Abstract
Antioxidants are recommended to prevent and treat oxidative stress diseases. Plants are a balanced source of natural antioxidants, but the poor solubility of plant active molecules in aqueous media can be a problem for the formulation of pharmaceutical products. The potential of PlantCrystal technology is known to improve the extraction efficacy and antioxidant capacity (AOC) of different plants. However, it is not yet proved for plant waste. Black tea (BT) infusion is consumed worldwide and thus a huge amount of waste occurs as a result. Therefore, BT waste was recycled into PlantCrystals using small-scale bead milling. Their characteristics were compared with the bulk-materials and tea infusion, including particle size and antioxidant capacity (AOC) in-vitro. Waste PlantCrystals possessed a size of about 280 nm. Their AOC increased with decreasing size according to the DPPH (1,1-diphenyl-2-picrylhydrazyl) and ORAC (oxygen radical absorbance capacity) assays. The AOC of the waste increased about nine-fold upon nanonization, leading to a significantly higher AOC than the bulk-waste and showed no significant difference to the infusion and the used standard according to DPPH assay. Based on the results, it is confirmed that the PlantCrystal technology represents a natural, cost-effective plant-waste recycling method and presents an alternative source of antioxidant phenolic compounds.
Highlights
All human beings are exposed to oxidative stress during their lifespan, caused by byproducts of metabolism, environment and lifestyle-related factors [1]
The bulk of black tea waste showed weak antioxidant activity, which was significantly improved by using the natural, ecofriendly and cost-effective PlantCrystal- technology, i.e., the obtained “Nano-Wastes” (PlantCrystals obtained from organic waste) demonstrated a better antioxidant activity compared to its bulk and this agreed with a study performed by Griffin et al in which the authors could prove that nanonization can unlock the antioxidant potential remaining in the plants waste [3]
DPPH (1,1-diphenyl-2- picrylhydrazyl) Assay The antioxidant capacity of the produced PlantCrystals of the black tea, its waste and the tea infusion used in this study was investigated using the DPPH (Sigma–Aldrich Chemie GmbH, Steinheim am Albuch, Germany) assay according to the method proposed by Sharma and Bhat [3,5,6,31,35] and compared to AOC of the bulk materials, where ascorbic acid (Sigma Chemical Co., Louis, MO, USA) was used as standard
Summary
All human beings are exposed to oxidative stress during their lifespan, caused by byproducts of metabolism, environment and lifestyle-related factors [1]. The bulk of black tea waste showed weak antioxidant activity, which was significantly improved by using the natural, ecofriendly and cost-effective PlantCrystal- technology, i.e., the obtained “Nano-Wastes” (PlantCrystals obtained from organic waste) demonstrated a better antioxidant activity compared to its bulk and this agreed with a study performed by Griffin et al in which the authors could prove that nanonization can unlock the antioxidant potential remaining in the plants waste [3] This higher AOC of the produced BT waste PlantCrystals in this study is related to the higher extraction efficacy shown in the higher TPC, TFC and TCC values after nanomilling process (Table 3). It is worth saying that the obtained results are useful to further identify the specific polyphenolic compounds responsible for the antioxidant activities and to study their structure–function interactions, i.e., to specify the released compounds upon nanonization and enable the development of pharmaceutical and cosmeceutical products
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