Anna K. Hjelmeland

Glycosidically Bound Volatile Aroma Compounds in Grapes and Wine:: A Review

Volatile aroma compounds in plants are typically found both as “free” and “bound” to a sugar moiety. When bound, these compounds are not odor active; however, upon hydrolysis of the glycoside, these compounds may then be volatilized. In grapes and wine, a large proportion of volatile aroma compounds are found in the bound form. A review of glycosides in grapes and in wine is presented with a focus on identified glycoside structures, their biosynthesis, their potential roles in the plant, and methods for their analysis. Studies of these compounds and their concentration changes during the winemaking process are discussed.

Regional sensory and chemical characteristics of Malbec wines from Mendoza and California

Malbec grapes are widely grown and studied in Argentina, whereas the smaller production in California is less well known. This study sought to define and compare Malbec wine compositions from various regions in Mendoza, Argentina and California, USA. The Malbec wines were clearly separated, based on their chemical and sensory profiles, by wine region and country. Descriptors of Malbec wines were aromas of cooked vegetal, earthy, soy and volatile acidity, as well as acidic taste and astringent mouthfeel, regardless of the region of origin. Malbec wines from Mendoza generally had more ripe fruit, sweetness, and higher alcohol levels, while the Californian Malbec wines had more artificial fruit and citrus aromas, and bitter taste. Compositional differences between the two countries were related more to altitude than precipitation and growing degree days. To our knowledge, this is the first time that an extensive regionality study has been attempted for Malbec wines.

Characterizing the Chemical and Sensory Profiles of United States Cabernet Sauvignon Wines and Blends

Cabernet Sauvignon is one of the most reputable red grape varieties grown in the United States; however, limited information is available on the chemical and sensory composition of the resulting wines. The purpose of this study was to develop a rapid, targeted profiling method for measuring volatile compounds with sensory impact in U.S. Cabernet Sauvignon wines and blends. We developed a semiquantitative, automated headspace solid-phase microextraction (HS-SPME) gas chromatography–mass spectrometry (GC-MS) method combined with synchronous selected ion monitoring (SIM)/scan detection to measure 61 volatile compounds. The compounds monitored included grape-derived norisoprenoids and terpenes; fermentation-derived esters, higher alcohols, and aldehydes; Brettanomyces-related compounds; and oak-derived compounds. Methoxypyrazine was also measured using HS-SPME-GC-MS/MS. Twenty-four commercial U.S. Cabernet Sauvignon varietal and blended wines from several regions in California and Washington State were selected to encompass a broad range of wine styles and were analyzed using the GC methods developed. The results were compared to a descriptive sensory analysis of the wines using 11 trained assessors to determine the extent to which the chemical analyses could predict sensory profiles. The rapid, targeted profiling method was able to predict a number of aroma sensory descriptors. The Cabernet Sauvignon wines and blends differed in their chemical and sensory profiles and were differentiated, in part, as a result of the direct and indirect influences of varying alcohol levels. This work provides the wine industry with the ability to rapidly assess wine volatile composition in order to further elucidate the relationships between the chemical compounds and sensory profiles of wines.

High-Throughput, Sub ng/L Analysis of Haloanisoles in Wines Using HS-SPME with GC-Triple Quadrupole MS

Haloanisole contamination causes development of “cork taint,” a musty off-aroma in affected wines. Cork taint results in significant economic loss for the wine and allied industries every year, therefore extensive quality-control procedures have been established at wineries and cork production facilities to monitor levels of haloanisoles in cork products. Because of the extremely low human sensory thresholds for these compounds (~1 to 4 ng/L for 2,4,6-trichloroanisole in wine), highly sensitive analytical methods are needed to detect the haloanisoles at threshold concentrations or lower. We present a method for the simultaneous analysis of four haloanisoles in wine—2,4,6-trichloroanisole (TCA); 2,3,4,6-tetrachloroanisole (TeCA); 2,3,4,5,6-pentachloroanisole (PCA); and 2,4,6-tribromoanisole (TBA)—that have been frequently associated with cork taint aromas in wines. Headspace solid-phase microextraction (HS-SPME) coupled to a GC-triple quadrupole MS was used to obtain limits of quantification that were ≤1.0 ng/L and below sensory threshold levels. The method is fully automated, requires no sample preparation other than the addition of internal standards, and is high throughput, with a 10-min extraction time and a 5-min incubation prior to extraction. This method can be readily adapted to screen for haloanisoles in cork extracts.

