Design and fabrication of a new colorimetric sensor based on hematoxylin for freshness monitoring of shrimp during storage

Shrimp is one of the seafood that its wholesomeness plays a major role in human health. Shrimp spoils very quickly due to having unsaturated fatty acids. However, with timely and early detection, many economic losses can be avoided. For this purpose, various methods are used to detect healthy shrimp from spoiled ones. The most common methods are the sensory and physical examination of shrimp, chemical and microbial tests. In this study, a colorimetric indicator was fabricated using biodegradable polyvinyl alcohol/Chitosan film based on the color changes of hematoxylin at different pH values. Changes in pH, total volatile basic nitrogen contents (TVBN), and colorimetric characteristics of shrimp specimens were examined by contact with this color indicator. The suggested indicator in response to pH shows a variety of colors ranging from light yellow to dark purple in mildly acidic to strong alkaline environments. The performance of the proposed indicator in the detection of shrimp freshness by contact and non-contact methods confirmed that does not necessarily need to be in direct contact with the shrimp and has the ability to show its reaction to the shrimp freshness even in the presence of shrimp. In addition, there is a strong correlation between the total volatile basic nitrogen contents due to shrimp spoilage and the color characteristics of the indicator. The results showed that the proposed indicator is good sensitive to pH changes and shows shrimp spoilage through color changes. Therefore, this colorimetric indicator can be easily used in smart packaging.