Biopolymer Encapsulation Research Articles

Betalains as Natural Dyes and Applications

Betalains are natural pigments that include betacyanin and betaxanthin, found in plants such as beets and cacti. In the food industry, betalains are used as natural colorants due to their color stability and health benefits, including antioxidant and anti-inflammatory properties that support the prevention of degenerative diseases. With increasing demand for natural ingredients, betalains are also being promoted in the cosmetics and health product industries. In the healthy food sector, new extraction techniques like microwave-assisted extraction and aqueous two-phase technology have improved the purification efficiency and quality of betalain pigments. In cosmetics, betalains are utilized as anti-aging and anti-inflammatory components, with innovative approaches like biopolymer encapsulation to enhance product stability. Geographical trends show significant interest in betalain use in natural cosmetics and healthy foods in Europe and Asia, while research in Latin America focuses on its potential as a supplement and food colorant. In renewable energy technology, betalains act as photosensitizers in dye-sensitized solar cells (DSSCs), though their stability still requires optimization, such as through co-sensitization with other pigments. These innovations suggest that betalains hold considerable potential in the food, cosmetics, and energy industries, making them a versatile and globally relevant natural material.

Enhancing concrete self-healing capabilities of Bacillus sphaericus spores through the encapsulation in biopolymeric microcapsules

This study examined the encapsulation of Bacillus sphaericus LMG 22257 spores in biopolymeric microcapsules (MCs) for use in cement mortar, with a focus on enhancing self-healing properties. Biopolymers, including alginate (ALG), chitosan (CTS), carboxymethyl cellulose (CMC), and ALG/CMC blends at various ratios, were employed to fabricate the MCs through ionotropic gelation and freeze–drying. The physicochemical properties of MCs, including size, morphology, and swelling behavior under simulated concrete conditions, were assessed. Among these, ALG/CMC-MCs exhibited superior characteristics and demonstrated the highest urea hydrolysis activity when incorporated into the mortar, indicating optimal spore protection. Despite an initial decrease in compressive strength, the ALG/CMC blend with an ALG:CMC mass ratio of 6:4 achieved a crack healing efficiency of 96.7% over 28 days under cyclic wet-dry conditions. These findings highlight the potential of biopolymer encapsulation for embedding functional microorganisms in construction materials, contributing to a more durable and sustainable infrastructure.

Biopolymer encapsulation for improved probiotic delivery: Advancements and challenges

<p>Probiotics, known for their health benefits as living microorganisms, hold significant importance across various fields, including agriculture, aquaculture, nutraceuticals, and pharmaceuticals. Optimal delivery and storage of probiotic cells are essential to maximize their effectiveness. Biopolymers, derived from living sources, plants, animals, and microbes, offer a natural solution to enhance probiotic capabilities and they possess distinctive qualities such as stability, flexibility, biocompatibility, sustainability, biodegradability, and antibacterial properties, making them ideal for probiotic applications. These characteristics create optimal environments for the swift and precisely targeted delivery of probiotic cells that surpass the effectiveness of unencapsulated probiotic cells. Various encapsulation techniques using diverse biopolymers are employed for this purpose. These techniques are not limited to spray drying, emulsion, extrusion, spray freeze drying, layer by layer, ionic gelation, complex coacervation, vibration technology, electrospinning, phase separation, sol-gel encapsulation, spray cooling, fluidized, air suspension coating, compression coating, co-crystallization coating, cyclodextrin inclusion, rotating disk, and solvent evaporation methods. This review addresses the latest advancements in probiotic encapsulation materials and techniques, bridging gaps in our understanding of biopolymer-based encapsulation systems. Specifically, we address the limitations of current encapsulation methods in maintaining probiotic viability under extreme environmental conditions and the need for more targeted and efficient delivery mechanisms. Focusing on the interactions between biopolymers and probiotics reveals how customized encapsulation approaches can enhance probiotic stability, survival, and functionality. Through detailed comparative analysis of the effectiveness of various encapsulation methods, we identify key strategies for optimizing probiotic deployment in challenging conditions such as high-temperature processing, acidic environments, and gastrointestinal transit. The findings presented in this review highlight the superior performance of novel encapsulation methods using biopolymer blends and advanced technologies like electrospinning and layer-by-layer assembly, which provide enhanced protection and controlled release of probiotics by offering insights into the development of more robust encapsulation systems that ensure the sustained viability and bioavailability of probiotics, thus advancing their application across multiple industries. In conclusion, this paper provides the foundation for future research to refine encapsulation techniques to overcome the challenges of probiotic delivery in clinical and commercial settings.</p>

