The effect of plasma chemical structure and rhological properties of pectin

Abstract

Background: Pectin is an anionic high-molecular weight polysaccharide which is widely used in food and pharmaceutical industries as gelling and thickening agent. Recently, it received growing attention because of its biological function and novel applications in the fields of nano and biotechnology. Numerous studies have been performed to modify structures and properties of pectin via depolymerization, demethoxylation and substitution of functional group such as amidation, sulfation and thiolation, etc. Amidated and low methoxypectin are the main pectin derivatives that have different physicochemical and functional behaviors. Chemical methods are commonly used for preparation of amidated or low methoxy pectin (125). The disadvantages of chemical methods are the utilization of hazardous chemical substances and extensive depolymerization reaction. Alternative technology such as pulse electric field, UV and gamma irradiation, and low temperature plasma (LTP) has been recently considered for the modification of natural polysaccharide. Materials and Methods: High-methoxylated pectin treated with plasma using AC glow discharge plasma unit with O2 and N2 gas. The structural, physicochemical, and functional properties were analyzed using viscosity measurement, rheometry, X-ray Diffraction (XRD), Fourier transform-infrared (FT-IR), Thermo Gravimetric Analysis (TGA), high performance size exclusion chromatography (HPSEC). Results: The intrinsic viscosity of pectin increased in plasma treated pectin using N2 and O2 which could be resulted structural change. Change of intrinsic viscosity occurred within 7 min of exposure to plasma treatment and then remained constant. According to Fourier Transform Infrared Spectrometry (FT-IR) analysis, the intensity of carboxylate peaks increased in PTP samples due to de-esterification of pectin. Moreover, by decreasing the degree of esterification (DE) in PTP samples, the results of FT-IR were confirmed. Based on high performance size-exclusion chromatography (HPSEC) analysis, the molecular weight of PTP reduced. PTP gel had higher storage and loss modulus and shorterlinear viscoelastic region. Moreover, X-ray diffraction (XRD) studies indicated an increase of crystallinity in PTP using nitrogen due to the formation of hydrogen bonds but no significant effect was seen in oxygen assisted plasma. Conclusion: Results revealed that AC glow discharge plasma had significant influence on physicochemical and functional properties of pectin. This method has promising potential towards modification of pectin.