FTIR Characterization of isolated fruit cuticles from tomato species

Abstract

The plant cuticle is a lipid extracellular membrane which covers the outer surface of leaves, stems and fruits of higher plants acting as a real interphase between the plant and the environment. The cuticle plays a pivotal role in epidermal development, control of water loss, fruit integrity, firmness and resistance to various disorders [1]. From a morphological point of view, the cuticle (Figure 1) can be described as acutinizedepidermal cell wall [2]. Based on its structural and chemical composition, the cuticle is mainly constituted by a polyester matrix of long chainpolyhydroxy fatty acids named cutin. Additionally, a significant amount of polysaccharides (mainly cellulose, hemicellulose and pectin) is also present. Cuticular waxes, a mixture of different very long chain aliphatic compounds, can be either embedded into the cutin matrix (intracuticular waxes) or deposited on the outer surface of the cuticle (epicuticular waxes) [3]. Finally, phenolic compounds (cinnamic acid derivatives and flavonoids) are also present. In tomato, cuticular flavonoids participate in fruit coloration and their presence is influenced by environmental conditions and the stage of development.As it can be observed in Figure 1, the cuticle has an asymmetrical distribution of its components. In its outer surface waxes and aliphatic compounds are very abundant, while the inner surface is rich in polysaccharides from epidermal cell wall. Two parameters have been studied, the esterification index (the ratio between the intensities of the stretching vibration band related to ester functional groups (1730 cm-1) and the stretching vibration associated with methylene groups (2918 cm-1)), which isa relative measure of the cross-linking degree of the cutin matrix, and the amount of flavonoids, calculated as the sum of 1606 cm-1and 1624 cm-1 band areas.