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. 2022 Oct 28;32(2):145–156. doi: 10.1007/s10068-022-01181-1

Phenolic features and anthocyanin profiles in winemaking pomace and fresh berries of grapes with different pedigrees

Lei Zhu 1,2, Xin Wu 1, Xixi Hu 3, Xinyue Li 1, Shanshan Lv 1, Chuan Zhan 1, Yunhua Chen 1, Changyuan Wang 1,✉, Jingyu Xu 4,✉
PMCID: PMC9839939  PMID: 36647526

Abstract

The total contents and antioxidant activities of phenolic compounds as well as anthocyanin profiles were analyzed and compared in fresh berries and fermented pomace of three grape cultivars with different pedigrees. The phenolic contents and antioxidant activities decreased significantly in skins (p < 0.05), while relatively large amounts of them were retained in seeds after fermentative maceration. Fermentative maceration also had a significant impact on the anthocyanin compositions. The proportions of anthocyanins with more stable structures, such as malvidin derivatives, methylated, diglucosides and nonacylated anthocyanins, increased significantly in the pomace skins (p < 0.05). There were obvious differences in phenolic features and anthocyanin profiles among the three cultivars. ‘NW196’, a wine hybrid of Vitis vinifera and V. quinquangularis, was characterized by the highest total anthocyanin contents and degree of diglucosylation. The results obtained in this study could contribute to the primary data for the development and utilization of winemaking pomace, especially from local non-Vitis vinifera grapes.

Keywords: Winemaking pomace, Phenolic content, Anthocyanin profile, Antioxidant activity

Introduction

Grape is one of the most widely developed fruit crops worldwide. Over 70 million tons of grapes are produced each year (Bordiga et al., 2019), of which about 75% are transformed into wine (Ilyas et al., 2021; Zhu et al., 2015). Currently, China is one of the largest grape growers and consumers worldwide. Along with the development of the wine industry, a tremendous amount of winemaking pomace is generated every year, accounting for approximately 20% of the original grape weight (Bordiga et al., 2019). In addition to pulp rest and stem residues, seeds and skins are the major components of wine pomace. The traditional applications of wine pomace have been in the production of different types of wine alcohol (Silva et al., 2000), and in use as animal feed or fertilizer (Arvanitoyannis et al., 2006), which can result in resource waste and environmental pollution (García-Lomillo et al., 2017). The sustainable application of wine pomace, especially skins and seeds, generated by the wine industry has attracted much attention (García-Lomillo et al., 2017; Ilyas et al., 2021).

Phenolic compounds are important secondary metabolites in grape berries and are especially rich in skins and seeds. The phenolic compounds in grapes can be divided into two categories according to their chemical structures. One is named flavonoids with a C6-C3-C6 structure, including anthocyanins, flavonols and flavan-3-ols. The other is nonflavonoid compounds containing phenolic acids and stilbenes. These phenolic compounds have not only important influences on the color, astringency and flavor of wine, but also strong bioactivities (Farias et al., 2021; Pantelić et al., 2016). In fact, only 30–40% of natural phenolic compounds in grape berries can be extracted into wines through maceration, alcoholic fermentation and pressing, and quite a number of them remain in the pomace. Based on antioxidant and anti-inflammatory bioactivities, phenolic compounds extracted from wine pomace can prevent cancer, endothelial dysfunction, hypertension, hyperglycemia, diabetes and obesity (Gerardi et al., 2021). It was also proved that the phenolics of wine pomace had antifungal and antimicrobial functions (Ky et al., 2014). Thus, these products made from wine pomace phenolics have mainly been applied to the food, pharmaceutical and cosmetics industries (Bordiga et al., 2019). For example, the anthocyanins extracted from grape pomace can be used as functional food additives and colorants (Cascaes Teles et al., 2020; Li et al., 2013; Milinčić et al., 2021).

There are many studies on phenolic compounds and their antioxidant capacities in fresh berries and the corresponding winemaking pomace of Vitis vinifera (Guaita and Bosso, 2019; Ky et al., 2014), but few reports on grape cultivars with the pedigree of Vitis species originating from East Asia. This work involved three red grapes with different pedigrees including ‘NW196’, ‘Kyoho’ and ‘Cabernet Sauvignon’. ‘NW196’ (V. quinquangularis Rehd × V. vinifera L), originated from Southwest China, is superior to V. quinquangularis grapes, in terms of cultivation characteristics and winemaking qualities. ‘Kyoho’ (V. labrusca × V. vinifera) introduced from Japan is a prevalent table grape in China, and it is also used to make juice and wine in some regions not suitable for open field cultivation of V. vinifera grapes. ‘Cabernet Sauvignon’ planted throughout the world is an excellent grape cultivar for the production of wines, and used as a V. vinifera reference. This study was mainly aimed at analyzing and comparing the variations in phenolic features and anthocyanin profiles between the winemaking pomaces and fresh grape berries. The differentiation of these characteristics was also investigated among the three grape cultivars. The results would provide essential data for the development and utilization of grape pomace, especially non-V. vinifera, as food additives and health products.

Materials and methods

Grape samples

Three grape cultivars used in this study, including ‘NW196’, ‘Kyoho’ and ‘Cabernet Sauvignon’, were cultivated in the experimental vineyard of Guangxi Academy of Agricultural Science (Nanning, China). The grapes were harvested at their optimal maturity. Three 50-berry batches were randomly selected from the top, middle and bottom portions of 30 clusters, which were collected from 30 grapevines for the fresh samples of each cultivar. The pomace of each cultivar was obtained from winemaking under laboratory conditions according to Zhu et al. (2012a). Maceration and alcoholic fermentation were performed simultaneously for 8 days at around 26 °C. Skins and seeds are separated manually from fresh berries and pomace, then freeze-dried (Alpha 1–4 LSCbasic, Martin Christ Co., Osterode, Germany) and ground (BLF-YB2000, Bailifu Co., Shengzhen, China). The grounded seeds were defatted twice with petroleum ether for 3 h. The final samples were stored at − 20 °C for subsequent analysis.

