Kinetics and Thermodynamics Study of Ultrasound-Assisted Depolymerization of k-Carrageenan in Acidic Solution

Abstract

K-carrageenan is a natural polymer with high molecular weight ranging from 100 to 1000 kDa. The oligocarrageenan with low molecular weight is widely used in biomedical application. The aim of this work was to depolymerize k-carrageenan in an acidic solution with the assistance of ultrasound irradiation. The ultrasonication was conducted at various pH (3 and 6), temperatures (30-60 °C), and depolymerization time (0-24 minutes). The results show that the depolymerization reaction follows pseudo-first-order kinetic model with reaction rate constant of 1.856×10-7 to 2.138×10-6 s-1. The reaction rate constant increases at higher temperature and lower pH. The Q10-temperature coefficients of the depolymerization are 1.25 and 1.51 for pH 6 and 3, respectively. The enthalpy of activation (ΔH‡) and the Gibbs energy of activation (ΔG‡) are positive, while the entropy of activation (ΔS‡) is negative, indicating that the activation step of the ultrasound-assisted depolymerization of k-carrageenan is endothermic, non-spontaneous, and the molecules at the transition state is more ordered than at the ground state. The ΔH‡ and the ΔS‡ are not affected by temperature, while the ΔG‡ is a weak function of temperature. The ΔH‡ and ΔS‡ become smaller at higher pH, while the ΔG‡ increases with the increase of pH. The kinetics and thermodynamics analysis show that the ultrasound-assisted depolymerization of k-carrageenan in acidic solution is possibly through three mechanisms, i.e. bond cleavage due to cavitational effect of microbubbles, hydroxyl radical and hydrogen peroxide, as well as proton. Copyright © 2020 BCREC Group. All rights reserved

Effect of microwave and ultrasonic irradiation on the enzymatic hydrolysis of water hyacinth biomass in the presence of surfactants

“…These radicals then collided, forming hydrogen gas and hydrogen peroxide. It is known that hydrogen peroxide is a strong oxidant that can depolymerize polymer (cellulose) by cleaving glycosidic bonds [48]. Hence, ultrasound can enhance the hydrolysis of water hyacinth biomass.…”

Antiviral Activity of Carrageenans and Processing Implications

“…Ultrasound positively contributed to depolymerization of κ-carrageenan involving an enhancement in the corresponding biological activities [ 137 ]. A sonication operation at a wide range of pH values (3–6), temperatures (30–60 °C), and times (<24 min) promoted an adequate depolymerization of carrageenans, obtaining oligocarrageenans with low molecular weights, which are relevant for biomedical applications [ 138 ]. The depolymerization of this kind of biopolymers using ultrasound-assisted extraction in acid media also increased the anticoagulant activity [ 139 ].…”

“…Carrageenan oligosaccharides exhibit promising biological properties and potential pharmacological and therapeutic applications [ 10 , 33 , 38 , 39 , 40 , 44 , 64 , 69 ]. The conditions for depolymerization of carrageenan aided by acid, enzymes, high pressure, microwave, ultrasound, ozone, or irradiation and the range of molecular weights of the resulting carrageenan oligomers can be found in some reviews [ 135 , 138 , 139 ].…”

Fermented Sugar From Ultrasound-Assisted Acid Hydrolysis Berenuk Fruit (Crecentia Cujete L.)

“…Utilization of ultrasonic waves can increase mass transfer and shorten reaction time [8]. Furthermore, ultrasonic waves can extract and hydrolyze natural materials, which have been carried out in several studies, such as the hydrolysis of pineapple peel waste [7], acid hydrolysis and ultrasonic waves on bamboo stems [9], carrageenan depolymerization process [10], Ant nest flavonoid extraction [11], and acid hydrolysis of palm leaves [12]. Cavitation bubbles are created from ultrasonic waves in solution material.…”