Introduction

Maize (Zea mays L.) is the staple food of the diet in Mexico and other cultures. Mexico is the center of origin for maize, whose nixtamalization provides an important nutritional contribution to this cereal. Nixtamalized maize products like tortillas and other snacks are consumed in countries as diverse as China and Australia.

White and yellow maize are the main varieties used in nixtamalized products, but in other regions, especially in central Mexico, other pigmented varieties like red, blue, purple, and black are used. These colors are due to the anthocyanins that are present, principally in the pericarp and the aleuronic layer. People in this region prefer to consume “tortillas”, “tamales” and “atoles” with these pigmented varieties of maize because they say that the taste and texture is different than those foods made with white and yellow maize. While studies with the starch of pigmented corn have shown similar physiochemical, molecular and structural characteristics (^{Agama-Acevedo et al., 2005}, ²⁰⁰⁸), research has shown that tortillas elaborated with these pigmented maize varieties have less digestibility of starch (^{Hernández-Uribe et al., 2007}), which could be an effect of the anthocyanins. There are studies of pigmented maize that focus on the isolation of the anthocyanins for its pharmaceutical and food use, while others focus on pigmented maize to elaborate food that have antioxidant properties.

This essay shows the importance of the interaction between anthocyanins and carbohydrates, the possible mechanisms to reduce the digestion and absorption of glycemic carbohydrates, as well as where future research should focus to advance the knowledge on this topic.

Generalities about maize

Maize is one of the plants with greater domestication and evolution, and moreover, its genetic diversity is concentrated in Mesoamerica, principally Mexico, which is the principal center of origin, domestication and diversification of this plant. The diversification is very extensive, and in the country there are 59 maize races described (^{Sánchez et al., 2000}), which is a significant percentage of the 220 to 300 species that exist in the Americas (^{Kato et al., 2009}). The race show pigmented grain varieties, with colors that range from black to light pink, with the most common being red and blue/purple (^{Salinas, 2010}).

The annual world production of maize is greater than 1000 million Mg, with the principle producers being the United States, China, Brazil, the European Union, Argentina and Ukraine (^{FAO, 2015}; ^{Singh et al., 2011}). In Mexico the production of maize in 2012 was 22,069,254 Mg (^{SIAP, 2013}). However, there are no official statistics about the world or national production of pigmented maize and this data is only reported in the states of Chiapas (^{Salinas et al., 2012a}), Sinaloa, Tlaxcala (^{Agama-Acevedo et al., 2011}) and the Estado de Mexico (^{Salinas et al., 2010}). This is due to the fact that pigmented maize is produced by subsistence farmers on small parcels and the majority of their production is for self-consumption. In the Estado de Mexico and state of Puebla, the cost-benefit relationship of the production of blue maize is 2.24, which is greater than the ratio 1.57 of commercial maize of white grain (^{Keleman y Hellin, 2009}). The development and the cultivation of other pigmented varieties and hybrids have increased in Bolivia, Germany, China and the United States

In Mexico, the daily consumption of maize is 335 g, which is equivalent to 122 kg each year^-1 (^{FAO, 2012}), and comes in the form of tortillas, gorditas, pinoles, atoles, toasted tortillas, snacks, tamales, corn on the cob and many others (^{Figueroa et al., 2005}). Maize is also used in various industries like textile, cosmetics, and food (^{Rooney y Serna-Saldivar, 2003}), which make it economically important globally.

Pigmented maize and its products

Pigmented maize genotypes are common in the Peruvian Andes, as pigmented maize is understood as those that owe their color to pigments like carotenoid (yellows), as well as those that have anthocyanin pigments (reds, purples, pinks, among others) in the pericarp and the aleuronic layer or in both structures of the grain (^{Wellhausen et al., 1951}; ^{Salinas, 2010}). There is a marginal presence (0.07 a 008 mg grano^-1) of these polyphenols in the endosperm and the embryo (^{Cui et al., 2012}). The accumulation of pigment in the grain structures determines the possible use of these varieties of maize. For example, if the pigment concentrates in the aleuronic layer, the grain can be used for the nixtamalization and produce products with blue tones. However, if the pigment concentrates in the pericarp the and amount is sufficient enough, the pigmented grain could be used for the extraction of pigments (^{Salinas et al., 1999}; ^{Salinas, 2009}).