Preparation of curcumin-chitosan composite film with high antioxidant and antibacterial capacity: Improving the solubility of curcumin by encapsulation of biopolymers

Curcumin is a kind of natural antioxidant antibacterial agent, but the poor water solubility and stability limit its application in the field of food packaging. To solve this problem, dialdehyde starch-curcumin-gelatin particles (hereafter denoted as DCG particles) were prepared by wrapping curcumin into the cross-linked body formed by dialdehyde starch and gelatin. The strong hydrophilicity of the outer cross-linked body increases the water solubility of curcumin by 3162.7% from 0.43 μg/mL to 13.6 μg/mL. DCG particles were added to chitosan to form a composite film to evaluate the application of the particles. The Chromogenic group and phenolic hydroxyl group in curcumin endowed the composite film with good ultraviolet resistance and antioxidant capacity, which could shield 94.48% of ultraviolet radiation, and the free radical clearance rate reached 99%. Besides, chitosan and curcumin can destroy bacterial cell film and inhibit bacterial division and proliferation. The inhibition zone of composite film against E. coli and S. aureus was 21.4 mm and 19.9 mm, and the cell survival rate treated with film solution was 113.16%. The weight loss rate and decay rate of fruit soaked in film solution were 60% and 10% compared with untreated fruits, respectively. Overall, this study advanced a novel method for improving the water solubility of curcumin and making natural food packaging materials.

Fertilizers for food and nutrition security in sub-Saharan Africa: An overview of soil health implications

Sub-Saharan Africa (SSA) faces chronic food insecurity associated with soil degradation and the peculiar aftermath of climate change and exacerbated by rising population and historically poor agricultural practices. Notably, use of mineral fertilizers has the potential to counteract soil degradation in SSA; it drives an increased agricultural production required to feed the rising population while sustaining the quality and health of soils. However, limited financial resources deprive SSA of the promise of fertilizers, wherein application rates are historically low, and regimes are characterized by unbalanced nutrient composition and poor fertilizer quality. Although current global fertilizer use is generally characterized by low efficiency, SSA is most affected due to the already low usage and the quality of available fertilizer products. About 70% of fertilizer-nitrogen is lost through unregulated transformation to ammonia, nitrous oxide, and nitrate that are either volatilized or emitted into the atmosphere or leached into water bodies. Similarly, the preponderance of fertilizer-phosphorus is lost via run-off and leaching, unavailing it to plants while overloading streams and rivers and, together with nitrate, causing eutrophication. These environmental problems are accentuated in SSA where fertilizer quantity and quality issues are already a limiting factor. Notably, recent advances happening outside of SSA indicate that nutrients, when strategically formulated, such as by nano packaging, (bio)polymer encapsulation, and tunable to respond to environmental cues, can provide multiple outcomes, particularly, healthy soils with higher productivity. Therefore, presumably, a proper synthesis of the gamut of soil properties influencing plant nutrient release and availability, options for plant exposure and uptake is critical for realizing these benefits in SSA. Despite these possibilities, there is a lack of deeper context on fertilizer-related issues as they affect food and nutrition security and the health of soils in SSA. This paper provides an overview of the fertilizer-nutrient and associated agronomic, food insecurity and soil environmental challenges and opportunities, which though not exclusive to SSA per se, can be reasoned with the peculiarity of the region. This provides the impetus to increase fertilizer use efficiency, improve soil and environmental health, sustainable crop production, and food and nutrition security in SSA.

