Quality improvement of agar through desulfation with microorganisms

Abstract

Agar is a polysaccharide mixture extracted from red algae. Agar has been widely used in food, medicine and biochemistry, because of its gelling properties and stability. However, sulfate groups in the structure of agar weaken the gel strength of agar; hence, sulfate removal is necessary to improve the agar quality. The commonly used alkali desulfation greatly pollutes the environment, and enzymatic desulfation is costly due to the need for a large amount of the enzyme. In this work, microorganisms were for the first time used for agar desulfation, taking advantage of the sulfur demand of microorganisms themselves. This allows the removal of agar sulfate groups to be eco-friendly and effective. Firstly, microorganism strains were screened with agar as the sole sulfur source. Then 4 microorganism-based agar desulfation techniques, sulfate removal from agar liquid at 60 °C, from an solid agar plate at 37 °C, from freshly-prepared agar slices in liquid medium, and from agar strips without pretreatment (ASWP) in liquid medium, were established and compared. Finally, by using Priestia megaterium WMX, the sulfate removal rate from ASWP reached 74.67%, and the gel strength increased by 187%, reaching 1173 g cm⁻². Therefore, the agar quality was greatly improved by sulfate removal with microorganisms. The microorganism-based agar desulfation technique established in this work is easy-to-perform, cost effective, and an eco-friendly way to improve agar quality and has the potential to be applied on the industrial scale.