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Review

Use and Roles of Tannins in Polysaccharide-Based Bioplastics and Biocomposites

by
Carlo Santulli
1,*,
Serena Gabrielli
2 and
Graziella Roselli
2
1
Geology Section, School of Science and Technology, Università di Camerino, Via Gentile III da Varano 7, 62032 Camerino, Italy
2
Chemistry Section, School of Science and Technology, Università di Camerino, Via Madonna delle Carceri, 62032 Camerino, Italy
*
Author to whom correspondence should be addressed.
Organics 2025, 6(2), 19; https://doi.org/10.3390/org6020019
Submission received: 14 November 2024 / Revised: 14 March 2025 / Accepted: 29 April 2025 / Published: 1 May 2025
(This article belongs to the Special Issue Chemistry of Heterocyclic Compounds)
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Abstract

:
Most bioplastics are based on polysaccharides, which are either synthesized from a variously sourced monomer or extracted from some biomass waste. In many cases, some lignocellulosic fibers are then added to the obtained bioplastics to form biocomposites and extend their range of applications beyond packaging films and generically easily biodegradable materials. Plant-extracted tannins, which, as such, might also be building blocks for bioplastics, do nonetheless represent a useful complement in their production when added to polysaccharide-based plastics and biocomposites, since they offer other functions, such as bioadhesion, coloration, and biocidal effect. The variety of species used for tannin extraction and condensation is becoming very wide and is also connected with the local availability of amounts of bio-waste from other productions, such as from the food system. This work tries to summarize the evolution and recent developments in tannin extraction and their increasing centrality in the production of polysaccharide-based plastics, adhesives, and natural fiber composites.

1. Introduction

Tannins are plant polyphenols, typically developed as metabolites to defend their leaves against herbivorous insects, either because their odor repels them or, more directly, due to their toxicity [1]. They take their name from their traditional use in the tanning of leather materials, which involves soaking and mechanical softening, other than protection from environmental degradation [2]. Studies on tannin extraction, spanning over a few decades, have also identified their possible medical and pharmacological use, for example, as a potential substitute for antibiotics [3]. However, their very variable toxicity, depending on their origin, and their capacity to reduce nutrient bioavailability in the gut suggests that a targeted pharmaceutical use against some inflammatory diseases, together with non-food applications, is an improved way to apply them [4]. It has also been highlighted, e.g., in the case of cassava, that treatment at temperatures such as 60 °C would reduce leaf toxicity and solubilize tannins [5].
Other possibilities are related to their anti-inflammatory potential, e.g., on arthritis, using tannins obtained from Anacardium occidentale [6], due to their interaction with some therapeutic target proteins, as is the case with black myrobalan (Terminalia chebula) fruits [7], or on nonmalignant respiratory diseases, such as allergic asthma [8]. Beyond their medical use, the application of tannins in materials can be of interest. As a source of phenols, they can be applied and functionalized as raw materials to produce bio-based resins, for example, from green tea, to obtain bio-epoxies [9]. Bio-epoxies, though at least partially bio-based, are not more easily recyclable than conventional ones, also, because they are often, on the grounds of mechanical performance, used as blends with petrochemical ones, with only limited bio-content, as low as 20% or less [10]. Another possibility, which requires the complete separation of tannins from sugars, is their application in polysaccharide-based bioplastics, which is one form of obtaining bio-polyesters from renewable resources [11].
The principal families of polysaccharide-based bioplastics are the following:
  • Poly(lactic acid) (PLA) is normally obtained from the saccharose dimer, as extracted from biological sources, such as corn starch [12]. In this case, for example, to obtain mechanical improvement of the polymer, tannins from Quebracho wood mixture and Kraft lignin were added in different amounts [13].
  • Bacterial poly(hydroxyalkanoates) (PHA) [14]: also in this case, tannins are able to provide stabilization to the relevant bioplastic structure [15].
  • Thermoplastic starches (TPSs), which represent a general category of compounds useful as a matrix for bioplastics, especially when disposing of biomass waste of different origins, are most often used for food packaging films [16]. In this case, normally glycerol is used as the main plasticizer, of which tannin-rich biomasses, such as spent coffee grounds (SCGs), can act as effect enhancers [17].
The objective of this review is to discuss the various roles of tannins in polysaccharide-based plastics. In particular, these molecules are obtained from a large number of species and do represent by-products of other sectors, such as the production of food additives, or the development of medical treatments. The actions that tannins are able to perform in this sector are diverse, from recently promoting enzymatic polymerization of biomass-derived polyphenols, e.g., obtained from biorefinery processes [18], to offering an antioxidant effect on bioplastics [19]. Ordering and classifying the various potential actions represents an essential task given that waste biomass bioplastics are being developed in competition and at the expense of monomer-based ones, such as poly(lactic acid) (PLA). This indicates the timeliness and necessity of the present review.
The structure of this work includes a section (Section 2) in which the variety of origin of various tannins from different parts of the plant is discussed. Following this, the different functions of tannins in these materials are explored (Section 3), discussing, in particular, their use as polyesters and, hence, biomatrices (Section 3.1), as bio-adhesives on a differently obtained polysaccharide matrix (Section 3.2), or as coloring agents (Section 3.3), and, finally, in combination with lignocellulosic fibers to form biocomposites (Section 3.4).

