Effects of Different Drying Processes on the Bioactivity and Rutin Content of Prunus spp. (Plums)

The aim of this study was to investigate the effects of drying process preparations, solvent type, and different species of Prunus spp. (European, Japanese, and cherry plums) on bioactive properties (antioxidant, anti-lipid peroxidation, anti-tyrosinase, and anti-inflammatory activities) and rutin content. Leaves and fresh fruits of plums were dried using a cold process (vacuum freeze dryer at -105 ± 5°C) and a hot process (hot air oven at 50 ± 0.5°C). The dried plant material was then extracted using ethanol and propylene glycol to obtain ethanolic crude extracts and propylene glycol extract solutions. These extracts were then tested for phenolic and flavonoid contents and their potential biological activities and analyzed for rutin content using the HPLC method. The results showed that the ethanolic extract of plum leaves obtained via the cold-drying process exhibited higher total phenolic and flavonoid contents (96.94 ± 6.73-112.34 ± 9.08 mg GAE/g sample and 105.10 ± 11.31-185.94 ± 23.35 mg QE/g sample, respectively), as well as greater potential for antioxidant activity (DPPH with IC₅₀ = 29.97 ± 1.17 to 31.44 ± 4.16 μg/mL), anti-tyrosinase activity (40.34 ± 1.27%-46.91 ± 0.22%), and anti-lipid peroxidation activity (34.10 ± 4.88%-38.27 ± 2.12%). They also exhibited higher anti-inflammatory activity by inhibiting NO (20.16 ± 0.12%-40.05 ± 0.42%), IL-6 (37.81 ± 3.01%-42.37 ± 8.92%), and TNF-α (45.96 ± 7.93%-63.28 ± 6.44%) compared to fresh plum fruit extracts and other extraction procedures. These activities correlated with the rutin content, which was high in the plum leaf extracts (28.52 ± 0.00%-43.82 ± 0.13% w/w). European plums tended to exhibit greater bioactivities and higher rutin content compared to other species. These findings indicate that plum leaf extracts are a promising source for further applications in food, nutrition, and health products.