Low frequency, high power ultrasound: a non-thermal green technique improves phenolic fractions (free, conjugated glycoside, conjugated esters and bound) in fermented seabuckthorn beverage
Phenolic compounds were characterized after traditional extraction method (TEM) and ultrasound-assisted extractions (UAEs) for 10 min (US10) and 15 min (US15). Four fractions (free, bound, conjugated esters, and conjugated glycosides) were obtained and characterized using RP-HPLC-PDA. The US10 extracted 22.1% (454.3 mg/kg) phenolic compounds while US15 extracted 66.6% (1,369.7 mg/kg) phenolic compounds compared to traditional extraction method (TEM) after 1 hr of extraction. US10 and TEM extracted a similar amount of aglycones (112.3 ± 4.0 and 109.0 ± 12.9 mg/kg, respectively) while US15 showed a significant decrease in aglycone extraction (58.9 ± 4.1 mg/kg) (P < 0.05). In seabuckthorn kombucha, US decreased initial microbial load by 2.6 log CFU/mL, increased ORAC value by 3% and increased water solubility index (WSI) by 40% (from 6.64 to 9.29 g/g) without syneresis. Results from this study suggest that application of US can enhance phenolic functionality during fermentation and is capable of decreasing syneresis, increasing oil yield, decreasing microbial load, and increasing ORAC with minimal loss of nutritional quality.