2. Origins and Modes of Extraction of the Various Tannins Used in Bioplastics

Tannins can be extracted from a number of botanical species in different parts of the plant; this is particularly relevant whenever waste biomass is used to produce bioplastics [20]. A comprehensive table of the species is provided in [21], dividing the tannins into condensable and hydrolysable ones and focusing especially on their use for active packaging. On the other hand, restricting polysaccharide-based plastics to the packaging sector does constitute a limitation, especially when aiming to progress towards a real circular economy [22].
In particular, the parts of plants from which tannins can be extracted include the bark, buds, leaves, roots, seeds, stems, and wood. Some studies on tannins extracted from various elements of the plants are reported in Table 1, especially as regards properties that can be potentially applied to the production of bioplastics. Factors that can be considered in this regard include, e.g., the facility and completeness of the extraction of tannins, the seasonality of production, possible antioxidant and antibacterial action, and the separation or grafting of tannins on sugars. All these elements are essential in fields such as edible packaging and the potential application of these materials in the biomedical sector. However, it is fair to say that the use of bio-based plastics and composites does gradually expand towards other applications. The consequence is that not all extracted tannins are equally adapted to their use in bioplastics, a fact that needs to be considered before proceeding to further action.
In particular, tannins from chestnut are hydrolysable, and their reactivity has therefore been considered comparable with the phenol resins’, as from evidence obtained from earlier studies. The highly complex structure of hydrolysable tannins is depicted in Figure 1 [39]. Recent considerations linked with circular economy do suggest intensifying the use of secondary raw materials from waste, which, in the particular case of tannins, often implies their availability from food residues. In some cases, such as for the production of wine, tannin extraction has been seen as being a part of a more circular approach to this system [40]. Tannins are available in a number of foodstuff items other than grapes [41]; these include various berries [42] and different types of nuts (walnuts, cashew nuts, hazelnuts, etc.) [43]. In general terms, their principal value is given by them representing a source of antioxidants. A relation has been demonstrated between antioxidant action and mechanical performance in some cases, e.g., when used in the production of bioplastics microwave-extracted tannins from walnut shells; more specifically, this demonstrated to be effective in poly(lactic acid) (PLA)/poly(butylene adipate-co-terephthalate (PBAT) blends [44].
The combination of two characteristics mainly suggests whether the use of tannin in materials is recommendable: improving mechanical performance and enhancing tolerance to weathering damage [45]. When blending with polysaccharides, tannins have the possibility to form complexes; a well-known interaction is the one between tannins and hyaluronic acid for the formation of colloidal structures [46]. In the case of polysaccharide-based bioplastics, given the compliance with a circular economy approach, substances obtained from vegetable waste are likely to be introduced in the production process [47]. This is the more general case for flavonoids, whose extraction from agro-waste to serve the production of materials has been discussed in a previous review [48]. As described above, the use of tannins, due to their antioxidant potential, can also offer other possibilities, such as their UV-blocking action [49], which has also been developed in combination with other well-renowned agents, such as titanium dioxide [50]. To extend the aims for which tannins are potentially available, their fractionation from industrial waste is necessary; this can occur in a single stage or a multi-stage procedure [51].
The agents that are commonly used for tannin extraction are ethanol or acetone, whose effectiveness can be compared, such as in [52] on grape skins, deep eutectic organic solvents [53], supercritical fluids, e.g., carbon dioxide and alcohol mixtures [54], or ultrasonic/microwave-assisted extraction [55]. The possible antifungal effects of different wood tannins, such as valonia ones, have also been discussed, which can assist in the development of bioplastics and biocomposites [56].

