Effect of different drying processes on an antioxidant potential of three species of the Lamiaceae family



Introduction: Spice plants are a rich source of biologically active compounds. Processes of drying, limits the development of microorganisms and biochemical reactions in raw herbs, at the same time modifies their chemical composition. Objective: The aim of this work was to evaluate the effect of drying process of selected plants on their antioxidant potential and the content of biologically active compounds. Methods: The herbal materials thyme herb (Thymus vulgaris L.), sage leaves (Salvia officinalis L.) and rosemary leaves (Rosmarinus officinalis) were dried using two methods: convective (at 30° C), and freeze-drying. In both, fresh and subjected to drying processes herbs, changes in total polyphenol and antioxidant potential (with the DPPH radical), vitamin C (in the form of ascorbic acid) and chlorophyll pigments contents, were studied. Results: The highest content of polyphenols and vitamin C was recorded in rosemary, while sage was characterized by the highest content of chlorophylls. It was found that the drying processes caused large losses of vitamin C (ascorbic acid) and dyes in comparison to the fresh material. The highest losses of vitamin C occurred in convection dried sage (95%), while most was preserved in lyophilised thyme (losses 74%). Drying had also influenced the reduction of the content of chlorophylls with the largest loss of these compounds, at 94% observed in the freeze-dried rosemary. However, the content of polyphenols increased, underscoring a large impact on the antioxidant activity of herbs. Conclusions: Drying processes resulted in the release of phenolic compounds, so their content increased three to four times in the case of rosemary and sage. The largest increase was observed in the case of lyophilised thyme. Simultaneously, the antioxidant potential was significantly increased. Herbal droughts proved to be a rich source of antioxidant compounds with promising applications as a food additive.
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