Microwave-Assisted Extraction Applied to Merlot Grapes with Contrasting Maturity Levels: Effects on Phenolic Chemistry and Wine Color

Abstract

Merlot grapes were harvested with three maturity levels (21.1, 23.1, and 25.1 Brix), and processed with or without the application of microwave-assisted extraction (MW). The detailed phenolic composition and color were followed during winemaking. The MW treatment did not affect the basic chemical composition of the wines. Upon crushing, MW caused a 211% improvement in anthocyanins in the wines of the first harvest and an 89% improvement in the wines of the third harvest. At bottling, MW favored the formation of pyranoanthocyanins and tannin-anthocyanin dimers. Tannin extraction was not affected by MW just after application of this process, but improvements of 30, 20, and 10% on MW-treated wines of the first, second, and third harvest, respectively, were recorded at pressing. The formation of polymeric pigments during aging generally increased along with harvest date and was only favored in MW-treated wines of the first and third harvest, with preferential formation of small polymeric pigments, in accordance with enhanced anthocyanin extraction in these wines. Initial improvements of wine color upon application of MW in the wines of the first, second, and third harvest were of 275, 300, and 175%, respectively. Although these differences subsided or disappeared for the wines of the second and third harvest during aging, the wines of the first harvest treated with MW retained 52% more color than Control wines at day 150 post-crushing. Results suggest the MW treatment was more efficient in extracting and retaining phenolics and color when applied to unripe fruit.Fermentation 2019, 5, 15 2 of 16 varieties), and tannins (located both in skins and seeds) change during ripening, winemakers usually define harvest decisions based on a complex combination of factors that include weather forecast and disease pressure, fruit basic chemistry (including Brix, pH, and titratable acidity), and phenolic composition (including anthocyanins and tannins).Studies in Cabernet Sauvignon, Merlot, and Tempranillo have found a direct link between grape maturity, usually defined in terms of color and phenolic composition, and wine composition [1,3,8]. This accumulated knowledge has, in turn, allowed the production of wines with specific sensory features based on harvest time. Bindon et al. (2014) [9] studied the effect of five different harvest dates, with sugar levels spanning from 20 to 26 Brix, and corresponding alcohol contents in the finished wines spanning from 12 to 15.5% v/v. It was found that wine anthocyanins and tannins increased with harvest date, as well as an enhanced extraction of skin-derived phenolics [9]. From a sensory standpoint, later harvest dates produced wines with less green or vegetative attributes and more dark fruit attributes [1].Because grape maturity plays such a critical role in wine composition, it is expected that the outcomes of a given winemaking technique may be different based on when the fruit is harvested. In turn, variations in ethanol due to changes in fruit maturity may have an effect in phenolic e...

Combination of pre-fermentative and fermentative strategies to produce Malbec wines of lower alcohol and pH, with high chemical and sensory quality

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Chemistry and Reactivity of Tannins in Vitis spp.: A Review

“…Microwave-assisted extraction is a method commonly used in the food industry that showed an improvement of tannin extraction in Pinot noir wines, but not in Cabernet sauvignon or Merlot wines [78,79]. In a recent study carried out by Cassassa et al, 2019 [63] on the use of microwaves for the extraction of tannins in unripe, ripe, and fully ripe Merlot grapes, this technique showed a higher tannin content in wines after microwave-assisted extraction compared to the control, but the phenolic extraction was higher in unripe grapes. These results were similar to some thermovinification treatments, suggesting that cell wall materials are affected by those treatments, which likely reduces the extraction of tannins.…”

Improvement of Naturally Derived Food Colorant Performance with Efficient Pyranoanthocyanin Formation from Sambucus nigra Anthocyanins Using Caffeic Acid and Heat

“…In this time period of 3 to 4 years, concentration of anthocyanins had significantly decreased, leading to an increase in the caffeic acid to anthocyanin ratio [ 8 ]. One study looked at using microwave-assisted extraction to increase PACN formation at differing grape ripeness levels [ 9 ]. Another study was able to reduce PACN formation to 42 days by increasing storage temperature to 25 °C [ 10 ].…”