3. Function of Tannins in Bioplastics

3.1. Esterification of Condensed Tannins for Processing in Plastics for Various Uses

Condensed tannins (CTs), depicted in Figure 2, can be functionalized as renewable building block polymers for blending in thermoplastics [57]. In particular, they can be esterified through anhydrides with the idea of promoting their facile melt processing in plastics, which has been proved effective on poly(lactic acid) (PLA) [58]. CTs derived from Pinus radiata bark were added to biodegradable polyesters BionolleTM and BiopolTM; in this case, forming longer alkyl chain hexanoate esters promotes tannin miscibility to the biopolymers, while short-chain acetate esters acted rather as fillers in the postprocessing phase [59]. With this process, it was also possible to offer an improvement of properties to bacterial polymers, such as poly(hydroxybutyrate) (PHB), comparing the effect of tannic acid obtained from grape pomace through a hydroalcoholic extract and that of lignocellulosic biomass [60]. The valorization of grape pomace can, via a biorefinery approach, lead to the production of various chemicals, such as PHB, polyphenols, volatile fatty acids, and biogas. As discussed above, this is only one of the possibilities from the more general use of waste from wine production, such as grape stalks and residue in biopolymers as fillers for PLA, PHB, and poly(butylsuccinate) (PBS) with functionalization for the scope, yet without any real role attributed to tannins [61,62,63]. On the other side, provided a sufficient dispersion is achieved, CT can be blended with biopolymers, such as is the case for poly(hydroxybutirate-co-valerate) (PHBV) in the formation of multifunctional additives; a solvent casting process has allowed the content of tannins to be increased up to 10% [64]. Among the advantages, when introducing tannins in bioplastic packaging, is the possible colorimetric detection of ammonia vapors, which will allow detecting the possible spoilage of some food items (e.g., fish) [65]. The antioxidant properties of condensed tannins, specifically extracted from Acacia Mangium, were confirmed again, both on PLA [66] and poly(vinyl alcohol) (PVA) [67].
One crucial question concerning bio-based polymers is the potential of dispersion of tannins into them; in particular, on PBS, by mapping FTIR key absorptions, acetylated tannins appeared to form discrete aggregates, able to penetrate PBS particles up to a dimension of 100 microns [68]. Aggregation capability has also been demonstrated for colloidal particles, namely using Valonia oak tannins, which improved the coagulation effect obtained by the bare use of aluminum sulfate [69]. Coagulation properties were exploited for the purpose of wastewater primary treatment for tannins extracted from Acacia Mearnsii and compared with potato starch and chitosan from crabs and prawns [70]. Tannin coagulants outperformed starch as water treatment agents in a number of aspects: for total phosphorus (70% reduction), turbidity (82% reduction), and, also, total organic carbon (TOC) (22% reduction). Their recommended concentration was measured to be equal to 5 mL/L.

