| dc.description.abstract | According to statistics from the Council of Agriculture, Executive Yuan, approximately 160,000 tons of discarded oyster shells are produced in Taiwan annually. In the past, most of the shells were dumped randomly. This improper disposal not only results in the occupation of space and environmental damage to the picturesque landscape of the fishing village but also poses a significant threat to the quality of life and the health of the neighboring residents. In recent years, Taiwan has actively promoted the recycling plan for discarded oyster shells. While this approach effectively addresses the waste issue, the domestic application and development of oyster shells remain limited to feed additives.
Furthermore, their added value and utilization rate are small. Again, chemical antiseptics have become increasingly widespread with the continuous advancement of industrial technology and the rapid development of chemical synthesis technology. Unfortunately, this general use has escalated to the point of abuse, posing a significant and imminent threat to human beings and the environment. Many scholars have been researching natural antibacterial agents to address these challenges in recent years. While previous literature has confirmed that oyster shells can be transformed into high-value antibacterial agents through high-temperature calcination, there are different perspectives on their antibacterial mechanisms. Reactive oxygen species (ROS) are generally considered the primary antibacterial mechanism, while singlet oxygen (1O2) is regarded as a highly reactive oxidant critical in the antibacterial process.
This study represents the primary investigation focusing on the impact of calcination conditions on the generation of 1O2 in oyster shells. Furthermore, the study aims to assess the correlation between the concentration of 1O2 and the antibacterial efficiency of oyster shells. Additionally, a comprehensive analysis of the characteristics of calcined oyster shells was conducted. Three types of antibacterial materials were prepared: oyster shell powder calcined at 900°C and 1000°C (represented as 900HOS and 1000HOS, respectively), and oyster shell powder calcined at 900°C under a nitrogen atmosphere (900N-HOS). The antibacterial ability of these materials against Escherichia coli was evaluated at different time points. The antibacterial efficacy of these three materials was evaluated under conditions simulating the growth of Escherichia coli.
The results demonstrated that at a dosage of 1 g/L, the antibacterial effects of the materials after 60 minutes were 0.87-log, 0.74-log, and 0.63-log for 1000HOS, 900N-HOS, and 900HOS, respectively. The antibacterial capacity followed the order: 1000HOS>900N-HOS> 900HOS, confirming that increasing the calcination temperature and conducting calcination under a nitrogen atmosphere effectively enhanced the antibacterial capability of oyster shells. The calcined oyster shells exhibited remarkable antibacterial properties, with 1000HOS achieving nearly 100% (7.59-log) antibacterial effect after 120 minutes, while 900N-HOS and 900HOS reached complete antibacterial efficacy within 240 minutes.
To further validate the antibacterial mechanism, electron spin resonance (ESR) spectrometer technology was employed to detect the content of the antibacterial species 1O2. The analysis showed a direct correlation between the 1O2 content and the antibacterial efficacy, thus confirming the crucial role of 1O2 in the antibacterial mechanism.
Based on the results above, this research is expected to contribute to the application of discarded oyster shells. At the same time, practice the circular economy concept, promote the diversification of discarded oyster shells, and create commercial value of fishery waste. | en_US |