Preparation of a novel rape pollen shell microencapsulation and its use for protein adsorption and pH-controlled release

Calcium carbonate-modified plant sporopollen capsule as an eco-friendly microvehicle for controlled release of pesticide

BACKGROUND

In this work, natural club moss (Lycopodium clavatum, LC) spores with a porous surface morphology and highly uniform size distribution were engineered into controlled-release microvehicles for pesticide delivery. As a proof of concept, a widely used fungicide, fluazinam (FLU), was successfully loaded into LC spores and then modified with different amounts of CaCO₃ (CaC) to extend the efficacy duration of FLU. Significantly, as the control target of FLU, clubroot disease is a worldwide destructive disease of cruciferous crops, and its development is favored by acidic soils and can be suppressed at high Ca concentrations.

RESULTS

Fabricated FLU@LC-CaC microcapsules, FLU loading and CaCO₃ deposition were systematically characterized by field emission scanning electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The as-prepared FLU@LC-CaC microcapsules showed sustained-release behaviors and were potentially able to supplement the Ca concentration in acidic environments. This approach synergistically enhanced in vivo bioactivity for the on-demand control of clubroot disease. An in vivo bioassay revealed that the control efficacy of FLU@LC-CaC against clubroot disease in pak choi (Brassica chinensis) (66.4%) was 1.7-fold higher than that of a commercial FLU suspension concentrate (38.2%) over the course of the cultivation period (35 days).

CONCLUSIONS

This work provides new ideas not only for developing eco-friendly and scalable microvehicles for pesticide delivery based on natural sporopollen, but also for unconventional research perspectives in on-demand pest management based on their occurrence characteristics. © 2022 Society of Chemical Industry.

Higher Essential Amino Acid and Crude Protein Contents in Pollen Accelerate the Oviposition and Colony Foundation of Bombus breviceps (Hymenoptera: Apidae)

Pollen is an important source of nutrition for bumblebees to survive, reproduce, and raise their offspring. To explore the nutritional requirements for the egg laying and hatching of queenright Bombus breviceps colonies, camellia pollen, oilseed rape pollen, apricot pollen, and mixtures of two or three types of pollen in equal proportions were used to feed the queens in this study. The results showed that the camellia pollen with a higher essential amino acid content was superior to the pollen with a lower essential amino acid content in the initial egg-laying time (p < 0.05), egg number (p < 0.05), larval ejection (p < 0.01), time of first worker emergence (p < 0.05), and the average weight of workers in the first batch (p < 0.01). It took less time for colonies under the camellia pollen and camellia-oilseed rape-apricot pollen mix treatments, both with a higher crude protein content, to reach ten workers in the colony (p < 0.01). On the contrary, the queens fed apricot pollen never laid an egg, and larvae fed oilseed rape pollen were all ejected-both pollens with a lower essential amino acid content. The results emphasize that the diet should be rationally allocated to meet the nutritional needs of local bumblebees at various stages when guiding them to lay eggs, hatch, and develop a colony.

Role of Sporopollenin Shell Interfacial Properties in Protein Adsorption

Sporopollenin shells isolated from natural pollen grains have received attention in translational and applied research in diverse fields of drug delivery, vaccine delivery, and wastewater remediation. However, little is known about the sporopollenin shell's potential as an adsorbent. Herein, we have isolated sporopollenin shells from four structurally diverse pollen species, black walnut, marsh elder, mugwort, and silver birch, to study protein adsorption onto sporopollenin shells. We investigated three major interfacial properties, surface area, surface functional groups, and surface charge, to elucidate the mechanism of protein adsorption onto sporopollenin shells. We showed that sporopollenin shells have a moderate specific surface area (<12 m²/g). Phosphoric acid and potassium hydroxide treatments that were used to isolate sporopollenin shells from natural pollen grains also result in the functionalization of sporopollenin shell surfaces with ionizable groups of carboxylic acid and carboxylate salt. As a result, sporopollenin shells exhibit a negative ζ potential in the range of -75 to -82 mV at pH 10 when dispersed in water. The ζ potentials of sporopollenin shells remain negative in the pH range of 2.5-11, with the absolute value of ζ potential showing a decrease with the decrease in pH. The negative surface charge promotes the adsorption of protein onto the sporopollenin shell via electrostatic interaction. Despite having a moderate surface area, sporopollenin shells adsorb a significant amount of lysozyme (145-340 μg lysozyme per mg of sporopollenin shells). Lysozyme adsorption onto sporopollenin shells alters the surface, and the surface charge becomes positive at acidic pH. Overall, this study demonstrates the potential of sporopollenin shells to adsorb proteins, highlights the critical role of sporopollenin shell's interfacial properties in protein adsorption, and identifies the mechanism of protein adsorption on sporopollenin shells.