Chemicals and standards

Folin and Ciocalteu’s phenol reagent (2 N), 2,2-diphenyl-1-picrylhy-drazyl (DPPH, ≥ 97%), and 6-Hydroxy-2,5,7,8-tetramethylchro-man-2-carboxylic acid (Trolox, ≥ 98%) were obtained from Aladdin (Shanghai, China). Standards used in colorimetric methods, gallic acid (99%), catechin (≥ 95%) and rutin (98%), were obtained from Macklin (Shanghai, China). The anthocyanin standards for HPLC, malvidin-3-O-glucoside (≥ 90%) and malvidin-3, 5-O-diglucosides (≥ 90%), were purchased from Sigma-Aldrich (St. Louis, MO, USA). Formic acid and acetonitrile were chromatographic grade reagents and obtained from Fisher Scientific Co. (Fairlawn, NJ, USA). All other chemicals were analytical grade and purchased from Chinese Reagent Network (http://www.labgogo.com/).

Extraction of phenolic compounds

The extraction of phenolic compounds was carried out according to the method of Zhu et al. (2012b). Briefly, 500 mg of skin and seed powder were extracted with 20 mL of methanol/water/acetic acid (70:29:1, v/v/v) and methanol with 0.1% acetic acid, respectively. The conical flask used in extraction was placed in a shaker (SHZ-88A, Taicang Experiment Equipment Factory, Jiangsu, China) at 300 rpm for 2 h at 25 °C. Then, the liquid supernatant of each sample was separated after centrifugation (Beckman Coulter Ltd, Palo Alto, CA, USA). The extraction process was repeated three times. After removing a volume of 2 mL used in colorimetric determination, the rest of the skin extract for each replicate sample was rotatory evaporated (RE-52A, Yarong Biochemistry Instrument Factory, Shanghai, China) at 30 °C, and then re-dissolved in 10% methanol solution containing 1% acetic acid to a unified volume of 5 mL for anthocyanin analysis.

Determination of total phenolic contents with colorimetric methods

Total phenolics (TP) were determined according to Singleton and Rossi (1965) using a UNICO UV-2800 spectrometer (UNICO, New York, NY, USA). For each sample, 1 mL of extracts diluted by 20 times with the extracting agent mixed in sequence with 1 mL of Ciocalteu reagent and 4 mL of Na2CO3 solution (20%). After shaking, the reaction system was incubated at 40 °C in the dark for 30 min. The absorbance at 760 nm was converted into TP expressed as gallic acid equivalents (mg GAE/g DW).

Total flavonoids (TFO) were measured by a colorimetric method Dewanto et al. (2002) with slight modification. Briefly, 1 mL of diluted extract was mixed with 300 μL of NaNO2 solution (5%), and 5 min later with 600 μL of AlCl3·6H2O solution (10%). After 6 min, 2 mL of NaOH solution (1 mol/L) was added, and 6.1 mL of distilled water was subsequently transferred into the reaction system to make the volume up to 10 mL. After 15 min, the absorbance was recorded at 510 nm. The results were calculated and expressed as rutin equivalents (mg RAE/g DW).

Total flavan-3-ols (TFA) were determined using the vanillin method Sun et al. (1998). Briefly, 1 mL diluted extract was mixed in sequence with 2.5 mL of 1% vanillin/methanol solution and 2.5 mL of 25% H2SO4/methanol solution. The reaction system was incubated in the dark at 30 °C for 15 min. The TFA was expressed as catechin equivalents (mg CAE/g DW) calculated with the absorbance at 500 nm.

Anthocyanin analysis with HPLC–MS/MS

Anthocyanin analysis was performed with an Agilent 1100 series LC-MSD trap (Agilent Technologies, Ltd., Santa Clara, CA, USA) according to Jin et al. (2009). The samples were filtrated through a 0.45 µm inorganic membrane and directly injected (30 µL) into a reversed-phase Kromasil-C18 column (250 × 4 mm, 6.5 µm) at 50 °C. The mobile phase included 6% (v/v) acetonitrile containing 2% (v/v) formic acid (solvent A) and 54% (v/v) acetonitrile containing 2% (v/v) formic acid (solvent B). The gradient profile with 1.0 mL/min of flow rate was 10% B for 1 min, from 10 to 25% B for 16 min, isocratic 25% B for 3 min, 25% to 40% B for 10 min, 40% to 70% B for 5 min and 70% to 100% B for 4 min. The detection wavelength of the UV detector was 525 nm. Electrospray ionization (ESI) was used, positive ion model, 35 psi nebulizer pressure, 10 mL/min dry gas flow rate, 350 °C dry gas temperature and 100–1000 m/z scan range. Anthocyanin monoglucoside and diglucosids were quantified using malvidin-3-O-glucoside and malvidin-3, 5-O-diglucoside as standards, respectively, and expressed as μg MGE/g DW.

Free radical-scavenging activity on DPPH

The DPPH assay referred to the method of Brand-Williams et al. (1995). Briefly, 0.5 mL of diluted extract was mixed with 3.9 mL of DPPH methanolic solution of (0.0025 g/100 mL). The reaction system was incubated in the dark for 60 min. The absorbance at 515 nm was recorded and the results were converted into Trolox equivalents (µmol TE/g DW.).

Statistical analysis

The results with three duplicates were expressed as mean ± standard deviation (S.D.). Statistical methods included one-way ANOVA and correlations analysis with SPSS 20.0, as well as principal components analysis (PCA) with Origin Pro 2018.

