Study of microwave hydrothermal production of lactic acid from seaweed-derived alginate using a response surface methodology based on the Box-Behnken design

A microwave hydrothermal treatment was used for the chemical production of lactic acid from alginate extracted from the brown seaweed Padina Durvillaei, collected in the coastal area of Ecuador. The microwave hydrothermal treatment was studied through a response surface methodology based on the Box-Behnken design, using temperature, reaction time, and catalyst concentration as the manipulated variables and the yield as a response factor. The characterization of alginate was performed by Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). The lactic acid produced was quantified using Gas Chromatography - Ion Mobility Spectrometry (GC-IMS). The results show that temperature and catalyst concentration played the most critical roles in alginate extraction and lactic acid production. The optimal experimental conditions for alginate extraction from brown seaweed were: temperature = 92.91°C, time = 110.81 min and catalyst (Na2CO3) concentration = 2.60%, with a yield = 29.19%. Although the experimental evidence indicates a positive influence of microwaves' use on the production of lactic acid from alginate through hydrothermal treatment, a new study considering temperatures above 220°C and reaction times below 60 min should be developed.