Proanthocyanidins, also known as condensed tannins, are important plant secondary metabolites, bioactive phytochemicals synthesised via the flavonoid pathway that contribute to human and animal health and plant survival by performing anti-inflammatory, antioxidant functions against pathogens and other diseases. They can bind to proteins.

In nature they are found in fruit, bark, leaves and seeds of plants (Cinnamonum verum, Heisteria acuminata), protecting them against predators. 

Industrially, Proanthocyanidin comes in the form of a fine reddish-brown powder.

What they are used for and where

In food and are used to determine astringency and flavour in fruit juices, wines, teas. 

Medical

Obesity, which has increased dramatically in recent years, is linked to various diseases such as type 2 diabetes mellitus, stroke, cancer, hypertension and hyperlipidaemia. Among the various remedies that scientific research has been able to develop to combat and reduce this chronic metabolic disease that is becoming endemic in the most industrialised countries, grape seed proanthocyanidin extract has shown an anti-obesity effect. This extract can reduce fat deposition, improve lipid metabolism and insulin resistance (1).

Proanthocyanidins and polyphenols have drawn research attention to the wine consumption of the French population, which has a low incidence of coronary heart disease. This study summarises the literature on proanthocyanidins with a focus on their chemical structure, occurrence, daily intake from food, bioavailability and metabolism, and evidence of a protective effect against cardiovascular disease (2).

In this other study, it is noted that the efficacy of Proanthocyanidins contained in blueberry products is directly linked to the amount of Proanthocyanidins which should exceed at least 2 grams to demonstrate efficacy against urinary tract infections (3).

Proanthocyanidins studies

Typical commercial product characteristics Proanthocyanidin 

• Molecular Formula C₃₁H₂₈O₁₂
• Molecular Weight     592.5
• CAS  18206-61-6
• UNII    
• EC Number   605-956-8
• DSSTox Substance ID  DTXSID10274250
• IUPAC  (3R)-2-(3,5-dihydroxy-4-methoxyphenyl)-8-[(2R,3R,4R)-3,5,7-trihydroxy-2-(4-hydroxyphenyl)-3,4-dihydro-2H-chromen-4-yl]-3,4-dihydro-2H-chromene-3,5,7-triol
• InChI=1S/C31H28O12/c1-41-31-20(37)6-13(7-21(31)38)28-22(39)10-16-17(34)11-19(36)25(30(16)43-28)26-24-18(35)8-15(33)9-23(24)42-29(27(26)40)12-2-4-14(32)5-3-12/h2-9,11,22,26-29,32-40H,10H2,1H3/t22-,26-,27-,28?,29-/m1/s1
• InChl Key      JPFCOVZKLAXXOE-XBNSMERZSA-N
• SMILES COC1=C(C=C(C=C1O)C2C(CC3=C(O2)C(=C(C=C3O)O)C4C(C(OC5=CC(=CC(=C45)O)O)C6=CC=C(C=C6)O)O)O)O
• MDL number  
• PubChem Substance ID    

Synonyms:

• Polyhydroxyflavan-3-ol
• Ouratea proanthocyanidin A
• Zangrado

References_______________________________________________________________________

(1) Liu M, Yun P, Hu Y, Yang J, Khadka RB, Peng X. Effects of Grape Seed Proanthocyanidin Extract on Obesity. Obes Facts. 2020;13(2):279-291. doi: 10.1159/000502235. 

(2) Rasmussen SE, Frederiksen H, Struntze Krogholm K, Poulsen L. Dietary proanthocyanidins: occurrence, dietary intake, bioavailability, and protection against cardiovascular disease. Mol Nutr Food Res. 2005 Feb;49(2):159-74. doi: 10.1002/mnfr.200400082. 

(3) Asma B, Vicky L, Stephanie D, Yves D, Amy H, Sylvie D. Standardised high dose versus low dose cranberry Proanthocyanidin extracts for the prevention of recurrent urinary tract infection in healthy women [PACCANN]: a double blind randomised controlled trial protocol. BMC Urol. 2018 May 2;18(1):29. doi: 10.1186/s12894-018-0342-7. 

Compendium of the most significant studies with reference to properties, intake, effects.

Wang TK, Xu S, Li S, Zhang Y. Proanthocyanidins Should Be a Candidate in the Treatment of Cancer, Cardiovascular Diseases and Lipid Metabolic Disorder. Molecules. 2020 Dec 16;25(24):5971. doi: 10.3390/molecules25245971.

