Exploring Ultrasound, Microwave and Ultrasound-Microwave Assisted Extraction Technologies to Increase the Extraction of Bioactive Compounds and Antioxidants from Brown Macroalgae

Abstract

This study aims to determine the influence of (1) ultrasound-assisted extraction (UAE), (2) microwave-assisted extraction (MAE) and (3) a combination of ultrasound-microwave-assisted extraction (UMAE) on the yields of fucose-sulphated polysaccharides (FSPs), total soluble carbohydrates and antioxidants extracted from A. nodosum. Scanning electron microscopy (SEM) was used to evaluate the influence of the extraction technologies on the surface of macroalgae while principal component analysis was used to assess the influence of the extraction forces on the yields of compounds. UMAE generated higher yields of compounds compared to UAE and MAE methods separately. The maximum yields of compounds achieved using UMAE were: FSPs (3533.75 ± 55.81 mg fucose/100 g dried macroalgae (dm)), total soluble carbohydrates (10408.72 ± 229.11 mg glucose equivalents/100 g dm) and phenolic compounds (2605.89 ± 192.97 mg gallic acid equivalents/100 g dm). The antioxidant properties of the extracts showed no clear trend or extreme improvements by using UAE, MAE or UMAE. The macroalgal cells were strongly altered by the application of MAE and UMAE, as revealed by the SEM images. Further research will be needed to understand the combined effect of sono-generated and microwave-induced modifications on macroalgae that will allow us to tailor the forces of extraction to target specific molecules.

Keywords: antioxidant; biorefinery; carbohydrate; fucoidan; functional food; innovative technology; polyphenol.

Figure 1

Scheme summarizing the preparation, pre-treatments and extraction conditions applied to A. nodosum to generate macroalgal extracts together with the chemical analyses performed.

Figure 2

Yields of fucose-sulphated polysaccharides (FSPs), total soluble carbohydrates, phenolic compounds and antioxidant activities (FRAP and DPPH) of extracts from A. nodosum obtained by UAE at ultrasonic amplitudes (20%, 50% and 100%). Light and dark bars represent ultrasound-assisted extraction (UAE) treatments of 2 or 5 min, respectively. Results are expressed as average ± standard deviation of the mean (n = 6). The statistical differences between different treatment times for each UAE combination are expressed as follows: * P < 0.05, ** P < 0.01, *** P < 0.001.

Figure 3

Yields of FSPs, total soluble carbohydrates, phenolic compounds and antioxidant activities (FRAP and DPPH) of extracts from A. nodosum obtained by microwave-assisted extraction (MAE) at microwave powers (250, 600 and 1000 W). Light and dark bars represent MAE treatments of 2 or 5 min, respectively. Results are expressed as average ± standard deviation of the mean (n = 6). The statistical differences between different treatment times for each MAE combination are expressed as follows: * P < 0.05, ** P < 0.01, *** P < 0.001.

Figure 4

Yields of FSPs, total soluble carbohydrates and phenolic compounds of extracts from A. nodosum obtained by ultrasound–microwave-assisted extraction (UMAE). The recoveries were explored using multiple combinations of ultrasonic amplitude (20%, 50% and 100%) and microwave power (250, 600 and 1000 W). Light and dark bars represent the yields of each compound obtained when extracting macroalgae for 2 or 5 min, respectively. Results are expressed as average ± standard deviation of the mean (n = 6). The statistical differences between different treatment times for each UMAE combination are expressed as follows: * P < 0.05, ** P < 0.01, *** P < 0.001.

Figure 5

Antioxidant activities (FRAP and DPPH) of extracts from A. nodosum obtained by UMAE at multiple combinations of ultrasonic amplitude (20%, 50% and 100%) and microwave power (250, 600 and 1000 W). Light and dark bars represent the yields of each compound obtained when extracting macroalgae for 2 or 5 min, respectively. Results are expressed as average ± standard deviation of the mean (n = 6). The statistical differences between different treatment times for each UMAE combination are expressed as follows: * P < 0.05, ** P < 0.01, *** P < 0.001.

Figure 6

Principal component analysis scatter plot representing the scores for the extraction yields of FSPs, total soluble carbohydrates, phenols and antioxidant activities (FRAP and DPPH) of extracts from A. nodosum obtained using sonication and microwave technological treatments.

Figure 7

Scanning electron microscopy images of (I) dried and milled A. nodosum biomass before extraction, (II) macroalgal residue after MAE (250 W, 2 min) and (III) macroalgal biomass after the process of UMAE (1000 W, 100%, 5 min). Scale bars (A) 200 µm (magnification: 250×) and (B) 50 µm (magnification: 1000×).

Figure 8

Schemes showing the technological designs (I) ultrasound-assisted extraction (UAE), (II) microwave-assisted extraction (MAE) and (III) ultrasound–microwave-assisted extraction (UMAE) used to generate macroalgal extracts.