In the states of Chiapas, Oaxaca and the State of Mexico, the maize species are pigmented: Olotillo, Tehua, Olotón, Tepecintle, Vandeño, Zapalote Chico y Grande, Bolita, Cónico, Mushito and Tuxpeño (^{Salinas-Moreno et al., 2012a}, ²⁰¹³), but there are no statistics about their production. The diversity of pigmented maize, and its diverse uses, can be observed in its physical properties (Table 1), which is important to choose the variety of pigmented maize and the characteristics of texture and taste for the products that will be elaborated from these.

The consumption of pigmented maize increased in the United States, whereas in Mexico, pigmented maize is primarily used to elaborate tortillas for self-consumption, as well as on a small-scale, in commercial establishments to be used as traditional food. However of the total production of maize in Mexico, the pigmented maize only represents 10%, which indicates low achievement, since its nutritional content and nutraceutical properties represents a significant opportunity for the development of new products with new or better functional and nutritional characteristics.

The nutraceutical properties of pigmented maize are related to its high content of anthocyanins, which y Grande, Bolita, Cónico, Mushito and Tuxpeño (^{Salinas-Moreno et al., 2012a}, ²⁰¹³), but there are no statistics about their production. The diversity of pigmented maize, and its diverse uses, can be observed in its physical properties (Table 1), which is important to choose the variety of pigmented maize and the characteristics of texture and taste for the products that will be elaborated from these.

The consumption of pigmented maize increased in the United States, whereas in Mexico, pigmented maize is primarily used to elaborate tortillas for self-consumption, as well as on a small-scale, in commercial establishments to be used as traditional food. However of the total production of maize in Mexico, the pigmented maize only represents 10%, which indicates low achievement, since its nutritional content and nutraceutical properties represents a significant opportunity for the development of new products with new or better functional and nutritional characteristics.

The nutraceutical properties of pigmented maize are related to its high content of anthocyanins, which possess beneficial biological activity (antioxidants), derived from its secondary metabolites (^{Ruiz et al., 2008}; ^{Mora-Rochin et al., 2010}; ^{Mendoza-Díaz et al., 2012}). These compounds have a positive effect on health: their antioxidant activity reduces mutagenesis (^{López-Martínez et al., 2009}; ^{Zhao et al., 2009}) and the proliferation of the growth of cancerous cells (^{Jing et al., 2008}; ^{Urias-Lugo et al., 2015}), and anti-inflammatory cells (^{Li et al., 2012}; ^{Zhu et al., 2013}). Besides, anthocyanins in the maize grain have a protecting action against nephropathy that develops in patients with type-2 diabetes (^{Li et al., 2012}). However, these properties are lost during the boiling of the maize before its consumption. As such, the cooking method and the duration of the thermal treatment should be studied to see how these factors affect the properties of the anthocyanins in the human body.

Chemical composition

The chemical composition of the maize grain is affected by the genotype (variety), the environment and by the conditions during cultivation (Table 2).

On average, makes up 10 % of maize and the majority of it is found in the endosperm of the grain. Pigmented maize (blue and black) has an 8.2 to 9.4 % composition of proteins (^{Agama-Acevedo et al., 2005}; ^{Utrilla-Coello et al., 2009}), whereas in the state of Oaxaca, the species of pigmented maize that has adapted to tropical climates have 9.5 to 10.4 % protein makeup and a 10.1 to 10.6 % in subtropical climates, and in some segregating varieties of the species Bolita, there is a positive relationship between the hardness of the grain and the protein composition that is attributed to a greater presence of protein bodies (prolamins) that surround the starch granules (^{Salinas-Moreno et al., 2013}). A vitreous endosperm relationship can be present in the maize grain: floury of 2:1, but it varies considerably according to the race (^{Inglett et al., 1970}).

The lipid content of the maize grain is about 5 % and is principally located in the seed. In pigmented maize, the content varies between 3.7 to 5 % (^{Agama-Acevedo et al., 2004}; ^{Salinas-Moreno et al., 2013}), but in the endosperm of blue maize, there is only 0.52 % (^{Utrilla-Coello et al., 2009}). The ash content, that is the minerals present in pigmented maize, is ≈ 1 to 2 %, and the majority is in the seed of the grain.

