Conclusions
The characterization by HPLC–DAD–ESI–MSn of polyphenols obtained from radish red skin by an environmentally friendly extraction procedure showed the presence of anthocyanin derivatives, i.e. four pelargonidin (pelargonidin-3-O-sophoroside-5-O-(6-O-malonyl)-glucoside, perlargonidin-3-O-glucoside, pelargonidin-3-O-(6-O-caffeoyl)-neohesperidoside-5-O-(6-O-malonyl)-glucoside, and pelargonidin-3-O-(6-O-p-coumaroyl-2-O-caffeoyl)-sophoroside-5-O-(6-O-malonyl)-glucoside) and two cyanidin derivatives (cyandin-3-O-(6-O-caffeoyl)-sophoroside-5-O-glucoside and cyanidin-3-O-(6-O-caffeoyl)-rutinoside-5-O-(6-O-malonyl)-glucoside) differently glycosilated and acylated never before identified in the skin extract of red radish. Furthermore, other polyphenols belonging to hydroxycinnamic acid group and their esters with sugar moiety, kaempferol and eriodictyol derivatives were detected. Again, two small organic acids – citric and quinic acids – were characterized.
The investigation about the effects of storage at room temperature (20 °C), − 40 °C and 4 °C, and also the effect of thermal treatment (50 °C, 70 °C, and 95 °C) in the presence or in the absence of oxygen on the color stability of the anthocyanins present in red skin radishes indicated a good stability at low temperatures and up to 20 °C, that was higher in the absence of oxygen, whereas the stability decreased at higher temperature so that at 95 °C no anthocyanins were revealed in the extract after heating for 1 h.
The obtained results are promising and provide interesting information also regarding the color stability of the extract when mixed with one common inert material used in nutraceutical/pharmaceutical field, such as mPEG. As for the extract alone, a good color stability of the pellets was achieved when stored at low temperatures, even if similar results were obtained for room temperature storage, provided that oxygen is absent.
In conclusion, these results indicated that at pH value of 5.0 the eco-friendly extract could be used to improve the color of products, both in pharmaceutical/nutraceutical and cosmetic fields, if stored in absence of oxygen even at room temperature. Further investigations are needed to evaluate the stability of this polyphenolic extract when mixed with other eccipients used in solid and/or liquid oral formulation, and also in cosmetic preparation.