Suberin chemical nature

Based on detailed analyses of the chemical nature of SOM, Hatcher and Spiker (1988) have extended this humification model to include other resistant biopolymers, including plant cutin and suberin, and microbial melanins and paraffinic macromolecules. During decomposition, these biopolymers are selectively preserved and modified to become part of what can be operationally defined as humin (acid and alkali insoluble component of humus) (Hatcher and Spiker, 1988 Rice, 2001). The humin becomes progressively enriched in acidic groups leading to the formation of first humic acids and then fulvic acids, which under this degradative scheme of SOM formation would be regarded as the most humified of humic substances (Stevenson, 1994). 

Kolattukudy PE, Espelie KE (1989) Chemistry, biochemistry and function of suberin and associated waxes. In Rowe J (ed) Natural products of woody plants, chemicals extraneous to the lignocellulosic cell wall. Springer, Berlin Heidelberg New York, p 304... 

The molecular structure as well as the dynamics of natural polymers are important in understanding their properties. For intact plant materials such as lignin, cutin and suberin, the principal chemical constituent moieties have been identified and quantified by solid-state NMR [130-133]. 

The present chapter aims essentially at presenting the potentials of suherin as a renewable source of chemicals and more specifically of macromonomers. Suberin is a naturally occurring aromatic-aliphatic crosslinked polyester widespread in the plant kingdom, where it plays a key role as a protective barrier between the plant and the surrounding environment. It is found mainly in the cell walls of normal and wounded external tissues of aerial and/or subterranean parts of many plants, mainly in the outer bark of higher plants and in tuber periderms [ 1 ]. 

As mentioned above, and despite the fact that suberin is widespread in plants [1], only two species produce suberin-rich biomass residues in amounts that justify the exploitation of this natural polyester as a renewable source of chemicals for polymer synthesis, namely, Quercus suber and Betula pendula. Betula pendula is one of the most important industrial hardwood species in Northern Europe, where it is mainly used as raw material in the pulp and paper industry, which generates considerable amounts of bark. Typically, a mill with a pulp production of 400 000 ton per year, leaves about 28000 ton per year of outer bark [37]. Considering a suberin content ranging from 32 to 59 per cent, [14], birch s outer bark has, like cork, an enormous potential as a source of suberin and suberin components. 

Benitez et al. [82], recently reported the synthesis of a polyester resembling cutin, a natural polymer whose structure is close to that of aliphatic suberin [83], by a circular approach, which consisted in depolymerizing cutin through ester cleavage and then submitting the ensuing monomer mixture to a chemical polyesterification process. 

In a preliminary study, the volatile fraction of cork samples at different stages of processing (raw material and finished stoppers) was analyzed [43]. One hundred seven components were identified by GC-MS, several of which had not been previously reported in cork. Predominant volatiles were hydrocarbons, alcohols, acids, and carbonyl compounds. A natural origin, such as chemical or enzymatic degradation of the cork, could explain the occurrence of many substances. All the identified compounds with a phenyl ring and with a linear structure, e.g., vinylbenzene, benzyl alcohol, and 2-hydroxybenzaldehyde, could be derived from suberin and lignin. 

Suberin is a natural biopolymer typically found in the cell walls of plants [46]. The structure of suberin in cork (i.e. its main chemical component) is not yet fully understood. It... 

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