Carbohydrates are the major component of the maize grain, and in pigmented maize they vary from 76 to 84 % (^{Agama-Acevedo et al., 2004}). Starch is the main carbohydrate in maize and is formed by amylose, or linear component, and amylopectin, or branched component (Table 3). The starch in pigmented maize presents ≈20 % of amylose, but there are species with 13 % (^{De la Rosa-Millán et al., 2010}), which indicates differences in the organization of these components inside the starch granule and as such, there are differences in the functional and nutritional properties. Despite the diversity in the species of pigmented maize, there are few studies about the characteristics of their starch, which is a topic that should be further investigated to strengthen its use and application.

Anthocyanins

Anthocyanins are phenolic compounds from the flavonoid group (^{Escribano-Bailón et al., 2004}) and in their formula there are two aromatic rings connected by a three-carbon structure (^{Gross, 1987}). In their natural form, this structure is found esterified to one or two sugars, denominating them simple anthocyanins; however, if in addition to the sugar in the molecule, there is an acyl radical, then, these are called acrylate anthocyanins (^{Strack and Wray, 1989}). The anthocyanin content varies between species (Table 4); maize with low anthocyanin content are yellow and pink maize; those with medium levels of anthocyanins are blue; and maize with the highest levels are those with purple and black grains (^{Salinas-Moreno et al., 2013}).

In maize, anthocyanins are peonidin (^{Aoki et al., 2002}; ^{Abdel-Aal et al., 2006}; ^{Montilla et al., 2011}; ^{Zilic et al., 2012}; ^{Salinas-Moreno, et al., 2012b}), malvidin (^{Caldwel and Peterson, 1992}), cyanidin, (^{Aoki et al., 2002}; ^{Abdel-Aal et al., 2006}; ^{Zilic et al., 2012}) and pelargonidin (^{Aoki et al., 2002}; ^{Montilla et al., 2011}; ^{Zilic et al., 2012}), and the anthocyanin glycosides are the anthocyanins. Salinas-Moreno et al. (1999) analyzed the anthocyanin in blue and red grain maize in four species, and found that in the blue grain maize, the anthocyanin are derived from cyanidin and malvidin, and are predominately derived from the former; red-grain maize is derived from pelargonidin, cyanidin, malvidin and an unidentified aglycone. The characterization of the type of anthocyanins in pigmented maize is important, but the effect associated with the consumption of pigmented maize after its processing (i. e. nixtamalization) is even more important. ^{Urias-Lugo et al. (2015)} evaluated anthocyanins from blue maize hybrid and native blue maize for the proliferation of cancer cells in breasts (MCF7), liver (HepG2), colon (Caco2 y HT29) and prostate (PC3); they found that acidified extracts presented greater anti-proliferative activity.

Antioxidant capacity and bioavailability

Pigmented maize has potential benefits beyond its nutritional value. For example, blue and red maize inhibit colorectal carcinogenesis in male rats (^{Hagiwara et al., 2001}), they present anti-mutagen properties (^{Yoshimoto et al., 1999}) and they capture free radicals (^{Del Pozo-Insfran et al., 2006}, ²⁰⁰⁷); this last point is an accepted mechanism for antioxidant activity related to the inhibition of lipid peroxidation (^{Brand-Williams et al., 1995}). The function of anthocyanins in plants is similar to the function of all of the flavonoids: antioxidants, light protection, defense mechanisms, as well as other ecological functions (^{Escribano-Bailón et al., 2004}).

Because the interest in developing foods with blue maize for its antioxidant properties, the processing method is important in the conservation of bioactive prosperities. In this sense, the effect of the nixtamalization process on the phytochemical profiles (total phenols, anthocyanins, ferulic acid, carotenoids) has been studied, along with the antioxidant capacity of five types of maize processed into dough, tortillas and tortilla chips; the nixtamalization process was observed to significantly reduce the content of total phenols and the antioxidant capacity, in comparison to raw grains (^{De la Parra et al., 2007}). Besides, ^{Bello-Pérez et al. (2015)} studied the effect of ecological nixtamalization (using calcium salts) on the content of total anthocyanins and the antioxidant capacity of blue maize tortillas; they found that the ecological method was not aggressive and conserved the antioxidant capacity in the tortillas, in comparison to lime, which is used in the traditional nixtamalization process.

To establish the final intake of anthocyanins and the antioxidant capacity of food, such as those elaborated with blue maize (Table 5), one must take into consideration pre-treatments, the type of cooking method, as well as the type of product used (whether it is to be mixed with other ingredients or used as raw material). The anthocyanin stability depends on the processing of the food and the formation of the food matrix, which can protect against factors such as light, temperature and humidity during the processing, and storage and consumption of the product (^{Escribano-Bailón et al., 2004}). Phenolic compounds, with biological and chemical properties interact through non-covalent bonds with macromolecules (proteins, lipids and polysaccharides) in biological systems, (^{Bordenave et al., 2014}), with a positive impact on the texture, nutritional and sensorial properties of the product, which has implications on its bioavailability. However, the studies on the use of blue maize for the development of functional food are limited and as such require more research.

