2. Plant proteins and their potential for green excipients

2.1 Main protein sources and their current use

Proteins are natural nitrogenous polymers ranging in size from several thousand to several million daltons. Made up of one or more peptide chains, their unit is the amino acid. All amino acids share a common structure, consisting of a carboxylic acid function, a primary amine and a side chain. The latter presents a wide variety of chemical structures, giving proteins their particular properties. The amino acid sequence has its own three-dimensional organization (or folding). From sequence to folding and association, there are four levels of protein structural organization:

• the primary structure, defined by the linear sequence of amino acids linked by peptide bonds;

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