Results and discussion

Total contents of phenolic compounds

The contents of phenolic compounds extracted from winemaking pomace were affected by many factors, such as grape species/cultivars, vineyard terroir, cultural practice and vinification technique (Ky et al., 2014). The total contents of phenolic compounds in pomace skins and seeds were significantly reduced by vinification, including destemming, crushing, maceration and pressing (Guaita and Bosso, 2019). In this study, we collected the fresh berries and corresponding winemaking pomaces with the same vinification of three red grape cultivars, including ‘NW196’ (V. quinquangularis × V. vinifera), ‘Kyoho’ (V. labrusca × V. vinifera) and ‘Cabernet Sauvignon’ (V. vinifera). The total contents of phenolic compounds in the winemaking pomace decreased significantly compared with those in the fresh berries (p < 0.05, Fig. 1A–C). Vinification has a more substantial influence on the skins than on the seeds (Ky et al., 2014; Nieuwoudt and Buica, 2017). After 8-day fermentative maceration, the TP, TFO and TFA in the skins of the three grape cultivars decreased by 80.36%, 80.41% and 70.47% on average, respectively. To avoid the dissolution of inferior tannins and oils, grape seeds should not be broken in the process of crushing and pressing for lignified shells to provide protection for seed inclusions. Therefore, the pomace seeds still retained high levels of total phenolics, which were 75.13%, 71.86% and 65% of the TP, TFO and TFA in the fresh seeds, respectively. In general, the extractable phenolic contents in pomace skins retained only 20% of those in the fresh skins, and the respective figure for the seeds was 71%.

Fig. 1.

Fig. 1

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Total phenolics (TP, A), total flavonoids (TFO, B), total flavan-3-ols (TFA, C) and DPPH radical scavenging capacities (DPPH, D) of phenolic compounds extracted from fresh berries and pomaces of three grape cultivars. The different capital letters above the columns represent significant differences (p < 0.05) existed among samples of the same grape cultivar. The different small letters above the columns represent significant differences (p < 0.05) existed among grape cultivars with the same sample

However, differences in the degrees of decrease existed in different phenolic types, which also existed between the skins and the seeds. The TP and TFO fell further than the TFA in the pomace skins (p < 0.05). Perhaps due to the conditions of fermentative maceration and the integrity of grape skins, macromolecular compounds (flavan-3-ol polymers) were not sufficiently extracted into the wine. This can be supported by a research result where the mean degree of tannin polymerization in pomace increased by vinification (Ky et al., 2014). In contrast, there was no significant difference in the retention rates among the total contents in the seeds.

Among the three grape cultivars, the differences in total phenolics in the winemaking pomaces were generally similar with those in the fresh berries (Fig. 1A–C). The skins of ‘Kyoho’ possessed significantly higher TP, TFO and TFA than the skins of ‘Cabernet Sauvignon’ and ‘NW196’ (p < 0.05). Total contents of phenolics in the ‘Cabernet Sauvignon’ seeds was 2–3 times that in the ‘Kyoho’ and ‘NW196’ seeds (p < 0.05). So ‘Cabernet Sauvignon’ had the highest total content of phenolic compounds in the whole berry and pomace (p < 0.05).

The total contents of phenolics in the fresh seeds were significantly higher than those in the fresh skins (p < 0.05, Fig. 1), which was consistent with the previous reports (Xia et al., 2014; Zhu et al., 2012a). Especially for ‘Cabernet Sauvignon’, the total contents in the fresh seeds were 3-to-6-fold higher than those in the fresh skins. The difference in total phenolic contents between skins and seeds was further enlarged in the pomace (Fig. 1A–C). This was because the phenolic compounds in skins were more easily macerated into the wine during fermentation. As a result, the pomace seeds after winemaking were the superior source of phenolic compounds for health care products and food additives.

Anthocyanin profiles

Anthocyanins were analyzed using with HPLC‒ESI‒MS/MS. In this study, a total of 35 anthocyanin compounds were detected in all of the skins samples, including 26 monomeric anthocyanins from fresh berries and 9 derived pigments from fermentation (Table 1; Fig. 2).

Table 1.

The retention time (tR), ion mass (MS/MS2) and content (mg MGE/kg DW) of each anthocyanin compound detected in the fresh and pomace skins of the three grape cultivars

