Development of a Cellulose-Based Freshness Sensor (II) : Manufacture of Multilayer Freshness Sensor Using Cellulose-based Materials and Evaluation of Its Color Expression

Abstract

Lately, the increase in consumers’ demand for food packaging safety standards to be followed has spurred a general interest in intelligent packaging technology that can monitor the status of the products in the packaging system. Commercialized sensors can indicate the freshness of food by expressing the colors based on the concentration levels of carbon dioxide (CO₂) in the food item. However, most of the freshness sensors are manufactured from synthetic polymer materials; therefore, it is necessary to develop an eco-friendly freshness sensor that uses biodegradable and recyclable cellulose-based materials.<BR>In this study, a multilayer freshness sensor was manufactured using cellulose-based materials such as commercial filter papers and cellulose nanofibers (CNFs) prepared in a laboratory. The filter paper with small pore size and large number of pores (No. 3) was selected by observing the color change of the immersed filter paper in a pH-sensitive dye, and used as a matrix expressing the specific color according to the CO₂ concentration. The top layer was prepared using enzyme-pretreated CNF (EN-CNF) to make a transparent film, and the middle and bottom layers were prepared using the biowax-coated filter papers with the lowest air permeability due to the largest pore size (No. 4). Finally, a eco-friendly freshness sensor was assembled using the matrix, CNF film, and biowax-coated filter papers, whose color expressions clearly differed based on their CO₂ concentration levels.