## 2 Discussion
The supernatant of the mixture was evaporated and redissolved in the mixture of methanol/tetrahydrofuran to be analyzed by HPLC with a photodiode array detector and a C18 column. The maize samples exhibited the presence of lutein and b-carotene, which were identified by the comparison of the HPLC profiles against the curves previously prepared with the pure standards. As exposed by the authors, the findings of the carotenoid content of maize, particularly provitamin A or b-carotene, reveals the importance of these bioactive compounds in preparing functional foods. One example could be trying to diminish the levels of incidence of vitamin A deficiency, associated with acquired blindness in children, growth retardation, and anemia [121]. Resins  
Resins are complex mixtures of compounds such as monoterpenes, di terpenes, tri terpenes, polysaccharides, fatty acids, and esters. The compound that prevails depends on the type of resin--for example, mono- and di terpenes prevail in copal resin, polysaccharides, proteins, and terpenes in myrrth, mono- and sesquiterpenes, abietic acid, and other organic acids in turpentine. Some of these resins, such as copal, are used in traditional Mexican medicine to cure headaches, diarrhea, and as anti-inflammatory [122] and in some religious mites. Copal resin contains mono- and sesquiterpenes in its volatile part and triterpenes in its nonvolatile part and may also contain lignans [123]. Myrrh essential oil has antifungal properties [124]. Figure 6 shows the structures of two representative resins, curzerene and 13-epi-manool; additionally, Table 1 exhibits one example of a bioactive resin, its source, and the spectroscopic and spectrometric methods used for its analysis. Figure 5: Examples of some terpenes and terpenoids. Lignans  
Lignans are dimeric phenylpropanoids derived from phenylalanine through cinnamic acid and _p_-coumaric acid (Figure 7). The monomers of the lignans can be synaptic acid, ferulic acid, caffeic acid, _p_-coumaridyl alcohol, coniferyl alcohol, and synapyl alcohol. Ligans such as podophyllotoxin have been used to treat different cancers [125] as well as other lignans [126]. Table 1 shows an example of bioactive lignan, its source, and the spectroscopic and spectrometric methods used for its analysis. Lignans are formed essentially by oxidative polymerization of various cinnamyl alcohols, corresponding to cinnamic acid. Phenylpropanols are joined to form the polymer by the action of enzymes called peroxididases that catalyze the oxidation of alcohols generating free radicals that combine in non-enzymatic and random processes to give lignin; resulting in a complex and branched structure in all three dimensions. As there is no common repeating unit as in starch, rubber, or cellulose, each lignin molecule can be unique. Alkaloids are nitrogenous organic compounds found in 20% to 30% of vascular plants. Nitrogen is generally part of a heterocyclic ring. Its name derives from the fact that most of these compounds are alkaline. At the pH where they are generally found in the cell (pH = 5-7), nitrogen is protonated, so the alkaloid is positively charged and is generally soluble in water. Alkaloids are classified according to their basic structures into derivatives of pyrrolidine, tropane, piperidine, pyrrolidine, quinolizidine, isquinoline, and indole (Figure 8). Among the bioactivities they possess are those that affect the central nervous system causing different types of reactions, from sedation, hallucination, and even death. However, there are several that are used in medicine as anesthetics [127], in the treatment of cardiovascular diseases [128]; others showed cytotoxic activity in tumor cells [129]. Figure 6: The chemical structure for curzerene and 13-epi-manool, components of myrrh and copal resins, respectively. Figure 7: The chemical structure for lignans. Furanocoumarins and naphthodianthrones  
Furanocoumarins are heterocyclic compounds that contain a furan ring fused to a coumarin (Figure 9).