Mucilage: Structure, Properties, and Applications

• Mucilage is a plant-originated polysaccharide used in food industries due to its broad-spectrum applications.
• It can be obtained from various plants or their parts, including Aloe vera, Salvia hispanica seeds, and Plantago psyllium

Health and Food Properties

• Plant-derived mucilage is increasingly being utilized as a critical active ingredient across various sectors, particularly in pharmaceuticals, functional foods, and nutraceutical products. Its incorporation is largely attributed to its numerous health benefits, which include its capacity to enhance digestive health, support weight management, and provide antioxidant effects. These properties make mucilage valuable not just for therapeutic applications but also for improving overall wellbeing in nutritionally focused products.
• Health benefits include anticancer, angiotensin-converting enzyme inhibition (extends to diabetes), and immunity stimulation

Structural Composition

• Mucilage, a polymeric polysaccharide, is mainly composed of carbohydrates with branched structures.
• Monomer units include L-arabinose, D-xylose, D-galactose, L-rhamnose, and galacturonic acid.
• Mucilage contains glycoproteins and bioactive components like tannins, alkaloids, and steroids.
• Hydrolysis of mucilage produces monosaccharides, classified into pentose sugars (xylan) and hexose sugars (cellulose and starch).

Relationship to Gums

• Mucilage and gum share structural similarities with hemicelluloses, which are complex carbohydrates composed mainly of xylose, mannose, and galactose. However, they exhibit distinct hydrolysis profiles, resulting in different types and ratios of sugars, influencing their functional applications.
• Mucilage can be utilized in various applications, such as edible coatings that enhance food preservation and texture, wound healing materials that promote healing and reduce infection, tablet formation for controlled drug release, encapsulation to protect sensitive compounds, water purification for filtration processes, and nanocarriers for targeted drug delivery systems.

Functional Properties and Applications

• Mucilage has demonstrated a range of functional properties and plays a crucial role in several applications, including the formation of films and emulsions. Its ability to create stable structures is enhanced by hydrogen bonding, which contributes to the formation of coated metal nanoparticles. Additionally, mucilage facilitates gel formation, enhancing the stability and functionality of various products in food, pharmaceuticals, and materials science.to its capacity for hydrogen bonding, which allows it to create stable structures that can encapsulate active ingredients. Additionally, mucilage facilitates the creation of coated metal nanoparticles, enhancing their stability and effectiveness in various applications, including drug delivery and biomedicine.
• Nanostructured hydrogels and mucilage-coated metal nanoparticles are used as delivery vehicles for hydrophilic and hydrophobic components.
• Mucilage can act as a primary biopolymer or cross-linking component in nanohydrogel formulation.
• Nanohydrogels formulated with mucilage exhibit higher stability than conventional plant-based biopolymers.

Role in Drug Delivery

• Metal nanoparticles coated with polymeric carbohydrates like starch, dextran, chitosan, and mucilage are used for targeted drug delivery.
• Polymeric shells increase blood circulation time and enable drug transfer and release during biodegradation.

Origin of Mucilage

• Mucilage is a water-soluble adhesive material that constitutes carbohydrates and uranic acids in plant parts like seeds, bark, leaves, and buds.
• Myxospermy: The process in which most plants produce mucilage from the seed coat.
• Myxocarpy: The process in which some plant species produce it from the fruit epicarp.

Plant Families

• Plants producing mucilage from the seed coat belong to families like Plantaginaceae, Acanthaceae, Linaceae, and Brassicaceae.
• Myxocarpy is found in families like Poaceae, Asteraceae, and Lamiaceae.
• Mucilage on the seed coat prevents early seedling development and drought stress during germination.

Mucilage Classification

• Hair secretion, intracellular mucilage, and cell membrane mucilage varies depending on the origin
• Seed coat mucilage is classified into endosperm non-starch polysaccharide, cell wall material of the endosperm, and mucilaginous constituents of the seed coat.
• Mucilage develops a jelly-like structure around fruit, maintains moisture, and acts as a hydrating agent and energy reservoir.
• Root mucilage, exhibited from the outer layers of the root cap, produces chemical substances like flavonoids, amino acids, and sugars.

