GRAPE SKIN INFUSION AS A PROMISING SOURCE OF ANTHOCYANINS

Wine production is an industrial activity that generates a large volume of waste. Grape skin (GS) is a wine by-product with a high content of polyphenolic compounds, such as anthocyanins. These pigments are important antioxidants that can contribute to health due to its anti-inflammatory, antioxidant, neuro- and cardioprotective properties. Infusions, which are among the most popular beverages consumed worldwide, present a variety of flavors and therapeutic applications for health. Considering GS is endowed with a remarkable content of phenolic and aromatic compounds, it represents a potential raw material for the production of infusions. This study aimed to analyze the anthocyanin content of GS dried by different methods and its infusions. Cabernet Sauvignon grape pomace (crop 2015, Pinto Bandeira, RS, Brazil), a by-product of the winemaking process, had its seeds removed and was dried by different methods and time-temperature combinations: (i) hot air-dried, by using an oven with forced air circulation (Sample GS-60: 60 °C, 300 min and Sample GS-100: 100 °C, 75min); (ii) freeze-dried (Sample FD). The drying process was conducted until the samples reached a moisture content of 12% (recommended for tea powders). Infusions were prepared with 1 g of dried GS and 40 mL of hot distilled water (100 °C). After steeping for 3 minutes, the solid content was removed by filtration and the infusion was cooled in a water bath (<5 °C). The anthocyanins were exhaustively extracted from dried GS using acidified methanol (1% HCl v/v) and analyzed by high-efficiency liquid chromatography (HPLC). GS infusions were directly injected in HPLC equipment after filtration. By HPLC analysis it was possible to identify the anthocyanins malvidin-3-glucoside, delphinidin-3-glucoside, peonidin-3-glucoside, and cyanidin-3-glucoside. The GS total anthocyanins, expressed as malvidin equivalent (g/100g db), were 2.24 ± 0.01 (GS-60), 1.79 ± 0.04 (GS-100), and 2.36 ± 0.08 (FD). No significant differences were found between GS-60 and FD (p < 0.05) for GS TA. The anthocyanins content of GS infusions (mg/100mL) were 18.12 ± 0.62 (GS-60), 5.78 ± 0.40 (GS-100), and 52.52 ± 2.05 (FD). The percentual of anthocyanins present in the infusions related to the anthocyanins content of their corresponding GS was 37.16% (GS-60), 14.33% (GS-100), and 83.35% (FD). Both dehydration techniques, freeze drying and hot air drying, can be effective in GS anthocyanins preservation depending on the time-temperature combination. However, the rehydration capacity of freeze-dried food is higher than air-dried possibly due to its highly porous structure. This phenomenon can explain the highest content of anthocyanins in freeze-dried GS infusion (p < 0.05), whose anthocyanins could be better extracted to the solution. Even after distinct drying processes, the GS was proven to contain a high content of anthocyanins. Several studies have shown that grape products have beneficial health effects because of their unique mix of polyphenolic compounds. Therefore, GS infusions represent a functional product and a promising alternative for waste management in the wine industry.