COMPARISON OF LIQUID AND LYOPHILIZED SERPYLLI HERBA WASTE EXTRACTS PREPARED AT DIFFERENT pH VALUES

Abstract

Polyphenol recovery and physico-chemical properties of the extracts depend on the type of solvents and their pH values. Additionally, due to the presence of different biologically active compounds in plant waste, plant extracts obtained from industrial by-processing can find potential applications in various products. In the present study, Serpylli herba waste extracts were prepared using maceration (60 min), a solid-to-solvent ratio of 1:30, the particle size of plant waste 0.3 mm, and two types of the extraction medium: 50% ethanol (pH 6) and 50% ethanol with glacial acetic acid (pH 2.5). The lyophilization process was chosen as the next step (-75°C, 0.011 mbar, for 24 h). Comparison of liquid and lyophilized extracts prepared at different pH values was done via analyzing total polyphenol content (TPC, Folin-Ciocalteu method), total flavonoid content (TFC, colorimetric assay), antioxidant capacity (ABTS and DPPH assays), zeta potential, and conductivity (photon correlation spectroscopy). TPC of liquid extracts prepared at pH 2.5 and pH 6 amounted to 1.38 and 1.23 mg GAE/mL, respectively, while lyophilized parallels had 271.7 and 188.8 mg GAE/g, respectively. The same trend is noticed in the case of TFC: 0.368 and 0.334 mg CE/mL for liquid extracts obtained at pH 2.5 and pH 6, respectively, and 102.5 and 99.7 mg CE/mL for lyophilized parallels. ABTS radical scavenging activity of the liquid extracts at pH 2.5 and pH 6 was 0.767 and 0.750 mmol TE/L, respectively and for the lyophilized parallels was 0.136 and 0.111 mmol TE/g. IC50 (concentration for neutralization of 50% of DPPH free radicals) was 1.12 and 1.75 mg/mL for the liquid extracts prepared at pH 2.5 and pH 6, respectively and 0.331 and 0.391 mg/mL for the lyophilized parallels. The zeta potential of the liquid extracts at pH 2.5 and pH 6 was 1.74 and -2.56 mV, respectively, whereas the zeta potential of lyophilized parallels was -3.55 and -18.7 mV. Conductivity of the liquid extracts was 0.864(pH 2.5) and 0.423 mS/cm (pH 6), whereas for the lyophilized extracts it was 0.199 (pH 2.5) and 0.452 mS/cm (pH 6). The presented results provide the information on physico-chemical properties of Serpylli herba waste liquid and lyophilized extracts that can add value and improve the quality of the existing food, functional food, pharmaceutical and cosmetic products, as well as for drinking water and wastewater treatment.