Abstract. This review article demonstrates the physical and biological properties of proanthocyanidins  (PAs), summarizes the health benefits of PAs found by researchers previously, and shows the possibility and importance of being a dietary treatment substance.

Jagannathan V, Viswanathan P. Proanthocyanidins-Will they effectively restrain conspicuous bacterial strains devolving on urinary tract infection? J Basic Microbiol. 2018 Jul;58(7):567-578. doi: 10.1002/jobm.201800131.

Abstract. Overall, this review assesses the merits of proanthocyanidins and its effective oppression on adherence, motility, QS, and biofilm formation of major UTI strains such as Escherichia coli, Pseudomonas aeruginosa, and Proteus mirabilis by comparing and evaluating results from many significant findings.

Wei J, Yang J, Jiang W, Pang Y. Stacking triple genes increased proanthocyanidins level in Arabidopsis thaliana. PLoS One. 2020 Jun 25;15(6):e0234799. doi: 10.1371/journal.pone.0234799.

Abstract. In this study, we attempted to improve proanthocyanidins level by gene stacking in Arabidopsis thaliana as prove-of-concept. 

Cos P, De Bruyne T, Hermans N, Apers S, Berghe DV, Vlietinck AJ. Proanthocyanidins in health care: current and new trends. Curr Med Chem. 2004 May;11(10):1345-59. doi: 10.2174/0929867043365288.

Abstract. The present review is focused mainly on the antioxidant activity of proanthocyanidins and its relevancy in vivo. The three most important mechanisms of their antioxidant action will be discussed, i.e. free radical scavenging activity, chelation of transition metals, and inhibition of enzymes. In addition, the protective role of proanthocyanidins against lipid peroxidation and peroxynitrite, as well as their antimicrobial properties will be discussed. To study the in vivo relevancy of the proanthocyanidin activities, the knowledge of their pharmacokinetic parameters is crucial. 

He F, Pan QH, Shi Y, Duan CQ. Chemical synthesis of proanthocyanidins in vitro and their reactions in aging wines. Molecules. 2008 Dec 4;13(12):3007-32. doi: 10.3390/molecules13123007.

Abstract. The present paper aims at summarizing the research status on chemical synthesis of proanthocyanidins, including non-enzymatic synthesis of proanthocyanidin precursors, chemical synthesis of proanthocyanidins with direct condensation of flavanols and stereoselective synthesis of proanthocyanidins.

Jonker A, Yu P. The Role of Proanthocyanidins Complex in Structure and Nutrition Interaction in Alfalfa Forage. Int J Mol Sci. 2016 May 23;17(5):793. doi: 10.3390/ijms17050793.

Abstract. This review aims to firstly describe the events involved in the rapid release of protein from alfalfa and its effect on ruminant nutrition, environmental pollution, and pasture bloat; secondly, to describe occurrence, structure, functions and benefits of moderate amounts of proanthocyanidin; and finally, to describe the development of alfalfa which accumulates moderate amounts of proanthocyanidins. 

Prior RL, Gu L. Occurrence and biological significance of proanthocyanidins in the American diet. Phytochemistry. 2005 Sep;66(18):2264-80. doi: 10.1016/j.phytochem.2005.03.025.

Abstract. It has been shown that  proanthocyanidins (PAs) account for a major fraction of flavonoids ingested in the US diet and infants and children appear to ingest more PAs than adults on the basis of body weight. These data will provide an opportunity to examine the association between PA intake and health and disease outcomes in epidemiological studies. PA analysis and the significance of PAs in nutrition and diet are reviewed.

Tang C, Tan B, Sun X. Elucidation of Interaction between Whey Proteins and Proanthocyanidins and Its Protective Effects on Proanthocyanidins during In-Vitro Digestion and Storage. Molecules. 2021 Sep 8;26(18):5468. doi: 10.3390/molecules26185468.

Abstract. Whey proteins and oligomeric proanthocyanidins have nutritional value and are widely used in combination as food supplements. However, the effect of the interactions between proanthocyanidins and whey proteins on their stability has not been studied in depth. In this work, we aimed to characterize the interactions between β-Lactoglobulin (β-LG) and α-lactalbumin (α-LA) and oligomeric proanthocyanidins, including A1, A2, B1, B2, B3, and C1, using multi-spectroscopic and molecular docking methods.