Advancement of Protein- and Polysaccharide-Based Biopolymers for Anthocyanin Encapsulation

Although evidence shows that anthocyanins present promising health benefits, their poor stability still limits their applications in the food industry. Increasing the stability of anthocyanins is necessary to promote their absorption and metabolism and improve their health benefits. Numerous encapsulation approaches have been developed for the targeted release of anthocyanins to retain their bioactivities and ameliorate their unsatisfactory stability. Generally, choosing suitable edible encapsulation materials based on biopolymers is important in achieving the expected goals. This paper presented an ambitious task of summarizing the current understanding and challenges of biopolymer-based anthocyanin encapsulation in detail. The food-grade edible microencapsulation materials, especially for proteins and polysaccharides, should be employed to improve the stability of anthocyanins for effective application in the food industry. The influence factors involved in anthocyanin stability were systematically reviewed and highlighted. Food-grade proteins, especially whey protein, caseinate, gelatin, and soy protein, are attractive in the food industry for encapsulation owing to the improvement of stability and their health benefits. Polysaccharides, such as starch, pectin, chitosan, cellulose, mucilages, and their derivatives, are used as encapsulation materials because of their satisfactory biocompatibility and biodegradability. Moreover, the challenges and perspectives for the application of anthocyanins in food products were presented based on current knowledge. The proposed perspective can provide new insights into the amelioration of anthocyanin bioavailability by edible biopolymer encapsulation.

Disposable superoxide dismutase biosensors based on gold covered polycaprolactone fibers for the detection of superoxide in cell culture media.

A novel and disposable biosensor based on superoxide dismutase (SOD) immobilized on gold metallized polycaprolactone electrospun polymeric fibers (PCl/Au) has been developed for the determination of superoxide (O2•-) in cell culture media. SOD biosensors were constructed employing three immobilization methods: cross-linking with EDC/NHS at a cysteine self-assembled monolayer (PCl/Au/SODCYS), biopolymer encapsulation with chitosan (PCl/Au/SODCHI) and cross-linking with glutaraldehyde (PCl/Au/SODGA). Scanning electron microscopy was performed at the three different biosensors to evaluate their surface morphologies. Biosensors were employed for the electrochemical detection of superoxide by fixed potential amperometry at different applied potentials, with two distinct enzymatic mechanisms being proposed: i) the reduction of the enzymatically generated peroxide, at -0.3V, for which the PCl/Au/SODCHI biosensor presented the highest value of sensitivity of 40.1μAmM-1cm-2, and ii) the regeneration of the enzyme catalytic copper centre, at +0.3V, for which the PCl/Au/SODCYS biosensor had the highest sensitivity value of 16.1μAmM-1cm-2. The proposed recognition mechanisms were further confirmed by cyclic voltammetric measurements, which enabled also to determine the amount of immobilized electroactive SOD, with highest value corresponding to the PCl/Au/SODCYS biosensor. The biosensors with best analytical performance, PCl/Au/SODCYS and PCl/Au/SODCHI, were further investigated for stability and selectivity, with best results for the PCl/Au/SODCYS, chosen for superoxide monitoring in cell culture media. The study is promising for future application of PCl/Au/SODCYS for the on-line superoxide monitoring of superoxide in cell cultures, grown directly on the biosensor itself.

Subacute feeding toxicity of low-sodium sausages manufactured with sodium substitutes and biopolymer-encapsulated saltwort (Salicornia herbacea) in a mouse model.

