Search

Background In Florida, 90% of citrus is processed into juice, leaving large amounts of peel waste that could be processed into food ingredients such as pectins for other applications. Pectins of low degree of methylation ( DM < 50) have important functional properties for use in foods and pharmaceuticals. Thus determination of DM is important, but DM analyses are difficult to perform and assays can have interference due to the presence of salts or neutral sugars. Results A chromatography method has been developed for determination of DM of food pectin using alkaline hydrolysis followed by pectin digestion with a commercial pectinase. Analysis was performed by ion exclusion chromatography ( IEC) to obtain methanol ( MeOH) concentrations and by anion exchange chromatography ( AEC) to obtain galacturonic acid ( GalA) concentrations. Data were compared with values obtained using other DM analysis procedures. For example, a 55-75 DM pectin assayed as 55.5, 59.6, 60.1 and 57.0 DM by IEC, AEC, colorimetric and conductivity detection methods respectively. Conclusion The chromatography procedure described in this paper provides an alternative method for determination of DM of food pectins for accurate and efficient analysis when confronted with limited quantities or large numbers of samples. Published 2013. This article is a U.S. Government work and is in the public domain in the USA. [ABSTRACT FROM AUTHOR]

One of the four pectin methylesterase types isolated from Citrus sinensis var. Valencia fruit was used to demethylesterify a model homogalacturonan (HG) to 30%, 50% and 70% degree of methylesterification (DM) at pH 4.5 and 7.0, respectively. Introduced demethylesterified blocks (DMBs) were released by a limited endo-polygalacturonase (EPG) digestion, separated and quantified by HPAEC. Average DMB size ( B S ¯ ) and number of such blocks per molecule ( B N ¯ ) differed depending on final DM and reaction pH ( P < 0.05). B S ¯ and B N ¯ were significantly higher in 30% DM HG than 50 and 70 DMs. pH 4.5 series showed significantly larger B S ¯ compared to pH 7.5 series ( P < 0.01). Distribution of DMBs released by limited EPG digest was predicted by mathematical modeling and in silico modeled processive (degree of processivity = 10), multiple attack mode of action best explains the experimental block distributions. Absolute degree of blockiness (DB abs ) obtained from exhaustive EPG digestions, displayed a linear relationship with DM regardless of reaction pH (P < 0.001). Significant correlation coefficients between B S ¯ , B N ¯ , DB abs , and DM manifested the effectiveness of the block information gained from both EPG digestion to estimate DMB distribution pattern (P < 0.05). However, comparison of block distribution information of three isozymes revealed that difference in block pattern could be manifested by parameters from limited EPG digest ( B S ¯ , B N ¯ ) but not by those from exhaustive digest (DB/DB abs ). The results suggested the possibility to control B S ¯ and to customize specific population of demethylesterified pectin molecules using PME isozymes from Valencia orange. [ABSTRACT FROM AUTHOR]