Peaks Compound tR/min MS/MS2 NW196 R (%) Kyoho R (%) Cabernet Sauvignon R (%)
Fresh Pomace Fresh Pomace Fresh Pomace
1 Cy-3,5-diglc 3.43 611/449, 287 355.91 ± 3.95 34.96 ± 0.41  − 90.18 ND ND NC ND ND NC
2 Dp-3-glc 3.67 465/303 337.20 ± 3.97 15.20 ± 0.17  − 94.12 327.52 ± 3.64 ND  − 100.00 201.04 ± 2.23 17.02 ± 0.19  − 91.53
3 Pn-3,5-diglc 4.40 625/463 1121.67 ± 13.20 ND  − 100.00 286.37 ± 3.18 29.95 ± 0.20  − 89.54 ND ND NC
4 Mv-3,5-diglc 4.56 655/493 2964.80 ± 24.71 537.10 ± 5.97  − 81.88 512.55 ± 6.03 30.54 ± 0.23  − 94.04 ND ND NC
5 Cy-3-glc 4.91 449/287 ND ND NC 101.81 ± 1.20 8.81 ± 0.10  − 91.35 30.02 ± 0.35 ND  − 100.00
6 Pt-3-glc 5.66 479/317 334.80 ± 3.72 10.71 ± 0.13  − 96.80 263.09 ± 2.19 ND  − 100.00 177.48 ± 1.48 22.32 ± 0.26  − 87.42
7 Pn-3-glc 7.74 463/301 469.58 ± 3.13 11.53 ± 0.10  − 97.54 330.07 ± 3.67 11.12 ± 0.13  − 96.63 260.77 ± 2.90 17.14 ± 0.14  − 93.43
8 Mv-3-glc 8.37 493/331 1078.34 ± 8.30 48.30 ± 0.55  − 95.52 1213.41 ± 13.79 51.29 ± 0.43  − 95.73 1964.32 ± 22.32 412.11 ± 4.58  − 79.02
9 Mv-3-ac-5-diglc 9.19 697/535, 493, 331 36.46 ± 0.41 ND  − 100.00 147.33 ± 1.23 ND  − 100.00 ND ND NC
10 Dp-ac-3-glc 9.44 493/331 ND ND NC ND ND NC 98.33 ± 0.82 ND  − 100.00
11 Mv-3-glc-pyruvic acid(Vitisin A) 10.41 561/399 ND 7.74 ± 0.11  + 100.00 ND ND NC ND 35.96 ± 0.40  − 100.00
12 Dp-3-cm-5-diglc 11.38 774/611, 465, 303 15.96 ± 0.18 ND  − 100.00 68.31 ± 0.76 ND  − 100.00 ND ND NC
13 Mv-3-glc-acetaldehyde(Vitisin B) 11.58 517/355 ND ND NC ND ND NC ND 10.23 ± 0.07  + 100.00
14 Cy-ac-3-glc 12.08 492/311 ND ND NC ND ND NC 34.75 ± 0.39 ND  − 100.00
15 Mv-3-ac-pyruvic acid(ac-vitisin A) 12.74 603/399 ND 7.84 ± 0.11  + 100.00 ND ND NC ND 26.89 ± 0.21  + 100.00
16 Pt-ac-3-glc 13.09 521/317 ND ND NC 41.64 ± 0.35 ND  − 100.00 65.38 ± 0.44 10.75 ± 0.12  − 83.56
17 Cy-3-cm-5-diglc 13.80 758/595, 449, 287 ND ND NC 28.78 ± 0.33 ND  − 100.00 ND ND NC
18 Mv-3-cf-5-diglc 14.27 818/655, 493, 331 54.08 ± 0.90 ND  − 100.00 109.59 ± 0.84 26.85 ± 0.18  − 75.50 ND ND NC
19 Mv-3-ac- acetaldehyde (ac-vistins B) 14.50 559/355 ND ND NC ND ND NC ND 11.15 ± 0.12  + 100.00
20 Pn-3-cm-5-diglc 15.23 771/609, 463 ND ND NC 82.06 ± 0.91 6.00 ± 0.09  − 92.69 ND ND NC
21 Pn-ac-3-glc 15.70 505/301 ND ND NC ND ND NC 148.98 ± 1.15 13.48 ± 0.11  − 90.95
22 Dp-cm-3-glc 15.93 611/303 24.19 ± 0.28 ND  − 100.00 174.73 ± 1.16 ND  − 100.00 ND ND NC
23 Mv-ac-3-glc 16.78 535/331 27.63 ± 0.31 ND 100.00 185.17 ± 2.06 8.40 ± 0.09  − 95.46 1113.42 ± 15.91 142.45 ± 1.58  − 87.21
24 Mv-3-cm-5-diglc 17.00 801/639, 493, 331 111.99 ± 0.75 19.30 ± 0.13 82.77 1251.50 ± 8.34 35.52 ± 0.39  − 97.24 ND ND NC
25 Pn-cf-3-glc 18.20 625/301 6.95 ± 0.08 ND NC ND ND NC ND ND NC
26 Mv-3-cm-pyruvic acid (cm-vistins A) 18.38 707/399 ND ND NC ND ND NC ND 8.86 ± 0.10  + 100.00
27 Cy-cm-3-glc 18.62 595/287 17.90 ± 0.15 ND 100.00 25.19 ± 0.19 ND  − 100.00 ND ND NC
28 Mv-cf-3-glc 18.73 655/331 ND ND NC 15.35 ± 0.26 8.13 ± 0.09  − 47.04 34.58 ± 0.27 19.34 ± 0.28  − 44.07
29 Pt-cm-3-glc 19.40 625/317 22.12 ± 0.25 ND 100.00 133.10 ± 1.90 ND  − 100.00 7.78 ± 0.09 ND  − 100.00
30 Mv-3-cm- acetaldehyde (cm-visitin B) 20.86 633/355 ND ND NC ND 6.22 ± 0.05  + 100.00 ND ND NC
31 Pn-cm-3-glc 22.34 609/301 18.90 ± 0.21 ND 100.00 108.39 ± 1.20 7.81 ± 0.09  − 92.79 16.38 ± 0.11 7.53 ± 0.05  − 54.03
32 Mv-cm-3-glc 22.84 639/331 71.93 ± 0.60 ND 100.00 777.02 ± 5.18 15.42 ± 0.13  − 98.02 89.35 ± 1.49 27.80 ± 0.21  − 68.89
33 Mv-3-glc-4-vinylphenol (pigment A) 26.16 609/447 ND ND NC ND ND NC ND 12.40 ± 0.15  + 100.00
34 Mv-3-glc-vinylguaiacol 27.39 639/447, 331 ND ND NC ND ND NC ND 5.94 ± 0.10  + 100.00
35 Mv-3-ac-4- vinylphenol (ac-pigment A) 28.61 651/447 ND ND NC ND ND NC ND 8.10 ± 0.07  + 100.00
TAC 7079.81 ± 65.14a 711.19 ± 7.75e  − 89.96 6182.97 ± 58.41b 259.00 ± 2.31f  − 95.81 4256.28 ± 50.08c 823.90 ± 8.90d  − 80.64
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R represents the changed proportions of anthocyanin contents in pomace skins compared with fresh skins. TAC represents total anthocyanin contents. ND means not detected. NC means the changed proportion can not be calculated. The different small letters in the last line represent significant differences (p < 0.05) existed among the TAC of different samples. Abbreviations of anthocyanin compounds: Dp delphinidin, Cy cyaniding, Pt petunidin, Pn peonidn, Mv malvidin, glc monoglucoside, diglc diglucosides, ac 6-acetyl, cm 6-coumaroyl, cf 6-caffeoyl

Fig. 2.

