The concentration-modified physicochemical surface properties of sodium carbonate-soluble pectin from pears (Pyrus communis L.)

Structural and rheological properties of diluted alkali soluble pectin from apple and carrot

Pectin, a complex polysaccharide found in plant cell walls, plays a crucial role in various industries due to its functional properties. The diluted alkali-soluble pectin (DASP) fractions that result from the stepwise extraction of apples and carrots were studied to evaluate their structural and rheological properties. Homogalacturonan and rhamnogalacturonan I, in different proportions, were the main pectin domains that composed DASP from both materials. Atomic force microscopy revealed that the molecules of apple DASP were longer and more branched. A persistence length greater than 40 nm indicated that the pectin molecules deposited on mica behaved as stiff molecules. The weight-averaged molar mass was similar for both samples. Intrinsic viscosity values of 194.91 mL·g-1 and 186.79 mL·g-1 were obtained for apple and carrot DASP, respectively. Rheological measurements showed greater structural strength for apple-extracted pectin, whereas carrot pectin was characterized by a higher linear viscoelasticity limit. This comparison showed that the pectin fractions extracted by diluted alkali are structurally different and have different rheological properties depending on their botanical origin. The acquired insights can enhance the customized use of pectin residue and support further investigations in industries relying on pectin applications.

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

This study focuses on pectin covalently linked in cell walls from two sources, apples and carrots, that was extracted using diluted alkali, and it describes changes in the rheological properties of diluted alkali-soluble pectin (DASP) due to enzymatic treatment. Given DASP's richness of 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 a 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 Fourier transform infrared spectra. ABF treatment led to a decrease in the stability of pectic gels, while the 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, which involve side chains as short-range attachment points or an extended linear homogalacturonan conformation favoring inter-chain interactions over self-association.

Influence of pectin domains and protein on the viscosity and gelation properties of alkali-extracted pectin from green tea residue

Alkaline pectin extract (APE) from green tea residues has lower viscosity and gelation properties than commercial citrus pectin. To improve the viscosity and gelation properties of APE, four treatments, namely degradation of homogalacturonan (HG) or rhamnogalacturonan (RG) I domains, esterification, and protein removal and degradation, were applied. With proper degradation of the HG or RG I domains (arabinan or galactan), the viscosity of APE increased from 12 to 2.5×104 or 5.0×103 mPa·s, respectively, and the numbers further increased by approximately 500 times with the addition of Ca2+. Other treatments had slight effects on APE viscosity. The strongest gel (G' = 6.7 × 103 Pa and G″ = 930 Pa) was made using the polygalacturonase treated APE with Ca2+ addition. Degradation of the HG domain or protein enhanced APE's self-crosslink effect, while all methods except protein degradation improved the calcium bridging effect, potentially improving the market potential of pectin from biowaste.

Application of atomic force microscopy in the characterization of fruits and vegetables and associated substances toward improvement in quality, preservation, and processing: nanoscale structure and mechanics perspectives

Fruits and vegetables are essential horticultural crops for humans. The quality of fruits and vegetables is critical in determining their nutritional value and edibility, which are decisive to their commercial value. Besides, it is also important to understand the changes in key substances involved in the preservation and processing of fruits and vegetables. Atomic force microscopy (AFM), a powerful technique for investigating biological surfaces, has been widely used to characterize the quality of fruits and vegetables and the substances involved in their preservation and processing from the perspective of nanoscale structure and mechanics. This review summarizes the applications of AFM to investigate the texture, appearance, and nutrients of fruits and vegetables based on structural imaging and force measurements. Additionally, the review highlights the application of AFM in characterizing the morphological and mechanical properties of nanomaterials involved in preserving and processing fruits and vegetables, including films and coatings for preservation, bioactive compounds for processing purposes, nanofiltration membrane for concentration, and nanoencapsulation for delivery of bioactive compounds. Furthermore, the strengths and weaknesses of AFM for characterizing the quality of fruits and vegetables and the substances involved in their preservation and processing are examined, followed by a discussion on the prospects of AFM in this field.

Structure and functionality of Rhamnogalacturonan I in the cell wall and in solution: A review

Rhamnogalacturonan I (RG-I) belongs to the pectin family and is found in many plant cell wall types at different growth stages. It plays a significant role in cell wall and plant biomechanics and shows a gelling ability in solution. However, it has a significantly more complicated structure than smooth homogalacturonan (HG) and its variability due to plant source and physiological state contributes to the fact that RG-I's structure and function is still not so well known. Since functionality is a product of structure, we present a comprehensive review concerning the chemical structure and conformation of RG-I, its functions in plants and properties in solutions.

Structural properties of diluted alkali-soluble pectin from Pyrus communis L. in water and salt solutions

The self-assembly and gelation of low-methoxyl diluted alkali-soluble pectin (LM DASP) from pear fruit (Pyrus communis L. cv. Conference) was studied in water and salt solutions (NaCl and CaCl₂, constant ionic strength) without pH adjustment at 20 °C. The samples at different LM DASP concentrations were characterized using rheological tests, Fourier-transform infrared spectroscopy, dual-angle dynamic light scattering and atomic force microscopy. LM DASP from pear fruit (Pyrus communis L.) showed gelling ability. The indices (aggregation index and shape factor) based on light scattering may be useful for the characterization of structural changes in polysaccharide suspension, particularly for the determination of a gel point. The results obtained may be important for the food, cosmetic and pharmaceutical industries where pectin is used as a texturizer, an encapsulating agent, a carrier of bioactive substances or a gelling agent.