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Characterization of Biopolymer Cutin and Other Cuticular Fractions from Tomato Waste

INTRODUCTION The processing of fruits and vegetables results in the accumulation of large amounts of byproducts of little or no commercial value. In effect, these materials are sold for minimal prices to farmers for use as animal feed. There are components of these waste products that are of potential value if they could be recovered economically. For example, tomato peels contain cuticular waxes, cutin and other hydrophobic compounds such as lycopene. Cutin is an insoluble and amorphous biopolymer that consists largely of hydroxylated and epoxy-hydroxylated C16 and C18 esterified fatty acids. It has a very low water sorption and permeability, high specific heat and as such could be a potential substrate for biofilm production. METHODOLOGY This work reports methodology of cuticular fractions isolation, i.e. bulk, dewaxed, and nonhydrolyzable cuticles from tomato industrial waste. The dried tomato peels were firstly treated with oxalic acid/ammonium oxalate solution at 90 °C for 24 h to remove the pectinaceous glue that attaches the cuticle to the epidermal layer. After that the waxes were removed by Soxlet extraction with application of different organic solvents to obtain the best extraction yield. Subsequently, the dewaxed tomato peels were hydrolysed with 6 M HCl, under reflux to obtain the pure cutin biopolymer. The extracted cuticular fractions were characterized using FTIR spectroscopy. Before extraction procedure, the chemical compositions of tomato peel were determined using different analytical measurements. RESULTS AND DISCUSSION The obtained FTIR spectra of dewaxed cuticular fraction indicate the presence of two strong absorption bands located at 2916 and 2848 cm-1, associated with the asymmetric and symmetric stretching vibrations of the methylene groups and relatively strong bands at 1745 and 1162 cm-1, assigned to the carbonyl stretching of the carboxyl group and C-O-C stanching vibrations in the ester group. The hydrolysis of dewaxed cuticular fraction with 6 M HCl caused the ester bonds in cutin polymer to break, corresponding to removal of hydroxy fatty acids. CONCLUSION The results of FTIR spectroscopy confirm that extraction procedures are efficient, i.e. all cuticular fractions were isolated from tomato peels. Obviously, the FTIR spectroscopy can be used as excellent tool for characterisation and validation of isolated compounds from tomato waste industry. Further investigations should be focused on modification of extractions of cutin and cuticular fractions to avoid large volumes of organic solvents and meet the needs of green chemistry.

biopolymer cutin; extraction; FTIR spectra; tomato waste

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