Total phenolic content (TPC) were estimated using the Folin–Ciocalteau’s (FC) method with modifications [15 (link)]. Briefly, an aliquot (5 mL) of the gallic acid solution was transferred to a glass tube; reactive 10−1 diluted FC reagent (20 mL) is added after 5 min; sodium carbonate (Na2CO3, 5 mL, 7.5% w/v) was added and the mixture shaken. After 30 min of incubation at ambient temperature in the dark, 200 µL samples were placed in 96-well plates. Finally, the absorbances were measured in a spectrophotometer (Infinite Pro M200 series, TecanTM, Männedorf, Switzerland) at 765 nm and compared to a gallic acid calibration curve for TPC (prepared using 0 to 1 mg/mL concentration gallic acid solution). Results were expressed as mg gallic acid equivalent (GAE)/100 mL. All measurements were done in duplicate.
Gallic acid content (GAC) was determined using HPLC (Agilent 1100 system, Agilent Technologies, Santa Clara, CA, USA) equipped with a Zorbax SB-C18 column according to the methodology presented in [16 (link)]. This was carried out to measure the changes in gallic acid concentration due to photodegradation. Results were expressed as mg GAC/100 mL solution.
To determine the antioxidant activity (AA) of gallic acid solutions, 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assay was used. A standard curve was constructed using TroloxTM (20 µM) solution. For sample wells, gallic acid (20 µL) was added. In both standard and sample wells of a 96-well microtiter plate, 1 mM DPPH (20 µL) was added. The blank well consisted of HPLC grade methanol (200 µL). The plate was incubated for 10 min at room temperature in the dark. Then the plate absorbances were read at 519 nm by a microtiter plate reader (TecanTM Infinite M200 Pro). All reagents were dissolved in HPLC grade methanol. Antioxidant capacity reported in mM TroloxTM equivalents (TE) per mL of solution.
Gallic acid content (GAC) was determined using HPLC (Agilent 1100 system, Agilent Technologies, Santa Clara, CA, USA) equipped with a Zorbax SB-C18 column according to the methodology presented in [16 (link)]. This was carried out to measure the changes in gallic acid concentration due to photodegradation. Results were expressed as mg GAC/100 mL solution.
To determine the antioxidant activity (AA) of gallic acid solutions, 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assay was used. A standard curve was constructed using TroloxTM (20 µM) solution. For sample wells, gallic acid (20 µL) was added. In both standard and sample wells of a 96-well microtiter plate, 1 mM DPPH (20 µL) was added. The blank well consisted of HPLC grade methanol (200 µL). The plate was incubated for 10 min at room temperature in the dark. Then the plate absorbances were read at 519 nm by a microtiter plate reader (TecanTM Infinite M200 Pro). All reagents were dissolved in HPLC grade methanol. Antioxidant capacity reported in mM TroloxTM equivalents (TE) per mL of solution.
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