Production of unpurified agar-based extracts from red seaweed Gelidium sesquipedale by means of simplified extraction protocols

Abstract

This work reports on the production and characterization of agar-based extracts from the seaweed Gelidium sesquipedale by means of simple protocols based on hot water and sonication treatments. The combination of sonication with the hot water treatment reduced 4-fold the extraction time without significantly affecting the extraction yield (ca. 10–12%) and the extracts' properties. Apart from agar, the extracts contained proteins, polyphenols and minerals, which conferred them high antioxidant capacity and led to the production of brownish softer gels. The application of an alkali pre-treatment yielded almost pure agars, with higher molecular weights and crystallinities than commercial agar, resulting in stiffer gels. However, the partial digestion of agar by the alkali led to low extraction yields (ca. 2–3%). These results show the efficiency of the combined heat and sonication method to generate cost-effective agar-based extracts with potential applications within the food industry.