Specord 205 uv vis spectrophotometer

The quantification of condensed tannin was carried out using the Makkar (2003) method with Gallic acid and tannic acid as standards [26 (link)]. Absorbance at 725 nm was read using a spectrophotometer (Eleco, SL 171 Mini Spec, Kolkata, India) after incubation of the reaction mixture at room temperature for 40 min using a Specord 205 UV-VIS spectrophotometer, Analytik Jena Inc. (Jena, Germany).
Condensed tannins were quantified according to the method of Makkar (2003) using tannic acid as a standard. Thus, the final solutions prepared according to the method for the determination of total tannins were again incubated for 40 min at room temperature, after which the absorbance rate was determined at 725 nm using a Specord 205 UV-VIS spectrophotometer, Analytik Jena Inc. (Jena, Germany). The different tannin contents were expressed in mg tannic acid equivalents/g using the tannic acid curve in the concentration range 20–200 mg/g.

The method applied to quantify the total phenolic content (TPC) was based on the oxidation of hydroxyl groups of phenolic compounds in alkaline media using Folin–Ciocalteu reagent, as described by Tolve et al. [25 (link)] and Blanch at al. [51 (link)]. Prior to analysis, the alcoholic extracts were diluted with distilled water, as follows: 1:2.5 (v/v) for SF, pastry products and dough, and 1:50 (v/v) for GP. Further, 0.5 mL of diluted extracts were mixed with 2.5 mL of Folin–Ciocalteu reagent previously diluted 1:10 (v/v) with distilled water. Next, 2 mL of 7.5% Na₂CO₃ solution was dosed and the obtained mixture was allowed to incubate for 30 min at 50 °C in the INB500 thermostat (Memmert GmbH, Schwabach, Germany), after which the absorbance was recorded at a wavelength of 750 nm using the Specord 205 UV–Vis spectrophotometer from Analytik Jena Inc. (Jena, Germany) versus a blank sample prepared under the same experimental conditions. TPC was calculated based on a calibration curve plotted by using standard gallic acid solutions with concentrations ranging from 0.1 to 1.0 µM gallic acid equivalents (GAE)/mL. TPC was reported as mg GAE/100 g dry weight (DW) of sample.

The method of Petchidurai (2019), with minor modifications, was used for the determination of total tannins [25 (link)]. Thus, 0.1 g of extract were dissolved in 10 mL of Folin Ciocalteu solution (Sigma-Aldrich Chemie GmbH, Munich, Germany) diluted with water 1:20 (v/v). The obtained mixture was incubated for 3 min at room temperature, followed by the addition of 2 mL of Na₂CO₃ 35% aqueous solution. The final solution was re-incubated for 30 min before reading the absorbance at 725 nm using a Specord 205 UV-VIS spectrophotometer from Analytik Jena Inc. (Jena, Germany). The total tannin content was expressed on the basis of the tannic acid standard curve, which was indicated in mg/gram in the range 20–200 mg/g.