Low-sodium sausages were manufactured using sodium substitution and biopolymer encapsulation. A diet comprising 10% treatment sausages (six treatment groups: C (100% NaCl), T1 (55% sodium substitute + 45% saltwort salt), T2 (55% sodium substitute + 45% saltwort salt with chitosan), T3 (55% sodium substitute + 45% saltwort salt with cellulose), T4 (55% sodium substitute + 45% saltwort salt with dextrin), and T5 (55% sodium substitute + 45% saltwort salt with pectin)) was added to a 90% commercial mouse diet for 4 weeks. Subacute toxicity, hematology, liver function, and organ weight tests in low-sodium sausage groups showed results similar to those of the control group, and all toxicity test levels were within normal ranges. All low-sodium sausage types tested are suggested to be safe in terms of subacute toxicity. Moreover, low-sodium sausages can be manufactured by biopolymer encapsulation of saltwort using pectin, chitosan, cellulose, and dextrin without toxicity. © 2019 Society of Chemical Industry.

Analysis of the effects of biopolymer encapsulation and sodium replacement combination technology on the quality characteristics and inhibition of sodium absorption from sausage in mice

The effects of biopolymer encapsulation and sodium replacement combination technology on quality characteristics (i.e., bitter taste) and inhibition of sodium absorption from pork sausage in mice were evaluated. The sausages were divided into three different sodium replacement groups (none, 40%, and 50%) and three different biopolymer encapsulation groups (none, cellulose, and chitosan) in combination. In groups with 50% sodium replacement by KCl and MgCl2, T8 (chitosan encapsulation) showed the highest inhibition of the sodium absorption rate. However, chitosan encapsulation groups (T2, T5, and T8) had higher bitterness and lower overall acceptability than other treatment groups. In contrast, in the group with 40% sodium replacement by KCl, T4 (cellulose encapsulation) exhibited the highest inhibition of sodium absorption without a bitter taste. This is the first report showing that 40–50% sodium replacement combined with 3% cellulose encapsulation reduced sodium absorption from sausage by 60% without causing a bitter taste.

Development of Sausage with Inhibition of 60% Sodium Intake, Using Biopolymer Encapsulation Technology and Sodium Replacers

To develop sausage with inhibition of 60% sodium intake, using biopolymer encapsulation technology and sodium replacer, the sausages were subdivided into five treatment groups: control was the normal sodium amount without sodium substitution and biopolymers; and four treatments involved encapsulation with four different biopolymers (T1: pectin, T2: chitosan, T3: cellulose, T4: dextrin), with sodium substituted by 55% with sodium replacers (a mixture of potassium, magnesium, and calcium chlorides). The experimental sausages were fed to mice for 48 h, and sodium absorption and its inhibition were measured. T2 sausage (3% chitosan with a sodium replacer) and T3 sausage (3% cellulose with a sodium replacer) showed the highest rates of inhibition of sodium absorption: 69.65 and 67.34%, respectively. These results indicated that the final goal of 60% inhibition of sodium intake was accomplished by 55% sodium replacement and more than 15% inhibition of sodium absorption with minimal deterioration of sausage quality.

Effect of dietary bioactive compounds and biopolymer encapsulated lipids on metabolism of lipids in high fat diet‐fed mice

We determined the effects of dietary bioactive components and biopolymer encapsulation on lipids’ metabolism in obese mice. Six random groups of 60 obese mice were fed the following diets for 95 days: Basal diet; cellulose encapsulated lipids; pectin and chitosan encapsulated lipids (EPC); Camellia sinensis and Coix lacryma enhanced diet; C. sinensis and C. lacryma diet plus pectin and chitosan encapsulated lipids; hydroxycitric acid, caffeine, and vitamin C enhanced diet plus pectin and chitosan encapsulated lipids (HCVEPC). The HCVEPC group usually presented lower body and total adipose tissue weight compared to other diet groups. Intestine length was not significantly different among all dietary groups. Serum leptin, triglycerides, and cholesterol were significantly lower in EPC and HCVEPC compared to other groups. However, serum glucose was not significantly different among groups. Our results indicate that bioactive compounds and biopolymers’ encapsulation act synergistically in the reduction of body and adipose tissue weight.Practical applications: Based on the results described above, it is suggested that bioactive components and biopolymer encapsulation with some natural products has synergistically in the reduction of body and adipose tissue weight on in vivo models. In addition, through this results suggest that can be used information and utilization of lipids metabolism, this research is to highlight the potential of selected natural products as a source of functional Substances. Therefore, lipids encapsulated with dietary biopolymers and bioactive compounds should be considered as a prospective functional food and pharmaceuticals application.We investigated effects of dietary bioactive components and biopolymer encapsulation on lipids’ metabolism in obese mice. Bio‐active components could enhance the effect of body and adipose tissue weight reduction in obese mice models. Dietary bio‐active compounds together with biopolymer encapsulated lipids showed a great reduction in serum triglycerides and cholesterol.

