Ultrasound-Assisted Extraction of Antioxidant and Antibacterial Phenolic Compounds from Steam-Exploded Sugarcane Bagasse

Sugarcane bagasse is most directly used as fuel; therefore, its economic value is not maximized. Steam explosion and ultrasound-assisted extraction (UAE) was investigated to develop an effective process for the production of valuable phenolic compounds from sugarcane bagasse lignin. The influence of steam explosion (temperatures: 190, 200 and 210 °C, and times: 5, 10, 15 and 20 min) as well as UAE (solvent types: 95% ethanol, 70% ethanol, distilled water and ethyl acetate, and conditions—powers: 20, 40 and 60 W, and times: 3, 6 and 9 min) was explored. The yield, total phenolic content (TPC), and trolox equivalent antioxidant capacity (TEAC) of the extract increased with increasing temperature and time, but beyond 10 min at 210 °C, a negative impact was observed. The optimal UAE (40 W and 6 min) using 95% ethanol gave the highest TPC (29.11 mg gallic acid equivalent/g), the highest TEAC (82.54 mg TE/g), and the lowest minimal inhibitory concentration (1.77 mg/mL) against Staphylococcus aureus TISTR029 and (7.10 mg/mL) against Escherichia coli O157:H7. The free radical scavenging activity of the extract was comparable to that of ascorbic acid. Reversed-phase high-performance liquid chromatography analysis revealed the presence of gallic acid, hydroxybenzoic acid, vanillic acid, p-coumaric acid, ferulic acid, syringic acid, and sinapic acid. The advantage of UAE over maceration was 10 times shorter time. The results indicated that the phenolic compounds from sugarcane bagasse lignin had a potential use as a natural antioxidant and antibacterial, which caused a great impact on the sugar industry.