GC-FID determination of pectin monomers from industrial orange residue polymers after acid and enzymatic hydrolysis

Trabajo presentado a las 15as Jornadas de Análisis Instrumental, celebradas en Barcelona (España) del 3 al 5 de octubre de 2017.The orange residues reach 13.5 million tonnes per year causing pollution and economic losses. Although these by-products are mainly transformed into animal feed, they are a source of bioactive compounds such as pectin, an important heteropolysaccharide with important applications in the food and pharmaceutical industries. One of the molecular characteristics of pectin is its monomeric composition that is usually determined by chromatographic methods such as GC-FID previous hydrolysis of polymers. Enzymatic hydrolysis represents mild operation conditions, low energy requirements and high costs of application, compared to acid hydrolysis, but the selection of the method depends mainly on the effectiveness of hydrolysis together with the preservation of the interest compounds, such as galacturonic acid (AGal) and other monosaccharides characteristic of pectin. The objective of this research was to determine the monomeric composition of pectin extracted from orange residues, after acid and enzymatic hydrolysis. Samples of fresh orange residue, dehydrated residue, pressing liquor and animal food were supplied by García-Carrión (Spain). Acid hydrolysis was carried out with 2 M trifluoroacetic acid (TFA); after the formation of oximes and trimethylsilyl derivatives the analysis of monomers was performed by GC-FID on an Agilent Technologies 7890a GC, using a DB-5HT column (15m x 0.32mm x 0.10 µm). The injector and detector temperatures were 280 and 350 °C, respectively, and that of the oven from 150 to 300 °C or 380 °C. The residues with the highest amount of AGal were treated with Celluclast at 25 µL/mL for 18 h and their hydrolysis was performed with Viscozyme at 25 µL/mL for 24 h or with TFA under the conditions described above. The highest yield of extracted pectin was 25%, corresponding to the fresh residue. After acid and enzymatic hydrolysis AGal, xylose, arabinose, rhamnose, galactose and mannose were found in all the pectins. The enzymatic hydrolysis was the most adequate procedure for obtaining the highest content of AGal before GC-FID analysis. Hardly any effect was found of the industrial processing, and AGal amount was similar in all solid samples (70.4-74.4%), indicating their suitability as a pectin source.J. García Carrión S.A., projects: AGL2014-53445-R and ALIBIRD-CM S-2013 / ABI-272 and the support of SENESCYT-Ecuador.Peer reviewe