Compositional and structural characterization of pectic material from Frozen Concentrated Orange Juice

摘要

In citrus juices pectin is one of the major components of the suspended cloud material that imparts desirable appearance, texture and flavor. Citrus pectin is a structurally diverse polysaccharide with a backbone of α-(l,4)-galacturonic acid (GalA) residues, a variable proportion of which may be methyl-esterified, and interspersed with regions containing repeating rhamnogalacturonan dimers. We have acid extracted pectin from commercial Frozen Concentrated Orange Juice (FCOJ) and assessed its macromolecular properties, including soluble sugar composition and molecular weight as well as its degree (DM) and pattern (DB, DB_(abs)) of methyl-esterification. The extracted material was composed mainly of polysaccharides (82%) dominated by galacturonic acid (39.2%), arabinose (13.2%) and galactose (25.6%). Protein accounted for approximately 4% of the extracted material and included arabinogalactan protein (AGP). The Number Average Molecular Weight (M_n) of the extracted material as determined by MALLS-SEC was estimated at 1.462 × 10~6 Da indicating the presence of aggregates. The pectin DM was relatively high at 74.7% with very few contiguous demethylesterified GalA residues (DB = 15.92, DB_(abs) = 4.03). Treatment with various pectinolytic, hemicellulytic, or proteolytic enzymes allowed us to evaluate the contribution of various structural domains to the macrostructural architecture of the extracted material. Various enzyme treatments of the extract produced of a second, lower M_n peak and a loss of material in the larger M_n peak. The M_n varied according to the enzymatic digestion method employed, from 1.5 × 10~6 Da for the parent material, to 1.4 × 10~3 Da when treated with Rapidase Adex-P.