Effect of biopolymer encapsulation on the digestibility of lipid and cholesterol oxidation products in beef during in vitro human digestion

In this study, beef patties were encapsulated with 3% chitosan, pectin, onion powder, or green tea powder and the beef patties were then passed through an in vitro human digestion model. The total lipid digestibility was lowest (p<0.05) in beef patties encapsulated with chitosan and pectin after digestion in the small intestine. Thiobarbituric acid reactive substance (TBARS) values were significantly lower (p<0.05) for beef patties encapsulated with chitosan and pectin, when compared with the control, after digestion in the small intestine. In contrast, the 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radical–scavenging activity was highest (p<0.05) in beef patties encapsulated with onion powder and green tea powder after digestion in the small intestine. The total cholesterol oxidation product (COP) content was significantly lower (p<0.05) in beef patties encapsulated with biopolymers than in the control after digestion in the small intestine.

Therapeutic foam scaffolds incorporating biopolymer-shelled mesoporous nanospheres with growth factors

A novel therapeutic scaffolding system of engineered nanocarriers within a foam matrix for the long-term and sequential delivery of growth factors is reported. Mesoporous silica nanospheres were first functionalized to have an enlarged mesopore size (12.2nm) and aminated surface, which was then shelled by a biopolymer, poly(lactic acid) (PLA) or poly(ethylene glycol) (PEG), via electrospraying. The hybrid nanocarrier was subsequently combined with collagen to produce foam scaffolds. Bovine serum albumin (BSA), used as a model protein, was effectively loaded within the enlarged nanospheres. The biopolymer shell substantially prolonged the release period of BSA (2–3weeks from shelled nanospheres vs. within 1week from bare nanospheres), and the release rate was highly dependent on the shell composition (PEG>PLA). Collagen foam scaffolding of the shelled nanocarrier further slowed down the protein release, while enabling the incorporation of a rapidly releasing protein, which is effective for sequential protein delivery. Acidic fibroblast growth factor (aFGF), loaded onto the shelled-nanocarrier scaffolds, was released over a month at a highly sustainable rate, profiling a release pattern similar to that of BSA. The biological activity of the aFGF was evidenced by the significant proliferation of osteoblastic precursor cells in the aFGF-releasing scaffolds. Furthermore, the aFGF-delivering scaffolds implanted in rat subcutaneous tissue for 2weeks showed a substantially enhanced invasion of fibroblasts with a homogeneous population. Taken together, it is concluded that the biopolymer encapsulation of mesoporous nanospheres effectively prolongs the release of growth factors over weeks to a month, providing a nanocarrier platform for a long-term growth factor delivery. Moreover, the foam scaffolding of the nanocarrier system is a potential therapeutic three-dimensional matrix for cell culture and tissue engineering.

