# Intelligent Packaging for Real-Time Monitoring of Food-Quality: Current and Future Developments
## 1 Introduction  
According to the World Health Organization, every year, more than 600 million cases of illness are related to supplies of contaminated food and more than 400,000 people die due to foodborne contamination [1]. Indeed, even in highly developed countries, foodborne illnesses are still a serious cause of sickness and lead to several deaths per year [2]. Generally speaking, food quality can be identified by a broad number of factors including healthiness, consumer standards, nutritional values, and stability [3, 4]. Hence, these factors represent a topical indicator to assess the effect of food on consumer health. In this sense, the food industry has recently started to pay great attention to evaluating food quality [5, 6]. Nowadays, expiration dates are commonly employed for this purpose and to define product recall times. However, despite the existence of strict standard regulations, the complete lack of real-time monitoring of food preservation state is a threat to consumer health [7, 8]. With these premises, it is not surprising that the worldwide food industry urges for the development of systems that can be easily incorporated into food packaging and are able to provide real-time quality insights. The efforts made in recent years have led to a promising emerging field, comprised of innovative packaging technologies showing the potential to substitute conventional materials [9, 10, 11]. Traditionally, common packaging technologies consist of the use of passive, inactive, and inert barriers with the function to prevent moisture, oxygen, and contaminants from becoming in contact with the food products. Hence, their main action is to maintain food quality over a certain period of time, protecting it against diverse physicochemical stresses [12, 13]. On the contrary, innovative food packages may present one or multiple active functions able to play an active role in food preservation and quality indication. In this sense, the number of functionalities that can be embedded in smart packages is rapidlygrowing. These new materials promise to cover a topical role in improving food safety, enhancing food quality, and minimizing food waste. Several terms such as \"smart\", \"active\", and \"intelligent\" are commonly employed to describe novel packaging technologies. Despite these terms being used interchangeably in the literature, they are representative of different concepts [14]. Specifically, intelligent packages do not directly act on food products, but only monitor their condition, whereas active packages have the role to increase the food shelf-life by acting on the environment surrounding the food. Remarkably, intelligent and active packaging may work in synergy, creating what is nowadays indicated as smart packaging [10; 15]. Generally speaking, given the properties shown by actives packaging materials, these can be simply considered an extension of the traditional food packaging systems and are nowadays broadly employed in several commercial products [16; 17]. Conversely, the purpose of intelligent packages is the real-time quality evaluation of food products and/or the surrounding environment through a variety of signals [13; 18; 19; 20]. Specifically, diverse quality indicators (e.g., pH, humidity, temperature, specific chemicals, etc.) can be exploited for this purpose [7; 21; 22; 23; 24; 25]. However, even though several food quality monitoring devices have been developed in the past and the number of scientific articles on the topic has been quickly increasing in the past decade, excluding temperature-based sensing systems (see Section 3.5), intelligent packages able to ensure real-time monitoring on a large commercial scale are still far from being achieved [26]. The main problems of such systems encompass the high cost, the requirement of sophisticated instrumentations, and the difficult integration in existing packaging materials.