Effect of enzymatic modification on the structure and rheological properties of diluted alkali soluble pectin fraction rich in RG-I

Abstract This study focuses on pectin covalently linked in cell walls and extracted using diluted alkali (DASP) from two sources: apples and carrots, describing changes in rheological properties due to enzymatic treatment. Given DASP's richness in rhamnogalacturonan I (RG-I), RG-I acetyl esterase (RGAE), rhamnogalacturonan endolyase (RGL), and arabinofuranosidase (ABF) were employed in various combinations for targeted degradation of RG-I pectin chains. Enzymatic degradations were followed by structural studies of pectin molecules using atomic force microscopy (AFM) as well as measurements of rheological and spectral properties. AFM imaging revealed significant increase in the length of branched molecules after incubation with ABF, suggesting that arabinose side chains limit RG-I aggregation. Structural modifications were confirmed by changes in the intensity of bands in the pectin fingerprint and anomeric region on FTIR spectra. ABF treatment led to decrease in stability of pectic gels while simultaneous use of ABF, RGAE and RGL enzymes did not increase the degree of aggregation compared to the control sample. These findings suggest that the association of pectin chains within the DASP fraction may rely significantly on intermolecular interactions. Two mechanisms are proposed, involving side chains as short-range attachment points or an extended linear homogalacturonan conformation favoring inter-chain interactions over self-association.