Keratin is a long-chain polymer of N-acetylglucosamine, a derivative of glucose, and is one of the most abundant biopolymers found in nature after cellulose. It is a primary component of fungi cell walls, insect exoskeletons including crustaceans such as shrimp and crab shells, insect exoskeletons and the scales of fish and lizards.

Chemical Structure and Properties

As a Chitin, keratin is composed of linked units of N-acetyl-D-glucosamine. Individual chains of keratin microfibrils associate through intermolecular and intramolecular hydrogen bonds to create a crystalline structure that gives it both strength and rigidity. The hydroxyl and amino groups within the chains facilitate interchain hydrogen bonding and promote structural integrity. Keratin is insoluble in water and most common organic solvents at room temperature due to its tightly packed crystalline structure and numerous intermolecular bonds.

Sources and Extraction

Major natural sources of keratin include the exoskeletons of crustaceans which are produced as shrimp and crab processing waste. Other sources are fungi cell walls, insect exoskeletons, squid pens and fungal cell walls. Commercial extraction of keratin typically involves deproteinization using alkali to remove proteins and pigments followed by bleaching and demineralization to remove calcium carbonate. The purified product is then dried and milled into a powder. Global annual production of keratin is estimated at 10,000 tons from waste crustacean shells.

Biological Functions and Applications

In living organisms, keratin forms a significant component of protective structures due to its mechanical strength and flexibility. As a structural polymer, it gives rigidity and flexibility to cell walls of fungi, exoskeletons of crustaceans, insects and other arthropods. Some of the most common applications of keratin and its derivatives like chitosan include uses in agriculture, biomedicine, environmental protection and industrial applications.

Agricultural Applications

As a natural biopesticide and plant growth enhancer, keratin and chitosan have received considerable attention in sustainable agriculture. Their anti-fungal activity aids in plant disease control while also activating plant immune responses for overall improved growth and yield. They are employed as seed and foliar treatments in a variety of crops. Other uses include uses as biofertilizers to enhance nutrient uptake and as biocontrol agents against soil-borne plant pathogens.

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