A comparison of sorptive extraction techniques coupled to a new quantitative, sensitive, high throughput GC–MS/MS method for methoxypyrazine analysis in wine

Methoxypyrazines are volatile compounds found in plants, microbes, and insects that have potent vegetal and earthy aromas. With sensory detection thresholds in the low ng L(-1) range, modest concentrations of these compounds can profoundly impact the aroma quality of foods and beverages, and high levels can lead to consumer rejection. The wine industry routinely analyzes the most prevalent methoxypyrazine, 2-isobutyl-3-methoxypyrazine (IBMP), to aid in harvest decisions, since concentrations decrease during berry ripening. In addition to IBMP, three other methoxypyrazines IPMP (2-isopropyl-3-methoxypyrazine), SBMP (2-sec-butyl-3-methoxypyrazine), and EMP (2-ethyl-3-methoxypyrazine) have been identified in grapes and/or wine and can impact aroma quality. Despite their routine analysis in the wine industry (mostly IBMP), accurate methoxypyrazine quantitation is hindered by two major challenges: sensitivity and resolution. With extremely low sensory detection thresholds (~8-15 ng L(-1) in wine for IBMP), highly sensitive analytical methods to quantify methoxypyrazines at trace levels are necessary. Here we were able to achieve resolution of IBMP as well as IPMP, EMP, and SBMP from co-eluting compounds using one-dimensional chromatography coupled to positive chemical ionization tandem mass spectrometry. Three extraction techniques HS-SPME (headspace-solid phase microextraction), SBSE (stirbar sorptive extraction), and HSSE (headspace sorptive extraction) were validated and compared. A 30 min extraction time was used for HS-SPME and SBSE extraction techniques, while 120 min was necessary to achieve sufficient sensitivity for HSSE extractions. All extraction methods have limits of quantitation (LOQ) at or below 1 ng L(-1) for all four methoxypyrazines analyzed, i.e., LOQs at or below reported sensory detection limits in wine. The method is high throughput, with resolution of all compounds possible with a relatively rapid 27 min GC oven program.

Impact of the [GAR+] Prion on Fermentation and Bacterial Community Composition with Saccharomyces cerevisiae UCD932

The efficiency and efficacy of alcoholic fermentation by yeast is crucial for the winemaking process. Sluggish or arrested fermentations can negatively affect winery operations and wine quality. Here, we present a novel mechanism by which problem fermentations can arise. Yeast can induce a prion known as [GAR+] that allows the cell to circumvent glucose repression of alternative carbon substrates. We have confirmed that Saccharomyces cerevisiae strain UCD932 can spontaneously generate the [GAR+] phenotype and that this phenotype exhibits the genetic traits of a prion. Differences were observed in the fermentative behavior of UCD932 wild-type [gar−] versus [GAR+] yeasts in laboratory-scale model juice fermentations. To further understand these differences, fermentations were performed in Chardonnay juice to study the interaction of the [GAR+] prion and presence of sulfur dioxide (SO2) on fermentation kinetics, bacterial community composition, and volatile compound production. Cells harboring the [GAR+] prion displayed reduced fermentation capacity, which was especially evident in the absence of SO2. Presence of SO2 and fermentation time had the most significant effects on the types of bacteria present in the fermentation. However, [GAR+] yeasts without added SO2 were especially sensitive to bacterial competition. This difference was also reflected in the bacterial and volatile profiles of the finished wine. We hypothesize that the bacterial induction of the [GAR+] prion by yeast during fermentation is another possible mechanism by which stuck or sluggish fermentations may become established.

Impact of Mechanical Harvesting and Optical Berry Sorting on Grape and Wine Composition

The impact of mechanical harvesting, optical berry sorting, and their possible synergistic effect on grape and wine composition was investigated. Pinot noir grapes from the Russian River Valley American Viticultural Area were harvested by hand, by a standard bow-rod mechanical harvester, or by a mechanical harvester with a Selectiv’ Process on-board. For each harvest method, half of the grapes were unsorted and half were optically sorted at the winery. The grapes, wines at bottling, and wines after three months of bottle aging were analyzed by reversed-phase high-performance liquid chromatography (RP-HPLC), ultraviolet-visible spectroscopy (UV-vis), and headspace solid-phase microextraction (HS-SPME) gas chromatography mass spectrometry (GC-MS) for color expression and phenolic and aroma profiling. The machine-harvested grapes had higher levels of β-damascenone, linalool, β-myrcene, and α-terpinene, potentially caused by glycosidic hydrolysis triggered by berry damage during harvest or from induced synthesis as a wounding response. In general, differences in wine composition attributable to harvest method were diminished or eliminated by optical sorting. The machine harvester with the Selectiv’ Process on-board led to wines with the most phenolics, although these differences may have been decreased or eliminated had the grapes been crushed before fermentation as the wines were produced by whole-berry fermentation. Descriptive sensory analysis conducted on wines three months after bottling determined that the wines made from hand-harvested fruit had significantly greater tropical fruit aroma, while wines made from optically sorted treatments had less hue saturation. With only two significant differences among the 18 aroma, taste, and mouthfeel attributes tested, it was concluded that all treatments led to wines of similar character.