Centrifugal Spinning of Anthocyanin-Infused Microfibers: Impact of Methanol Extraction on Color Change and Antioxidant Activity in Intelligent Packaging

Although many studies investigated the effect of different solvents on the extraction efficiency of anthocyanins and the type of compounds extracted, there is no study so far that analyzes the effect of methanol concentration on the color change of anthocyanins for intelligent packaging. Therefore, one of the objectives of this study is to investigate the effect of methanol extraction concentration on the color change of anthocyanin and to produce an intelligent-active microfiber film with the anthocyanin extract. For that purpose, different concentrations of methanol (100%, 75%, 50%, 25%, and 0%) were utilized to extract red cabbage extract and the cyanidin-3-glucoside; antioxidant activities were measured. Furthermore, the color changes with respect to pH (1–12) were also investigated colorimetrically and spectrophotometrically. Although the anthocyanin extracted by 100% methanol (M100) had the highest anthocyanin content (321.95 ± 4.62 mg/L), it had the lowest antioxidant activity (8.99 \(\pm\) $\pm$ 0.98%). Nonetheless, the samples treated with 50% methanol (M50) had one of the highest antioxidant activities (42.12 \(\pm\) $\pm$ 0.11%) and a reasonably high anthocyanin content (289.89 ± 5.68 mg/L). To produce the intelligent fibers, gelatin and polyethylene oxide (PEO) were selected, and M50 extract and a range of extract concentrations (5%, 7%, and 9%) were added to the spinning solution. The effect of rotational speed on the fiber size and morphology was investigated. The fiber diameter of the samples decreased as the rotational speed was increased from 3300 rpm, which produced fibers with a size of 1915 ± 431 nm, to 4200 rpm, which produced fibers with a size of 1425 ± 357 nm. All polymeric solutions showed non-Newtonian behavior. The TGA results showed that main degradation temperatures of the fibers (420 °C) were higher than the main decomposition peak of gelatin (349.12 °C) and PEO (401.59 °C). Therefore, it can be concluded that the thermal stability of the films was relatively increased with the addition of anthocyanin. The reversibility of the films was tested based on ammonia and acetic acid vapor. Samples containing 7 mL extract (PG_7) almost exhibited the same “a” and “b” values in CIELab scale through 3 cycles.