Carbohydrates

Carbohydrates, the main component of pigmented maize, are found in the cells of the endosperm, principally in the form of starch. Carbohydrates represent about 78% of the dry weight of the grain, while in some races, variants of blue maize (Table 2), this can reach up to 84%. There is a minimum amount of simple carbohydrates (monosaccharaides and disaccharides) known as sugars in the maize grain and these represent close to 2% of the dry weight of the grain. Starch is the principal carbohydrate in maize, and there is more starch in pigmented maize than in white maize (Table 3), which is related to the biosynthesis of the polysaccharide and requires further study. Starch, as the main component in the maize grain, is what most influences the functional (texture) and nutritional (caloric intake) properties of the products that are elaborated with this cereal, like tortillas, tamales, bread, cookies, etc. Starch is formed by macromolecules of glucose (amylose and amylopectin); amylose is an essential linear component while amylopectin is a branched component. The proportion of both components in the starch has implications in its functionality. In this sense, starches with 98-99% of amylopectin provide high viscosity, and starches with higher content of amylose form gels that harden (retrograde) more rapidly (^{Biliaderis, 1991}). The maize used in the food industry has a proportion (%) of amylose: amylopectin of 30:70, denominated normal starches. According to ^{De la Rosa-Millán et al. (2010)}, amylose varies between 13-28 % in blue maize.

Starch is organized in discreet particles known as granules, whose size and shape depends on the botanical source (cereal, tubers, legumes, fruit). Starch from maize has two populations: small granules of 1-10 mm, and large granules between 15-40 mm. Even though the two populations of granules are inside the same source, they have different amylose content and physicochemical properties. (^{Jane, 2006}). In isolated starch of blue maize, granules between 20 y 40 μm were found (^{Agama-Acevedo et al., 2008}). ^{Utrilla-Coello et al. (2010)} found a bimodal distribution in the starch of blue maize, where the highest point of the first spike was at 3 mm, which represented 24 % of the total volume; the highest point of the second spike was at 9 mm, which is related to the population of large granules and represents 76%. The starch of pigmented maize, like the starch of other cereals (wheat, rice, barley) presents A-type diffraction pattern (^{Agama-Acevedo et al., 2008}; ^{De la Rosa-Millan et al., 2010}).

^{Agama-Acevedo et al. (2013)} evaluated the characteristics of starch and its relation to the enzymes of its biosynthesis during the development of the grain of two maize varieties (white and blue); 50 days after the pollination (ddp), the blue maize accumulated a greater amount of starch and had less amylose content. Besides, they found two isoforms from the branched enzyme in the starch of the blue maize, which is related to the production of highly branched amylopectin molecules with short chains, leaving less available space inside the granular structure for amylose synthesis. In that study, the starch from the blue maize presented a higher temperature and enthalpy of gelatinization than the white maize, which is important during the cooking of maize and the other products made with this cereal. In other studies, there were no differences in temperature of gelatinization, only small changes in its enthalpy (^{Agama-Acevedo et al., 2008}; ^{De la Rosa-Millán et al., 2010}; ^{Utrilla-Coello et al., 2010}). However, the organization and distribution of the chains of amylopectin inside the starch granule needs to be researched since this influences the physiochemical properties and digestibility.

Starch digestibility

Starch is the majority component of maize; thus, the products of this cereal represents an important supply of glucose in humans’ diets. In the early 1990s, a fraction of starch was found not to hydrolyze, for which it was called resistant starch (RS) (^{Englyst et al., 1992}). The consumption of RS was related to various health benefits, for which a number of foods were analyzed in order to know the amount of RS (^{Muir et al., 1994}; ^{Kritchevsky, 1995}; ^{Cummings et al., 1996}). One type of RS was formed when foods rich in starch were cooked and stored, which was due to the phenomenon of starch retrogradation that consists of a re-arrangement of its structure that is not recognized by the salivary and pancreatic a-amylases and cannot be hydrolyzed, following its course to the large intestine, where is then fermented by the bacteria found in the colon. In nixtamalized maize tortillas (white or yellow grain) the increase in RS was directly proportional to the storage time and was favored by a temperature of 4 °C (^{Agama-Acevedo et al., 2005}). However, the properties of starch digestibility in tortillas elaborated with blue maize were not affected by time or temperature in storage. The available starch and the RS did not see a change after 48 hours of storage (^{Hernández-Uribe et al., 2007}). This characteristic of blue maize tortillas was related to its thermal properties, due to a low tendency for retrogradation. It was unknown if the differences found in the digestibility of the starch in blue maize tortillas were due to the physical characteristics of the maize grain, the starch per se or the anthocyanins present in the grain.

