The effects of chamber drying under controlled temperature and moisture conditions and fermentation process on blueberry juices to obtain three wines were studied in this work. Drying was carried out with a view to increase the sugar content and obtain wines with an ethanol content similar to a commercial grape wine or to obtain sweet wines. Analyses included color parameters; browning index; and anthocyanin, flavonols, flavan-3-ol derivatives, and tannin concentrations, as well as vitamin C concentration and antioxidant activity. Based on the results, drying increases color and the concentration of anthocyanins and tannins most probably by the effect of dehydration of the berries and diffusion of the colored compounds from the skin to the pulp due to the structural alterations in their skin. In addition, drying decreases flavonols, flavan-3-ol derivatives, and vitamin C concentrations. The browning index, anthocyanins, and tannins decreased with the fermentation time, and vitamin C was constant with the fermentation time. The sensory analysis showed that the wines with the best sensory characteristics were those with residual sugar, partial fermented wines 1 and 2.
Blueberries,
Blueberries are functional food due to their health benefits (e.g., antioxidant, anti-inflammation, neuroprotection, antimetastatic, cardioprotective, antimicrobial, renoprotective, opthalmoprotective, antidiabetic, hepatoprotective, gastroprotective, antiosteoporotic, and antiaging) [
The addition of sucrose is the most common method to increase the sugar content of blueberry juices [
The aim of this work was to evaluate the changes in bioactive compounds, color, and antioxidant activity during the drying process and subsequent fermentation of sugar-rich juices to obtain blueberry wines.
Hydrochloric acid, metaphosphoric acid, formic acid, acetic acid, methanol, acetonitrile, sodium metabisulphite, potassium chloride, sodium acetate, acid potassium dichromate, ethyl acetate, and potassium dihydrogen phosphate were purchased from Merck (Madrid, Spain). Anthocyanins (malvidin-3-O-galactoside chloride), flavan-3-ol derivative ((+)-catechin, (−)-epicatechin, epigallocatechin gallate, procyanidin B1, and procyanidin B2), Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), DPPH (2,2-diphenylpicrylhydrazyl), and DTT (DL-dithiothreitol) were purchased from Sigma-Aldrich Chemical Co. (Madrid, Spain).
The blueberries used for this study were Star variety
Three batches of blueberries were dried in a Frisol Climatronic chamber at a constant temperature of 40°C and an initial relative humidity of 20%. During the drying process, a sample was collected daily and the weight loss and reducing sugar concentration of the blueberries were measured using a refractometer, model Atago Master.
The drying process was finished when the reducing sugar content reached approximately 24.2°Brix. The blueberries were pressed on a vertical press similar to industrial models, obtaining the final juice. The maximum pressure reached in each of the two pressing cycles was 300 bar. The musts were centrifuged at 5000 rpm, filtered, and analyzed in triplicate.
The sweet juice was divided into three batches and was mixed with the solid parts of the berries in a ratio of 1 : 1 (w/v). The mix was added with a yeast inoculum of commercial
After fermentation/maceration, the berries were pressed a second time on a vertical press and skin residues were removed from the wine. The resulting wines were centrifuged at 5000 rpm, filtered, and analyzed in triplicate.
This parameter was determined according to the EEC official methods as described in Regulation 2676/1990 [
Isolation of volatile acids is carried out according to the method of the OIV [
Spectrophotometric measurements were made on a PerkinElmer (Waltham, MA) Lambda 25 spectrophotometer, using quartz cells of 1 mm light path. Samples were previously passed through Millipore (Billerica, MA) HA filters of 0.45
Absorbances at 420, 520, and 620 nm were measured. Hue indicates the proportion between orange and red colors;
To obtain PPC values, 5 mL of wine was added with 15 mg of Na2S2O5; after 45 min, the absorbance at 520 nm was measured. Anthocyanin monomers were immediately decolorized by the excess Na2S2O5 added, so the residual color was due to the polymeric forms of the pigments.
Antioxidant activity was analyzed through the DPPH assay according to Alén-Ruiz et al. [
The total monomeric anthocyanin pigment content was measured by the pH differential method described by Lee et al. [
The total tannins were determined by measurement of the absorbance at 550 nm after acid hydrolysis of the samples diluted at 1 : 50 with distilled water and a blank. The resulting absorbance (
Ethanol content was determined according to Crowell and Ough [
A volume of 2 mL of must was passed through a Sep-Pak C18 cartridge, with 900 mg of filling (Long Body Sep-Pak Plus; Waters Associates, Milford, Massachusetts) that was previously activated with 5 mL of pure methanol and washed with aqueous 0.01% (v/v) HCl. The cartridge was successively washed with 10 mL of 0.01% aqueous HCl. The cartridge was eluted with 5 mL of pure ethyl acetate. This collected fraction was evaporated on a rotary evaporator thermostated at 35°C and resolved in 1 mL of pure methanol. The fraction was passed through a filter of 0.45
A volume of 50
In the case of identification and quantification of flavan-3-ol derivatives, the samples were diluted 25 times in ultrapure water. The identification and quantification were carried out in an HPLC (Thermo Spectra Physics Series P100) with a fluorescence detector (PerkinElmer Series 200a), on a LiChrospher 100 RP-18 column (250 mm × 4.6 mm, 5
0.7 mL of 4.5% metaphosphoric acid was added to 0.7 mL of juice, and the mix was centrifuged at 5000 rpm for 10 minutes at 4°C. 1 mL of the mix was added to 0.2 mL of DTT (DL-dithiothreitol) solution and the sample was kept in the dark for 2 hours in order to reduce the dehydroascorbic acid to L-ascorbic acid. After complete conversion, the sample was filtered with a nylon filter of 0.45
The wines were assessed for aroma, flavor, and color acceptability in accordance with ISO 8586-1:1993. The tasting room was kept at 20°C and wines were served in coded tasting glasses certified in accordance with ISO 3591:1977. The sixteen tasters were instructed in advance in their task and the rules to be followed and were given a scoring sheet. The evaluation of the quality of wines was made according to ISO 4121:2003, with options of desirable (5-6), acceptable (3-4), and undesirable (1-2).
