Abstract
The microwave-assisted carboxymethylation of agar to improve its physicochemical properties was investigated. Microwave power, reaction time, and temperature, ethanol concentration, and amounts of chloroacetic acid and sodium hydroxide were assessed for their effects on synthetic yield and degree of substitution (DS). All factors were positively correlated with DS within a certain range. Using optimized conditions, samples with different DS were prepared, and the physicochemical properties of unmodified and carboxymethyl agars prepared by microwave and conventional methods were compared. Carboxymethylation significantly changed the physicochemical properties of the agar, improving gel transparency and reducing dissolution temperature, gel strength, gel hardness, molecular weight, and molecular size; DS was the key factor. Specifically, higher DS values resulted in greater changes. The microwave-assisted method significantly shortened the reaction time and preserved molecular weight, gel strength, and texture hardness of the agar. Therefore, as an environmentally friendly method, microwave-assisted synthesis shows great promise for producing carboxymethyl agar.
Highlights
Based on our previous research, in order to further refine the effects of carboxymethylation on agar and improve its performance in new applications, we investigated the synthetic conditions for microwave-assisted carboxymethylation of agar in this study and analyzed its influence on the physicochemical properties of the modified agar, comparing them to those of agar prepared using the conventional method
Comparing the properties of the carboxymethyl agar prepared using different methods, we found that the dissolution temperature, gel temperature, and gel melting temperature of CAg were not significantly different from those of MAg (p > 0.05), whereas the gel strength of MAg was significantly higher than that of CAg (p < 0.05)
The modification of agar through carboxymethylation improved its physical and chemical properties, and the degree of change in the properties differed compared to the preparation method
Summary
The microwave-assisted carboxymethylation of agar to improve its physicochemical properties was investigated. Carboxymethylation significantly changed the physicochemical properties of the agar, improving gel transparency and reducing dissolution temperature, gel strength, gel hardness, molecular weight, and molecular size; DS was the key factor. The microwave-assisted method significantly shortened the reaction time and preserved molecular weight, gel strength, and texture hardness of the agar. Agar is one of the oldest polysaccharide mixtures and is extracted from marine red algae of the orders Gelidiales and Gracilariales. It is widely used in foods, drinks, and medicine, especially in microbiological media and in tissue engineering, because of its unique gelling power, gel reversibility, and high hysteresis [1–3].
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