Functionality and Storage Evaluation of Fish Freshness Indicators Based on the Incorporation of Anthocyanins Extracted From Winery Grape Pomace Into Polyvinyl Alcohol/Starch Films

Novel smart packaging systems demonstrate great potential in addressing challenges related to cold chain management and in reducing food waste. This study focused on the development of smart indicators composed of polyvinyl alcohol and starch, infused with anthocyanins extracted from winery residues. The extract held an adequate amount of anthocyanins (~339 mg/L cyanidin-3-glucoside equivalents) and showed increased pH sensitivity. Similarly, the obtained smart indicators exhibited high pH responsivity (ΔΕ = 39.37) and exhibited sensitivity to volatile amines, as tested with trimethylamine (ΔΕ reached 53.34), dimethylamine (ΔΕ reached 54.71) and ammonia vapour solutions (ΔΕ reached 57.69). Based on microstructure and infrared spectra, the incorporation of anthocyanins slightly enhanced the miscibility of the polymers. Water solubility, swelling index and wettability values did not show significant variations between the control indicators and the smart indicators. The films were also evaluated for water adsorption, water solubility, wettability and colour stability over a 45-day storage period under three different temperatures (5°C, 15°C and 25°C) and five distinct relative humidity (33%, 56%, 75%, 90% and 98%) environments. Increased temperature and relative humidity conditions compromised the functional properties of the films. Subsequently, the smart indicators were incorporated into sealed packages of gilthead sea bream to monitor fish freshness under constant and variable temperature conditions. Fish spoilage was verified using microbiological (total viable counts, Pseudomonas spp. and Enterobacteriaceae) as well as physicochemical (pH, total volatile basic nitrogen) indices. The colour change (from pinkish-red to pale green-blue) of the smart indicators, along with the total colour difference (ΔΕ reached 23.5 at constant and 35.7 at variable temperature conditions), indicated that the fabricated smart labels were capable of reflecting temperature fluctuations during fish storage and providing insights into the spoilage level of the packaged fish.