Article pubs.acs.org/JAFC
Chemical and Sensory Study on the Evolution of Aromatic and Nonaromatic Compounds during the Progressive Oxidative Storage of a Sauvignon blanc Wine Carien Coetzee,*,† Elizma Van Wyngaard,† Katja Šuklje,§,# Antonio C. Silva Ferreira,⊥,† and Wessel J. du Toit† †
Department of Viticulture and Oenology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa Agricultural Institute of Slovenia, Central Laboratories, Hacquetova ulica 17, 1000 Ljubljana, Slovenia # National Wine and Grape Industry Centre, Charles Sturt University, Locked Bag 588, Wagga Wagga, New South Wales 2678, Australia ⊥ Escola Superior de Biotecnologia, Universidade Católica Portuguesa, 4200-072 Porto, Portugal §
S Supporting Information *
ABSTRACT: The effect of repetitive controlled oxidation on the chemical and sensory composition of a fresh and fruity style Sauvignon blanc wine was investigated. Chemical analyses were conducted together with extensive sensory profiling. A decrease in volatile thiols responsible for the fruity nuances and an increase in oxidation-related compounds, such as acetaldehyde, during the course of the oxidation was observed. The wine evolved from a fresh and fruity one to one with slight oxidation and then developed extreme oxidative characteristics. The control samples (no oxygen added) developed a “cooked” character that could indicate the formation of “reductive” compounds in these wines. Conversely, the wines that received a single dose of oxygen did not develop this flavor and were perceived to be fresher and fruitier than the control samples. The color of the wine evolved before the disappearance of the pleasant aroma. KEYWORDS: Sauvignon blanc, oxygen, wine aroma, sensory
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INTRODUCTION The shelf life of, especially, white wine is of great concern for the wine industry. Oxidation may play an important role in white wine’s composition and its sensory characteristics. The shelf life of young white wines and the rate of oxidation in general are influenced by various factors such as the composition of the wine (antioxidants, pH, etc.), storage time, storage temperature, type of closure (oxygen ingress and adsorption), and storage position.1−3 Sauvignon blanc wines can have a large diversity of flavors such as fruity (“grapefruit”, “passion fruit”, “gooseberry”, “citrus”, “tropical”) and green characters (“green pepper”, “grassy”, “asparagus”). These descriptors have been attributed to key chemical aroma and flavor compounds occurring in the wine. The volatile thiols (4-sulfanyl-4-methylpentan-2-one (4SMP), 3-sulfanylhexan-1-ol (3SH), and 3-sulfanylhexan-1-ol acetate (3SHA)) can contribute to “tropical/fruity” style wines, whereas the methoxypyrazines, especially 3-isobutyl-2-methoxypyrazine (IBMP), can give the wine a “green pepper”, “grassy”, and “asparagus” odor.4 These two groups of compounds are considered to be character impact compounds for Sauvignon blanc wines; however, they are not solely responsible for the overall aroma. Various other chemical groups such as esters, higher alcohols, fatty acids, and terpenes can also contribute significantly to the aromatic composition.5 Comprehensive reviews on Sauvignon blanc aroma (with a focus on volatile thiols) and the reaction of various aroma groups to oxidation as well as the contribution of aging and oxygen on aromatic © XXXX American Chemical Society
and nonaromatic compounds and sensory composition of Sauvignon blanc wine have recently been published.4,6,7 Wine oxidation results in a loss of “fruity” and “fresh” wine sensory attributes and favors the production of compounds such as acetaldehyde, methional, phenylacetaldehyde, and sotolon. These compounds are often associated with unpleasant sensory descriptors reminiscent of “green apple”, “potato”, “honey”, and “curry”.8,9 The presence of these oxidation compounds could also interact with remaining pleasant aroma compounds, leading to the suppression of certain positive attributes.10,11 In some cases, a certain amount of oxygen can significantly improve wine aroma and quality by preventing the formation of ‘reductive’ off-odors in the bottle. Aroma attributes associated with these off-odors are “rotten egg”, “cabbage”, and “garlic”, and the compounds hydrogen sulfide and methyl mercaptan have been indicated as being primarily responsible for postbottling reduction.12,13 The effects of oxygen and aging on various aspects of dry white wines have been investigated,6,14 and the evolution of wine sensory quality is thought to reach a peak after a period in the bottle; however, the time period necessary and the amount of oxygen required to reach this peak remain unknown.15 The amount needed would depend on how the wine was intended Received: May 13, 2016 Revised: September 26, 2016 Accepted: October 2, 2016
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DOI: 10.1021/acs.jafc.6b02174 J. Agric. Food Chem. XXXX, XXX, XXX−XXX
Article
Journal of Agricultural and Food Chemistry
After distribution of the wine into the 5 L bottles, the first treatment (T0 control) was sampled and frozen at −20 °C. T0 control would thus serve as the “beginning” of the trial (no time lapse). All of the oxidation treatments (T1−T5 ox) then received oxygen by using a micro oxygen sparger connected to a cylinder containing high-purity (99.5%) medical oxygen (Afrox, South Africa). During sparging, the oxygen concentration was constantly monitored by using oxygen sensor spots (Pst3; PreSens, Regensburg, Germany) fitted inside each bottle in contact with the wine, allowing a noninvasive measurement over time. Sparging stopped as soon as the required dissolved oxygen concentration was reached. The bottles were then hermetically sealed using a tight-sealing plastic screw cap. No oxygen was added to the control samples (T0−T5 control). The bottles were stored in the dark at 15 °C during oxygen consumption. As soon as all of the oxygen in the oxidation samples was consumed (dissolved oxygen concentration
