Simulation and Validation of a Novel Colorimetric Three‐Layer Intelligent Indicators With Different Binders to Monitor Freshness of Atlantic Bonito (Sarda sarda) Under Two Different Atmospheres

Abstract

ABSTRACTReal‐time monitoring of spoilage/freshness of perishable food products using intelligent indicators under commercial packaging conditions is of interest. Thus, this study is aimed at fabricating intelligent indicators to determine the possibility of using developed indicators to monitor fish freshness packaged under real packaging conditions. Bromothymol blue (BTB) dye and two different binders (methyl cellulose [MC] and cellulose acetate [CA]) were used to fabricate four different indicators, with the addition of NaOH for carbon dioxide (CO2) or HCl for total volatile basic nitrogen (TVB‐N) sensitive indicators. The colour of produced indicators was observed during 10‐day simulations using CO2 and trimethyl amine (TMA) at different concentrations (0%–30% for both) at 4°C. BTB‐MC‐NaOH changed from blue to green at 15% CO2, while BTB‐CA‐NaOH changed from green to yellow at 25% CO2. Both BTB‐MC‐HCl and BTB‐CA‐HCl indicators changed colour completely at 15% TMA (BTB‐MC‐HCl from yellow to navy and BTB‐CA‐HCl from yellow to green). Indicators were used to monitor the spoilage of Atlantic bonito for 10 days at 4°C under two different modified atmosphere packaging (MAP) conditions (30% CO2, 70% nitrogen (N2) and 100% N2). Headspace gas analysis, pH, TVB‐N, TMA, microbiology, sensory and colour analyses were conducted. For 30% CO2 70% N2, CO2‐sensitive indicators showed a colour change responding to CO2 used, while TVB‐N sensitive indicators showed no visible colour change since the TMA level in packages did not reach the spoilage threshold. Colour transition was also not clear in any of indicators under 100% N2‐packaging, since neither colour‐changing range of CO2 or TMA was reached.