Role in Plant Growth

• Root mucilage plays roles in root-to-soil touch, root tip lubrication, soil microaggregate stabilization, water storage, and ion absorption.
• Secreted by hypersecretory root cap cells as a coagulated polysaccharide (poly-galacturonic acid).
• Helps leaves retain water when soil deficits emerge, aiding in food and water storage.

Extraction Methods

• Mucilage can be extracted from any plant part and is a source of polysaccharides for pharmaceutical and food applications.
• The yield, functional characteristics, and rheological properties of mucilage are significantly influenced by the extraction technique used, including factors such as temperature, solvent type, and duration of extraction..
• Maceration: A simple extraction method that involves soaking raw material in a solvent at room temperature with regular agitation.

Extraction Factors

• Maceration for mucilage extraction typically uses low solid-liquid ratio and hot water treatment.
• Acid solutions, ammonium oxalate, and EDTA can improve mucilage extraction.
• Water-extracted mucilage shows high viscosity compared to alkali and acid-extracted mucilage.
• Limitations of maceration methods includes higher protein levels, low yields of mucilage, and subsequent denaturation.
• Protein presence affects purity and restricts industrial use due to instability, leading to microbial spoilage.

Solvent Treatment

• Solvent treatment involves extracting mucilage from dry plant parts using hot distilled water under continuous shaking and stirring, followed by filtering, precipitating with alcohol, and drying.
• Ultrasonication is a non-thermal technique for mucilage extraction.
• Ultrasonic treatment can help extract the inner layer of the seed coat composed of rhamnogalacturonan I.
• Low-frequency ultrasound disrupts the biological cell wall through pore formation, and the cavitation bubbles produces high spots with higher pressure.

Microwave Assistance

• Microwave can be used for mucilage extraction, improving extraction efficiency, reducing solvent consumption, and time reduction.
• Conventional aqueous extraction methods include the effects of solvent, pH, and temperature, which change the nutritional value, functional and structural property of mucilage.
• Hot water extraction with a long period is cost-effective but can reduce consistency.

Additional Hot Water draw backs

• Hot water extraction methods can result in the loss of heat liable compounds of mucilage.
• Microwave-assisted extraction at 300 to 400 W for 120 to180 s can result in a high mucilage yield.

Enzymes

• Enzymes play a crucial role in the extraction process for their wide range of applications in the food industry.
• Enzymatic hydrolysis is an essential process in which specific enzymes such as rhamnase, arabinase, xylanse, and mannonase are employed to break down complex carbohydrates in mucilage. These enzymes facilitate the degradation of polysaccharides, leading to a significant reduction in both viscosity and molecular weight, ultimately enhancing the extractability and functionality of mucilage in various applications.
• Cold extraction can produce more viscous mucilage, but with a lower yield compared to hot extraction.

Solid to liquid Ratio

• An increase in the ratio of solid-liquid is proportional to more yield because there is more driving foce of mucilage from raw plant material.

pH

• Regarding the pH effect on the extraction yield of mucilage, a significant yield was observed with an increase in pH.
• Lower pH values are likely to improve protein recovery due to protein solubilization, although, below 3 pH, the action of acid can result in a lower protein yield due to its hydrolysis.
• Deionized water can also be used for the extraction of mucilage.

Structural Chemistry

• Mucilage is a water-soluble component constituting chemical components with potential human health benefits.
• Mucilage and gum are subgroups of hydrocolloids containing monosaccharides linked with organic acids, and are close to each other because of the hydrophilic and hydrocolloid.
• Plant hydrocolloids contain pentose, galactose and methyl pentose sugar joined to uranic acid residues by glycosidic linkages.
• Monosaccharides are the most common carbohydrate molecules that cannot be broken down into simpler sugar molecules by hydrolysis
• Mucilage present in plant consists of two main polysaccharides pectin and hemicellulose each of which is comprised of rhamnogalacturonan, and arabinoxylans.
• Mucilage rhamnogalacturonan I (RG-I) comprise a backbone of the repeating disaccharide of a-(1,2)-rhamnose and a-d-(1,4)-galacturonic acid.