Fig. 2

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HPLC chromatograms at 520 nm of anthocyanins detected in the skins, including fresh ‘NW196’ (A), pomace ‘NW196’ (B), fresh ‘Kyoho’ (C), pomace ‘Kyoho’ (D), fresh ‘Cabernet Sauvignon’ (E) and pomace ‘Cabernet Sauvignon’ (F). Each elution peak with the numbers represents one anthocyanin compounds identified by the MS/MS2 data, as shown in Table 1

Among the fresh skins of the three grapes, the total anthocyanin content (TAC) in ‘NW196’ was the highest, and the lowest TAC was in ‘Cabernet Sauvignon’ (p < 0.05). The acidic matrix of alcoholic fermentation is more beneficial for the anthocyanins to be solubilized and released, such that more anthocyanins are extracted into the wine (Ky et al., 2014; Lorrain et al., 2011). In this study, up to 88% of the initial TAC was extracted during fermentative meceration, and it was obviously higher than the other total phenolic contents (p < 0.05). However, the rates of decrease varied in the order of ‘Kyoho’ (95.81%) > ‘NW196’ (89.95%) > ‘Cabernet Sauvignon’ (80.64%). As a result, the pomace skins of ‘Cabernet Sauvignon’ had the highest TAC, followed by ‘NW196’, while ‘Kyoho’ pomace skins retained the lowest TAC (p < 0.05, Table 1). In a previous report, the decreased rate of TAC in ‘Cabernet Sauvignon’ after fermentation was 95.42% (Li et al., 2013). The difference may be related to the process of fermentative maceration and pressing (Guaita and Bosso, 2019) as well as the extraction method (Nogales-Bueno et al., 2020).

The glucosides of five anthocyanidins, cyaniding (Cy), delphinidin (Dp), petunidin (Pt), peonidin (Pn) and malvidin (Mv), were detected in all fresh skins. Mv-derivatives were the most abundant type not only in fresh samples but also in pomace samples of the three grape cultivars, which was consistent with the previous study (Liang et al., 2011), followed by Pn-derivatives except for ‘NW196’ pomace skin (Table 2). Mv-3-glucoside, Mv-3,5-diglucoside and their acetyl/coumaryl derivatives were the main anthocyanin compounds with high contents (Table 1). After fermentative maceration, the Mv-derivative percentages of TAC increased significantly in all pomace skins (p < 0.05). The proportions of Pn-derivatives decreased obviously in the pomace skins of ‘NW196’ and ‘Cabernet Sauvignon’ (p < 0.05), but increased in the ‘Kyoho’ pomace skins. For other minor types, Cy- and Pt-derivatives were not found in the ‘Kyoho’ pomace skins, and Dp-derivatives were not found in the ‘Cabernet Sauvignon’ pomace skins. Only ‘NW196’ pomace skins retained all of the anthocyanidin types (Tables 1, 2). Two factors may have resulted in the differences in anthocyanidin compositions between fresh and pomace skins. First, Mv- and Pn-derivatives had more stable chemical structures (Di Lorenzo et al., 2019). Second, the contents of Cy-, Dp- and Pt-derivatives were too low to be detected in the pomace skins after fermentation.

Table 2.

The anthocyanin compositions (%) in the fresh and pomace skins of three grape cultivars

NW196 Kyoho Cabernet Sauvignon
Fresh Pomace Fresh Pomace Fresh Pomace
Cy 5.29 ± 0.01a 5.10 ± 0.00b 2.50 ± 0.00d 3.51 ± 0.01 c 1.53 ± 0.00e ND
Dp 5.34 ± 0.01c 2.22 ± 0.00d 9.23 ± 0.00a ND 7.06 ± 0.00b 2.10 ± 0.00d
Pt 5.05 ± 0.01c 1.56 ± 0.00e 7.08 ± 0.01a ND 5.91 ± 0.08b 4.09 ± 0.00d
Pn 22.87 ± 0.02a 1.68 ± 0.00f 13.05 ± 0.02c 22.34 ± 0.01b 10.04 ± 0.13d 4.71 ± 0.01e
Mv 61.56 ± 0.06f 89.43 ± 0.00a 68.12 ± 0.04e 74.16 ± 0.01 75.46 ± 0.20c 89.10 ± 0.01b
3', 4'- 28.16 ± 0.03a 6.79 ± 0.00e 15.57 ± 0.03c 25.84 ± 0.01b 11.57 ± 0.13d 4.71 ± 0.01f
3', 4',5'- 71.94 ± 0.03f 93.21 ± 0.00b 84.43 ± 0.03d 74.16 ± 0.01e 88.43 ± 0.13c 95.29 ± 0.01a
Nonmet 10.62 ± 0.02b 7.32 ± 0.00d 11.75 ± 0.01a 3.51 ± 0.01e 8.58 ± 0.01c 2.10 ± 0.00f
Met 89.47 ± 0.02e 92.68 ± 0.00c 88.25 ± 0.01f 96.49 ± 0.01b 91.42 ± 0.01d 97.90 ± 0.00a
Monoglc 34.08 ± 0.02d 13.66 ± 0.00e 59.78 ± 0.02b 47.55 ± 0.02c 100.00 ± 0.00a 100.00 ± 0.00a
Diglc 65.92 ± 0.02b 86.34 ± 0.00a 40.22 ± 0.02d 52.45 ± 0.02c ND ND
Ac 0.91 ± 0.00e ND 6.05 ± 0.00c 3.42 ± 0.01d 34.43 ± 0.11a 26.29 ± 0.01b
Cm 4.00 ± 0.00d 2.82 ± 0.01e 42.85 ± 0.07a 28.81 ± 0.04b 2.68 ± 0.01f 5.46 ± 0.01c
Cf 0.86 ± 0.01d ND 2.02 ± 0.00c 14.24 ± 0.02a 0.82 ± 0.00e 2.39 ± 0.01b
Nonac 94.23 ± 0.01b 97.18 ± 0.01a 49.08 ± 0.07f 53.53 ± 0.04e 62.08 ± 0.13d 65.86 ± 0.02c
MA 100.00 ± 0.00a 98.86 ± 0.00b 100.00 ± 0.00a 97.47 ± 0.00c 100.00 ± 0.00a 85.23 ± 0.01d
DP ND 1.14 ± 0.00c ND 2.53 ± 0.00b ND 14.77 ± 0.01a
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Anthocyanidin composition: Dp delphinidin, Cy cyaniding, Pt petunidin, Pn peonidn, Mv malvidin. Hydroxylation composition: 3', 4'- dihydroxylated anthocyanins including Cy- and Pn-derivatives, 3', 4',5'- trihydroxylated anthocyanins including Dp-, Pt- and Mv-derivatives. Methylation composition: Nonmet nonmethylated anthocyanins including Dp- and Cy –derivatives, Met methylated anthocyanins including Pt-, Pn- and Mv-derivatives. Glucosylation composition: Monoglc 3-glucoside, Diglc 3-glucoside-5-glucoside. Acylation composition: Ac 6-acetyl, Cm 6-coumaroyl, Cf 6-caffeoyl, Nonac non-acylated anthocyanins. MA monomeric anthocyanins from fresh berries, DP derived pigments from fermentation. The different small letters in the same line represent significant differences (p < 0.05) existed among the samples with the same anthocyanin type

