Exploring pilot scale ultrasound-microwave assisted extraction of organic acids and phytochemicals from brown seaweed Alaria esculenta

Abstract

This study investigates ultrasound (US) and microwave (MW) technologies – both applied individually (ultrasound-assisted extraction (UAE), microwave-assisted extraction (MAE)) and simultaneously (ultrasound–microwave-assisted extraction (UMAE)) for extracting bioactive compounds from a brown seaweed Alaria esculenta. This research emphasizes sustainability by using wet biomass and water for extraction. Employing a range of power (336–1340 W (MW); 50–200 W (US)) and time (5–20 min) conditions, the study evaluates multiple phytochemicals as well as antioxidant activities in the obtained extracts. The highest total soluble carbohydrate contents (32.68 mg glucose equivalents (GE)/100 mg extract) were achieved by UAE (200 W, 20 min). UMAE (50 W (US), 1340 W (MW), 10 min) had the highest levels of total phenolic contents (2.07 mg gallic acid equivalents (GAE)/100 mg extract) and FRAP (38.36 μM Trolox equivalents (TE)/mg extract). The highest protein content (15.62 ± 1.69 bovine serum albumin equivalents (BSAE) mg/100 mg extract) was recorded by UMAE (100 W (US), 1340 W (MW), 20 min). MAE (1340 W, 20 min) achieved the highest levels of succinic (7.52 mg/g extract) and lactic acids (39.08 mg/g extract), while UMAE (670 W (MW), 100 W (US), 5 min) extracted the highest amounts of malic (3.02 mg/g extract) and α-ketoglutaric acids (2.41 mg/g extract). Lactic acid, followed by pyruvic acid was the major organic acid present in the extracts. Scanning electron microscopy images confirmed increased cell damage in the biomass by all the treatments, with higher levels of surface roughness and enlarged pores appreciated after UMAE. Hence, this work being among the first to demonstrate US and MW application, both individually and simultaneously, on Alaria esculenta, utilizing an integrated commercially available pilot-scale system and a green extraction solvent, sheds light on the extraction of valuable phytochemicals including underexplored organic acids which hold immense potential for diverse applications.