Fe-functionalized paramagnetic sporopollenin from pollen grains: one-pot synthesis using ionic liquids

The preparation of Fe-decorated sporopollenins was achieved using pollen grains and an ionic liquid as solvent and functionalizing agent. The integrity of the organic capsules was ascertained through scanning electron microscopy studies. The presence of Fe in the capsule was investigated using FT-IR, X-ray photoemission spectroscopy and energy-dispersive X-ray spectroscopy. Electron paramagnetic resonance and magnetization measurements allowed us to demonstrate the paramagnetic behavior of our Fe-functionalized sporopollenin. A few potential applications of pollen-based systems functionalized with magnetic metal ions via ionic liquids are discussed.

Carboxymethylpachymaran entrapped plant-based hollow microcapsules for delivery and stabilization of β-galactosidase

β-Galactosidase (β-Gal) as a dietary supplement can alleviate symptoms of lactose intolerance. However, β-Gal is deactivated due to the highly acidic conditions and proteases in the digestive tract. In this work, β-Gal was encapsulated into L. clavatum sporopollenin exine capsules (SECs) to fabricate an oral-controlled release system and increase the stability of β-Gal in the digestive tract. The SEC extraction process was optimized. A 3-hour vacuum loading was determined as the optimal loading time. Five different initial ratios of SECs : β-Gal were optimized with the maximum enzyme retention rate reaching 79.40 ± 1.96%. Furthermore, β-Gal-loaded SECs entrapped in carboxymethylpachymaran (CMP) could control the release of β-Gal under simulated gastrointestinal conditions (SGC). The optimal enzyme retention rate reached 65.33 ± 1.46% within 24 h under SGC. Collectively, these results indicated that the entrapped SECs could be used as an effective oral delivery vehicle of β-Gal to improve its performance as a dietary supplement in the digestion of lactose.

Extraction of Plant-based Capsules for Microencapsulation Applications

Microcapsules derived from plant-based spores or pollen provide a robust platform for a diverse range of microencapsulation applications. Sporopollenin exine capsules (SECs) are obtained when spores or pollen are processed so as to remove the internal sporoplasmic contents. The resulting hollow microcapsules exhibit a high degree of micromeritic uniformity and retain intricate microstructural features related to the particular plant species. Herein, we demonstrate a streamlined process for the production of SECs from Lycopodium clavatum spores and for the loading of hydrophilic compounds into these SECs. The current SEC isolation procedure has been recently optimized to significantly reduce the processing requirements which are conventionally used in SEC isolation, and to ensure the production of intact microcapsules. Natural L. clavatum spores are defatted with acetone, treated with phosphoric acid, and extensively washed to remove sporoplasmic contents. After acetone defatting, a single processing step using 85% phosphoric acid has been shown to remove all sporoplasmic contents. By limiting the acid processing time to 30 hr, it is possible to isolate clean SECs and avoid SEC fracturing, which has been shown to occur with prolonged processing time. Extensive washing with water, dilute acids, dilute bases, and solvents ensures that all sporoplasmic material and chemical residues are adequately removed. The vacuum loading technique is utilized to load a model protein (Bovine Serum Albumin) as a representative hydrophilic compound. Vacuum loading provides a simple technique to load various compounds without the need for harsh solvents or undesirable chemicals which are often required in other microencapsulation protocols. Based on these isolation and loading protocols, SECs provide a promising material for use in a diverse range of microencapsulation applications, such as, therapeutics, foods, cosmetics, and personal care products.

Natural Sunflower Pollen as a Drug Delivery Vehicle

In nature, pollen grains play a vital role for encapsulation. Many pollen species exist which are often used as human food supplements. Dynamic image particle analysis, scanning electron microscopy, and confocal microscopy analysis confirmed the size, structural uniformity, and macromolecular encapsulation in sunflower pollen, paving the way to explore natural pollen grains for the encapsulation of therapeutic molecules.

Eco-friendly streamlined process for sporopollenin exine capsule extraction

Sporopollenin exine capsules (SECs) extracted from Lycopodium clavatum spores are an attractive biomaterial possessing a highly robust structure suitable for microencapsulation strategies. Despite several decades of research into SEC extraction methods, the protocols commonly used for L. clavatum still entail processing with both alkaline and acidolysis steps at temperatures up to 180 °C and lasting up to 7 days. Herein, we demonstrate a significantly streamlined processing regimen, which indicates that much lower temperatures and processing durations can be used without alkaline lysis. By employing CHN elemental analysis, scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), and dynamic image particle analysis (DIPA), the optimum conditions for L. clavatum SEC processing were determined to include 30 hours acidolysis at 70 °C without alkaline lysis. Extending these findings to proof-of-concept encapsulation studies, we further demonstrate that our SECs are able to achieve a loading of 0.170 ± 0.01 g BSA per 1 g SECs by vacuum-assisted loading. Taken together, our streamlined processing method and corresponding characterization of SECs provides important insights for the development of applications including drug delivery, cosmetics, personal care products, and foods.

Extraction of sporopollenin exine capsules from sunflower pollen grains

A simple extraction process was developed to isolate sunflower sporopollenin exine capsules (SECs). The sunflower SECs holds significant potential as biomaterial for applications in drug delivery, cosmetics, and food technology.