These five types of anthocyanidin derivatives can also be classified based on their molecular structures. They are divided into 3′4ʹ-substituents (Cy- and Pn-derivatives) and 3′4′5′-substituents (Dp-, Pt- and Mv-derivatives) according to the degree of hydroxylation in the B rings, which influences the hue and stability of anthocyanin color (Woodward et al., 2009). The methylated substituents (Pt-, Pn- and Mv-derivatives) refers to the anthocyanins whose phenolic hydroxyl groups in B rings were replaced by the methoxy groups. In this study, the 3′4ʹ5ʹ- and methylated substituents were predominant in all skin samples. Their proportions in the pomace skins were significantly higher than those in the fresh skins (p < 0.05) belonging to the same grape cultivar. However, there was an exception: the 3′4ʹ5ʹ-substituents proportion in ‘Kyoho’ pomace skins was obviously reduced after fermentative maceration (p < 0.05, Table 2). These variations in hydroxylation and methylation compositions were mainly caused by the differences in Mv- and Pn-derivatives between fresh and pomace skins.

According to the number of glucosyl groups, the anthocyanins in grapes comprise monoglucosides and diglucosides ones. There were no diglucosides anthocyanins detected in ‘Cabernet Sauvignon’, and they can barely be synthesized by V. vinfera grapes (Jánváry et al., 2009). For the two interspecific hybrids containing V. vinifera pedigree, monoglucoside anthocyanins accounted for more than half of TAC (59.78%) in fresh ‘Kyoho’, while diglucosides anthocyanins were the main type (65.92%) in fresh ‘NW196’. The proportions of diglucosides anthocyanins increased by 12.23% and 20.42% in ‘Kyoho’ and ‘NW196’, respectively, after fermentative maceration (Table 2). The more stable molecular structures of diglucosides anthocyanins might allow them to retain more contents in the pomace compared with monoglucoside anthocyanins.

Acylation plays an important role in the enhancement of color intensity and the shift in blue color for anthocyanins (Zhao et al., 2017). In grapes, acetyl and p-coumaryl derivatives were the main acylated anthocyanins. There were obvious differences in the degrees of acylation among the fresh skins of the three grape cultivars (p < 0.05). ‘Kyoho’ had the highest proportion of acylated anthocyanins (50.92%), followed by ‘Cabernet Sauvignon’ (37.92%), while ‘NW196’ had the lowst (5.77%). Among the acylated anthocyanins, acetyl derivatives were leading in ‘Cabernet Sauvignon’, and p-coumaryl derivatives were predominant in ‘Kyoho’ and ‘NW196’. In addition, a small amount of caffeoyl derivatives (1.23% of TAC on average) also exsited in all of the fresh samples (Table 2).

García-Beneytez et al. (2003) believed that acetylated anthocyanins were more easily hydrolyzed under acidic conditions so that their contents in pomace skins showed a more significant decline after fermentation. Some previous studies also found that the wine-making process would lead to a relative increase in p-coumaryl derivatives and a relative decrease in acetyl derivatives (Fournand et al., 2006; Milinčić et al., 2021). In this study, the proportions of acylated anthocyanins generally decreased for the three grape cultivars (3.73% on average) after fermentative maceration, which was consistent with the result of Li et al. (2013). However, the variations in acylated types between the fresh and pomace skins were different among the grape cultivars. The proportion of acetyl derivatives decreased significantly (p < 0.05), and p-coumaryl and caffeoyl derivatives increased after fermentation in ‘Cabernet Sauvignon’. In ‘Kyoho’, both acetyl and p-coumaryl proportions were reduced obviously by fermentation (p < 0.05), while the caffeoyl proportion rose significantly (p < 0.05). Due to the low content of acylated anthocyanins in fresh ‘NW196’, the acetyl and caffeoyl derivatives were not ultimately detected, and the proportion of p-coumaryl was reduced and very low in the pomace skins (Table 2). Based on the current results, fermentative maceration could significantly reduced acetylation degree of anthocyanins (p < 0.05), but the composition variations of acylated anthocyanins were related to the grape cultivars and the initial contents in fresh skins.

