Acta Scientiarum Polonorum Technologia Alimentaria

Background. The Mirabelle plum fruit is a known and valuable source of biologically active compounds, including antioxidants. This fruit is used in the food industry due to its savory taste as well. The leaves, despite their high content of active compounds, are used much less. This study aimed to optimize the extraction process of Mirabelle plum leaf and fruit. The effect of the freezing-thawing process on the antioxidant activity of extracts was evaluated, as was the content of selected phenolic compounds. The concentration of some plant pigments in fresh and frozen raw material and the content of a few phenolic acids in the selected leaf extracts were also determined.
Materials and methods. The extracts of Mirabelle plum leaf and fruit (peel and flesh separately) were prepared using ultrasound-assisted extraction. Evaluation of antioxidant activity was performed using in vitro techniques such as DPPH, ABTS, FIC, CUPRAC, and FRAP. The  polyphenol, flavonoid, anthocyanin, chlorophyll, and carotenoid contents were also determined spectrophotometrically, as was the concentration of some phenolic acids in the selected leaf extracts by HPLC.
Results. The leaf extracts had higher antioxidant activity, polyphenols, and plant pigment contents than in the fruit. The lowest potential was observed for flesh extracts. The freezing-thawing process had rather an unfavorable effect on the activity of the leaf and peel extracts. The 120–180-minute extraction seemed to be more effective as compared to the 15–30-minute process. However, the prolongation of extraction up to 240  inutes led to a decrease in antioxidant potential and total polyphenol content. The leaf extracts had a relatively high concentration of phenolic acids, particularly chlorogenic acid (2.833 to 5.035 mg/100 mL of extract, on average).
Conclusion. To sum up, many factors, such as the plant part, extraction time, and the freezing-thawing process, could affect the antioxidant activity and content of biologically active agents in Mirabelle plum extracts. Due to the high content of active compounds including antioxidants in the Mirabelle leaves, their application in many areas of industry could be taken into consideration.