Development of Microencapsulated Product from Verbascum sinaiticum Leaf Extract for Antimicrobial Applications
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Date
2024-12
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Addis Ababa University
Abstract
Verbascum sinaiticum (V. sinaiticum), an Ethiopian medicinal plant, is rich in bioactive compounds, including antioxidants, antimicrobials, and anti-inflammatory agents. Traditionally used for treating infections, wound healing, and respiratory ailments, it also aids in food preservation by inhibiting spoilage microorganisms. In this study, V. sinaiticum was dried at 50, 60, and 70 °C in a fluidized bed dryer with a constant air velocity of 1.5 m/s. Five thin-layer drying models were evaluated using nonlinear regression analysis, with the Page model showing the best fit (R² = 0.9999, RMSE = 0.0036, SSE = 0.0001). Effective moisture diffusivity ranged from (2.135 ×10−10) to (5.895 × 10−10) m²/s, and activation energy values were 43.6 kJ/mol for unblanched and 41.6 kJ/mol for blanched samples. Blanching significantly reduced moisture content, impacting color and functional properties. UHPLC-ESI-QTOF-MS/MS analysis was employed to evaluate the effects of different drying methods on bioactive compounds in V. sinaiticum leaf extracts. Leaves were dried using oven (50, 60, 70 °C) and freeze dryers, and extracted with 50 %, 70 % aqueous ethanol, and 100 % water. Freeze drying with 70% ethanol produced the highest total phenolic content (TPC, 181.73 mg GAE/g) and total flavonoid content (TFC, 78.57 mg CE/g). TFC showed a strong correlation with DPPH radical scavenging activity (R² = 0.9082). FTIR analysis revealed reduced intensity of phenolic -OH groups in freeze-dried samples compared to oven-dried samples. Twenty-nine metabolites were identified, including 14 phenolic and flavonoid compounds, such as kaempferol, catechin, gallic acid, and myricetin derivatives, aligning with antioxidant activity results. Ultrasonic-assisted extraction (UAE) optimization yielded the highest TPC (179.8 mg GAE/g), TFC (64.49 mg CE/g), and antioxidant activities (DPPH: 61.85 μg/mL, ABTS: 38.89μg/mL) compared to maceration extraction. Optimal UAE parameters were extraction temperature (41.43 °C), sample-to-solvent ratio (36.32 g/mL), and extraction time (33.22min). Scanning electron microscopy revealed structural changes induced by UAE. Seventeen phenolic compounds were identified, confirming antioxidant capacities. Encapsulation of V. sinaiticum extract was studied using freeze-drying with maltodextrin (MD), gum arabic (GA), and a mixed matrix (MD:GA, 8:2). MD encapsulates showed superior water solubility (98.48 %), encapsulation efficiency (81.31 %), and phenolic stability (71.84 % retention at 4 °C over 32 days). XRD, FTIR, and SEM confirmed phenolic compound retention within microcapsules. Encapsulation masked unpleasant flavors and odors, enhancing the extract’s suitability for functional food applications. Encapsulated extracts demonstrated antimicrobial efficacy against Bacillus cereus, Escherichia coli, Candida albicans, Staphylococcus aureus with inhibition zones of 17–29 mm. Encapsulation improved thermal stability and reduced degradation temperatures. Encapsulated samples delayed microbial growth, maintaining an aerobic plate count of 2.94–3.01 Log CFU/g over 15 days at 4 °C, compared to 7.01 Log CFU/g in controls. Sensory evaluations confirmed the preservation of aroma and color during storage. This enhancement is attributed to the phenolic and flavonoid bioactive compounds, such as catechin, umbelliferone, kaempferol and myricetin derivatives, verbascoside, and proanthocyanidins, highlighting V. sinaiticum’s potential as a sustainable source of natural antimicrobial agents. These findings emphasize the potential of V. sinaiticum extract and encapsulated as a natural preservative for food, nutraceutical, and pharmaceutical applications.
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Keywords
Verbascum sinaiticum, · Ultrasonic extraction, · Drying kinetics, · Phenolic compounds, · Antioxidant activity, · Encapsulation, and · UHPLC-ESI-QTOF-MS/MS