The Effects of Biopolymer Encapsulation on Total Lipids and Cholesterol in Egg Yolk during in Vitro Human Digestion

The purpose of this study was to examine the effect of biopolymer encapsulation on the digestion of total lipids and cholesterol in egg yolk using an in vitro human digestion model. Egg yolks were encapsulated with 1% cellulose, pectin, or chitosan. The samples were then passed through an in vitro human digestion model that simulated the composition of mouth saliva, stomach acid, and the intestinal juice of the small intestine by using a dialysis tubing system. The change in digestion of total lipids was monitored by confocal fluorescence microscopy. The digestion rate of total lipids and cholesterol in all egg yolk samples dramatically increased after in vitro human digestion. The digestion rate of total lipids and cholesterol in egg yolks encapsulated with chitosan or pectin was reduced compared to the digestion rate of total lipids and cholesterol in other egg yolk samples. Egg yolks encapsulated with pectin or chitosan had lower free fatty acid content, and lipid oxidation values than samples without biopolymer encapsulation. Moreover, the lipase activity decreased, after in vitro digestion, in egg yolks encapsulated with biopolymers. These results improve our understanding of the effects of digestion on total lipids and cholesterol in egg yolk within the gastrointestinal tract.

Effects of Dietary Conjugated Linoleic Acid and Biopolymer Encapsulation on Lipid Metabolism in Mice

Forty mice were randomly divided into four groups on the basis of the diet to be fed as follows: 5% (low) fat diet (T1: LF); 20% (high) fat diet (T2: HF); 20% fat containing 1% conjugated linoleic acid (CLA) (T3: HFC); and 20% fat containing 1% CLA with 0.5% biopolymers (T4: HFCB). The high-fat with CLA diet groups (HFC and HFCB) and the low-fat diet group (LF) tended to have lower body weights and total adipose tissue weights than those of the high-fat diet group (HF). Serum leptin and triglyceride were significantly lower in the high fat with CLA-fed groups (HFC and HFCB) and the low-fat diet group (LF) than those in the high-fat diet group (HF). It is noteworthy that the high-fat with CLA and biopolymers group (HFCB) showed the lowest serum triglyceride and cholesterol concentrations. In the high-fat-fed group (HF), voluntary travel distance as a measure of physical activity decreased after three weeks of feeding. However, the CLA-fed groups showed increased physical activity. The groups fed high-fat diets supplemented with CLA alone and with CLA and biopolymers had higher viscosity of small intestinal contents than that in the low- and high-fat dietary groups.

Effects of biopolymer encapsulation on trans fatty acid digestibility in an in vitro human digestion system

The purpose of this study was to examine the effects of biopolymer encapsulation on the digestion of trans fatty acids by using an in vitro human digestion model. We simulated the main components of the human digestive system using a dialysis tubing system that contained synthetic saliva, gastric juice, and digestive enzymes of the small intestine. Trans fatty acid-enriched fat was encapsulated with 1% chitosan, pectin, cellulose, and β-glucan, and passed through the model system. Samples of trans fatty acid-enriched fat that were unencapsulated were more digestible than those that were encapsulated in biopolymers. Moreover, the levels of trans octadecenoic acids (18 : 1t) formed during the digestion of trans fatty acid-enriched fat were decreased upon biopolymer encapsulation. Fat samples enriched with trans fatty acids that were encapsulated with pectin or chitosan had lower free fatty acid contents and lipid oxidation values than unencapsulated control samples. These findings improve our understanding of the effects of biopolymer encapsulation on the digestion of total lipids and trans fatty acids within the gastrointestinal tract.

Aqueous phase separation as a possible route to compartmentalization of biological molecules.