The results for all samples were subjected to analysis of variance at the 95.0% confidence level; in addition, homogeneous groups were calculated in order to establish significant differences between means. The software used was the Statgraphics Computer Package v.5.0 from Statistical Graphics Corp.
The first stage in the elaboration of blueberry wine was a drying process in order to increase the sugar content to obtain a fermented beverage with an ethanol content similar to a grape wine. The blueberry variety presented a sugar content of 13.2°Brix. This content increased to 24.2°Brix after 48 hours of drying. During the drying process, evaporation of water occurred, causing the concentration of other compounds besides the sugars. A sweet juice was obtained from the dried blueberries and this juice was subjected to a fermentation process obtaining three wines with different sugar contents due to the different times of fermentation. Wine 1 was a sweet wine with 117 g/L of residual sugars, wine 2 was a semisweet wine (28.8 g/L of residual sugars), and wine 3 was a dry wine (0 g/L of residual sugars).
The volatile acidity was measured in order to control the quality of wines. This parameter represents the amount of volatile acids in the wines, acetic acid being the majority. The volatile acidity increased with the fermentation time with values of 5.4, 5.9, and 8.9 meq/L for wine 1, wine 2, and wine 3, respectively. The latter presented a value higher than the limit established in the Official State Bulletin [
Color is the first attribute perceived by the consumer in food. The absorbances at 420, 520, and 620 nm as well as the hue were measured and expressed as absorbance units (a.u.). These three absorbances represent the contribution of browning and red and blue compounds, respectively. As can be seen in Figure
Changes in (a) absorbance at 420 nm (a.u.), (b) absorbance at 520 nm (a.u.), (c) absorbance at 620 nm (a.u.), and (d) hue for blueberry juices and wines.
The polymeric pigments color measured in wines shows that the fermentation process produced a decrease of PPC with time (0.699, 0.517, and 0.373 in wine 1, wine 2, and wine 3, resp.), so the contribution of pigment polymers to color decreases. On the one hand, the high value of wine 1 was due to the concentration resulting from the loss of water by evaporation during the drying process. On the other hand, the maceration with solid parts should increase the values during the fermentation. Nevertheless, these compounds decreased during the maceration, possibly due to other reactions in which they may be involved.
Anthocyanins are polyphenolic pigments which are responsible for the red color of blueberry juices and wines. The drying process increased the concentration of these compounds due to the water evaporation and the diffusion process from skin to juice due to the structural alterations in fruit skin [
Changes in anthocyanins, vitamin C, and tannins of blueberry juices and wines.
Regarding the concentration of total vitamin C, fresh blueberries showed the highest value (28.1 mg/L) (Figure
Tannins are polymer compounds responsible for the astringency of wines. In wines, certain astringency is appreciable, although if it is excessive it becomes a defect. Drying process raised its content from 4.13 to 8.95 g/L (Figure
Table
Flavan-3-ol and flavonols concentrations (mg/L) and homogenous groups for blueberry juices and wines at different fermentation times.
Fresh juice | Juice after drying | Wine 1 | Wine 2 | Wine 3 | |
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Quercetin-3-O-galactoside |
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Quercetin-3-O-glucoside |
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Syringetin-3-O-galactoside |
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Syringetin-3-O-glucoside |
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Total flavonols |
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Procyanidin B1 |
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Epigallocatechin gallate |
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Catechin |
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Procyanidin B2 |
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Epicatechin | ND |
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Total flavan-3-ol |
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ND: not detected. Values in the same row with different superscript letters are significantly different,
Also, five flavan-3-ol derivatives were identified and quantified: 3 monomers and 2 procyanidins. The major compound in juice from fresh fruit was procyanidin B1 followed by catechin. Drying and fermentation stages caused a decrease in concentration of total flavan-3-ol derivatives, although procyanidin B1 increased during drying and epicatechin could be quantified. These compounds are involved in different reactions. Catechins and proanthocyanidins are the main substrates for condensation with monomeric anthocyanins and their subsequent evolution to polymeric anthocyanins [
Figure
Antioxidant activity for blueberry juices and wines.
Figure
Sensory evaluation of the obtained wines.
The winemaking of blueberry wines caused changes in color and concentration in bioactive compounds. The drying process increased the absorbances at 420, 520, and 620 nm, so the browning index and the contribution of red compounds were higher in the juice after drying. The concentration of anthocyanins and tannins also increased with drying; however, flavonols, flavan-3-ol derivatives, and vitamin C decreased in this stage. The fermentation stage caused a decrease in phenolic compounds, tannins, and antioxidant activity, while the concentration of vitamin C was constant. Wine 3 presented lower values of anthocyanins and tannins as well as antioxidant activity, in addition to high volatile acidity. The sensory analysis showed that partially fermented wines had the best score. In this sense, in the production of blueberry wines, the drying process is suitable to obtain juices rich in sugars; partial fermentation obtains better results than total fermentation. Further study on the drying stage as well as the fermentation could improve the characteristics of these wines.
The authors declare that there are no conflicts of interest regarding the publication of this paper.