## 1 Introduction  
Carrot (_Daucus carota_ L.) is one of the most widely cultivated vegetables in the world. Its consumption has progressively increased in the last few years thanks to its pleasant flavor and the health benefits related to its nutritional value. Carrot is an important source of carotenes, minerals, vitamins and dietary fiber [1]. Apart from the conventional orange-root carrots, there are materials with different colors owing to the accumulation of different carotenoids and anthocyanin pigments. In particular, black or purple carrots are rich in anthocyanins, which are known for their health-promoting properties. In general, diets including both pigment types, carotenoids and anthocyanins, have been associated with reduction in the risk of chronic pathologies such as cardiovascular, cancer, stroke and neurodegenerative diseases [2]. Nevertheless, the chemical composition of foods is often altered over the storage period, which affects both their sensorial characteristics and nutritional value. Carotenoids are usually degraded in the presence of oxygen, light, high temperatures and certain enzymes due to their highly unsaturated structure [3]. Also, anthocyanins are modified by pH, enzyme activity, oxygen and, in particular, high temperatures [4]. In relation to organoleptic properties of carrots, it is common to observe loss of water content and firmness, slimy texture, discoloration, bitterness and an oxidized odor [5]. For these reasons, it is essential to carefully select the storage conditions with attention to assuring sensory and health-related quality. Several methods to store carrots exist, such as freezing, drying or canning. However, they bring about undesired modifications in sensorial quality as compared with fresh roots. Specifically, softer texture in frozen carrots has not yet been avoided with any freezing technique reported to date [6]. Also, discoloration and development of an off-flavor is still observed in dried carrots, whereas addition of salt, sugar and preservatives, together with a bizarre metallic taste, is currently the result of canning [7]. In this context, refrigeration is undoubtedly the most efficient method to store carrots. Nevertheless, the temperature has to be carefully controlled in order to achieve a high-sensorial quality product [8]. In this respect, it is interesting that milder temperatures (i.e., around 20 \({}^{\circ}\)C) have been demonstrated to offer advantages over cold temperatures, since they promote increase in carotenoids [9]. In addition, room temperature storage has been recommended rather than colder values to minimize anthocyanin degradation in black carrot juice [10]. On the other hand, it is evident that the temperature used to store carrots must always guarantee the absence of rooting and decomposition. In this regard, raw carrot shelf-life without refrigeration varies from 5 to 7 days. The use of cold temperature can prolong this period until 3 or 4 weeks at the most [11]. We intended to develop a procedure based on the use of refrigeration that enabled purple carrot shelf-life to be prolonged by means of preservation of organoleptic characteristics and, as much as possible, health-related compounds. In this context, the exogenous application of natural phytoregulatory has already been described to enrich plant-based foods in biologically active compounds such as carotenoids and anthocyanins [12; 13; 14]. Nonetheless, the effect of natural phytoregulators on dark-colored carrots has been scarcely studied in general [15; 16] and, in particular, with regards to their deterioration during storage, no studies can be found in the literature up to now. The aim of this research was to study the effect of the post-harvest treatment with natural phytoregulators in combination with cold temperatures on purple carrot quality in terms of both organoleptic and health-promoting properties. To that end, quality physicochemical parameters, content in carotenoids and anthocyanins and antioxidant activity were measured.