## 2 Discussion
The antioxidant activity was measured by applying the ABTS radical method expressing its antioxidant capacity as umol equivalent Trolox. Tannins are phenolic polymers of plant origin used in leather tanning, since it binds to the collagen proteins of the skin, increasing its resistance to water, heat, and microorganisms; this property is also responsible for generating astringency when they are consumed. They are often found in barks and other plant tissue. We can find them in food grain such as those of some legumes and fruits, such as grapes, among others [113,114]. There are two categories of tannins: (1) condensates and (2) hydrolysable (Figure 4). Condensed tannins are compounds formed by the union of flavonoid units of the catechin or flavanonols type. While the hydrolyzable tannins are heterogeneous polymers made up of phenolic acids, mainly gallic acid and simple sugars as the central core; these are smaller than condensed tannins and can be easily hydrolyzed with dilute acids. The strong bond that exists between tannins and proteins is the reason for the indigestibility of these compounds and causes them to be considered without nutritional value; in addition, they can cause a decrease in intake, growth rate, and energy obtained through food, especially in populations whose diets are based on legumes [115]. Table 1 shows an example of a bioactive tannin, its source, and the most common spectroscopic and spectrometric methods for its identification and quantification. Terpenes and terpenids are a group of metabolites widely distributed in nature made up of repeating isoprene units. The compounds of this group comply with the so-called \"isoprene rule\", which says that terpen are made up of an integer number of isoprenes joined \"head-to-tail\" or \"head-to-head\". However, there are exceptions to this rule derived from some rearrangements that can undergo throughout their biosynthesis. Those compounds that do not strictly comply with this rule, but their structures are modified by one or more rearrangements, are known by the name of terpenids. These compounds can be cyclic or open-chain and are classified according to the number of isoprenic units that form them: monoterpenes (2 units), sesquiterpenes (3 units), diterpenes (4 units), esterpenes (5 units), triterpenes (6 units), and tetraterpenes (8 units) (Figure 5). Figure 4: The structures of the main constituents of hydrolyzable tannins and condensed tannins. Terpenes have shown a wide variety of biological activities such as antimicrobial [116], anti-inflammatory [117], immunomododulatory [118], anticancer [119] activities. Table 1 shows an example of a terpene, its biological activity, the source of this compound, and some common spectroscopic and spectrometric methods used for its identification and quantification. More recently, we have been working on the extraction and stabilization of other bioactive compounds, particularly in carotenoids from mamey (_Pouteria sapota_) and carrot (_Daucus carota_). These compounds can be spectrophotometrically measured from the extracts obtained from the nonpolar extraction with a mixture of solvents hexane-acetone-ethanol. Once extracted, the sample was saponified, and the upper layer was recovered with ethanol to be concentrated in a rotary evaporator. The sample was then analyzed at 450 nm, and the results were compared to a calibration curve prepared using pure \(\beta\)-carotene. Similar to the analysis performed on the anthocyanins, the carotenoid extracts were tested for antioxidant activity to evaluate the potential use of these vegetal products as beneficial foods with excellent results (data unpublished). As mentioned earlier, [PERSON] et al. [86] isolated phenolic compounds and carotenoids from ten different colored maize genotypes. The carotenoids from the maize samples were identified and quantified following the methodology proposed earlier [120]. The carotenoids were extracted from the milled grain by adding Na\({}_{2}\)CO\({}_{3}\) and a mixture of methanol/tetrahydrofuran and continuous stirring.