3.2. Tannin-Based Bio-Adhesives

The opportunity and potential of using tannins as adhesives has been posed back in the 70s; the first application was performed in a blend with formaldehyde with the idea to modify adhesives for plywood [71,72]. The first tannin to be successfully commercialized was based on mimosa, which was more recently developed in a blend with cornstarch, aimed at being used in urea-formaldehyde resins [73]. Shear refinement enabled improving the conditions for processing mimosa tannins so that they would be processed in formaldehyde-free conditions with sufficient stability [74]. More recently, the field of mimosa tannins for bio-adhesives has also been expanded by including the M. tenuiflora species, which has been underused so far yet showed a performance to the level of commercial wood adhesives [75].
Unmodified tannins have several limitations in their application as-received for the development of bio-adhesives. These drawbacks are mainly related to the presence of non-tannin components, e.g., sugars and gums; in particular, the latter cause hydrogen bonding and electrostatic interaction, excessive viscosity, and high molecular weight of tannin extract, which can result in limited strength and ultimately in ineffective adhesion and short pot life [76]. On the other hand, tannin adhesives can generally improve water resistance of bio-based resins, e.g., those synthesized from soy oil [77]. The above issues are dealt with in different works; in particular, coupling tannins with itaconic polyamidoamine epichlorohydrin allowed multiple interactions and a higher density of cross-linking, while offering significant potential for their application in wood replacement boards [78]. Another possibility to improve the adhesive properties of tannins is the combination with bio-inspired structures; a well-known example of these is mussel byssus. Here, the bottleneck of the process is the extraction of the protein (over 95% collagen) from the byssus. On the other hand, the recombinant production has been considered with variable degrees of success, considering the three hierarchical levels of this structure, which represent collagen’s triple helix, the byssus thread, and the foot of the mussel [79]. In contrast, blending mussel protein with a soy meal/tannin mixture, inspired by a byssal cuticle, produced an adhesive with high resistance and low mildew effect [80].
In another sense, the concept of byssus adhesion and, hence, hierarchization of structure with different functions can also be applied using tannins. In particular, a recent investigation concerned the fabrication of hierarchized blended fibers between gallol and chitosan [81] (Figure 3), developed with the idea to mimic the polysaccharide–tannin interaction [82]. On the other hand, the use of tannic acid has a recognized plasticization effect on chitosan matrices, where it can offer some crosslinking potential [83]. A branched structure was also obtained in [84] for a biomedical adhesive including ε-polylysine to form a bridge between gallic acid and collagen.
Another question of interest is the possible application of bio-adhesives based on tannin to offer bonding to specific waste biomass, for example, that based on Triumfetta cordifolia needle-punched nonwovens, using tannins extracted from the bark of Aningeria altissima [85]. It is also worth noting that it is possible to obtain, using tannins, bio-adhesives with biocidal action by the addition of boric acid in the mixture [86].

3.3. Tannins as Coloring Agents in Bioplastics

Coloration of bioplastics, such as polylactic acid (PLA), poly butyl succinate (PBS), and polycaprolactone (PCL) in various wood-like (yellowish-brown) colors, using logwood pigments, was also proposed. One important aspect to be taken into consideration was the discoloration or, more precisely, the spectral changes by irradiation using UV-A ays to simulate accelerated aging. The changes were very limited, even using an amount of pigment one order of magnitude lower than with industrial pigments, i.e., 0.5% [87]. Another possible solution is the fabrication of hybrid nanopigments based on anthocyanin in the specific case from pomegranate peel waste mixed with calcined hydrotalcite and montmorillonite (MMT) nanoclays. The possibility of varying the colors in a wide range from reddish to bluish hues has been exploited by modifying the pH of the pigment [88]. Other clays, such as bentonite, can also contribute to the process of stabilization of anthocyanins on bioplastics [89]. A full range of color variation has also been realized with κ-carrageenan films added with pomegranate peel (PPE) and flesh extracts (PFE), working in a pH interval between 3 and 12. UV-vis spectroscopy results indicated a maximum absorption peak for PFE solution, gradually shifting with pH from 520 to 580 nm, which was deemed to be due to the structural change in anthocyanins; the highest intensities were obtained in alkaline conditions. In contrast, no obvious peak was revealed when using PPE solution [90] (Figure 4).
The sensitivity to pH by producing changes in color can also be exploited in the case of active packaging as a way to obtain information on the conditions of preservation for the contained food [91]. In other words, as reported also in the case of mulberry tannins blended into poly(vinylalcohol) (PVA)/chitosan bioplastics, this natural tannin-based dye can provide an accurate measurement of pH, acting as an indicator, which provides, on the other hand, data on how anthocyanins do change their chemical structure [92]. Anthocyanins from purple sweet potatoes (Ipomoea batatas) have also been proposed for the production of pH indicators in a carboxymethylcellulose/starch matrix to monitor the preservation of fish, offering additional indications about light transmittance rate and possible presence of ammonia [93].

