Chemical Fingerprinting of Medicinal and Aromatic Plant Extracts: HPTLC Bioautographic Assays as Preliminary Research Tool to Match Chemical and Biological Properties

Abstract

Chemical plant fingerprintin g generally identifies the distribution of compounds within a plant matrix defining its chemical imaging in relation to the different extraction approach adopted. The chemical picture obtained with fingerprinting target needs to represent the highest number of chemical compounds as possible, giving the most realistic portrait of the chemical identity of the plant matrix. The fingerprinting of plant matrices is a research approach aimed to point out chemical evidences related to biological researches and applications of natural compounds in many productive fields, from human, animal health and phytoiatry to environmental biomonitoring and bioremediation. The chemical portrait given by a fingerprinting is representative of the ecosphere where the plant grows, evidencing secondary metabolite patterns which are driven in quality and amount of compounds by the sensitivity of the plant to ecological variables. A chemical fingerprinting could allow to better understand the grown capacity of a plant species in a particular environment, to point out and select that particular genotype able to express a particular chemical phenotype useful for a particular applicative field for e.g. the production of bioactive compounds against particular human or plant pathogens to determine pollution levels and risk assessment for ecosystems by the presence/ accumulation of pollutants or particular qualitative and quantitative expression of secondary metabolites [1]. The plant fingerprinting focused on the secondary metabolites is particularly relevant because of the important applicative relapses that this particular chemical portrait concerns. Plant secondary metabolites, infact, represent from a biological point of view the capacity of plant species to relate to environment complexity and to control many metabolic functions, for e.g. the known role of supporting plant electron transports [2]. These aspects are particularly important for studying the physiology of officinal plants to improve their cultivation and quality. Moreover, from applicative points of view, for e.g. those relating pharmaceutical-healthy applications and agricultural relapses of plant compounds, the study of secondary metabolism through mapping the quality and amount of the occurring molecules to have a complete chemical fingerprinting, may lead to discover more effective and safer bioactive chemicals, and officinal plants with a chemical profile more fitting with specific applicative needs [3]. For all these last applicative aspects, with particular relevance to health and plant defense/biostimulation (phytoiatric applications), also chemical fingerprinting related to some primary metabolites (for e.g. poly-unsaturated fatty acids, proteins, fixed oils, waxes and butters) has been considered [4]. However, besides the general considerations about the meaning of chemical fingerprinting, it should be stressed that its scientific importance and applicative relevance are linked to the extraction approaches adopted. In general, a complete chemical fingerprinting of a plant matrix is given by the chemical qualitative and quantitative profile of large polarity spectrum of the extraction strategies. A complete chemical fingerprinting of the secondary metabolites profile of a plant matrix is given by the combination of the qualitative and quantitative evidences of low, medium and high polarity extracts obtained using specific solvents and strategies with appropriate physical-chemical properties. However, for the most known plant species, as for example those with medicinal and aromatic properties, the chemical fingerprinting is limited to that secondary metabolites fractions known for traditional healthy properties and uses, generally characterizing aqueous or hydro-alcoholic preparations [5].