How could the incredible complexity of modern cells evolve from something simple enough to have appeared in a primordial soup? This enduring question has sparked the interest of researchers since Darwin first considered his theory of natural selection. Organic molecules, even potentially functional molecules including peptides and nucleotides, can be produced abiotically. Amphiphiles such as surfactants and lipids display remarkable self-assembly processes including the spontaneous formation of vesicles resembling the membranes of living cells. Nonetheless, numerous questions remain. Given the presumably dilute concentrations of macromolecules in the prebiotic pools where the earliest cells are thought to have appeared, how could the necessary components become concentrated and encapsulated within a semipermeable membrane? What would drive the further structural complexity that is a hallmark of modern living systems? The interior of modern cells is subdivided into microcompartments such as the nucleoid of bacteria or the organelles of eukaryotic cells. Even within what at first appears to be a single compartment, for example, the cytoplasm or nucleus, chemical composition is often nonuniform, containing gradients, macromolecular assemblies, and/or liquid droplets. What might the internal structure of intermediate evolutionary forms have looked like?The nonideal aqueous solution chemistry of macromolecules offers an attractive possible answer to these questions. Aqueous polymer solutions will form multiple coexisting thermodynamic phases under a variety of readily accessible conditions. In this Account, we describe aqueous phase separation as a model system for biological compartmentalization in both early and modern cells, with an emphasis on systems that have been encapsulated within a lipid bilayer. We begin with an introduction to aqueous phase separation and discuss how this phenomenon can lead to microcompartmentalization and could facilitate biopolymer encapsulation by partitioning of solutes between the phases. We then describe primitive model cells based on phase separation inside lipid vesicles, which mimic several basic properties of biological cells: microcompartmentation, protein relocalization in response to stimulus, loss of symmetry, and asymmetric vesicle division. We observe these seemingly complex phenomena in the absence of genetic molecules, enzymes, or cellular machinery, and as a result these processes could provide clues to possible intermediates in the early evolution of cell-like assemblies.

Biopolymer encapsulated live influenza virus as a universal CD8+ T cell vaccine against influenza virus

Current influenza virus vaccines primarily elicit antibodies and can be rendered ineffective by antigenic drift and shift. Vaccines that elicit CD8+ T cell responses targeting less variable proteins may function as universal vaccines that have broad reactivity against different influenza virus strains. To generate such a universal vaccine, we encapsulated live influenza virus in a biopolymer and delivered it to mice subcutaneously. This vaccine was safe, induced potent CD8+ T cell immunity and protected mice against heterosubtypic lethal challenge. Safety of subcutaneous (SQ) vaccination was tested in Rag−/−γc−/− double knockout mice which we show cannot control intranasal infection. Biopolymer encapsulation of live influenza virus could be used to develop universal CD8+ T cell vaccines against heterosubtypic and pandemic strains.

Self-assembled vesicles of monocarboxylic acids and alcohols: conditions for stability and for the encapsulation of biopolymers

We tested the ability of saturated n-monocarboxylic acids ranging from eight to 12 carbons in length to self-assemble into vesicles, and determined the minimal concentrations and chain lengths necessary to form stable bilayer membranes. Under defined conditions of pH and concentrations exceeding 150 mM, an unbranched monocarboxylic acid as short as eight carbons in length ( n-octanoic acid) assembled into vesicular structures. Nonanoic acid (85 mM) formed stable vesicles at pH 7.0, the p K of the acid in bilayers, and was chosen for further testing. At pH 6 and below, the vesicles were unstable and the acid was present as droplets. At pH ranges of 8 and above clear solutions of micelles formed. However, addition of small amounts of an alcohol (nonanol) markedly stabilized the bilayers, and vesicles were present at significantly lower concentrations (∼20 mM) at pH ranges up to 11. The formation of vesicles near the p K a of the acids can be explained by the formation of stable RCOO −…HOOCR hydrogen bond networks in the presence of both ionized and neutral acid functions. Similarly, the effects of alcohols at high pH suggests the formation of stable RCOO −…HOR hydrogen bond networks when neutral RCOOH groups are absent. The vesicles provided a selective permeability barrier, as indicated by osmotic activity and ionic dye capture, and could encapsulate macromolecules such as DNA and a protein. When catalase was encapsulated in vesicles of decanoic acid and decanol, the enzyme was protected from degradation by protease, and could act as a catalyst for its substrate, hydrogen peroxide, which readily diffused across the membrane. We conclude that membranous vesicles produced by mixed short chain monocarboxylic acids and alcohols are useful models for testing the limits of stabilizing hydrophobic effects in membranes and for prebiotic membrane formation.