Naked-Eye Food Freshness Detection: Innovative Polymeric Optode for High-Protein Food Spoilage Monitoring

Abstract

An innovative smart label for naked-eye protein food freshness evaluation, based on polymeric sensing films, is presented. The proposed device consists of six miniaturized sensors, obtained by covalently binding six pH indicators, namely, mcresol purple (1), o-cresol red (2), bromothymol blue (3), thymol blue (4), chlorophenol red (5), and bromophenol blue (6), to an ethylene vinyl alcohol (EVOH) copolymer. All of the synthetic procedures for the functionalized polymers and their application as smart labels are thoroughly described and discussed. The innovative sensors are characterized using several instrumental techniques (DSC, FT-IR, EDX, SEM, and UV−vis). The application of the array of sensors to poultry meat and cod fillet spoilage monitoring by naked-eye evaluation and modeling by PCA is presented. Eventually, the composition of the food and the food's headspace in the selling tray is investigated and qualitatively characterized to validate the attributes of the array of sensors. The polymeric devices seem to be very promising for industrial scale-up, with the starting EVOH copolymer being extrudable and already employed in food packaging, as well as for large-scale application, being clear, efficient, and easy to read, even by untrained people.

Recent Progress, Challenges, and Trends in Polymer-Based Sensors: A Review

“…When an oxidized polymer (p-type) is exposed to a reducing agent (CO, NH 3 , CH 4 , H 2 , H 2 S, acetone, or ethanol), its resistivity rises; conversely, when the polymer’s surface reacts with an oxidizing agent (NOx, CO 2 , SO 2 , O 2 , or O 3 ), its resistivity reduces [ 50 , 51 ]. Korent et al [ 52 , 53 ] reported an inexpensive NH 3 sensor based on the polyaniline functionalization of a screen-printed electrode (SPE). The SPE was altered in this study by electrochemically polymerizing polyaniline in HCl.…”

pH-Sensitive Sensors at Work on Poultry Meat Degradation Detection: From the Laboratory to the Supermarket Shelf

“…A selection of commercial EVOH copolymers, characterized by different ethylene contents and melt flow rates (MFR), were functionalized with a panel of pH-indicators belonging to the sulfonphthalein class [26][27][28][29][30][31]. The commercial EVOH copolymers and the dye used are listed in Tables S1 and S2.…”

“…The commercial EVOH copolymers and the dye used are listed in Tables S1 and S2. The dye anchoring was achieved following the patented procedure reported in the literature [29][30][31][32][33][34][35]. Dye-EVOH@ were obtained in blocks of irregular shape that are pressed under heating to obtain thin sensing films.…”

“…Dye-EVOH@ were obtained in blocks of irregular shape that are pressed under heating to obtain thin sensing films. The pressing procedure was performed using a dual heated plate manual press and the setting parameters, reported in Table S3, were identified by full factorial design [29]. Miniaturized circular sensors (0.5 cm in diameter) were cut from Dye-EVOH@ films, which show uniform coloration, by a hole punch for paper.…”

“…Second, the sensors were fixed on an adhesive strip, placed forming a sort of bridge taped to closed container walls so that the sensing units make contact only with the headspace and never with the samples. To avoid the undesirable reaction of the sensors with the acid-base components of the adhesive strip, several commercial tapes had been previously tested and 3 M Magic Tape had been identified as inert [26][27][28][29].…”