Condensed Tannins, a Viable Solution To Meet the Need for Sustainable and Effective Multifunctionality in Food Packaging: Structure, Sources, and Properties

Condensed tannins (CT) have been the focus of increasing interest in the last years as a result of their potent biological properties, which have prompted their use in the food and feed sector as functional ingredients. The possible exploitation of these compounds as multifunctional additives for the implementation of active food packaging has also been recently appreciated. In this perspective, an overview of the structural features, accessible sources, methods of analysis, and functional properties of CT is provided, with the aim of critically emphasizing the opportunities offered by this widespread class of natural phenolic compounds for the rational design of multifunctional and sustainable food packaging materials.

Changes in Tannin Composition of Syrah Grape Skins and Seeds during Fruit Ripening under Contrasting Water Conditions

Tannin accumulation and composition were determined in skins and seeds isolated from Vitis vinifera cv. Syrah grapes submitted to contrasting water regimes under semiarid climatic conditions. Three irrigation treatments were conducted, starting at berry set through harvest of two growing seasons, 2011 and 2012: irrigation at 100% of crop evapotranspiration ETc (FI), irrigation at 50% of ETc (DI) and non-irrigated (NI). Seed total tannins did not vary with maturity but those of skins underwent a progressive decline (especially in 2011), expressed both on a fresh weight and on a per berry basis. Skin total tannin concentration and content per berry were increased under NI and DI conditions, mainly in 2012. In contrast, seed total tannins (in 2012) and flavan-3-ol monomers and tannin oligomers (both years) were higher in the fully irrigated vines (FI). Skin polymer size increased during ripening, NI and DI skins showing higher mean degree of polymerization (mDP) compared to FI at harvest. NI was also associated with a lower percentage of galloylation (%G) in skin oligomeric fraction (in 2012) and a lower percentage of prodelphinidins in the skin polymeric fraction (both years) at harvest. The mDP and %G of seed extracts did not vary during ripening and were higher in NI but only in 2012. According to the results, management of vine water status was shown to influence tannin amount and composition of Syrah grapes grown under semiarid conditions.

Prodelphinidins isolated from Chinese bayberry leaves induces apoptosis via the p53-dependent signaling pathways in OVCAR-3 human ovarian cancer cells

Chinese bayberry leaves are rich in prodelphinidins. Since the isolation and purification of prodelphinidins is difficult, the association between the degree of prodelphinidin polymerization and their anti-carcinogenic activity remains ambiguous. The cytotoxic and apoptotic activities of prodelphinidin Chinese bayberry leaf extracts (PCBLs), oligomeric proanthocyanidins (OPAs) and polymeric proanthocyanidins (PPAs), isolated by normal-phase preparative high-performance liquid chromatography were investigated in OVCAR-3 human ovarian cancer cells. The PCBLs, OPAs and PPAs inhibited cancer cell growth and induced apoptosis via the caspase-dependent pathway. Apoptosis was triggered through the intrinsic pathway by upregulating the expression of several B-cell lymphoma-2 (Bcl-2) family proapoptotic proteins, including p53-upregulated modulator of apoptosis (PUMA), Bcl-2-associated X protein and Bcl-2-associated agonist of cell death, and by downregulating the antiapoptotic protein Bcl-extra large. Apoptosis was also triggered through the extrinsic pathway via the upregulation of death receptor 5 (DR5) and Fas expression. In addition, OPAs and PPAs induced caspase-dependent apoptosis at least partially through the inhibition of the protein kinase B signaling pathway. The knockdown of p53 by specific small interfering RNA resulted in the depletion of p53, and inhibited the OPA and PPA treatment-induced increases in p53, which led to a decrease in the expression of p21, DR5, Fas, PUMA and phosphatase and tensin homolog proteins. These observations demonstrate that p53 is a mediator of OPA and PPA-induced apoptosis in OVCAR-3 cells. The PPAs exhibited stronger anti-proliferative and pro-apoptotic activities compared with OPAs and PCBLs. These results suggest that PCBLs, OPAs and PPAs may be useful for the treatment of ovarian cancer.

Structure-Activity Relationship of Condensed Tannins and Synergism with trans-Cinnamaldehyde against Caenorhabditis elegans

Parasitic gastrointestinal nematodes (GIN) of livestock are increasingly developing resistance to synthetic nematocidal drugs. Moreover, the use of nematocides can induce ecotoxicity by affecting free-living nematodes. Condensed tannins (CT) are a structurally diverse group of bioactive plant compounds possessing anthelmintic activity against GIN. We investigated the relationship between the chemical structure of contrasting, purified CT and nematocidal effects using Caenorhabditis elegans. We also explored whether the nematocidal activity of CT could synergize with trans-cinnamaldehyde (CIN). A nonsignificant correlation was evident between the ability of CT fractions to inhibit C. elegans motility and the molar proportion of prodelphinidin subunits in purified CT samples. Synergistic inhibition of motility was achieved by combinations of CT and CIN. Galloylation of procyanidins was also a key factor for synergy. To increase the nematocidal effect of CT, plant sources containing CT with specific structural features could be selected and combined with compounds acting in synergy.

¹H-¹³C HSQC NMR spectroscopy for estimating procyanidin/prodelphinidin and cis/trans-flavan-3-ol ratios of condensed tannin samples: correlation with thiolysis

Studies with a diverse array of 22 purified condensed tannin (CT) samples from nine plant species demonstrated that procyanidin/prodelphinidin (PC/PD) and cis/trans-flavan-3-ol ratios can be appraised by (1)H-(13)C HSQC NMR spectroscopy. The method was developed from samples containing 44-∼100% CT, PC/PD ratios ranging from 0/100 to 99/1, and cis/trans ratios ranging from 58/42 to 95/5 as determined by thiolysis with benzyl mercaptan. Integration of cross-peak contours of H/C-6' signals from PC and of H/C-2',6' signals from PD yielded nuclei-adjusted estimates that were highly correlated with PC/PD ratios obtained by thiolysis (R(2) = 0.99). cis/trans-Flavan-3-ol ratios, obtained by integration of the respective H/C-4 cross-peak contours, were also related to determinations made by thiolysis (R(2) = 0.89). Overall, (1)H-(13)C HSQC NMR spectroscopy appears to be a viable alternative to thiolysis for estimating PC/PD and cis/trans ratios of CT if precautions are taken to avoid integration of cross-peak contours of contaminants.