Article pubs.acs.org/JAFC
Temperature Dependency of Shelf and Thermal Stabilities of Anthocyanins from Corn Distillers’ Dried Grains with Solubles in Different Ethanol Extracts and a Commercially Available Beverage Elvira Gonzalez de Mejia,*,† Vermont P. Dia,† Leslie West,† Megan West,‡ Vijay Singh,§ Zhaoqin Wang,§ and Charlotte Allen‡ †
Department of Food Science and Human Nutrition, and §Department of Agricultural and Biological Engineering, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States ‡ Kraft Foods, 801 Waukegan Road, Glenview, Illinois 60025, United States S Supporting Information *
ABSTRACT: The objective was to determine the shelf and thermal stabilities of anthocyanins from distillers’ dried grains with solubles (DDGS) extracted with different ethanol concentrations as well as a semi-purified Maiz Morado (purple corn) anthocyanin extract added to a commercially available beverage. Storage for 6 weeks of DDGS showed an overall reduction of anthocyanins from 6.8 to 73.7%. In DDGS, an ethanol increase from 0 to 25% resulted in less sensitivity of anthocyanin to temperature changes. Acylation resulted in faster degradation and higher reaction rate constants than their corresponding nonacylated forms. Anthocyanin changes were accompanied by an overall increase in lightness and a decrease in redness. Storage of beverage for 12 weeks at 4 °C resulted in a 25.5% reduction of anthocyanin. Results have important implications in selecting colored corn as an economical source of food colorants. KEYWORDS: anthocyanins, corn, DDGS, reaction kinetics, shelf stability, thermal stability
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INTRODUCTION Anthocyanins are water-soluble flavonoids responsible for the red, purple, and blue colors of fruits and vegetables with reported health-enhancing properties, including antioxidant,1,2 anti-inflammatory,3,4 cancer prevention,5,6 and cardiovascular protection,7−9 among others. Their inherent instability toward different environmental factors suggests that conditions influencing anthocyanin stability and ways of stabilizing them have to be studied. For instance, several studies have shown that factors such as light,10 temperature,11 pH,12 and solvent and extraction conditions13,14 affected anthocyanin stability and their corresponding biological properties. On the other hand, the addition of compounds, such as pectin, cyclodextrin, and alginate,15−17 as well as encapsulation techniques18 resulted in improved stability of different anthocyanins. Colored corn (Zea mays L.) is a rich source of naturally occurring water-soluble anthocyanin pigments. It could be a potential economically feasible source of anthocyanins because corn is widely cultivated around the world. Because of the increasing scientific evidence of the health-promoting properties of anthocyanins, breeders and plant biotechnologists are trying to increase the anthocyanin content of different vegetables, including corn, using different approaches.19 Another approach is the use of different co-products of corn processing as a potential source of anthocyanins from corn. Distillers’ dried grain with solubles (DDGS) is one of the co-products of the corn dry grind ethanol industry. DDGS are obtained by drying the residual matter after corn fermentation, resulting in a high concentration of energy and protein with respect to the starting corn.20,21 Because of this and its low cost, DDGS have been used as a feed ingredient for different animal diets. Extraction of © 2015 American Chemical Society
anthocyanins from DDGS before using it as an animal feed presents another potential for adding value to this cornprocessing co-product. The objectives of this study were to determine the shelf and thermal stabilities of anthocyanins from different DDGS extracted with different ethanol concentrations and determine the kinetic parameters involved in the thermal degradation of corn DDGS anthocyanin. In addition, we evaluated the stability of water-extract, freeze-dried, and semi-purified anthocyanins from Maiz Morado, a purple corn cultivar, in a commercially available beverage to show potential food application. This is the first report showing the shelf and thermal stabilities of corn DDGS anthocyanin ethanol extracts as well as corn anthocyanins in a commercially available beverage.
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MATERIALS AND METHODS
Materials. Commercially available corn Maiz Morado (purple corn) cultivar was purchased from Angelina’s Gourmet (Swanson, CT), and proprietary purple (PC) and dark corn (DC) varieties in development were obtained from private companies. All chemicals used in this study were purchased from Sigma-Aldrich (St. Louis, MO), unless otherwise stated. Preparation of DDGS. DDGS were prepared using a starch granular hydrolyzing process (GC) as previously reported.22,23 Briefly, cleaned corn samples (50 g, dry basis) were ground in a hammer mill (model MHM4, Glen Mills, Clifton, NJ) at 500 rpm using a 0.5 mm sieve. Ground corn was mixed with deionized water to obtain a mash of 30% Received: Revised: Accepted: Published: 10032
May 28, 2015 October 25, 2015 November 2, 2015 November 2, 2015 DOI: 10.1021/acs.jafc.5b03888 J. Agric. Food Chem. 2015, 63, 10032−10041
Article
Journal of Agricultural and Food Chemistry
acetate buffer at pH 4.5). A total of 200 μL of diluted solutions at each pH was transferred to a 96-well plate, and the absorbance was read at 520 and 700 nm using a Synergy 2 multi-well plate reader (Biotek, Winooski, VT). The total monomeric anthocyanin concentration was calculated as cyanidin-3-glucoside (C3G) equivalents per liter as below
dry solids content. To the mash, 0.15 mL of the fermentation enzyme, a granular starch hydrolyzing enzyme (GSHE, Stargen 001, Dupont Industrial Biosciences, Palo Alto, CA) that contained α-amylase from Aspergillus kawachi and glucoamylase from Aspergillus niger with an activity of ≥456 granular starch hydrolyzing units (GSHU)/g, was added. Also, 0.02 mL of protease (GC212, Dupont Industrial Biosciences) with an activity of 2000 spectrophotometer acid protease units (SAPU)/g and 1 mL of yeast inoculum were added. Fermentation was conducted for 72 h at 32 °C. After fermentation, the broth was heated at 90 °C in a water bath for 3 h to evaporate ethanol. DDGS were recovered by drying in a convection oven at 49 °C for 72 h. DDGS produced were designated as GC-PC for purple corn cultivar and GC-DC for dark corn cultivar. Extraction of Anthocyanin from DDGS. Anthocyanins from DDGS were extracted using different ethanol concentrations in 2% aqueous formic acid solution (pH 2.2) containing 0−25% ethanol (pH 2.4) as previously reported.23 Preparation of Semi-purified Anthocyanin Extract from Maiz Morado. Whole corn kernels were extracted with 2% (v/v) aqueous formic acid (1:2 ratio of corn/acid) contained in a large flask after flushing the head space with argon and allowing the mixture to stand undisturbed at 5 °C for 20−24 h in the dark. The extract was filtered through grade 2 filter paper, followed by 0.45 μm nylon membrane filters. The clarified extract was passed down a column containing Amberlite FPX66, with a diameter of 13 cm and length of 30 cm (Dow Chemical, Midland, MI) resin (∼1:1 ratio of extract and resin volumes), previously washed with water and 2% (v/v) aqueous formic acid. The resin column was then washed with water until readings taken with a conductivity meter equipped with a flow cell (Traceable, Thermo Scientific, Waltham, MA) suggested that no significant amounts of unretained compounds and formic acid were still being eluted. Absolute ethanol (USP grade) was introduced onto the column to remove anthocyanins as well as other adsorbed phenolic compounds. Collection was started when color elution was observed and terminated when the eluate was colorless. Ethanol and water were removed under a water aspirator vacuum using a rotary evaporator at bath temperatures of
