietnamese folk medicine. However, limited studies have reported the application of WT flower in cosmeceutical area.

Purpose

This study explored the potentials of WT loaded fibroin microparticles (FMPs-WT) as a novel anti-aging cosmeceutical product.

Methods

The WT flower was firstly extracted by maceration with methanol, ethanol 60%, and ethanol 96%, and its chemical compositions and total polyphenol content were investigated. Then, the FMPs-WT were developed by desolvation method and physicochemically characterized. Finally, the product antioxidant activities were in-vitro determined using DPPH assay.

Results

The optimal WT extract was the ethanol 60% extract, which contains polyphenols, alkaloids, flavonoids, saponins, glycosides, and organic acids; with a total polyphenol content of 46.47 ± 2.32 mg GAE/g plant powder. The FMPs-WT were successfully formulated, with a distinct silk-II polymorph; varied sizes of 0.592 to 9.820 µm, depending on the fibroin concentrations and the WT extraction solvent; high entrapment efficiencies of >65%; and sustained-release patterns of polyphenol in pH 7.4 for >6 h. Regarding the antioxidant activity, the pure WT flower extracts possessed high scavenging actions with IC₅₀ of 7.98 ± 0.40 µg/mL, comparable with the standard ascorbic acid (IC₅₀ = 4.23 ± 0.21 µg/mL). Moreover, the FMPs-WT could retain the extract antioxidant capacity, and exert the effects in a timely manner, corresponding to its release profile.

Conclusion

The FMPs-WT could be further investigated to become a potential anti-aging cosmeceutical product in the market.

Hollow protein microparticles formed through cross-linking by an Au3+ initiated redox reaction

Hollow microparticles (MPs) are of great relevance in the materials industry for a wide range of applications, such as catalysis, coatings, and delivery of theranostics. Here, we report the formation of hollow MPs through the assembly of lipoproteins in CaCO₃ templates. Proteins interact in the pores of CaCO₃ templates through attractive hydrophobic forces and form dense edges of hollow MPs. To further cross-link the proteins, Au³⁺ was added to initiate a redox reaction, where proteins were oxidized forming inter- and intramolecular covalent bonds, while Au³⁺ was reduced and gold nanoparticles (AuNPs) were formed. The obtained protein-based hollow MPs have a diameter of 6 μm and the AuNPs are embedded on their surface. Through this research, we suggest a new route to design biobased Au-protein hollow MPs in simple steps, which can allow new possibilities for carrying functional molecules and bioimaging.

Extraction and Encapsulation of Phenolic Compounds of Tunisian Rosemary (Rosmarinus officinalis L.) Extracts in Silk Fibroin Nanoparticles

Rosemary (Rosmarinus officinalis L.) is known to be an effective potential source of natural antioxidants which confer benefits to human health. Their bioactive properties are mainly due to phenolic compounds but these molecules are highly vulnerable to oxidants, light, heat, pH, water and enzymatic activities. Therefore, the stability and shelf life of phenolic compounds should be increased by being protected from chemical and physical damage by means of encapsulation prior to application. Encapsulation is becoming increasingly important in the pharmaceutical, food, cosmetics, textile, personal care, chemical, biotechnology, and medicinal industries due to its potential for stabilization and delivery of delicate and precious bioactive compounds. The aim of the present work was to describe the polyphenolic profile of Tunisian Rosemary, collected from two different bioclimatic areas, and further loading in silk fibroin nanoparticles. The loaded nanoparticles were characterized in terms of morphology, size, polydispersity, Z-potential, secondary structure of the protein, encapsulation efficiency, loading content, and antioxidant activity. On one hand, HPLC analysis revealed the presence of 18 polyphenolic compounds of whichcarnosic acid and carnosol were found to be the most abundant compounds (46.3 to 76.4 and 22.4 to 43.5 mg of compound per gram of dry plant weight (mg/g DPW) respectively), Total phenolic content (TPC) ranged from 85.8 to 137.3 mg of gallic acid equivalent (GAE)/g DPW in post-distilled rosemary extracts andantioxidant activity reached the values of 5.9 to 8.3 µmol of ascorbic acid equivalent (AAE)/g DPW). On the other hand loaded nanoparticles were almost spherical and presented nanometric size and negative Z-potential. Although the encapsulation efficiency in silk fibroin nanoparticles and the drug loading content were low in the conditions of the assay, the encapsulated polyphenols retained near 85% of the radical scavenging activity against DPPH· after 24 h. of incubation at 37 °C. The results showed that post-distilled rosemary residues had an effective potential as natural antioxidants due to their significant antioxidant activity and seemed to be useful in both pharmaceutical and food industries with beneficial properties that might confer benefits to human health and these silk fibroin nanoparticles loaded with rosemary extracts are thus a promising combination for several applications in food technology or nanomedicine.

