Immobilization of Echium amoenum anthocyanins into bacterial cellulose film: A novel colorimetric pH indicator for freshness/spoilage monitoring of shrimp

The aim of this research was to develop an intelligent pH-sensitive indicator based on natural dye extracted from Echium amoenum flowers (EAE). The indicator was fabricated by incorporation of EAE into bacterial cellulose (BC) film, then characterized and used to monitor the freshness of packaged shrimp. The FT-IR analysis suggested the formation of new interactions between BC and anthocyanins. Evidence of disruption of crystalline structure and alteration of the morphological characteristics of BC film after immobilization of the EAE were observed by XRD and FE-SEM analyses, respectively. The fabricated BC-EAE indicator clearly responded to pH by changing color from red to yellow over the pH range of 2-12. The total volatile basic nitrogen (TVB-N), total viable count (TVC) and the pH of shrimp were monitored during refrigerated storage for 4 days, and the color changes of the indicator were recorded simultaneously. Visually-distinguishable color changes were observed as the shrimp aged, i.e. fresh (violet), use soon (gray), and spoiled (yellow) shrimp. These color changes were in accordance with the TVC and TVB-N values of the shrimp. The fabricated BC-EAE indicator visually identified shrimp spoilage by color changes, suggesting the suitability of E.amoenum anthocyanins as a novel pH-sensitive dye for intelligent packaging of protein-rich food.