Green extraction and characterisation of Ulvan from residual Ulva rigida alga recovered fron Orbetello lagoon

In the present study, firstly Ulva rigida recovered from the Orbetello lagoon was characterised in terms of biomass particle size, chemical composition, elemental analysis (EA), thermogravimetric analysis (TGA), and infrared spectroscopy (ATR-FTIR). Then, the effect of the main reaction parameters, such as temperature (60–120 °C), pH (1–7), reaction time (30–150 min) and type of heating system (traditional, microwaves and ultrasounds), was investigated and optimised in order to maximise the ulvan yield and purity (in terms of protein and ash content). In particular, water was selected as the green solvent, HCl as eventual homogenous catalyst and 50 g/L as biomass loading. Under the optimised extraction conditions under traditional heating (120 °C, pH 7, 90 min), the ulvan yields of 77 wt% with respect to the total sugars content and of 27 wt% with respect to the alga dry weight were achieved. Finally, the extracted ulvan was characterised by EA, TGA, ATR-FTIR, optical microscopy and its chemical composition confirmed the low content of proteins and ash. The extracted ulvan is wider applicated as a nutraceutical in aquaculture and as an antimicrobial agent in plant cultivation.