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, m-cresol 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.
Highlights
A complex combination of bacterial processes determines food spoilage, and monitoring these events is a pivotal consumer demand in light of maintaining a high qualitative standard of foods in general.[1]
Because this has been a hot topic in the past several years and involves primary economic and health interests, a wide variety of sensing approaches have been tested for these applications, ranging from biosensors[9,10] and electronic devices[7,11,15] to colorimetric devices.[2,6,12−14,16−21] Among all, the colorimetric devices, especially those relying on pH indicators as the sensing unit, seem to be highly promising for a naked-eye evaluation of food freshness based on two simple pillars
More advanced chemometric techniques could be employed in such analyses, but our aim was just to rationalize the color evolution and visualize the process; principal component analysis (PCA) was suitable for these purposes
Summary
A complex combination of bacterial processes determines food spoilage, and monitoring these events is a pivotal consumer demand in light of maintaining a high qualitative standard of foods in general.[1]. The decay of quality in meat is fast, because microorganism activities can quickly increase,[2] and can be affected by several factors during distribution.[3−5] Considering these assumptions, it goes without saying that the traditional, expensive, time-consuming methods commonly employed for meat spoilage monitoring are definitely inadequate and must be updated or even replaced by rapid, low-cost, and nondestructive techniques.[2,6−8] Because this has been a hot topic in the past several years and involves primary economic and health interests, a wide variety of sensing approaches have been tested for these applications, ranging from biosensors[9,10] and electronic devices[7,11,15] to colorimetric devices.[2,6,12−14,16−21] Among all, the colorimetric devices, especially those relying on pH indicators as the sensing unit, seem to be highly promising for a naked-eye evaluation of food freshness based on two simple pillars. First and foremost, biogenic amines (BAs) have been undeservedly granted a leading role in freshness detection but have never been detected in meat headspace during a storage time typical of a real-life situation.[8,24,25]
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