Ultrasound-enhanced extraction as a green intensification strategy for phenolic release and in vitro gastrointestinal bioaccessibility from longan byproducts

Abstract

Longan byproducts from industry, often discarded as waste, contain bioactive compounds with potential health benefits. In this study, temperature, solvent ratio, and extraction time were optimized using response surface methodology, comparing water bath and ultrasonic probe techniques. The optimized extracts were evaluated for percentage yield, total phenolic content (TPC), total flavonoid content (TFC), and antioxidant capacity. Ultrasonic-assisted extraction (UAE) achieved significantly higher yield (11.23%), as well as higher phenolic content (219.11 mg GAE/100 g DW), and antioxidant activity (DPPH IC₅₀: 3.78) than the water bath method. The optimized extracts were subjected to simulated gastrointestinal conditions. UAE extracts showed superior intestinal retention with more than 120 mg GAE/100 g DW of TPC compared with >20 mg GAE/100 g DW for the water bath extracts. Antioxidant activities were also higher, with UAE extracts retaining >95% activity, whereas water bath extracts showed only 55–75% activity retention. The digested UAE extract was analyzed using high-performance liquid chromatography (HPLC) to evaluate the impact of in vitro digestion on polyphenols. The compounds corilagin, ellagic acid, gallic acid, epicatechin, procyanidin A2, quercetin, and pinostrobin showed significant increases in oral digestion. These findings demonstrate that UAE increased the extraction efficiency of phenolics from longan processing waste and preserved their activity during oral digestion and, to a lesser extent, in the gastric and intestinal stages, as confirmed by HPLC results. Encapsulation to improve compound stability and the evaluation of cell absorption and digestion are recommended to improve the understanding of bioaccessibility. This study supports the valorization of longan processing waste as a sustainable source of nutraceutical ingredients.