Development of two types of intelligent indicators based on cellulose, black carrot, and grape anthocyanins for monitoring food freshness/spoilage

In this study, tracing paper (TP), which is made of cellulose fibers, was used as a base for the fabrication of freshness indicators using high (i.e., black carrot; C) and low (i.e., grape; G) acylated anthocyanins in order to track the freshness/spoilage of a variety of proteinous foods. The two anthocyanins were added to the TP by dipping method and color changes, chemical structure, and ammonia sensitivity of the TP-G and TP-C indicators were studied. Additionally, the ability of indicators to detect the freshness/spoilage status of minced beef, chicken fillets, and shrimp was checked. Total volatile basic nitrogen, pH, and total psychrotrophic count were used to estimate the onset of spoilage in samples. In general, the color of both TP-G and TP-C indicators was red at acidic pH and blue-purple at alkaline pH, with minor differences in the intensity. Fourier transform infrared spectroscopy results confirmed the immobilization of grape and carrot anthocyanins in the TP. The TP-C indicator indicated the fastest and highest sensitivity (34.7% after 1 min exposure) than TP-G (29.9% after 3 min exposure) to the ammonia. With the exception of the TP-G indicator in shrimp, both indicators could differentiate between fresh minced beef, chicken fillets, and shrimp and spoiled samples, while the TP-G indicator had an extra specification and it exhibited the ability to distinguish between fresh, medium spoiled, and spoiled shrimp during the storage. In conclusion, the TP-G and TP-C indicators had minor differences in color pattern in buffers and food models and were appropriate for food application.