• UAE with deep eutectic solvent (DES) extracted polyphenols of P. scandens. • Chcl-EG afforded the highest TFC among 16 DESs coupled with UAE. • Optimization of Chcl-EG-UAE was studied by two-level factorial experiment and RSM. • Chcl-EG-UAE had the highest extractability compared with other methods. • 30 polyphenols extracted by Chcl-EG-UAE were identified and quantified by UHPLC-MS.

Total phenolic content (TPC), phenolic profiles, and antioxidant activity of free and bound extracts of Sargassum polycystum , obtained by different extraction solvents and hydrolysis methods, were investigated. Aqueous acetone afforded the highest free TPC and antioxidant ability, followed by aqueous ethanol and aqueous methanol. Twelve free phenolic compounds were identified by ultra‐high‐performance liquid chromatography‐mass spectrometry (UHPLC‐MS), including two hydroxycinnamic acids, seven flavonoids, one stilbene, and two phlorotannins. Three to nine different free phenolic compounds were extracted by these solvents with different compositions, including nine by 70% acetone and eight by 70% methanol, 70% ethanol, and 50% ethanol. The highest total content of free phenolic compounds determined by high‐performance liquid chromatography‐diode array detection was obtained from 70% ethanol. Alkaline hydrolysis afforded higher bound TPC (274.27 mg GAE/100 g DW) and antioxidant ability than acid hydrolysis. Five bound phenolic compounds were characterized by UHPLC‐MS and five were released from alkaline hydrolysis, whereas two were released from acid hydrolysis. Total content of bound phenolic compounds released by alkaline hydrolysis was 14.68‐fold higher than that by acid hydrolysis. The free and bound TPC, phenolic profiles, and antioxidant activities depended on the extraction solvent used. These results indicate that S. polycystum is a potentially useful antioxidant source and contribute to the development of seaweed‐based functional foods. Practical Application: Phenolics are usually divided into free and bound forms based on their extractability and interaction with cell wall components. The nutritional effects of bound phenolics in algae have long been neglected. These topics contribute to the development of seaweed‐based functional foods.

The composition, in vitro bioaccessibility and antioxidant activities of the phenolic compounds in defatted rice bran (DRB) and its soluble and insoluble dietary fibres were systematically evaluated in this study. The total phenolic content of insoluble dietary fibre from DRB (IDFDRB) was much higher than that of the soluble dietary fibre from DRB (SDFDRB) but was 10% lower than that of DRB. Bound phenolics accounted for more than 90% of the total phenolics in IDFDRB, whereas they accounted for 34.2% and 40.5% of the total phenolics in DRB and SDFDRB, respectively. Additionally, the phenolic profiles and antioxidant activities were significantly different in DRB, SDFDRB and IDFDRB. The phenolic compounds in IDFDRB were much less bioaccessibility than those in DRB and SDFDRB due to the higher proportion of bound phenolics in IDFDRB. Considering that bound phenolics could be released from food matrices by bacterial enzymes in the large intestine and go on to exert significant beneficial health effects in vivo, further studies on IDFDRB are needed to investigate the release of the phenolics from IDFDRB via gut microbiota and the related health benefits.

Dietary uptake is well known as the predominant pathway of heavy metal bioaccumulation in organisms. Our study used a typical tropical reservoir and fish as a modeling system to test the hypothesis that feeding habits and living habitats significantly affect heavy metal bioaccumulation in fish. Specifically, Cr, Mn, Fe, Ni, Cu, Zn, Cd, and Pb concentrations in water, sediment, and fish, and δ¹³C and δ¹⁵N in 13 fish species were detected in the Songtao Reservoir of Hainan Province, southern China. Our results indicated that Zn concentration in carnivorous fish was higher than in omnivorous fish. Principal components analysis visually differentiated pelagic, benthopelagic, and demersal fish groups. Moreover, we found that the fish feeding in the demersal habitat showed higher heavy metal levels than those in the pelagic habitat. Additionally, the heavy metal contents in demersal fish were significantly positively correlated with sediments, while no positive correlation was observed in pelagic-feeding fish. The δ¹⁵N and the concentration of Ni, Zn in fish had a significantly positive correlation, suggesting the potential biomagnification. In contrast, Ni, Fe, Cu, and Cd negatively correlated with fish body weight/length, indicating the growth dilution effects. Finally, the estimated daily intake (EDI) of the metals was far below the provisional tolerable daily intake (PTDI), and target hazard quotients (THQ) were <1.0, indicating that the fish had no risk for consumption risks. Overall, our finding partially validated the hypothesis that the feeding habits and living habitats significantly influence heavy metal bioaccumulation in fish, which might be a broad generality for metal exposure scenarios in aquatic environments.