Investigation of enzyme-assisted methods combined with ultrasonication under a controlled alkali pretreatment for agar extraction from Gelidium sesquipedale

This study investigated the eco-friendly extraction of agar from Gelidium sesquipedale. Two extraction strategies namely ultrasonication combined with a controlled alkali pretreatment followed by enzyme-assisted extraction (EAE), and ultrasonication combined with EAE for agar extraction were employed in this study. Five typical enzymes classified in carbohydrase and proteinase groups were explored for the extraction uses. The EAE yields obtained were 2 to 6-fold higher compared to a non-enzyme extraction control method for a total extraction time of 2–3 h. Agar extracts were analysed using a cascade of characterisation methods. FT-IR spectroscopy and chemometrics was used to determine the promising extraction protocols. In addition, apparent viscosity, molecular weight, sulphate content, 3,6-anhydrogalactose content, gel strength, compositional analysis and thermogravimetric analysis were also carried out to profile the agar extracts and furtherly identify the most promising extraction protocols. Characterisation results showed that agar extracted using EAE with Viscozyme® most closely matched the measured properties of a high-quality agar product. Further scale-up studies of EAE combined with ultrasonication for agar extraction should be carried out to facilitate industrial adoption of this eco-friendly processing approach.