Genesys 150 uv vis spectrophotometer

The obtained bilberry pomace extracts’ total phenolic content was estimated as previously described in the literature [23 (link)]. Briefly, 150 μL of sample or blank was mixed with 750 μL of Folin–Ciocalteu’s reagent (1:9, v/v) followed by 600 μL Na₂CO₃ solution (75 g/L). Samples were kept in the dark for two h. The absorbance of optically clear supernatants was measured at 760 nm with a GENESYS 150 UV-Vis Spectrophotometer (Thermo Fisher Scientific, Waltham, MA). The TPC was expressed as gallic acid equivalents (mg GAE/g extract or recalculated per g DW of bilberry pomace residue after SFE-CO2 taking into consideration the extraction yield; mean values ± standard deviation, n = 4), employing a dose–response curve (0–80 μg/mL) for gallic acid.

The content of total phenolic compounds was estimated using the Folin–Ciocalteu method [16 (link)]. Before the analysis, the samples were filtered with a 0.22 µm filter, obtaining a remnant sample free of microorganisms.
First, the diluted reagent was prepared at a 1:1 volumetric ratio of the Folin–Ciocalteu reagent with distilled water. Briefly, 0.5 mL of juice samples was placed in test tubes, and 3.75 mL of distilled water was added. Then, 0.25 mL of the diluted Folin–Ciocalteu reagent was added, and the sample was homogenized at medium speed with a vortex mixer. An amount of 0.5 mL of the 10% w/v sodium carbonate solution was added to the homogenized samples and left to rest for one hour at room temperature in dark conditions. Subsequently, the absorbance of the samples was measured at a wavelength of 765 nm in a Genesys 150 UV–Vis spectrophotometer (Thermo Fisher Scientific, Waltham, MA, USA). A calibration curve with known concentrations of gallic acid was used for TPC quantification. Pure distilled water was used as a blank sample. The results were expressed in units of mg of gallic acid equivalents (GAE) per liter of juice.