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Physicochemical and Phytochemical Characterization and Storage Stability of Freeze-dried Encapsulated Pomegranate Peel Anthocyanin and In Vitro Evaluation of Its Antioxidant Activity

Azarpazhooh, Elham, Sharayei, Parvin, Zomorodi, Shahin, Ramaswamy, Hosahalli S.
Food and bioprocess technology 2019 v.12 no.2 pp. 199-210
2,2-diphenyl-1-picrylhydrazyl, Punica granatum, anthocyanins, antioxidant activity, bioactive compounds, calcium alginate, encapsulation, ethanol, freeze drying, glass transition temperature, half life, in vitro studies, inhibitory concentration 50, iron, maltodextrins, pomegranates, powders, relative humidity, storage quality, storage temperature, storage time
The acidified ethanol extract of pomegranate (Punica granatum L.) peel bioactive compounds was freeze-dried and encapsulated using a combination of maltodextrin (MDX 5, 10, and 15%) with calcium alginate (0.1%) with a weight ratio (w/w) of 1:5 (extract/wall material). The effects of various parameters on pomegranate peel extraction (POPx) and POPx-encapsulated powder were analyzed on bioactive components, physicochemical, morphological properties, and storage stability. The results revealed that process yield was positively influenced by increasing MDX concentration, due to the increase on mixture content. Encapsulated powder with 15% MDX had the highest total phenolic compounds (TPC, 73.1 mg GA/kg), the total anthocyanin content (TAC, 40.2 mg c3g/kg dmp and antioxidant capacity by FRAP, 405 (Fe²⁺, μmol/l)), the DPPH assay (RSA, 65.1%), the lowest IC₅₀, 0.56 ± 0.02 mg/ml, and the lowest glass transition temperature indicating that the highest antioxidant capacity among other wall materials. In respect to morphology, the particles of encapsulated powders with high concentration of MDX were larger and smoother. Stability and half-life of encapsulated powders were measured from 42 days of storage study at 4 °C and 25 °C, and 52 and 75% relative humidity. Storage tests revealed first-order degradation kinetics for anthocyanin. The TAC of the PoPx-microencapsulated powders with wall material of 15% and control decreased by 18% and 33%, respectively, after 42 days storage at 4 °C, while at the storage temperature of 25 °C, the decreases were in the order of 24% and 38%, respectively, over the same period of time. The highest anthocyanin content was observed in the freeze-dried MDX 15%-encapsulated powder at 4 °C storage temperature and 75% relative humidity with a half-life (t₁/₂) of 115 days, and the reaction rate constant (k) of 0.64 × 10⁻² min⁻¹.