What Is The Characteristics Of β-Chitosan?

β-chitosan is a natural high-molecular-weight polysaccharide with a molecular weight typically exceeding 1,000,000. It is mainly produced by deacetylating β-chitin, which is extracted from squid cartilage. Its production process adopts alkali treatment and enzymatic hydrolysis, avoiding acid treatment, thus exhibiting higher safety than the commonly used α-chitosan. The degree of deacetylation (DDA) of this substance can reach 85% to 90%. Its molecular structure is arranged in a simple parallel manner, with weak intermolecular forces, and its infrared (IR) and nuclear magnetic resonance (NMR) spectral characteristics differ significantly from those of α-chitosan.

β-chitosan has high solubility in weak acids, along with high viscosity, strong adsorption capacity, and biodegradability. Its physiological activities include inhibiting bacteria, adsorbing heavy metals, lowering cholesterol, and regulating blood pressure. Particularly in a weak acid environment, it can bind to amino groups to exert antibacterial effects. This substance can selectively inhibit harmful bacterial flora and is used as a chelating agent for the removal of radioactive materials. Compared with α-chitosan, β-chitosan has higher protein adsorption capacity, water retention, and serum degradation rate, making it suitable for processing into medical materials or food additives. Since the deacetylation process has a significant impact on molecular weight, production needs to adjust reaction conditions according to intended uses to balance purity and performance.

Near 1654 cm⁻¹, β-chitosan has only one amide I peak, while α-chitosan has multiple amide I peaks. For the amide II peak, β-chitosan and α-chitosan are located at 1598 cm⁻¹ and 1570 cm⁻¹, respectively. This explains the difference in molecular structure between β-chitosan and α-chitosan. Due to its simpler molecular structure and weaker intermolecular forces, β-chitosan exhibits four times the physiological activity of α-chitosan.

β-chitin has two peaks: a CH₃ peak at 23 ppm and a C=O peak at 173 ppm. These peaks are not observable in β-chitosan with a deacetylation degree of over 90%. The C-3 and C-5 peaks of α-chitin can be observed at 73 ppm and 75 ppm, respectively, while β-chitin shows only a single peak at 74 ppm. This indicates that α-chitin has an antiparallel (helical) structure, where all its hydroxyl groups are bound by hydrogen bonds—either between C-3 and C-5, or between CH₂OH and C-6. In contrast, β-chitin has hydrogen bonds only between C-2 atoms. This difference arises from the chemical structural transition of C-3 and C-5. In α-chitosan, the C-4 peak can be observed at 82 ppm, but this C-4 peak is not detectable in β-chitosan.

Chitosan is not 100% soluble in water, but it is soluble in organic acids such as formic acid and acetic acid, as well as dilute inorganic acids like dilute hydrochloric acid. The pH value of β-chitosan solution depends on its concentration and the type of acid used: it remains in a dissolved state when the pH is less than 6, and precipitates when the pH exceeds 6.

It is well-known that due to its unique molecular structure, β-chitosan has much higher solubility than α-chitosan. Therefore, it can be easily used in various food additives, as it can be readily degraded under weak acid conditions to enhance absorption.

A typical characteristic of β-chitosan solution is its high viscosity, which depends on its molecular weight, degree of deacetylation, ionic strength, and pH value. High temperatures and prolonged storage lead to reduced viscosity.

Owing to its unique molecular structure, β-chitosan has 40–50% higher activity than α-chitosan. It exhibits adsorption capacity for metal ions and chelates, making it suitable as a carrier for various indigestible substances. Additionally, its ability to bind to radioactive materials allows it to be applied in the removal of radioactive substances.

When β-chitosan needs to be heated for stability testing, its molecular structure does not undergo any changes. Moreover, when stored under different environments—such as dark conditions, indoor conditions, or indoor light for 2 years—no significant changes occur in its appearance or degree of deacetylation. Regarding toxicity testing of β-chitosan, no toxicity was observed in mice at a dosage of 10 g/kg. Furthermore, at dosages of 18 g/kg and 16 g/kg, releasable chitosan and formic acid-chitosan were also found to be safe.