Colorimetric films incorporated with nisin and anthocyanins of pomegranate/Clitoria ternatea for shrimp freshness monitoring and retaining

Colorimetric films are emerging as a facile and effective indicator for freshness monitoring. To meet the versatile demands of consumers, multifunctionality is desirable for the colorimetric films. Here, an antibacterial-antioxidant colorimetric film was developed by incorporating nisin and anthocyanins of pomegranate/Clitoria ternatea (PGA/CTA) into ethylene vinyl alcohol (EVOH) matrix. The precursor of EVOH/nisin10 was determined for the incorporation of PGA/CTA of 1:2. The pH-sensing nature and antioxidant activity were originated from the mixture of PGA/CTA, while the antibacterial activity was from nisin. The components of and PGA/CTA in the matrix were well-dispersed and hydrogen-bonded. The color changes of the target film of EVOH/nisin-(PGA/CTA)3 were distinguishable at pH 2–12 and film was sensitive to the pH-stimuli of volatile ammonia and acetic acid. In addition, the film exhibited good antioxidant activity (DPPH·scavenging activity of ~80 %) and antibacterial activity against S. aureus (approximating bactericidal effectiveness). The film can not only monitor shrimp freshness effectively but extend the shelf-life of the packaged shrimp by 100 % at storage of 4 °C, revealing its potential in active intelligent food packaging. The combination of two different sourced anthocyanins along with nisin provides a strategy for achieving an efficacy of freshness retaining plus monitoring.