MICROWINE - Microbial metagenomics and the modern wine industry

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Colour profile analysis of Port Wines by different instrumental and visual methods

Publication . Soares-da-Silva, Francisco A. G.; Campos, Francisco M.; Ferreira, Manuel L.; Ribeiro, Natália; Amaral, Bento; Simões, Tomás; Silva, Cristina L. M.

BACKGROUND: Wine colour is an important quality parameter, being the first sensorial attribute evaluated during wine tasting. The perception of wine colour can be different depending on many factors, including the depth of the sample under observation. The main objectives of the present study were to measure the colour of Port wines, using CIE L*a*b* parameters at different depths with different instrumental techniques (spectrophotometry and colorimetry), and to compare the obtained results with the sensory (visual) perception of colour samples. RESULTS: Representative profiles of Lightness (L*), Hue (H*) and Chroma (C*) at different depths were obtained using Port wine samples from different categories and ages. In general, relatively good correlations between the colorimetric and spectrophotometric methods were obtained for the L* and H* parameters. The results of the sensory tests also showed good correlations between the visually-assessed hue scores and the colorimetric measurements of the H* parameter, particularly at the lower depths tested (up to 4.0 mm). CONCLUSIONS: Overall, the results indicate that the colorimetric method can be used for estimating wine colour parameters, providing useful information about the colour profile of wines at different depths

2019Journal article

Open access

Changes in the composition of the lactic acid bacteria behavior and the diversity of oenococcus oeni isolated from red wines supplemented with selected grape phenolic compounds

Publication . Collombel, Ingrid; Campos, Francisco M.; Hogg, Tim

Phenolic compounds are important components of wine and are known to have an impact on the physiology of wine microbes. The influence of specific sub-sets of phenolic compounds on the growth and metabolism of lactic acid bacteria (LAB) and on the diversity of Oenococcus oeni in inoculated and non-inoculated red wines was investigated during malolactic fermentation (MLF) and subsequent storage. Representative O. oeni strains from wines treated with flavonols and trans-resveratrol were isolated and analyzed by pulsed-field gel electrophoresis of rare restriction enzyme digests (REA-PFGE). 28 days after MLF initiation, strains from all samples had entered the death phase, except those supplemented with trans-resveratrol. In the non-inoculated samples, the onset of lactic acid production was apparently delayed by all compounds tested, except for the flavan-3-ols. Increased levels of phenolics also delayed citrate consumption in inoculated samples. PFGE analysis revealed 22 genetic profiles, and some profiles were characteristics of specific samples. The commercial starter used in the inoculated wines did not dominate during MLF. The effect of the phenolics studied was dependent on the origin and concentration of each as well, as the fermentation stage and whether the wines were inoculated. The effect of flavonols and trans-resveratrol seemed to be strain-dependent, which could have implications on the final quality of wines.

2019Journal article

Open access

New insights into cinnamoyl esterase activity of Oenococcus oeni

Publication . Collombel, Ingrid; Melkonian, Chrats; Molenaar, Douwe; Campos, Francisco M.; Hogg, Tim

Some strains of Oenococcus oeni possess cinnamoyl esterase activity that can be relevant in the malolactic stage of wine production liberating hydroxycinnamic acids that are precursors of volatile phenols responsible for sensory faults. The objective of this study was to better understand the basis of the differential activity between strains. After initial screening, five commercial strains of O. oeni were selected, three were found to exhibit cinnamoyl esterase activity (CE+) and two not (CE−). Although the use of functional annotation of genes revealed genotypic variations between the strains, no specific genes common only to the three CE+ strains could explain the different activities. Pasteurized wine was used as a natural source of tartrate esters in growth and metabolism experiments conducted in MRS medium, whilst commercial trans-caftaric acid was used as substrate for enzyme assays. Detoxification did not seem to be the main biological mechanism involved in the activity since unlike its phenolic cleavage products and their immediate metabolites (trans-caffeic acid and 4-ethylcatechol), trans-caftaric acid was not toxic toward O. oeni. In the case of the two CE+ strains OenosTM and CiNeTM, wine-exposed samples showed a more rapid degradation of trans-caftaric acid than the unexposed ones. The CE activity was present in all cell-free extracts of both wine-exposed and unexposed strains, except in the cell-free extracts of the CE− strain CH11TM. This activity may be constitutive rather than induced by exposure to tartrate esters. Trans-caftaric acid was totally cleaved to trans-caffeic acid by cell-free extracts of the three CE+ strains, whilst cell-free extracts of the CE− strain CH16TM showed significantly lower activity, although higher for the strains in experiments with no prior wine exposure. The EstB28 esterase gene, found in the genomes of the 5 strains, did not reveal any difference on the upstream regulation and transport functionality between the strains. This study highlights the complexity of the basis of this activity in wine related O. oeni population. Variable cinnamoyl esterases or/and membrane transport activities in the O. oeni strains analyzed and a possible implication of wine molecules could explain this phenomenon.

2019Journal article

Open access