The use of chitosan in food, post-harvest，biofilm materials & coatings

Introduction to the application of chitosan

Chitosan is a natural biopolymer derived from the exoskeletons of crustaceans (such as shrimp and crabs), insects, fungi and some algae. It is obtained by deacetylation of chitin and has the characteristics of biocompatibility, biodegradability and non-toxicity, thus showing a wide range of application potential in many fields. Chitosan is a linear cationic polysaccharide composed of β-(1,4)-linked 2-amino-2-deoxy-D-glucose and 2-acetylamino-2-deoxy-D-glucose units. The structure of chitosan contains amino and hydroxyl groups, which give it unique chemical and biological properties.

Application of chitosan in food industry

Chitosan has a wide range of potential applications in food preservation due to its natural antimicrobial and antioxidant properties. It can inhibit the growth of a variety of foodborne microorganisms, including bacteria, yeast and fungi, thereby extending the shelf life of food.

• Food preservation :
• Antimicrobial mechanism : Chitosan inhibits microbial growth by destroying microbial cell membranes, chelating metal ions, interfering with protein synthesis and other mechanisms, and has an inhibitory effect on a variety of foodborne microorganisms.
• Application examples : It can be used to extend the shelf life of fresh fruits and vegetables, meat and poultry; used as a natural preservative in dairy products, baked products and ready-to-eat foods; used in combination with organic acids or salts to enhance the antimicrobial effect; synergistically with other antimicrobial substances
• Combination with other technologies : It can be used in combination with other preservation technologies such as pulsed electric field (PEF) to enhance the antibacterial effect.

Edible coating :

• Film-forming properties : Chitosan can form a selectively breathable film to control the gas exchange between fruits and vegetables and the external environment, thereby delaying the ripening and aging process of fruits and vegetables.
• Fresh-keeping function : reduce water loss and prevent fruits and vegetables from drying and losing weight; inhibit the growth of microorganisms and reduce spoilage; slow down the respiration rate of fruits and vegetables and reduce metabolic activity.
• Application examples : Applied to fresh fruits (such as mango, strawberry, apple, etc.) and vegetables (such as tomato, cucumber, pepper, etc.); combined with other biopolymers to prepare composite coatings; combined with other active substances (such as essential oils, antioxidants) to enhance the preservation effect.

Food packaging :

• Biodegradability : Packaging materials made of chitosan can be degraded in the natural environment, reducing pollution to the environment and are more environmentally friendly than traditional plastic packaging. Antibacterial properties : It has certain antibacterial activity, can inhibit the growth of microorganisms on the surface of food and improve food safety. Oxygen barrier properties : It has good oxygen barrier properties, which reduces the contact between food and oxygen, prevents oxidation and deterioration, and helps to extend the shelf life of food. Application examples : It can be used to produce biodegradable food packaging films to package various foods; it can be combined with other biopolymers to prepare composite packaging materials; chitosan nanocomposites can be used to prepare smart packaging materials (such as pH-sensitive films); chitosan films can be used to package active ingredients to enhance the preservation effect.
• Other applications : Chitosan can also be used as a food additive, such as a thickener in beverages and a clarifier in juices; it also has other applications in the food industry, such as an emulsifier, a clarifier, and a carrier for controlled release systems.

Application of chitosan in agriculture

Chitosan is a natural biological preservative in the postharvest protection of fruits and vegetables . It has attracted widespread attention due to its antibacterial, antioxidant and biocompatibility properties. It can effectively extend the shelf life of fruits and vegetables and reduce postharvest losses. The following are specific applications of chitosan in postharvest treatment:

1. Control post-harvest diseases

• Antimicrobial mechanism : Chitosan can inhibit the growth of pathogenic microorganisms such as fungi and bacteria by destroying microbial cell membranes, interfering with protein synthesis and other mechanisms, thereby reducing the decay of fruits and vegetables.
• Application Examples : Chitosan has been successfully used to control postharvest diseases of many fruits and vegetables, including strawberries, peaches, blueberries, etc. For example, it has a good control effect on gray mold of strawberries . It is also often used in combination with other antibacterial substances to enhance the antibacterial effect. Chitosan can also be combined with other treatments, such as heat treatment or essential oils, to achieve better preservation effects.