The monomeric anthocyanins from fresh grape skins can form derived pigments by cyclo-addition of other molecules such as pyruvic acid, acetaldehyde, phenolic acid and flavan-3-ols during alcoholic fermentation (Villiers et al., 2011). Pyruvic asid and acetaldehyde are two common metabolites produced by yeasts during wine fermentation (De Preitas and Mateus, 2011). The derived pigments have important and positive effects on the color stability of wines (He et al., 2012). A small amount of them can be left in the pomace after fermentation and pressing. In this study, all of the derived pigments detected in the pomace skins were derivatives of Mv-3-glucoside (Table 1), the most abundant anthocyanidin type. The content (118.68 mg MGE/kg) and proportion (14.77%) of derived pigments in ‘Cabernet Sauvignon’ were much higher than those in ‘Kyoho’ (6.22 mg MGE/kg, 2.53%) and ‘NW196’ (7.84 mg MGE/kg, 1.14%) (p < 0.05, Table 2). This is mainly because monoglucoside anthocyanins are more liable to cyclo-addition than diglucosides anthocyanins (Zhu et al., 2012b). The fresh skins of ‘Cabernet Sauvignon’ (4256.28 mg MGE/kg) had a significantly higher content of monoglucoside anthocyanins (p < 0.05) than ‘Kyoho’ (3696.48 mg MGE/kg) and ‘NW196’ (2409.65 mg MGE/kg).

At present, a comprehensive and systematic study on the effect of fermentative maceration on the anthocyanin composition of grape pomace is unavailable. In addition to the factors influencing phenolic contents, the structural stability of anthocyanin molecules is critical. In this study, the proportions of Mv-derivatives, methylated, diglucosides and nonacylated anthocyanins were significantly increased in skins after fermentative maceration (p < 0.05). These anthocyanin types are more stable than other corresponding types. It was likely that the pomace after fermentative maceration preferred to keep the anthocyanins with more stable structures. Moreover, some of them have higher bioactivity. For example, nonacylated anthocyanins have a higher inhibition capacity of tumor cell proliferation than acylated anthocyanins (Craig et al., 2007). Mv-derivatives usually have more potent antioxidant activity than the other anthocyanindin derivatives (Di Lorenzo et al., 2019). Thus pomace skins after fermentative maceration, which can retain certain contents of anthocyanins with higher bioactivity, are an economical source of the natural pigment to utilize in the food industry.

Antioxidant capacity

The antioxidant capacities of all samples were evaluated by free a radical scavenging assay on DPPH, which was remarkably correlated with other antioxidant measurements in vitro (Milinčić et al., 2021). The method is often used to preliminarily estimate the antioxidant abilities of grape berries and corresponding winemaking pomace (Guaita and Bosso, 2019; Nogales-Bueno et al., 2020). In general, the variation in antioxidant capacities among the pomaces of different grape cultivars was similar to that of the fresh berries. The DPPH value of the phenolic extract from ‘Kyoho’ pomace skins was significantly higher than those in ‘Cabernet Sauvignon’ and ‘NW196’ (p < 0.05). The pomace skins of the three grape cultivars only kept 15.61% of DPPH values in fresh skins on average. In contrast, the DPPH values of phenolic extracts from pomace seeds decreased by 21.31% on average after fermentative maceration. The pomace seeds extract of ‘Cabernet Sauvignon’ showed obviously stronger antioxidant abilities than ‘Kyoho’ and ‘NW196’ (p < 0.05, Fig. 1D).

Through Pearson’s correlation, the relationship between phenolic contents and bioactivities is analyzed, and the phenolic types/compounds that played a major role can be preliminarily screened (Mollica et al., 2021). In this study, the Pearson’s correlations among different indicators were also estimated (Table 3). In general, the total contents of phenolics except for TAC had positive and high correlation coefficients with the DPPH free radical-scavenging capacity. The correlations between DPPH and the total contents of phenolic compounds were more obvious in seeds than in skins. This might be related to the phenolic composition. Flavan-3-ols are the main phenolic type in grape seed (Lu et al., 2021), while a rich variety of phenolic compounds such as phenolic acids, flavonols, anthocyanins and flavan-3-ols, are found in grape skin (Zhu et al., 2012b) Among the total contents of phenolic compounds, TP, TFO and TFA were significantly correlated in all samples (p < 0.05), and this was also demonstrated with fresh berry (Xu et al., 2010), wine pomace (Deng et al., 2011) and wine (Mollica et al., 2021). However, the correlation coefficients of TAC with TP, TFO and TFA were low or negative. Although there was no significance, the correlation coefficient between TAC and DPPH was also high in the fresh skins (p > 0.05), but was negative in the pomace skins. In our published work on V. amurensis fresh skins, TA a had significant and positive correlation with TP, TFO and antioxidant activities; in contrast, the correlation coefficients of TFA were low and negative. It was indicated that anthocyanins rather than flavan-3-ols were the primary phenolic type in the fresh skins of V. amurensis (Zhu et al., 2021). In this study, the low or negative correlations of TAC might be because anthocyanins in all three cultivars were not as important as those in V. amurensis grapes and TAC was significantly reduced in pomace. However, significant and positive correlations were found between some anthocyanin types and DPPH in the fresh skins, including Dp- (p < 0.01), Pt- (p < 0.01) and Mv-derivatives (p < 0.05) as well as 3',4',5'- (p < 0.05), nonmethylated (p < 0.05), p-coumaryl (p < 0.05) and caffeoyl (p < 0.01) anthocyanins. However, only p-coumaryl anthocyanins had an obvious correlation with DPPH in the pomace skins (p < 0.05). The difference in the correlations of anthocyanins might result from the significant decline in anthocyanin contents and variation in anthocyanin compositions.

Table 3.