In terms of the physical characteristics of the blue maize grain, it has a floury endosperm (^{Serna-Saldivar, 2010}). Tortillas elaborated with white maize with a floury endosperm did not present an increase in RS content during the storage compared with the tortillas elaborated with white maize with an intermediate or vitreous endosperm (^{Osorio-Díaz et al., 2011}). Because of this, it was thought that the type of endosperm in blue maize influences the enzymatic hydrolysis of starch.

The possibility that morphological characteristics and the molecular organization of the starch could be responsible for the differences in the velocity of enzymatic hydrolysis, led to carrying out the characterization of starch from the blue variety, which differ in anthocyanin content. The two varieties of blue maize had a greater starch granule size, lesser content of amylose, and required more energy to disorganize due to a greater percentage of crystallinity compared to maize grains of the white variety (^{Agama-Acevedo et al., 2005},²⁰⁰⁸). Due to this, the digestibility properties of the starch in tortillas are associated with the differences found in the starch present in each type of maize. However, when blue maize was analyzed with similar values of anthocyanins, no considerable differences were observed, especially in the molecular characteristics. (^{De la Rosa-Millan et al., 2010}).

The interest in knowing the rate of starch hydrolysis and its repercussions began research that emulated conditions that occur during the digestive process in humans. The most used protocol is the one proposed by ^{Englys et al. (1992)}, that is based on the rate of starch hydrolysis; it considers that rapidly digestible starch (RDS) is hydrolyzed during the first 20 min, that slowly digestible starch (SDS) is hydrolyzed between 20 and 120 min, and after 120 min the starch that does not hydrolyze, or the RS is found. Beyond the velocity at which the starch is digested, the most important implication is the physiological effect that is produced when it is consumed.

The RDS is hydrolyzed in the first fraction of the small intestine, increasing the glucose in the blood immediately after its consumption, which is associated with multiple risk factors related to problems such as obesity, coronary diseases and heart troubles (^{Ludwin, 2002}; ^{Brennan, 2005}). Contrarily, SDS is digested slowly throughout the small intestine with the subsequent slow release of glucose, for which its consumption reduces the responses of postprandial and insulinemic glucose, as well as fatty acids (^{Seal et al., 2003}, ^{Ells et al., 2005}); likewise, even though it isn’t completely clear, this increases the feeling of satiety. This classification of starch, and the benefits attributed to SDS, the research to increase the SDS content in food, whether it is used as raw material (principally cereals that possess the characteristics that their starch without cooking is slowly digested) or to add to the development of food starches modified with a slow hydrolysis rate. In nutritional bars elaborated with a mix of oatmeal, barley, wheat and blue maize, there is a larger content of SDS (10.8 %), but less RS content (3.6 %), compared to the bars elaborated where blue maize was exchanged for white maize (7.1 % SDS y 4.4 % AR) (^{Utrilla-Coello et al., 2011}). The highest SDS content found in the bar where blue maize was used is attributed to the high content of lipids, proteins and indigestible soluble fraction, which form a matrix that causes slow starch hydrolysis. ^{Carrera et al. (2015}) report an SDS content of 39.8 and 24.6 % in the flour of raw and toasted blue maize, respectively, for the elaboration of pinol (a pre Hispanic drink); these values were higher than the ones obtained by white maize for the same process. These differences can be related to the anthocyanin content and its effect on the digestibility of carbohydrates, but it requires more research.