3.4. Tannins in Biocomposites Including Lignocellulosic Fibers

Further developments led to the production of natural fiber composites using tannins as their matrix. In particular, tannin/hexamine resin being reinforced with flax–hemp fibers has been studied; the tannin extracts have been obtained once again from mimosa [94], sulfited mimosa, and quebracho [95], whose properties have been separately identified. Another natural fiber that was used in a matrix synthesized from their tannin extracts to obtain biocomposites is banana stalk fiber; in this case, tannins extracted from the bark of various African trees were also proposed, such as African copaiba (Daniellia oliveri), sycamore (Ficus sycomorus), shea tree (Butyrospermum parkii, now Vitellaria paradoxa), and neem (Azadirachta indica) [96]. An alternative could be modifying starch–flax biocomposites with tannic acid to confer biocidal properties to these materials [97].
Another fiber that was experimented on to be used as a filler for filling a 50/50 tannin–phenol matrix is coir, which yielded a sufficient reinforcement effect in an amount of up to 70 wt.% when using fibers between 3 and 6 mm long, as verified by Izod impact tests [98]. With a similar amount (up to 70 wt.%) of longer (30 mm) sisal fibers, a 60/40 phenol–mimosa tannin matrix was used; in this case, Izod impact strength showed to be improved up to a 50 wt.% fibers content [99].
The combined presence of different natural materials, e.g., tannin extracts as the resin and lignocellulosic fibers as the reinforcement, does reveal the likeliness that mold growth would take place on the biocomposite. This has been investigated using the aniline blue method after inoculation with Aspergillus niger, as regards flax fiber–tannin resin composites, pretreating the nonwoven fiber material by boric acid, and proving that they are highly resistant to mold [100]. Also, the interaction of tannins with biodegradable thermoplastic materials based on poly (lactic acid) (PLA), starch, sugarcane fiber, and nutrient compounds was demonstrated to delay the biodegradation process [101].

3.5. Tannins as Compared with Other Building Blocks for Bioplastics and Biocomposites: Humins

To enter the sector of constructions, structures such as tannin-based polyurethanes [102] or biofoams [103] have also been developed. This has been realized also in combination with furan to obtain tannin–furanic foams, which may equally have a quasi-exclusive bio-based content [104], with the advantage, offered by furans, of potential high temperature applications [105]. The foaming action might also involve the incorporation of polysaccharide-based products, such as humins [106]. In practice, polyfuranic humins, a biorefinery product, served to promote the self-blowing action of mimosa-extracted tannin-based foams (Figure 5). This is attributed to the fact that, under very low pH, which is a condition that seldom occurs in soil, heated humins can self-crosslink, a reaction that can be accelerated through a strong acid initiator, e.g., p-toluene sulfonic acid (pTSA) and a foaming agent (DE). Humins are the insoluble part of soil biomass, which normally are not precisely defined as for chemical composition [107] yet are precipitated in the form of solid microspheres [108], and can be obtained by an acidic treatment of polysaccharides. This insolubility in water is the main characteristic that differentiates them from tannins [109]. In general terms, humins have been considered an issue for biomass processing, yet, on the other hand, their insolubility has allowed them being mixed with tannins with a characteristic self-blowing effect at room temperature. In particular, for materials processing, humins oligomers tend to form complex crosslinked networks through physical aggregation while absorbing other molecules [110], which enable their use as building blocks for durable polysaccharide-based bioplastics [111]. Flax-fiber-reinforced composites with similar properties between humins and tannins as potential matrices have been reported [112]. Tannins can also serve in non-furanic polyurethane adhesives to the improvement of humins’ properties, where the two biomaterials appeared to form a crosslinked network gradually disentangling with temperature [113].

