Article pubs.acs.org/JAFC
Flavor Chemistry of Lemon-Lime Carbonated Beverages Bethany J. Hausch,† Yaowapa Lorjaroenphon,§ and Keith R. Cadwallader*,† †
Department of Food Science and Human Nutrition, University of Illinois at Urbana−Champaign, 1302 West Pennsylvania Avenue, Urbana, Illinois 61801, United States § Department of Food Science and Technology, Faculty of Agro-Industry, Kasetsart University, 50 Ngamwongwan Road, Bangkok 10900, Thailand S Supporting Information *
ABSTRACT: The most potent aroma-active components of Sprite (SP), Sierra Mist (SM), and 7UP (7UP) were identified. Aroma extracts were prepared by liquid−liquid continuous extraction/solvent-assisted flavor evaporation (LLCE/SAFE). Twenty-eight compounds were detected by gas chromatography−olfactometry (GC-O) with linalool (floral, lavender), octanal (pungent orange), and 2,3-dehydro-1,8-cineole (minty) determined to be predominant aroma compounds based on their high flavor dilution (FD) factors by aroma extract dilution analysis (AEDA). The data indicate that lemon-lime flavor is composed of a small number of compounds (22 at the most in SM), and only a subset of these may be important because many compounds were detected only at low FD factors. Predominant aroma compounds (23) were quantified using static headspace solid phase microextraction (SPME) combined with stable isotope dilution assays (SIDA). In contrast to FD factors, the calculated odoractivity values (OAVs) indicate that octanal and limonene make the greatest contribution to the overall aroma of lemon-lime carbonated beverages, followed by nonanal, decanal, linalool, 1,8-cineole, and geranyl acetate. The results demonstrate that lemon-lime carbonated beverages share many of the same compounds but the relative abundance of these compounds varies by brand. KEYWORDS: lemon-lime, flavor chemistry, carbonated beverage, aroma extract dilution analysis (AEDA), stable isotope dilution assay (SIDA), odor-activity value (OAV), linalool, octanal, 2,3-dehydro-1,8-cineole, limonene
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flavor. Current details regarding the composition and chemistry of lemon-lime flavor in a beverage system are limited. A review of the literature on essential oils indicates that certain oils from Aloysia citriodora Palau (lemon verbena)4 and Citrus aurantifolia (Christm.) Swingle (lime) are important to the food industry.5 Much work has been done to identify and quantify the composition of various oils for the purposes of detecting oil adulteration6 or determining the antimicrobial activity of the oil.7 It is also well-known that terpenes, the largest class of compounds in lemon oils, are unstable in acidic environments and undergo rearrangements.8−12 Acid-catalyzed reactions of terpenes can occur at even mildly acidic pH (pH < ∼6).8 Numerous citrus varieties exist, and there is subsequently variation in the most abundant compounds in citrus. However, limonene is most abundant in lime oils on a percent by weight basis.4,8,13 Neral and geranial (citral isomers) have been found to be very abundant in some varieties of lemon verbena.4 Although acid-catalyzed reactions have been extensively studied, particularly in the case of citral, it is interesting to look at a real food system, namely, lemon-lime carbonated beverages, and find out which flavor compounds are important. Due to the large commercial value of lemon-lime carbonated beverages, this research has great potential to benefit the
INTRODUCTION
The first carbonated beverages came from natural sources in the form of effervescent mineral springs and yeast fermentation.1 Early scientific investigations of carbon dioxide in water date back to 1741, when carbonated water was produced using bicarbonate salts, and by the late the 1760s and 1770s, scientists had developed ways of dissolving carbon dioxide in water under pressure.1 The first commercial manufacture of carbonated water occurred in the late 1770s when Thomas Henry, a chemist and apothecary in Manchester, England, designed an apparatus that could carbonate up to 12 gal per batch and sold the product in corked glass bottles.1,2 The intended use of