The effect that anthocyanins found in blue maize have on the digestibility of starch is still not known with clarity. Anthocyanins are classified as flavonoids that are part of the group of polyphenol. It has been suggested that polyphenols can: 1) “Interfere” with digestive enzymes, changing the digestive process of starch with the reduction in the response of postprandial glucose; 2) have an effect on the on the carriers of glucose in the small intestine, and 3) provoke structural changes in starch because of the union with flavonoids through non covalent bonds. Up until now, the type of bond between starch and polyphenols has not been defined, since the possibility of hydrophobic interaction is also speculated (^{Barros et al., 2012}). Even though this last point is controversial, there are reportd that the presence of polyphenols (proanthocyanidin) reduces the digestibility of starch (^{Barros et al., 2012}); others report that the presences of flavonoids modifies the starch structure, causing the amylose to be more susceptible to the attack by amylases (^{Liu et al., 2011}). Besides the tannins increased the RS (^{Barros et al., 2012}; ^{Mkandawire et al., 2013}), they reduced SDS (^{Barros et al., 2012}). The latter information is unclear because the authors do not specify if the tannins are hydrolysable or condensed; the former are formed by malic acid, phenolic acids and free sugars polymerized heterogeneously, while the latter are polymerized flavonoids. These structural differences in the tannins impact functionality.

The effect that polyphenols can have on the digestibility of starch depends on the type and amount of polyphenols present, the elaboration process of the product and if they are found in their natural form or are added to the food. The polyphenols that are added to food (more than 10% based on the weight of the starch), will produce structural changes in the starch and subsequently, the reduction of their digestibility; whereas polyphenols that are found naturally in food act as enzyme inhibitors for a-amylase and amyloglucosidase (^{He et al., 2006}).

Dietary fiber

In maize, dietary fiber is found in the pericarp and is primarily made up of arabinoxylans, heteroxylans, cellulose and phenolic acids, principally ferulic and diferulic acid (^{Carvajal-Millan et al., 2007}). Ferulic acid is the predominant phenolic compound in maize bran and is found bound to the cell wall (^{Fry, 1986}). In pigmented maize grains, pigments have been found in the pericarp and in the aleuronic layer. The aleuronic layer of blue maize contains anthocyanin pigments, which gives its characteristic color. (^{Escalante-Aburto et al., 2013}). When wholegrain is used, the pigmented maize has the advantage of a material that can present antioxidant properties, which in recent years, has gained importance due to the effect that it can have on humans’ health (this depends on the process of the maize grain before its consumption).

Arabinoxylans are principally found on the cell wall of the endosperm, on the aleuronic layer and in the pericarp of the maize (^{Carvajal-Millán et al., 2007}). These compounds generate great interest due to their nutraceutical properties and the classification as a soluble fiber contributes to the control of diabetes and cardiovascular diseases. The effects of arabinoxylans on these illnesses are due to the increase in the absorption of minerals and the improvement of colon function; and they decreases the risk of colorectal cancer (^{Saedd et al., 2011}). Furthermore, arabinoxylans contribute to transporting of phenolic compounds (ferulic and coumaric acid) and oligomers to the colon, presenting antioxidant characteristics with potential health benefits (^{Vitaglione et al., 2008}).

In Mexico, nixtamalization is the principal way that maize is transformed for consumption. The alkaline cooking and the soaking that is involved in this process, provokes the dissolution and swelling of the pericarp layers. This makes the cell walls of the dietary fiber components of this part of the grain turn fragile, facilitating their soaking, which reduces the content of insoluble dietary fiber (^{Paredes-López et al., 2006}). The nixtamalization process of pigmented maize affects anthocyanins, since it significantly reduces its content, which is because large quantities of these compounds degrade due to the alkaline pH and high temperature. Furthermore, other chemical structures derived from polyphenols are affected by the rupture of ester bonds and subsequently, phenols are liberated into the cooking solution. The majority of these compounds is found in the pericarp of the grain and is eliminated during the washing of the nixtamal (^{De la Parra et al., 2007}; ^{Escalante-Aburto et al., 2013}). In this sense, new nixtamalization methods like fractioning and extrusion have been proposed, which in the case of pigmented maize has shown to retain a greater amount of anthocyanins (from 38 to 58 %) in products developed with these technologies. Additionally, during the processing, different compounds are formed or the content of the existing compounds is increased, which changes the profile of anthocyanins (^{Escalante-Aburto et al., 2013}).

Interaction of carboydrates and anthocyanins: nutraceutical aspects

The use of pigmented maize has significantly increased for the development of foods with functional character like tortillas (^{Del Pozo-Insfran et al., 2006}; ^{de la Parra et al., 2007}; ^{Del Pozo-Insfran et al., 2007}, ^{Mora-Rochin et al., 2010}; ^{Aguayo-Rojas et al., 2012}), cookies (^{Utrilla-Coello et al., 2011}) and snacks (^{Del Pozo-Insfran et al., 2006}, ²⁰⁰⁷), due to its content of anthocyanins and indigestible carbohydrates. However, there are very few studies that evaluate the interaction between carbohydrates (starch and non-starch polysaccharides) and anthocyanins in food, as well as their effect on the health of consumers.

