Tannins: Current knowledge of food sources, intake, bioavailability and biological effects

Abstract

Tannins are a unique group of phenolic metabolites with molecular weights between 500 and 30 000 Da, which are widely distributed in almost all plant foods and beverages. Proanthocyanidins and hydrolysable tannins are the two major groups of these bioactive compounds, but complex tannins containing structural elements of both groups and specific tannins in marine brown algae have also been described. Most literature data on food tannins refer only to oligomeric compounds that are extracted with aqueous‐organic solvents, but a significant number of non‐extractable tannins are usually not mentioned in the literature. The biological effects of tannins usually depend on their grade of polymerisation and solubility. Highly polymerised tannins exhibit low bioaccessibility in the small intestine and low fermentability by colonic microflora. This review summarises a new approach to analysis of extractable and non‐extractable tannins, major food sources, and effects of storage and processing on tannin content and bioavailability. Biological properties such as antioxidant, antimicrobial and antiviral effects are also described. In addition, the role of tannins in diabetes mellitus has been discussed.

Evaluation of the antimicrobial activity of pecan nut [Carya illinoinensis (Wangenh) C. Koch] shell aqueous extract on minimally processed lettuce leaves

“…It has been reported that pure polyphenols present antimicrobial activity against Gram-positive and Gram-negative bacteria (Puupponen-Pimiä et al, 2001;Serrano et al, 2009;Prado et al, 2014). Their mechanisms of action are related to oxidation of microbial cell membranes, complexation of essential metal ions, or inhibition of extracellular enzymes (Scalbert, 1991;Serrano et al, 2009). Lou et al (2012) reported that p-coumaric acid acts on altering the permeability of the cell membrane of Gran-negative bacteria.…”

“…Additionally, some fungi such as A. niger and Penicillium sp. can grow in the presence of tannins, using these compounds as a carbon source or due to production of polyphenol hydrolyzing enzymes (Scalbert, 1991;Serrano et al, 2009). Figure 1 shows the results for antimicrobial activity of pecan nutshell extract against yeast, mesophilic and psychrotrophic bacteria in lettuce leaves stored for 5 days at refrigeration temperature.…”

Chromatographic Studies on the Tannins of Aerva lanata (L.) Juss. Ex Schultes

“…In general, higher degree of tannins diversity has been observed in vegetative parts when compared to the reproductive parts. Maximum number (10) of tannins has been observed in flowers and seeds followed by leaves (9). …”

“…In particular, the tannin containing remedies are in use as antihelmintics [5], antioxidants [6], anti-microbials and anti-virals [7], and for the cancer treatment [8]. Tannins are widely distributed in almost all plant foods [9,10]. However, the primary source of tannins as active pharmaceutical ingredients are the medicinal plants while the polyphenolic compounds themselves are not always well characterized and there exist differences in polyphenol composition among various plant species [11].…”

Influence of postharvest processing and storage on the content of phenolic acids and flavonoids in foods

“…They nearly always occur together in plants. Due to the large number of references dealing with the oligomers, the proanthocyanidins will be discussed in a further overview of the COST action 926 [198].…”