Structurally colored chitosan membrane with dual-response for food spoilage detection

Colorimetric indicators of real-time food spoilage detection are typically fabricated using chromogenic agents or nanoparticles; however, their potential migration into food raises considerable safety concerns. Although structurally colored functional biomaterials, which do not pose such risks, represent promising alternatives, their application in food spoilage detection remains largely unexplored. In this study, a structurally colored chitosan membrane (CSM) was obtained from shrimp shells, and its responsiveness to acids and aldehydes was investigated. Fresh coconut water was used to evaluate the performance of CSM as a colorimetric spoilage indicator. Results indicate that CSM is a mesoporous material with a Bouligand structure and a deacetylation degree of 83.93 %. The specific surface area, average pore volume, and average pore size of CSM were 0.44 m 2 /g, 0.001 cm 3 /g, and 9.67 nm, respectively. CSM exhibited chromatic responsiveness to acids at a low pH of 3 due to the protonation of –NH 2 groups, as well as to aldehydes via the formation of imine bond (C=N). Acid and aldehyde exposure altered the crystalline polymorphism of chitosan in CSM. After 18 h of storage at room temperature, the membrane successfully detected spoilage in fresh coconut water through visible color changes, which can be attributed to the synergistic effects of organic acids and aldehydes accumulated during spoilage. These findings demonstrate the effectiveness of CSMs in detecting food spoilage. To our knowledge, this study is the first to demonstrate the potential application of structurally colored CSMs for detecting food spoilage, offering a novel approach for developing food spoilage indicators.