## 2 Discussion
The method exploits a colorimetric reaction evaluated by UV-vis spectrophotometry due to the formation of a blue chromophore of the phosphodynolpdenum-tungstic plus phenolic compound-complex at 765 nm [53; 54]. The most common standard used to generate a calibration curve is gallic acid; thus, the phenolic content results are usually expressed as mg gallic acid equivalents (GAE). In our group, we quantified the total phenolic compounds from blueberry (_Vaccinium ashiei_) spray-dried extracts with the Folin-Ciocalteu method. The obtained results represent the precision of the approach--in other words, high linearity, low limit of detection, high limit of quantification, high reproducibility, and excellent accuracy. First, we obtained microcapsules that can retain anthocyanins. A value of 24.92 umol GAE/g wet weight of blueberry was determined from the fruit slurry before microcapsule preparation. Consequently, we achieved a retention of more than 95% in one of the powders prepared by spray drying. The application of spectrophotometric techniques undeniably enabled the initial quantification following the evolution of the anthocyanin quantities during storage of the food product [55]. The total monomeric anthocyanins can be determined through the pH differential method, which is a simple spectroscopic assay involving anthocyanin transformation when a change in pH is applied. This is used as the standard methodology approved by the Methods Committee on Commodity Foods and Commodity Products as First Action of the Association of Official Agricultural Chemists for anthocyanin quantification [56]. The method is based on a sample of free anthocyanins presenting a particular hue (e.g., red, purple, and blue) at pH 1.0 and turned to colorless at pH 4.5; thus, the difference in absorbance can be measured. Beginning from an acidic pH of 1, individual (nonpolymerized) anthocyanins present colors on the interval of orange to purple due to the presence of its predominant form of the flavylium cation. Turning the pH to neutral (7.0) represents a color change to blue caused by the deprotonation of the flavylium cation to form the quinoidal base of the anthocyanin. On the contrary, the change of pH from 1.0 to less acidic pH of 4.5 implies the change of the flavylium cation form to a carbinol pseudo base as a cause of water introduction. This structure reaches equilibrium with a colorless chalcome structure. The quality of fresh and processed foods containing anthocyanins can be determined by spectrophotometrically following (520 nm) the anthocyanin evolution during the shelf life of fruit or vegetal juice, pulp from fruits, flowers, seeds, grains, wine, and pigments extracted from vegetables. The expression of the results is related to the main anthocyanin present in the product. For example, the major monomeric anthocyanin in wine is malvidin-3-O-glucose (M3G). Using the molar absorptivity coefficient (\(\varepsilon\)) of the evaluated anthocyanin is required. Thus, the results are commonly expressed as mg of M3G/g or mL sample [57]. Another wine illustration implies the spectrophotometric detection and quantification of polymeric anthocyanins. Therefore, the polymeric anthocyanin concentration must be established by mixing a sample of the product with 5% SO\({}_{2}\), then measuring the mixture absorbance at 520 nm [58]. The polymeric anthocyanin quantification through this methodology allowed the comparison between the content of polymeric anthocyanins in control wines and wines enzymatically treated with pectinolytic enzymes to improve the release of the bioactive compounds (an increase from 23% to 33%) responsible for the color and beneficial effects on human health [59]. Measuring the color of food products can be spectrophotometrically performed by applying the methodology proposed by the International Commission on Illumination, called the CIEL*a*b* system. The measures require the use of colorimeter equipment usually with color sensor wavelengths of 400 to 720 nm.