Non-starch polysaccharides (dietary fiber) have an essential function in intestinal health and could be significantly associated with cholesterol reduction and a glycemic response. Additionally, phenolic compounds have antioxidant properties and free radical inhibitors that protect against oxidative damage to cells (^{Quiros-Sauceda et al., 2014}). These properties are associated with the chemical structure of phenolic compounds, which determines their physiological and nutritional properties and should be considered during the development of nutraceutical foods. (Figure 1).

Figure 1 Effect of indigestible anthocyanins and carbohydrates for the development of nutracentical foods. 

Phenolic compounds, including anthocyanins, affect the digestibility of starch and the postprandial response of glucose by interfering with digestive enzymes (^{Lo Piparo et al., 2008}; ^{Barros et al., 2012}, 2014; ^{Miao et al., 2014}) and the transportation of glucose in the wall of intestinal brush (^{Hanhineva et al., 2010}), as well as in nutritional properties induced by the non-covalent interactions between flavonoids (polymeric or monomeric) and starch (^{Bordenave et al., 2014}). In studies carried out with foods that contain phenolic compounds and carbohydrates, the content of the RS was observed to have increased when there was greater concentration of phenolic compounds (^{Barros et al., 2012}). This increase in the RS content reduced the amount of starch digested as well as the rate with which it was digested, which means that the starch was digested slowly. Slow digestion of starch has been associated with beneficial health effects like the control of hunger and more evenly spaced consumption. Additionally, phenolic compounds had an effect on the in vitro digestibility of starch (^{Deshpande y Salunke, 2006}; ^{Barros et al., 2012}) and in vivo (^{Yoon et al., 1983}), as well as the reduction in the in vivo glycemic response (^{Kim et al., 2011}; ^{Liu et al., 2011}; ^{Rojo et al., 2012}; ^{Wedick et al., 2012}).

The effect of slow digesting carbohydrates and the high dietary fiber content in the development of functional products has been reported (^{Ovando-Martínez et al., 2009}, ^{Gallegos-Infante et al., 2010a}, ^2010b; ^{Khan et al., 2013}; ^{Sun-Waterhouse et al., 2013}), as well as how phenolic compounds affect human health (^{Saura-Calixto, 2012}; ^{Wedick et al., 2012}). However, the physiochemical, sensorial and nutritional aspects of the interaction between carbohydrates and anthocyanins and their effect on human health is still not completely clear. In the case of food elaborated with pigmented maize, the interaction between polysaccharides and anthocyanins is evaluated and its effect on the functional, sensorial and nutritional (beneficial effect on the health of its consumers) properties, requires more research.

Perspectives

The development of nutraceutical foods is a priority for the food industry, especially because of the interest in having healthy food that can help to prevent chronic-degenerative illnesses. Excess weight and obesity are two important risk factors for the development of those diseases, such as diabetes, high arterial pressure and cardiovascular diseases. Pigmented maize, which is cultivated around the world, has been underutilized, as white and yellow maize are more commonly consumed. The presences of anthocyanins in maize with shades ranging from black to red, makes maize a feasible raw material for the elaboration of nutraceutical foods like tortillas, breakfast cereals, snacks, and pastas. The interactions that are produced between anthocyanins and polysaccharides present in foods elaborated with pigmented maize and the impact on the digestion of starch, would help to understand the nutraceutical contribution of these products and advance the knowledge of the structural-functional relationship of said interactions.

Conclusions

Maize is a fundamental cereal in the diet of Mexico and in other countries. The use of pigmented maize in the development of food has been minimal when compared to white and yellow maize. Anthocyanins in pigmented maize have an antioxidant effect and can interact with polysaccharides (starch and dietary fiber), which limit the digestion of starch, and as such, the contribution of glucose into the bloodstream after consumption. Research has shown some beneficial effects on consumption of pigmented maize, but more studies must be done. Understanding the anthocyanin-polysaccharide interactions in foods elaborated with pigmented maize would aid in the development of nutraceutical foods, with a greater impact on the prevention of sicknesses like excess weight and obesity.