Changes in anthocyanins throughout the processing of muscadine (Vitis rotundifolia) wine

Abstract

Grapes from Vitis rotundifolia ( Muscadine) are rich sources of different phenolic compounds, (e.g. ellagic acid, myricetin, quercetin, kaempferol, resveratrol, etc.) which are purported to provide health benefits, possibly as antioxidants. Anthocyanins, a pigmented subgroup of the flavonoid group, are responsible for intense pigmentation in the grapes. Maximizing anthocyanins in products is a priority for color, and preservation of potential health benefits. This research focused on measuring changes in the anthocyanins as wine is produced commercially from a single crop of Vitis rotundifolia var. Ison grapes. Samples were taken at points throughout the vintification process, and phenolics and anthocyanins were analyzed. In addition to examining characteristics from the pre-fermented must and finished wine, skins, juice, and press cake were extracted and analyzed to quantify the distribution and changes in the anthocyanins in various fractions during the vinification process. HPLC using a mixed mode C18 column with a diode array detector analysis to detect monomeric glycosylated and polymerized anthocyanins. Potassium metabisulfite bleaching was used to determine polymerized anthocyanins. The study was limited to one crop year from one vineyard which limited annual and spatial variability. Results identified six anthocyanins: cyanidin, malvidin, petunidin, peonidin, delphinidin, and pelargonidin dihexoses, Concentration of each anthocyanin increased with time, increasing extraction of pigments from the skins until the pressing step. No significant difference was found in anthocyanin concentrations over time when analyzed by HPLC after pressing; however, microplate analysis of total monomeric anthocyanins by pH differential did show a significant loss in anthocyanins during fermentation, contrasting with concentrations observed by HPLC. Observed declines varied significantly among the identified anthocyanin forms; however, total phenolic levels by Folin-Ciocalteu did not exhibit this decline. Significant levels of polymerized anthocyanins were not detected by either method. These data show, under the study conditions, that anthocyanin forms within Ison variety muscadine grapes are differently resistant to the enological process. Cyanidin and delphinidin forms were most affected, with higher rates of extraction and declines throughout the process. Petunidin and peonidin dihexose forms, showing similar trends, were less drastically affected, malvidin and pelargonidin forms displayed a non-trend, remaining at similar concentrations throughout processing This research focused on measuring changes in the anthocyanins as wine is produced in a commercial winery from a single crop of Vitis rotundifolia var. Ison grapes. Samples were taken at various points throughout the vintification process, and the phenolics and anthocyanins were analyzed. In addition to examining characteristics from