Uv vis 2600 spectrophotometer

The total phenol content of okra extracts was evaluated by the Folin–ciocalteu method as described by (Wojdyło et al., 2007 (link)). About 1 ml of sample extracts or standard at different concentrations was mixed with 2 ml of Folin–ciocalteu reagent (10 times diluted) and incubated at room temperature for 3 min. After that, 10 ml of 20% sodium carbonate was added to the mixture and left for incubation at room temperature for an hour. The absorbance of the mixture was measured at 765 nm with a Shimadzu UV–VIS‐2600 spectrophotometer against a blank solution. The blank solution contained all the reagent mixture without extract or standard sample. Gallic acid standard curve was used to quantify total phenolic contents, and the results were expressed as mg of gallic acid equivalent (GAE) per gram of dried weight. All determinations were performed in triplicate (n = 3).

The TPC of exudate mucilage and cocoa bean shell was determined by the method described by Samaniego et al. [5 (link)]. For this, 2 mL of each sample was mixed with Folin–Ciocalteu reagent and 20% Na₂CO₃. Absorbance was measured using a Shimadzu UV–VIS 2600 spectrophotometer (Kyoto, Japan) at a wavelength of 760 nm. The results were compared against a calibration curve (y = 0.0085x + 0.0975; R² = 0.9989) of gallic acid (0 to 100 ppm). Measurements were made in triplicate for three days (n = 9). TPC was expressed in terms of mg of gallic acid (GAE) per 100 mL of sample on a fresh weight (FW) for cocoa exudate mucilage (FD) and dry weight cocoa husk (DW).

Smaller particle tends to absorb light at different wavelengths than their salt. The several nanoparticles mentioned above were analyzed under Shimadzu U.V./vis 2600 spectrophotometer and measured absorption maxima between 185 and 1000 nm.

Beer color was determined according to the European Brewery convention (EBC) spectrophotometric method on a dual-beam Shimadzu UV–Vis 2600 spectrophotometer (Shimadzu, Kyoto, Japan). The analysis was performed in duplicate, using quartz cuvettes with an optical thickness of 10 mm, with ultrapure water as a blank and each sample filtered. The absorbance was measured at 430 nm. Beer color, expressed in EBC units, was calculated by multiplying the absorbance value by 25.

The determination of thermal stress that beer undergoes during forced ageing was performed according to De Schutter et al. [27 ]. Sample preparation included adding 5 mL of TBA solution (288 mg of thiobarbituric acid in 100 mL acetic acid (90%)) and 10 mL of beer in a test tube. The mixture was kept in a water bath at 70 °C for 70 min. Then, samples were cooled on ice. Finally, the absorbance of the sample was read at 448 nm on a dual-beam Shimadzu UV–Vis 2600 spectrophotometer (Shimadzu, Kyoto, Japan). The analysis was performed in duplicate, using quartz cuvettes with an optical thickness of 10 mm, with untreated beer with TBA solution as blank. Subsequently, the TBA value was calculated using the Equation (1) (D: dilution factor).
$$TBA=10\times \left(D\times A_{448}-A_{blank}\right)$$

The TFC content of exudate mucilage and cocoa bean shell were determined according to the method described by Llerena et al. [29 (link)]. An aliquot of the sample previously extracted in a methanolic solution was taken and reacted with sodium nitrate, aluminum chloride and sodium hydroxide. The absorbance of the mixture was measured using a Shimadzu UV–VIS 2600 Spectrophotometer (Shimadzu, Kyoto, Japan) at 490 nm. TFC was determined using a catechin calibration curve (y = 0.0036x + 0.0678; R² = 0.9994) measured in triplicate for 3 days (n = 9). The results are expressed in mg of catechin equivalents (CE) per 100 g dry weight (DW).