Colorimetric Food Freshness Indicators Based on Phycobiliproteins from Cyanobacterium Nostoc sp. M2 Immobilized In Crosslinked Gelatin Films

Abstract

Phycobiliproteins from Nostoc sp. M2 which are natural pigments sensitive to pH and temperature, were integrated into crosslinked gelatin (Ge) films to create sustainable indicators to track freshness of shrimp during storage. The phycobiliproteins extract (PB) consisted of 59.2% C-phycoerythrin and 32.7% C-phycocyanin, both of which exhibited purity suitable for food applications. The purple color of PB solution remained stable below 30 °C and within the pH range of 5.0 to 9.0, regardless the presence or absence of light. Beyond these limits, the color faded due to changes in the chromophores conformation or denaturation of the phycobiliproteins. To create the colorimetric labels, PB (0.5, 1.0 and 1.5 wt.% total protein basis) was immobilized in crosslinked gelatin films produced by casting. Increasing PB content did not significantly affect the water resistance, thermal and tensile properties but it did alter the color coordinates (L, a*, b*) of Ge-PBfilms. When tested in simulated semisolid and gaseous media, the color of Ge-PB films changed from purple to colorless at pH≥10.0. Ge-1.5 PB films experienced the greatest variations in color and it was used to track shrimp spoilage under accelerated storage. After 12 h, the pH in the product increased from 7.0 to 8.1, resulting in a film color difference of 21. This colorimetric response was associated with the increase in volatile nitrogen basis due to microbiological deteriorationof shrimp. Overall, these findings suggest that Ge-PB films have the potential to serve as sustainable colorimetric labels for monitoring the freshness of seafood.