For residents of Zhanjiang, Guangdong province, few pleasures compare to savoring fresh seafood year-round. And for Liu Kaidong and Liang Fengyan, the local delicacies have yielded far more than culinary delight.

Liu, dean of the School of Life Science and Technology at Zhanjiang's Lingnan Normal University, and Liang, a teacher at the school, helmed a research team to develop a chitosan-based high-value utilization technology for shrimp and crab shell waste, turning the discarded byproducts into valuable resources.

The innovative technology has emerged as a technical cornerstone for fruit and vegetable preservation, as well as aquaculture disease control and aquaculture wastewater treatment.

"We extract chitin from shrimp and crab shells to obtain a natural polysaccharide called chitosan through deacetylation. Chitosan is naturally degradable and possesses antibacterial properties," Liu said in an interview with China Daily.

"With chitosan as the core material, we integrate physical, chemical and composite technologies to develop preservation materials, shrimp pathogen control agents and adsorption materials for marine aquaculture wastewater. The core goal of this technology is to cut losses and boost revenues."

By adopting the integrated approach of "functional modification plus forming processing", the solution incorporates technical pathways for dip-coating/spray-coating film formation, ionic-covalent cross-linking, and microencapsulation technology.

These technologies take full advantage of chitosan's natural film-forming properties, as well as the antimicrobial and antioxidant capabilities of natural plant extracts, enabling targeted customization to meet the preservation requirements of different fruits and vegetables.

"Through dipping/spraying coating, aerogel pad and microencapsulation methods, we can extend the shelf life of fruits and vegetables by two to three times, inhibit more than 80 percent of common pathogenic bacteria, and reduce moisture and nutrient loss significantly," Liu said.

"For instance, the ambient-temperature freshness preservation period for lychee can be extended to six to eight days, while the decay rate of papaya can be lowered to below 5 percent. Given that the preservation material is derived from natural biodegradable substances, it is fully degradable."

Liu said that compared to traditional chemical preservatives, chitosan is greener, safer, non-toxic and more eco-friendly, while delivering better preservation results. The technology can cut annual fruit and vegetable losses in Zhanjiang by 300,000 to 750,000 metric tons, translating to additional revenue of 600 million ($87 million) to 1.5 billion yuan.

"What's more, it helps high-quality produce command a price premium of 10 percent to 20 percent, boosting the region's total annual revenue by 8 million to 2 billion yuan and fueling industrial transformation," he said.

When it comes to preventing and controlling shrimp and crab pathogens, the technology is applied in two ways: water dispersion and feed supplementation. "This can inhibit over 90 percent of pathogens like Vibrio parahaemolyticus, lowering the incidence of shrimp vibriosis to below 5 percent and increasing survival rates by 15 percent to 25 percent. It is highly versatile, with strong compatibility for crustaceans, fish and shellfish," Liu said.

But for delicate seedlings such as sea cucumber fry and abalone fry, the concentration must be strictly controlled or low-irritation modified products should be adopted, while formula concentrations need to be adjusted based on whether the application scenario is a marine or freshwater aquaculture system, he added.

The technology has also brought substantial economic benefits to Zhanjiang's shrimp farming industry. Liu pointed out that it can raise the city's annual shrimp output by 80,000 to 240,000 tons, directly adding 2.4 billion to 7.2 billion yuan in revenue.

In addition, it cuts costs by 500 to 1,000 yuan per mu (about 0.067 hectares) and helps shrimp fetch a 10 percent to 15 percent price premium, creating comprehensive annual direct benefits ranging from 3 billion to 8.5 billion yuan.

Located on Leizhou peninsula, Zhanjiang, the southernmost coastal city on the Chinese mainland, has been dubbed the nation's "seafood capital". It boasts abundant shrimp and crab resources and a well-developed aquaculture and processing industry. Large quantities of shrimp and crab shells are discarded by local restaurants and hotels annually, and if not properly handled, such marine solid waste could easily lead to resource waste and environmental pressure, said Liu.

Liu said his team will continue to promote the integration of scientific research with local industrial development, driving future green growth of the marine economy.

Xie Ruiqi contributed to this story.

zhengcaixiong@chinadaily.com.cn