Current postharvest practices and aflatoxin contamination awareness amongst maize producers in Jimma Zone, Southwest of Ethiopia

Grain contamination by mycotoxins can cause significantly negative health and economic impact in areas where poor agricultural practices and food insecurity is prevalent. This study was conducted to investigate the current postharvest practices and aflatoxin contamination awareness level amongst maize producers in Jimma Zone, Ethiopia. Semi-structured questionnaires were used for quantitative and qualitative data collection from 90 randomly selected maize producers in two districts through a cross-sectional study design. The study revealed poor postharvest practices due to lack of proper infrastructure. Maize is harvested after maturation with the use of traditional sun drying. Plastic sheets are commonly used to protect harvested maize from rain during field drying. The majority of the respondents reported the use of traditional storage structures (81.1%) with great potential for possible mould proliferation and aflatoxin production. Maize producers of up to 62.2% were ignorant about aflatoxins and up to 26.7% reported the possible usage of aflatoxin contaminated maize in human food preparation and animal feed production. Up to 53.3% of the respondents were ignorant of aflatoxin risks in human health and stability during food processing hence the usage of mouldy maize for tella brewing. Further investigations on aflatoxin levels in maize-based food and beverages, and human exposure studies are needed. Moreover, there is a need to enhance the maize producers’ knowledge on good agricultural practices and mycotoxicosis through awareness programmes.

Tuning Microcapsule Shell Thickness and Structure with Silk Fibroin and Nanoparticles for Sustained Release

Microcapsules have attracted widespread interest for their unique properties in encapsulation, protection, and separation of active ingredients from the surrounding environment. However, microcapsule carriers with controllable shell thickness, permeability, good mechanical properties, and thermostability are challenging to obtain. Herein, robust and versatile composite microcapsules were fabricated using SiO₂ nanoparticle-stabilized (Pickering) oil emulsions as core templates, while silk fibroin (SF) was assembled at the oil/water interface. This process resulted in the formation of physically and chemically stable microcapsules with a thick (∼800 nm) shell that protected the encapsulated ingredient from high shear forces and high temperatures during spray-drying. SiO₂ nanoparticles were randomly distributed in the shell matrix after preparation, making the microcapsules mechanically robust (4.48 times higher than control samples prepared using surfactant Tween 80 instead of the SiO₂ nanoparticles), as well as thermostable (retained shape to 900 °C). The microcapsules displayed tunable drug release by adjusting the SF content in the shell. Under optimal conditions (weight ratio of SiO₂/SF = 7:10, corn oil content about 55 wt %), a model drug (curcumin) was encapsulated in the SF microcapsules with an encapsulation efficiency up to 95%. The in vitro drug release from these SF microcapsules lasted longer than control microcapsules, demonstrating the capability of these novel microcapsules in sustaining drug release.

Progress in Preparation of Silk Fibroin Microspheres for Biomedical Applications

As a natural biomaterial, silk fibroin (SF) holds great potential in biomedical applications with its broad availability, good biocompatibility, high mechanical strength, ease of fabrication, and controlled degradation. With emerging fabrication methods, nanoand microspheres made from SF have brought about unique opportunities in drug delivery, cell culture, and tissue engineering. For these applications, the size and distribution of silk fibroin particles (SFPs) are critical and require precise control during fabrication. Herein, we review common and emerging SFPs fabrication methods and their biomedical applications, and also the challenges and opportunities for SFPs in the near future. Lay Summary: The application of silk in textile has an extraordinarily long history and new biomedical applications emerged owing to the good biocompatibility and versatile fabrication options of its major protein component, silk fibroin. With the development of nanotechnology and microfabrication, silk fibroin has been fabricated into nano- or microspheres with precisely controlled shape and distribution. In this review, we summarize common and emerging silk fibroin particle fabrication methods and their biomedical applications, and also discuss their challenges and opportunities in the nearest future.

Silk nanoparticles: from inert supports to bioactive natural carriers for drug delivery

Silk proteins have been studied and employed for the production of drug delivery (nano)systems. They show excellent biocompatibility, controllable biodegradability and non-immunogenicity and, if needed, their properties can be modulated by blending with other polymers. Silk fibroin (SF), which forms the inner core of silk, is a (bio)material officially recognized by the Food and Drug Administration for human applications. Conversely, the potential of silk sericin (SS), which forms the external shell of silk, could still be considered under evaluation. At the best of our knowledge, nanoparticles based on silk sericin "alone" cannot be produced, due to its physicochemical instability influenced by extreme pH, high water solubility and temperature; for these reasons, it almost always needs to be combined with other polymers for the development of drug delivery systems. In this review, we focused on silk proteins as bioactive natural carriers, since they show not only optimal features as inert excipients, but also remarkable intrinsic biological activities. SF has anti-inflammatory properties, while SS presents antioxidant, anti-tyrosine, anti-aging, anti-elastase and anti-bacterial features. Here, we give an overview on SF or SS silk-based nanosystems, with particular attention on the production techniques.

Multiscale design and synthesis of biomimetic gradient protein/biosilica composites for interfacial tissue engineering

Continuous gradients present at tissue interfaces such as osteochondral systems, reflect complex tissue functions and involve changes in extracellular matrix compositions, cell types and mechanical properties. New and versatile biomaterial strategies are needed to create suitable biomimetic engineered grafts for interfacial tissue engineering. Silk protein-based composites, coupled with selective peptides with mineralization domains, were utilized to mimic the soft-to-hard transition in osteochondral interfaces. The gradient composites supported tunable mineralization and mechanical properties corresponding to the spatial concentration gradient of the mineralization domains (R5 peptide). The composite system exhibited continuous transitions in terms of composition, structure and mechanical properties, as well as cytocompatibility and biodegradability. The gradient silicified silk/R5 composites promoted and regulated osteogenic differentiation of human mesenchymal stem cells in an osteoinductive environment in vitro. The cells differentiated along the composites in a manner consistent with the R5-gradient profile. This novel biomimetic gradient biomaterial design offers a useful approach to meet a broad range of needs in regenerative medicine.