Correlation coefficients among phenolic contents and antioxidant activities

TP TFO TFA TAC DPPH
Fresh skins
 TFO 0.994**
 TFA 0.954** 0.964**
 TAC 0.113 0.104  − 0.111
 DPPH 0.745 0.736 0.569 0.737
 Dp 0.951** 0.948** 0.858* 0.415 0.917**
 Pt 0.768 0.762 0.605 0.724 0.998**
 Mv 0.317 0.309 0.097 0.978** 0.865*
 3',4',5'- 0.281 0.272 0.059 0.985** 0.845*
 Nonmet 0.340 0.332 0.121 0.973** 0.877*
 Cm 0.988** 0.987** 0.929** 0.264 0.842*
 Cf 0.928** 0.925** 0.821* 0.476 0.943**
Pomace skins
 TFO 0.995**
 TFA 0.999** 0.990**
 TAC  − 0.961**  − 0.984**  − 0.949**
 DPPH 0.962** 0.985** 0.951**  − 0.952**
 Cm 0.973** 0.945** 0.981**  − 0.872* 0.874*
Fresh seeds
 TFO 0.999**
 TFA 0.914* 0.932**
 DPPH 0.996** 0.996** 0.921**
Pomace seeds
 TFO 1.000**
 TFA 0.921** 0.924**
 DPPH 0.977** 0.979** 0.976**
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* and ** represent significance at P < 0.05 and P < 0.01, respectively

TP total phenolics, TFO total flavonoids, TFA total flavan-3-ols, DPPH DPPH radical scavenging capacities, Dp delphinidin, Pt petunidin, Mv malvidin, 3',4',5'- trihydroxylated anthocyanins including Dp-, Pt- and Mv-derivatives, Nonmet nonmethylated anthocyanins including Dp- and Cy –derivatives, Cm 6-coumaroyl, Cf 6-caffeoyl

Principle component analysis

To synthetically describe the phenolic features and anthocyanin profiles of the fresh and pomace samples, principle component analyses (PCA) were performed for grape skins and seeds, respectively (Fig. 3).

Fig. 3.

Fig. 3

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Distribution patterns of variables and samples for skins (A) and seeds (B) of three grape cultivars in two dimensional space of PC1 and PC2. The triangular marks represent fresh samples, the circular marks represent pomace samples. Each segment from the original point represents one variable. The abbreviations of variables: TP total phenolics, TFO total flavonoids, TFA total flavan-3-ols, DPPH DPPH radical scavenging capacities, Dp delphinidin, Cy cyaniding, Pt petunidin, Pn peonidn, Mv malvidin, 3', 4' dihydroxylated anthocyanins, 3',4',5' trihydroxylated anthocyanins, Nonmet nonmethylated anthocyanins, Met methylated anthocyanins, Monoglc 3-glucoside, Diglc 3-glucoside-5-glucoside, Ac 6-acetyl, Cm 6-coumaroyl, Cf, 6 caffeoyl, Nonac non-acylated anthocyanins, MA monomeric anthocyanins from fresh berries, DP derived pigments from fermentation

For the skins, the pomace samples were well separated from the fresh samples by PC1, which explained 45.57% of the total variance (Fig. 3A). The separation fully reflected the influences of fermentative maceration on the phenolic compounds and antioxidant capacity of the skins. PC1 was mainly represented by the total contents (TP, TFO, TFA and TAC), antioxidant activities (DPPH), the proportions of Dp-, Pt-, nonmethylated, p-coumaryl and monomeric anthocyanins with positive correlations; and the percentages of Mv-derivatives, methylated anthocyanins and derived pigments with negative correlations. The pomace skins of all three grape cultivars, located on the negative side of the PC1 axis, were characterized by lower phenolic contents and antioxidant abilities, and by having derived pigments, higher proportions of Mv-derivatives and methylated anthocyanins. PC2, explained 33.75% of the total variance and consisted primarily of the proportions of 3ʹ4ʹ5ʹ-substituents, monoglucoside and acetylated anthocyanins with positive PC2 values, as well as Cy- and Pn- derivatives, 3ʹ4ʹ- substituents, diglucosides and nonacylated anthocyanins with negative PC2 values. The ‘NW196’ fresh and pomace skin samples and ‘Kyoho’ pomace skin sample had negative PC2 values, mainly because of the higher percentages of Cy-, diglucosides, 3ʹ4ʹ- and nonacylated anthocyanins.

For the seeds, there was only one principal component (PC1), and it described 96.27% of the total variance. The ‘Cabernet Sauvignon’ seed samples were separated from ‘Kyoho’ and ‘NW196’ (Fig. 3B) because the phenolic contents and antioxidant capacities were significantly higher in ‘Cabernet Sauvignon’ seeds than in the other two grapes.

This research focused on the effects of fermentative maceration on the phenolic features and anthocyanin profiles in grape skins and seeds of three red grape cultivars with different pedigrees. Winemaking pomace still pssessed considerable contents of phenolic compounds with antioxidant activity. This work is a fundamental component in our ongoing effort to develop and utilize winemaking pomace, especially using local non-Vitis vinifera grapes.

Acknowledgements

We are grateful to Prof. Jiang Lu at Shanghai Jiao Tong University for help with this work and Yu Huang at Guangxi Academy of Agricultural Sciences for assistance in collecting berry samples. This work was supported by Natural Science Foundation of Heilongjiang Province (Grant No. LH2022C064), Initiative talents (Grant No. ZRCQC202105) and Platform Support Program (Grant No. PTJH202103) of Heilongjiang Bayi Agricultural University, Major Science and Projects of Technology Heilongjiang Province (Grant No. 2021ZX12B0203) and Innovation Leapfrog Project of Agricultural Science and Technology of Heilongjiang Academy of Agricultural Sciences (Grant No. HNK2019CX11-4-2).

Declarations

Conflict of interest

The authors declare no conflict of interest.

Footnotes

Publisher's Note

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Contributor Information

Lei Zhu, Email: zhulei2580@126.com.

Xin Wu, Email: wuxin12021@163.com.

Xixi Hu, Email: huxixi116@163.com.

Xinyue Li, Email: lixinyue3676@163.com.

Shanshan Lv, Email: Lvshanshan49@163.com.

Chuan Zhan, Email: zc18704649609@163.com.

Yunhua Chen, Email: cyhzxm123@sina.com.

Changyuan Wang, Email: byndwcy@163.com.

Jingyu Xu, Email: xujingyu218@outlook.com.

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