## 4 Discussion
This reasoning is supported by the correlation values found between the various methods for determining antioxidant capacity: DPPH and ABTS values were highly correlated with each other but not with FRAP or AUC values. Differently, FRAP and AUC values, especially AUC\({}_{0.5}\), are in good correlation with each other since both are based on direct electron transfer, and this is in accordance with previous studies [54; 55; 56]. The antioxidant capacity of the outer shell extracts is based on the contribution of all the identified and unidentified complex structures [27], but is primarily linked to the concentration of phenolic compounds that are capable of being oxidized at an E\({}_{\text{app}}\) lower than +0.5 V. In the absence of a mass spectrometric analysis, a lot of unknown molecules occurring in the investigated accessions cannot be considered, nor their specific reducing power. According to our HPLCanalysis, we can state that all seven compounds identified and quantified have a redox potential lower than +0.4 V and that all of them contributed to the antioxidant capacity according to their concentration in the extracts. Even though the obtained qualitative phenolic profile was similar to that reported by other authors, differences in quantitative content was found [4; 38; 46]: TP values similar to our MARVV and lower than those of the Sardinian accessions, but with shorter extraction times, were recorded by [PERSON] et al. [4], while condensed tannins values were comparable to our results. A content of TP approximately ten-fold higher than ours was found in chestnut waste consisting of inner and outer shell water extract [23]. This high variability assessed in the literature could be attributed to varietal differences, although a wide number of factors influence the phytochemical levels in vegetal matrices, such as geographical origin, pedoclimatic conditions, irrigation, seasonality, etc. Beyond all this, the role of temperature must be considered. The HPLC analysis showed that the temperature discriminates between the different molecules: the ellagic acid showed the highest concentration in the cold extracts, ellagitannins in the hot ones and, for the other molecules, specific cultivar-dependent trends were recorded. [PERSON] et al. [22] found a TP and flavonoids content much lower than ours in water extract at boiling temperature (for 40 min) of outer shell chestnut Campania cultivars. An increase in the castalagin and gallic acid concentration, consequence of an increase in the extraction temperature, was reported by [PERSON] et al. [4] as for our cultivar MARRV. The thermal stability at 60, 80 and 100 \({}^{\circ}\)C of water solutions of gallic acid, catechin, and vanillic acid was studied: it was demonstrated that the degradation of the phenolic compounds in grape seeds and spruce bark vegetal extracts was lower for all the temperatures than individual standard solutions, confirming that the complex chemical composition of vegetal extracts has to take into account to evaluate the thermal stability of phenolic compounds [57]. It was reported that high temperature and long extraction times can promote phenols oxidations and reduce antioxidant properties [7], that temperatures up to 90 \({}^{\circ}\)C increase the extraction of phenolic compounds [4; 22; 58], and that this increase is not always associated with the maximum antioxidant capacity [19] due to additive and synergic effects of individual phytochemicals. All the considerations made so far are based on in vitro studies, chemical and electrochemical tests, but to better understand the role of phenolic compounds, their biological activity on normal and cancer cells has been investigated. It is known that polyphenols decrease DNA damage by inducing various carcinogens acting as ROS scavengers, chelating transition metals, or modulating the expression and the activity of the enzymes related to oxidative stress [59].