Comparison of chemical, color stability, and phenolic composition from pericarp of nine colored corn unique varieties in a beverage model
Graphical abstract
Introduction
Despite some consumer concerns regarding the use of artificial food colorants (Feingold, 1975, Stevens et al., 2014, Weiss, 2011) the Food and Drug Administration (Barrows, Lipman & Bailey, 2003) accepted the increase in the amount of added colorants in food products > 5-fold from 1950 (12 mg/capita/day) to 2012 (68 mg/capita/day).
Anthocyanins (ANC) are possible alternative to artificial colorants (Dia et al., 2015). Pelargonidin, cyanidin, delphinidin, petunidin, peonidin, and malvidin are the six major anthocyanidins from which the majority of ANC found in food are derived (de Pascual-Teresa and Sanchez-Ballesta, 2008). Once glycosylated, ANC can be further modified by the addition of acyl groups or by condensation via covalent bonding to flavan-3-ols. ANC can be found in a variety of plants such as dried purple waxy corncobs (Intuyoda et al., 2014), blueberries (Esposito, Chen, Grace, Komarnytsky, & Lila, 2014), Chinese bayberries (Zhang et al., 2011), among others. Many species of corn are produced around the world and grow in a variety of colors such as red, yellow, purple, green, blue, brown, and white. Some of the different types of ANC in corn include cyanidin 3-O-β-d-glucoside, pelargonidin (Pg) 3-O-β-d-glucoside, cyanidin 3-O-β-d-(6-malonyl-glucoside), pelargonidin 3-O-β-d-(6-malonyl-glucoside), and peonidin (Pn) 3-O-β-d-(6-malonyl-glucoside) (Aoki, Kuze, Kato, & Gen, 2002). Many of which were isolated from Peruvian purple corn grains (Zea mays L.) with cyanidin 3-O-β-d-glucoside having the largest concentration (Aoki et al., 2002). Even though there are several methods to improve natural pigments stability (Cortez, Luna-Vital, Margulis, & Gonzalez de Mejia, 2017), it is also relevant to generate plant varieties with more stable compounds (Marcon et al., 2016).
The stability of ANC is a significant factor that affects the quality of these critical natural pigments. It has been claimed that acylation with various phenolic acids makes specific ANC more heat resistant and enhance overall stability (Xu et al., 2015). ANC are compounds that might determine the quality of colored foods and their corresponding final products. The stability of ANC is determined by many factors that must be taken into consideration. For instance, pre-press procedures, processing, freezing and thawing, mashing and pressing, clarification, concentration, and storage will further reduce the final ANC concentration (Weber & Larsen, 2017).
The effects of gallic, ferulic, caffeic acids on ANC stability was studied by Qian, Liu, Zhao, Cai, and Jing (2017). Interestingly, ANC degradation was faster than the color fading. In this study, gallic, ferulic, caffeic acids showed a hypochromic effect. However, these copigments did not protect ANC from thermal degradation. Authors proposed that the ANC self-stacking might offer better thermal resistance than the copigmentation with phenolics; additional phenolic acids might interrupt ANC self-stacking or self-association and accelerate the pigment degradation.
There is a need to meet the consumer desire to find foods with natural colorants that will be functional for the food industry. The purpose of this study was to test and compare the stability of the phenolic composition and color of nine ANC rich colored corn variety extracts in a beverage model at 4 °C, 22 °C, and 32 °C over a 12-week period.
Section snippets
Chemical and reagents
Varieties of purple corn each distinguished by their unique pigment composition were generated at the University of Illinois at Urbana-Champaign (UIUC) from materials collected from the North Central Regional Plant Introduction Station (PI; Ames, IA, USA), the Maize Genetic Cooperation Stock Center (MGCSC; Urbana, IL, USA) or Siskiyou Seeds (Williams, OR, USA). Pericarp was removed from each variety as previously described (Somavat, Li, Gonzalez de Mejia, Liu, & Singh, 2016). Some of the key
Tristimulus colorimetric measurements
Color squares of the nine corn varieties presented in Fig. 1 shows the degradation of color over time for each temperature. Colors from ANC-rich extracts were acceptable for all varieties at week 0 based on industry standards. Corn varieties V3 and V5 retained their color best of the nine varieties. V3 contained high Pg, low condensed forms, low Pn, high C3-mal, high Pg3-mal, and high Pn3-mal; and V5 had low levels of Pn, high condensed forms, high C3G, low Pg, high C3-mal, and low acylated
Conclusion
Nine unique ANC-rich colored corn extracts were added to a beverage model and stored at different temperatures for 12 weeks. It was found that the high presence of condensed forms with C3G in the pigments from corn pericarp could potentially contribute to the color parameters and stability. Corn samples with high Pn had less stable pigments. Low temperatures and low pH promoted color and ANC stability. The ideal pigment composition for purple corn varieties with stable pigments are those similar
Conflicts of interest
None.
Funding
This work was partially supported by the Kraft-Heinz company #C3745.
Acknowledgements
Dr. Pavel Somavat for separating pericarp from corn kernels, undergraduate research assistants: Regina Cortez, Sharon Li, and Thomas Novak for their technical assistance.
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