2. Extend shelf life

• Edible coating : Chitosan can form a selectively breathable film to reduce water loss in fruits and vegetables, slow down the respiration rate, and thus extend the shelf life.
• Application Examples : Chitosan coating can be applied to a variety of fruits and vegetables, such as mango, tomato, etc., to maintain their freshness and nutritional value.
• Combination with other technologies : Chitosan coating can be combined with other preservation technologies (such as refrigeration) to achieve better preservation effects.

3. Enhance plant resistance

• Induced defense mechanism : Chitosan can induce defense responses in plants, such as strengthening cell walls and increasing the activity of antioxidant enzymes, thereby improving the resistance of fruits and vegetables to diseases.
• Reduced use of chemical pesticides : By enhancing the plant’s own defenses, reliance on post-harvest chemical fungicides can be reduced, reducing the risk of pesticide residues.

4. Application method

• Pre-harvest treatment : Chitosan can be used as a pre-harvest treatment by spraying on crops to reduce the occurrence of post-harvest diseases.
• Post-harvest processing : Soaking : After picking, fruits and vegetables can be soaked in chitosan solution to achieve the purpose of preservation and freshness. Spray : Chitosan solution can also be sprayed on the surface of fruits and vegetables to form a protective film. Coating : Chitosan can be made into edible coatings and applied to the surface of fruits and vegetables.

5. Application advantages of chitosan

• Natural and safe : Chitosan is derived from natural substances, is harmless to the human body and the environment, and is a safe preservative.
• Biodegradability : Chitosan has good biodegradability and will not cause environmental pollution.
• Multifunctionality : Chitosan has multiple functions such as antibacterial, antioxidant, and film-forming, and can be used to preserve a variety of fruits and vegetables.

Application of chitosan in biomaterials and biomedicine

• Tissue Engineering : Chitosan is widely used in tissue engineering scaffolds for the repair of bones, cartilage, skin and liver due to its biocompatibility and biodegradability .
• Drug delivery : Chitosan can be used as a carrier in drug delivery systems for topical, oral and transdermal administration.
• Wound dressings : Chitosan can be used to make wound dressings to promote wound healing and prevent infection.
• Antibacterial materials : Chitosan can be made into antibacterial materials for use in medical devices and textiles to prevent the growth of microorganisms.
• Other Applications : Chitosan has other applications in the biomedical field, such as in gene delivery , the manufacture of contact lenses and artificial skin .

Modification of Chitosan

In order to expand the application of chitosan, researchers have made various modifications to it:

• Carboxymethylation : Carboxymethyl chitosan has better water solubility and is suitable for drug delivery and tissue engineering.
• Quaternization : Quaternized chitosan and its derivatives have enhanced antimicrobial activity, especially against fungi.
• Composite with other polymers : Chitosan is often composited with other polymers (such as starch, gelatin, pectin, etc.) to improve its properties, such as mechanical strength, gas barrier properties, etc.

Chitosan's mechanism of action

The antibacterial mechanism of chitosan mainly includes the following aspects:

• Destroy cell membranes : Chitosan can destroy microbial cell membranes, causing leakage of cell contents.
• Chelating metal ions : Chitosan can chelate metal ions and interfere with the normal metabolism of microorganisms.
• Interference with protein synthesis : Chitosan can interfere with the protein synthesis process of microorganisms.
• Inducing plant defense : Chitosan can induce defense responses in plants and enhance their disease resistance.

Preparation of chitosan

The preparation method of chitosan mainly includes:

• Chitin deacetylation : The acetyl group in chitin is removed by alkali treatment or enzymatic decomposition to obtain chitosan.
• Chemical modification : Chitosan is modified through chemical reactions to change its functional properties.
• Nanocomposite materials : Materials with special properties are prepared by combining chitosan with other nanomaterials.

Chitosan is a versatile and promising biopolymer with a wide range of applications in food, agriculture, biomaterials and biomedicine. Its biocompatibility, biodegradability, antibacterial and antioxidant properties make it an attractive alternative to meet the growing demand for sustainable and safe solutions. Future research directions include further exploring the modification of chitosan, its composite with other materials and optimizing its application in different fields to meet the demand for healthy, safe and sustainable food.