Optimizing the ultrasonic-assisted extraction of antioxidants from Ulva lactuca algal biomass using factorial design

Ultrasonic-assisted extraction (UAE) is increasingly emerging as a highly effective extraction technique. This extraction technique is affected by several experimental factors. The present work aimed to optimize the ultrasonic-assisted extraction of antioxidants from Ulva lactuca (sea lettuce), widespread macroalgae growing along the Mediterranean coast. In this respect, a full-factorial design (2 3 ) was employed to assess the effect of three different factors at two levels and their interactions on the extraction of antioxidants from sea lettuce algal biomass. The studied factors were extraction solvent, time of extraction, and temperature. The two levels chosen for extraction solvent were 100% ethanol and 50% ethanol, for the sonication time (1 h and 3 h) and temperature (25 °C and 40 °C). All experiments were done using an ultrasonic bath, and the biomass to solvent ratio was kept at 1:5. Total antioxidant capacity and quercetin concentration were set as the two responses for optimum output. The results showed that the temperature and solvent were the dominating factors that significantly affect the extraction process. The optimum extraction parameters were extraction time of 1 h, 50% ethanol, and temperature of 25 °C. Under these conditions, the maximum value for TAA was calculated as 2166.51 mg of ascorbic acid equivalent per gram (mg/g of AAE), and quercetin showed a maximum calculated value of 42.5 mg/g with combined desirability of 0.91 for the two responses. The present study results indicate that U. lactuca can be used as a source of antioxidants and phenolic compounds that can be applied in food and medicine at optimum extraction conditions. Graphical abstract