4. Discussion

Tannins’ use in bioplastics and biocomposites serves various purposes, which allow them to act as matrices or, generically, adhesives, coloring agents, antibacterial principles, and in combination with other principles, such as humins, to self-crosslink as foams. A scheme summarizing these different applications is given in Figure 6.
It is suggested that the perspectives of future applications would concentrate on some specific themes. These are listed below:
(i)
The development of effective crosslinkers to use tannins for wood-based panels; after initial attempts, early in this century, on polyethyleneimine [114], nowadays one of the most diffused is hexamethylenetetramine (HMTA) [115], which forms tannin and amino methylene bridges. This is a formaldehyde-free technology that is supposed to coexist with binderless principles, based on the modification of wood to promote adhesion [116]. Research is continuing: natural crosslinkers, such as those based on proteins, though thermoset, tend to become thermoplastic under the effect of moisture and generally contamination; this is the case for casein [117]. In practice, therefore, attention is concentrated on aldehyde (aliphatic, cyclic, or aromatic) or amine functional groups, according to the specific reactive groups on the various adhesives based on natural substances [118]. However, the drive towards achieving full-biobased adhesives is by no means exhausting; a glucose–tannin combination has in fact been also proposed for wood adhesion, which proved highly performant [119].
(ii)
As for other bio-based products, the principal bottleneck is the requirement for thorough characterization of these materials, especially as far as the market for thermosetting polymers and composites is concerned, where specifications need to be supplied and constantly verified for their variability over time. This occurs, e.g., in the field of bio-epoxies [120] and bio-polyurethanes [121]. In the latter case, the tannin-based resin can also be used as a modifier for lignocellulosic fibers to improve their adhesion to further matrices; this has been, for example, proposed with ramie fibers [122]. Fiber modification is generally a widely diffused practice; tannin-rich plants, such as persimmon, are important candidates for that purpose, despite limitations due to their seasonal availability, which may hinder the possible industrialization of the process [123].
(iii)
In the field of biocomposites and of the increasing number of lignocellulosic fibers that are employed with that purpose [124], tannin-based matrices provide a very suitable location for their effective bonding. It is no surprise that the last years have witnessed the development of tannin resin composites with various natural fibers, such as Urena lobata [125] and Grewia bicolor [126]. Together with high interfacial properties obtained, these materials are able to present also antibacterial and anti-mold properties [127], which represented a limit so far for fully bio-based biocomposites.
In more general terms, it can be suggested that, given the fact that tannins are necessary by-products of many food-based systems, their application in bioplastics could enhance their life perspective and move away from a single-use product (SUP) philosophy; in this sense, a reinforcement action is particularly adapted [128]. This also requires considering the improvement of the mechanical strength of the bioplastic obtained, which appears one of the most important challenges so far [129].
As is the case for natural materials, not different from obtaining cellulose or lignin from biomass, the extraction of tannins has very variable yield depending on the species yet also on the method followed. Further indications are given in [130], where the literature is classified according to the means of extraction (organic solvents, hot water, pressurized or not, ionic liquids, supercritical fluids or water, and assisted by microwave or ultrasound), methods which can also be combined. Some comparative studies do also exist, for example, in [131] performing different extraction methods (maceration, infusion, microwave, and microwave with water) on 10-year-old Acacia mollissima bark samples as regards polyphenols, hydrolisable, and condensed tannins. The results were suggestive of the potential of the innovative method using microwave, though, in terms of scaling-up towards industrialization, it might not always be convenient to go for it [132].
Further complications for global productions, though recommended in terms of circular economy, are the use of tannins from local cultivations, e.g., for the function of bio-adhesives to be used in wood boards; in some cases, such as for tannins from Aningeria, these proved particularly suitable for their use as bio-adhesives [133]. Other most recent tannin applications, such as the possibility to enhance enzymatic polymerization of lignin fractions through the laccase process by Pinus radiata bark extraction, appeared challenging due to the variability of properties and incomplete characterization of tannins [134]. In the same way, it is not easy to control the modification of biodegradability patterns introduced by the addition of tannins, such as in the case of chestnut bark ones [135]. It is suggested though that, also, given the variety and the potential of tannins and the possible combination with typically non-hydrolysable elements, such as humins, a sensible approach would tend to make use of them in bio-based yet durable items. In that case, controlled and limited biodegradability would be obviously preferable.
Finally, further uses of tannins in bioplastics can be envisaged, which have received very limited attention so far and cannot be considered already available at the present state-of-the-art. An example is the application of tannins as bio-based flame retardants for bioplastics; their ability to form stable char has already been clarified [136], though many competitors are present in that respect, for which reason it is not possible to propose their diffuse use. Tannins appear nonetheless an essential and versatile component of bioplastics, whose potential is still to be fully exposed, while the research in this field appears to gradually expand and diversify.

Author Contributions

Conceptualization, G.R. and S.G.; literature review, C.S. and S.G.; writing (original draft), C.S.; writing (final version), G.R. and S.G. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

No new data were generated.

Conflicts of Interest

The author declares no conflicts of interest.