carbonated water changed as new carbonation technologies were developing. Although artificially carbonated mineral water was originally used for medicinal purposes and was required to contain sodium bicarbonate, it became a source of refreshment; soda was eliminated, and flavorings were added.2 The early flavorings used in carbonated water for refreshment were largely from fruits and included sarsaparilla, lemon, pineapple, orange, strawberry, vanilla, peach, grape, almond, ginger, and cloves, among others.2 The volume of carbonated beverage sales has been declining since 2003. Yet, despite this trend, carbonated beverages accounted for $76.3 billion in 2013 sales for the United States.3 Lemon-lime was among the top 10 carbonated beverage types in 2013, with Sprite taking the sixth largest market share.3 Considering the market value of this product, it is important to understand the flavor profile and chemistry of lemon-lime © 2014 American Chemical Society
Received: Revised: Accepted: Published: 112
October 7, 2014 December 10, 2014 December 12, 2014 December 12, 2014 DOI: 10.1021/jf504852z J. Agric. Food Chem. 2015, 63, 112−119
Article
Journal of Agricultural and Food Chemistry
Figure 1. Structures of isotopically labeled compounds used for quantification (compound numbers correspond to those in Table 2). extraction, 500 mL of a carbonated beverage, 100 mL of deodorized deionized−distilled water, and 20 μL of an internal standard solution (417 μg/mL of 6-undecanone in methanol) were placed in the LLCE apparatus (Z101567, Sigma-Aldrich Co.). The device was connected to a 250 mL round-bottom flask containing the extraction solvent (200 mL of diethyl ether), which was subsequently refluxed by heating the flask in a 47 °C water bath, whereas the condenser of the LLCE apparatus was held at 5 °C. After extraction for 18 h at ambient temperature (∼23 °C) with constant stirring in the sample chamber, the ether layers were recovered and concentrated to 50 mL using a Vigreux column at 43 °C. Solvent-assisted flavor evaporation (SAFE) was performed for 2 h according to the method described by Rotsatchakul et al.18 The resulting aroma extract was further concentrated to 10 mL using a Vigruex column at 43 °C, dried over anhydrous sodium sulfate, and concentrated to a final volume of 500 μL using a gentle stream of nitrogen. Each aroma extract was stored in a 2 mL vial equipped with a PTFE-lined screw cap at −70 °C until analysis. Gas Chromatography−Olfactometry (GC-O) and Aroma Extract Dilution Analysis (AEDA). The relative potency of individual odorants was determined using AEDA according to the method previously described.19 Serial dilutions (1:3, v/v) of each aroma extract were prepared in diethyl ether and stored in a 2 mL vial equipped with a PTFE-lined screw cap at −70 °C until analysis. The GC-O system consisted of a 6890 GC (Agilent Technologies Inc., Palo Alto, CA, USA) equipped with a FID, an on-column injector (3 °C temperature tracking mode), and an olfactory detection port (DATU Technology Transfer, Geneva, NY, USA). Dilutions and concentrated extracts were analyzed on a polar capillary column (RTX-Wax, 15 m × 0.32 mm i.d.; 0.5 μm film; Restek, Bellefonte, PA, USA). Concentrated aroma extracts were also analyzed using a nonpolar capillary column (RTX-5MS, 15 m × 0.32 mm i.d.; 0.5 μm film; Restek) for calculation of retention indices (RI). For GC-O, column effluent was split 1:5 between the FID and olfactory detection port using deactivated fused silica tubing (1 m × 0.25 mm i.d.; Restek), with both detector temperatures held at 250 °C. The GC oven temperature was programmed from 40 to 225 °C at a rate of 10 °C/min with initial and final hold times of 5 and 30 min, respectively. Helium was used as
beverage industry. When a consumer reaches for their favorite lemon-lime beverage, the flavor of the product they drink is distinctly different from that which was manufactured at the plant. Our ultimate goal is to understand the changes that take place as a result of the dynamic nature of the complex lemonlime beverage system. Furthermore, this research aims to identify the key flavor compounds common to lemon-lime.
