PRESSURIZED LIQUID EXTRACTION OF ANTHOCYANINS FROM GRAPE PEEL AND APPLICATION IN PH-SENSITIVE FOOD PACKAGING

Summary: The use of biodegradable polymers has been a promising alternative for food packaging and to replace the use of petroleum-based plastics, which is a current environment problem. Anthocyanins are bioactive compounds that can be used as natural food coloring. The advantage in using anthocyanins is that these molecules can change the color according to the variations in pH and when applied in packaging films can be able to transmit information according to the oxidation of the food. Therefore, the aim of this study was to extract anthocyanins from grape agro-industrial by-products for application in the production of pH-sensitive food packaging. The extract was obtained by pressurized liquid extraction, using ethanol 70% (v/v) as solvent with a flow of 5 mL/min, at 60 °C and 15 MPa. The films were prepared with carboxymethyl cellulose (2.5% w/v) and glycerol (1% v/v) as plasticizer, incorporating grape extract at 10%, 30% and 50% (v/v). The films were dried in an oven at 35 °C for 24 hours. The extract obtained by pressurized liquid extraction presented high concentration of phenolic compounds (151.83 ± 15.04 µg/mL) and anthocyanins (220.27 ± 4.57 µg/mL). The films produced with the highest concentration of extract presented the highest content of phenolic compounds and anthocyanins. The films produced can be classified as pH-sensitive packaging, since change the color when exposed in different pH. For instance, the films with 50% of extract decreased the luminosity when exposed at pH 2 (51.8 ± 1.87), pH 6 (51.3 ± 1.04), and pH 10 (42.5 ± 0.95). The same behavior was observed for the color parameters a* (ranging from 4.1 ± 0.69 at pH 2 to 6.2 ± 0.31 at pH 10) and b* (ranging from 1.8 ± 0.18 at pH 2 to -1.01 ± 0.41 at pH 10). This behavior can be attributed due to the presence of anthocyanins incorporated in the films, which changed the color according to the pH exposed. In conclusion, the films produced can be used as pH-sensing packaging for the monitoring of the food quality during storage.