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Figure 1. Structure of the hydrolysable tannin from chestnut (Castanea spp.) (redrawn by the author).
Figure 1. Structure of the hydrolysable tannin from chestnut (Castanea spp.) (redrawn by the author).
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Figure 2. Typical structure of condensed tannin (redrawn by the author).
Figure 2. Typical structure of condensed tannin (redrawn by the author).
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Figure 3. Hierarchized blended fibers between gallol and chitosan, mimicking byssus function: (a) chemicals involved in adhesion; (b) biomimicry process [81].
Figure 3. Hierarchized blended fibers between gallol and chitosan, mimicking byssus function: (a) chemicals involved in adhesion; (b) biomimicry process [81].
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Figure 4. Color variations of κ-carrageenan films added with (A) pomegranate flesh extracts (PFE) and (B) pomegranate peel (PPE). UV-Vis spectra of (C) PFE and (D) PPE in a pH interval between 3 and 12 [90].
Figure 4. Color variations of κ-carrageenan films added with (A) pomegranate flesh extracts (PFE) and (B) pomegranate peel (PPE). UV-Vis spectra of (C) PFE and (D) PPE in a pH interval between 3 and 12 [90].
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Figure 5. Crosslinking action of humin–tannin foam through acid self-crosslinking [106].
Figure 5. Crosslinking action of humin–tannin foam through acid self-crosslinking [106].
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Figure 6. Some amongst the various roles of tannins in bioplastics.
Figure 6. Some amongst the various roles of tannins in bioplastics.
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Table 1. Some species for tannins extraction and specific characteristics.
Table 1. Some species for tannins extraction and specific characteristics.
Part of the PlantBotanical SpeciesPropertiesRef.
BarkMimosa (Acacia mearnsii)Inhibition of the growth of intestinal bacteria[23]
Spruce (Picea abies)Extraction of a mixture of tannins and sugars[24]
Siberian conifersResidue tan as a source of raw cellulosic product[25]
BudsPersimmonVariable level of astringency, which may have mechanical and antibacterial significance[26]
GrapevinePhenolic content increases during annual growth cycle[27]
LeavesOakSeasonality: condensed tannins appear in late May, while hydrolysable tannins are present throughout the season.[28]
MangroveImmediate lability of tannins from the leaves[29]
Cassava
(Manihot esculenta)		Need for detoxification through alkaline extraction[30]
Guava
(Psydium guayava)		Wide antibacterial action against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Aspergillum niger, and Candida albicans[31]
RootsRosaceaeAntibacterial action of the roots of five species of Rosaceae[32]
Lawsonia inermisPossible synthesis of galloylglucoses[33]
SeedsFaba (Vicia faba)Seed with less tannins are softer, take more water, and leach more solutes [34]
Raspberry and grapeAnti-inflammatory and antioxidant activity of raspberry tannins much higher than that of grape ones[35]
StemsCasuarina equisetifoliaAntioxidant tannins from both stem’s bark and fine roots[36]
Acacia ConfusaCondensed tannins with different polymer chain length (3–11 molecules for leaf and root bark; a maximum of 12 molecules for stem bark)[37]
WoodCastanea spp.Complete extraction of tannins from the surface surrounding the cell’s lumen, yet they remain partially unextracted from the cell corners and intercellular voids[38]
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Santulli, C.; Gabrielli, S.; Roselli, G. Use and Roles of Tannins in Polysaccharide-Based Bioplastics and Biocomposites. Organics 2025, 6, 19. https://doi.org/10.3390/org6020019

AMA Style

Santulli C, Gabrielli S, Roselli G. Use and Roles of Tannins in Polysaccharide-Based Bioplastics and Biocomposites. Organics. 2025; 6(2):19. https://doi.org/10.3390/org6020019

Chicago/Turabian Style

Santulli, Carlo, Serena Gabrielli, and Graziella Roselli. 2025. "Use and Roles of Tannins in Polysaccharide-Based Bioplastics and Biocomposites" Organics 6, no. 2: 19. https://doi.org/10.3390/org6020019

APA Style

Santulli, C., Gabrielli, S., & Roselli, G. (2025). Use and Roles of Tannins in Polysaccharide-Based Bioplastics and Biocomposites. Organics, 6(2), 19. https://doi.org/10.3390/org6020019

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