## 1 Introduction  
Potato is considered an important source of human nutrition and is ranked high in the global food production and consumption. Apart from their distribution as fresh commodity in the retail market, potatoes constitute the raw material for the food processing industry (e.g., in chips or frozen food production) or even for the chemical industry, as a source of ethanol and starch [1]. In order to fulfill the demand all year round, a common practice is to store the tubers for several months and thus increase their marketability, as well. However, during a long period of storage, the dormancy of the tuber is interrupted and consequently sprouts start to grow that are therefore often cut off before the product is distributed in the retail market. This practice is not perceivable by the consumers, because the remaining scars are either rapidly healed or not even evident at all. During storage of potato tubers, the respiration and the evaporation rate increase and a nutritional quality degradation is induced, while starch and ascorbic acid contents decrease, weight loss and peroxidase enzymic activity increase and reducing sugars, such as glucose and fructose are synthesized [2; 3; 4], and softening and periderm green discoloration also develop [1; 5]. As a result, the adverse storage conditions either postharvest or during transportation and marketing, are often accompanied by a substantial loss of a significant portion of the crop yield. Even worse, chemical reactions between the amino acids asparagine and glutamine, and the reducing sugars that are produced during long term potato storage, may lead to the synthesis of acrylamide in food preparation at high temperatures (Maillard reaction), which has been linked with carcinogenic hazards [6; 7; 8]. Apparently, both the quality and safety of the end product is based on the nutritional composition of the raw tubers at the time of processing [3], as well as on the degree of senescence of the potatoes [4; 9], namely, their freshness. Unfortunately, the precise assessment of potato freshness degree is a complex task. Several studies have already been conducted to discriminate the potato tubers into distinct maturity stages either at harvest or during storage and indeed, in order to accurately assess the degree of maturity, a combination of physical, physiological, and chemical maturity indexes of the tubers should be considered [10]. However, these methods are performed under laboratory conditions, are time-consuming, expensive, and require the disruption of tissue and consequently by no means can be implemented in a robust, on-line sorting procedure. There are studies attempting to assess the freshness and quality changes during storage of vegetable crops using various non-destructive techniques and the most common practice in monitoring the post-harvest life of fruits is the color measurement using a portable colorimeter. Chlorophyll fluorescence is another non-destructive and rapid technique that provides information about the physiological status of plant tissues [11; 12] and has already been successfully employed in the estimation of the ripening degree in tomato fruits [13] and senescence of leafy vegetables during storage [14; 15]. Moreover, [PERSON] et al. [16] determined the ripening stage of tomato fruits using a simple, portable digital camera. This type of camera creates images based on the visible part of the electromagnetic spectrum and after appropriate processing, it is possible to convert the image components into color coordinates. Even more quality changes during storage of eggplants have been assessed using various techniques such as Vis/NIR spectroscopy, FT-NIR spectroscopy, and hyperspectral imaging [17]. The implementation of non-destructive sorting technologies is more than important in order to increase the marketability of the fresh potato and to guarantee the optimal nutritional, healthy, and financial benefit for the consumers, the growers, the food industry, and the global trade.