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MATERIALS AND METHODS
Materials. Sprite (Coca-Cola Co., Atlanta, GA, USA), Sierra Mist (PepsiCo, Inc., Purchase, NY, USA), and 7UP (Dr. Pepper/Seven Up, Inc., Plano, TX, USA) were purchased in January 2009 and June 2010 at a local grocer (Urbana, IL, USA). Chemicals. Unless otherwise stated, chemicals and reagents were obtained from Sigma-Aldrich Co. (St. Louis, MO, USA) for unlabeled standards. Nerol and geraniol were obtained from Bedoukian Research, Inc. (Danbury, CT, USA), and acetic acid was obtained from Fisher Scientific (Fair Lawn, NJ, USA). The isotope 4-([2H3]methyl)-phenol was purchased from C/D/N Isotopes Inc. (Quebec, Canada). Published methods were used for the synthesis of (E)-4,5epoxy-(E)-2-decenal,14 2,3-dihydro-5-hydroxy-6-methyl-4(H)-pyran-4one (dihydromaltol),15 [2H2]-limonene,16 and [2H2]-linalool.17 The Supporting Information provides synthetic procedures or references with modified procedures for the following compounds: 2,3-dehydro1,8-cineole, [2H3]-2,3-dehydro-1,8-cineole, [2H3]-1,8-cineole, [2H4]octanal, [2H4]-nonanal, [2H4]-decanal, [2H3]-isoborneol, [2H6]-neral, [2H3]-borneol, [2H6]-geranial, [2H6]-nerol, [2H6]-geraniol, [2H7]-4terpineol, [2H3]-α-terpinyl acetate, [2H3]-α-terpineol, [2H2]-neryl acetate, and [2H2]-geranyl acetate. The structures of all isotope standards used can be found in Figure 1. All unlabeled compound purities were >90% (neat, hot split, 250 °C, GC-FID) except in the case of the isotope mixtures listed here: neral and geranial, 35.8 and 59.9%, respectively; [2H6]-neral and [2H6]-geranial, 21.8 and 52.3%, respectively; [2H6]-nerol and [2H6]-geraniol, 32.8 and 59.3%, respectively; and [2H3]-isoborneol and [2H3]-borneol, 48.3 and 47.0%, respectively. Preparation of Aroma Extracts. Volatile components were isolated by liquid−liquid continuous extraction (LLCE). For each 113
DOI: 10.1021/jf504852z J. Agric. Food Chem. 2015, 63, 112−119
Article
Journal of Agricultural and Food Chemistry
Table 1. Predominant Aroma-Active Components of Three Commercial Brands of Lemon-Lime Carbonated Beverages RIa c
no.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
compound unknown 2,3-dehydro-1,8-cineolef 1,8-cineolef octanalf nonanalf acetic acidg unknown decanalf unknown linaloolf butanoic acidh isoborneolf neralf borneolf geranialf nerolf unknown geraniolf 2,3-dihydro-5-hydroxy-6-methyl-4(H)-pyran-4-one (dihydromaltol)h 3-hydroxy-2-methyl-4(H)-pyran-4-one (maltol)h unknown (E)-4,5-epoxy-(E)-2-decenali 4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF)i 4-methylphenol (p-cresol)f eugenolh 3-hydroxy-4,5-dimethyl-2(5H)-furanone (sotolon)i unknown benzoic acidf
FD factorb d
WAX
RTX-5
odor description
1155 1196 1211 1297 1406 1450 1451 1511 1534 1545 1638 1692 1701 1725 1753 1771 1812 1854 1884 2000 2026 2029 2046 2096 2148 2225 2346 2449
− 985 1024 1002 1103 − − 1205 − 1099 − 1160 1240 1168 1271 1229 − 1254 − − − 1381 1088 1083 − 1111 − 1306
piney, terpiney minty, pine needles minty/eucalyptus pungent orange orange, sweet, pungent vinegar fresh, melony pungent, green, cilantro stale, burnt sugar floral, lavender cheesy camphorous lemony earthy, camphorous lemon oil, lemon cleaner lemon cleaner sweet, fruity lemon cleaner burnt sugar burnt sugar inky, phenolic unripe burnt sugar dung, stable cloves curry waxy, liver-like sweet, candy
e
SP
7UP
SM
3 81 − 81 3 − 9 9 3 243
