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Title: Removing the negative sensory impact of volatile phenols in red wine: Optimization and evaluation of different materials and their impact on wine quality
Authors: Ribeiro, Luís Filipe da Mota
Advisor: Nunes, Fernando Hermínio Ferreira Milheiro
Martins, Maria Fernanda Gil Cosme
Issue Date: 16-Feb-2018
Abstract: Red wine spoilage by Dekkera/Brettanomyces yeasts is a worldwide problem due to the development of a phenolic off-flavour affecting negatively the positive fruity and floral wine aromas known as “Brett character”. The main compounds responsible for this off-flavour are volatile phenols (VPs), 4-ethylphenol (4-EP) and 4-ethylguaiacol (4-EG) and to a lesser extent 4-ethylcatechol, formed by decarboxylation and reduction of the hydroxycinnamic acids precursors by Dekkera/Brettanomyces. Preventive measures were developed and authorised by OIV and EU, however the problem persists. Therefore, this study aims to develop efficient remedial treatments for reducing negative VPs without impacting on wine quality. A screening of eight products for reducing VPs levels in wines was performed. At the levels used, activated carbon (AC) was the most efficient in removing VPs from wines (57%) resulting in a 75% decrease of headspace abundance (HAA) of VPs. Other products although not reducing the total amount of VPs decreased their HA like chitosan (27%). From this screening ACs and chitosans were selected and further optimised. It has been showed that Dekkera/Brettanomyces can produce biogenic amines (BA) in grape must conditions. To have a deeper insight into the contribution of Dekkera/Brettanomyces activity in the BA wine levels, 79 red wines produced industrially from different vintages, grape varieties, Portuguese demarcated regions and winemaking processes, were analysed for their VPs (4-EP 4.5-5604 g/L; 4-EG 2.3-831 g/L) and BA levels (19.6-331 mg/L). Non-inoculated wines with lactic acid bacteria presented significantly higher histamine levels (8.7±1.0 mg/L) than those inoculated with starter cultures (0.4±1.9 mg/L), the inverse being observed for VPs levels. A significant negative correlation was observed between the VPs levels and histamine (4-EP =-0.314; 4-EG =-0.345) and putrescine levels (4-EP =-0.299; 4-EG =-0.336) in wines. Results suggest that Dekkera/Brettanomyces are not significant contributors to BA levels in industrial produced wines. To optimise the application of ACs for removing/reducing VPs and to understand their impact on wine quality, experiments were performed using AC with different characteristics (superficial and mesopore area, pore diameter and micropore volume). All ACs reduced significantly VPs (maximum 73%). Efficiency was related to their surface area and micropores volume. VPs reduction was more important for the recovery of the positive fruity attribute xvi perception than the Headspace aroma abudance. Optimal selection of AC characteristics, allowed removing efficiently VPs without impacting negatively on wine sensory quality. The influence of structural features of chitin and chitosans in the reduction of negative volatile phenols HAA was studied with chitins and chitosans with different deacetylation degrees (DD) (5-91%) and molecular weights (24-466 kDa). They decreased 7-26% of HA of VPs without changing their amounts in wines. Reduction efficiency increased with DD and applied dose. Reduction of HA of VPs by chitosans enabled significant decreases in the negative phenolic and bitterness attributes and increased positive fruity and floral attributes. Results show that chitosan with high DD, including fungal chitosan, already allowed in wine, is an efficient approach for reducing the negative sensory impact of VPs. Aiming the development of more specific removal procedures for VPs, molecularly imprinted polymers (MIPs) were synthetised, characterised and their efficiency in VPs removal in wine matrix studied. MIP produced by precipitation polymerisation showed good imprinting factors for both VPs (4.66±1.88 for 4-EP; 3.15±1.08 for 4-EG). Although the imprinting effect of MIPs in the binding capacity of VPs in wine were not as high as that determined by adsorption isotherms, VPs adsorption observed for this non-imprinting polymer (NIP) and MIP in wine presented interesting high values (29 and 38%; 54 and 63%, for medium and high spiking levels, respectively), corresponding to a decrease in HA of 63-69% of VPs. MIP and NIP reduced significantly the phenolic attribute of spiked wines and improved their fruity and floral attributes, with MIP showing a significantly higher efficient than NIP. The MIPs design can be a suitable tool to remove from wines these negative aroma compounds. Cork powder was explored and optimised for removing wine negative VPs. Cork performance optimisation by removal of dichloromethane and ethanol cork extractives, air removal and ethanol impregnation, removes 41-62% of 4-EP and 50-53% of 4-EG from VPs spiked wine at 250 g/hL. No significant impact on phenolic acids and monomeric anthocyanins were obtained, although being observed a decrease in HAA (40%). Optimised cork powder allowed decreasing significantly the negative phenolic, bitterness and astringency attributes, recovering the positive fruity and floral sensory attributes. Optimised cork powder can be a good solution for VPs removal without impacting negatively on the wine sensory quality and be used as new oenological fining agent.
Document Type: Doctoral Thesis
Appears in Collections:DQUI - Teses de Doutoramento
TD - Teses de Doutoramento

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