Development of an extraction and purification method for the characterization of the high molecular weight fraction of traditional balsamic vinegar

Traditional balsamic vinegar (TBV) is a seasoning produced in the provinces of Modena and Reggio Emilia (Italy) and known and appreciated worldwide. During his years-long seasoning many chemical reactions takes place, leading to the formation of antioxidants and bioactive compounds, including melanoidins [1]. They are a class of polymeric substances originating from sugars and amino acids, as a consequence of Maillard’s reaction. In literature only a relatively low number of studies on melanoidins contained in foods are present, mainly because of objective difficulties in their isolation. For this reason we decided to develop a method suitable for the extraction and the purification of high molecular weight melanoidins from a complex matrix, such as vinegars. Extraction with solvents as reported by Xu et.al [2], dialysis and ultrafiltration, were tested on TBV and on a good quality industrial balsamic vinegar (IBV). On the obtained fractions dry matter, antioxidant power and total phenolic content were determined. To evaluate the effect of purification procedures, 1H-NMR spectra of the different fractions were also recorded and compared to raw vinegars spectra. In the ultrafiltered sample low molecular weight compounds were still presents, so it is possible to affirm that dialysis is crucial to obtain an effective purification of the melanoidins. Nevertheless it is noticeable that polyphenols concentration is higher in ultrafiltered samples: although this step is not suitable, alone, to achieve a satisfactory purification, it is useful to concentrate the high molecular weight fraction isolated by dialysis in a smaller volume. IBV showed a behavior very similar to TBV, but its high molecular weight fraction generally presents a lower phenols concentration and antioxidant activity. Moreover, in general, does not appear to exist any kind of correlation between the fractions molecular weight and their antioxidant capacity. In conclusion, the combination between dialysis and ultrafiltration appears to be a valid procedure to extract and purify the high molecular weight fraction of TBV in a small volume, but results obtained from dialysis alone are more consistent and reproducible.