Title : Stability tests of mixed extracts based on blackberry leaves during freezing and freeze-drying process and storage
Medicinal plants commonly consumed worldwide contain different chemical substances that display a broad spectrum of biological activities. One of such plants is the blackberry, a valuable fruit plants which leaves are also used in folk medicine. The blackberry leaves (BL) contain astringent, antibacterial and antifungal agents, recommended internally in diarrhoea and inflammation of the gastrointestinal tract. Leaf infusions are also used externally for skin lesions and ulcers, and as a rinse in infections of the oral cavity and throat. Among many possible effects on biological processes in the human body, the antioxidant properties of phenolic compounds are the most important.The purpose of this study was to evaluate the in vitro antioxidant activity of mixed water extracts based on blackberries leaves and their stability during freezing, freeze dried and storage. The plant material were gathered and air dried at room temperature and grounded. The plant powder from base plant was combined with others (elderberry (EF) and viburnum (VF) flower, cistus (CL) and fireweed (FL) leaves) in calculated proportion and were subjected to extraction with hot distilled water assisted by ultrasounds. The extracts were stored in lyophilized and frozen form for 6 months. Fresh and stored extracts were tested for changes in antioxidant activity during storage.Among the analysed medicinal plants, blackberry leaf extract showed the highest antioxidant activity. It was also noticed a higher antioxidant activity of three component (BL-EF-FL) extract with comparison to single BL extract. Mixed extracts based on BL contained together EF and VF showed better stability during storage compared to mixed extracts contained only one flower. It was also noticed that freeze-drying and freezing caused a decrease in antioxidant activity, which depended on the composition of the extract and was in the range of 1.1-37.6%. The highest decrease in antioxidant activity was found for the binary (BL-VF and BL-EF) and five-component extracts.The study showed that blackberry leaves can be considered a good source of antioxidant compounds which can be enhanced by combining with other medicinal plants. There is clear potential for using blackberry leaves as a food additive, medicinal source or herbal tea.