Pomelo fruitlets have the potential for extracting cellulose. This study aimed to investigate characterization and functionality of cellulose extracted from pomelo fruitlets by different extraction methods. Cellulose extracted by acidic-alkaline hydrogen peroxide hydrolysis (CAA), alkaline hydrogen peroxide hydrolysis (CA), and ultrasonic assisted alkaline hydrogen peroxide hydrolysis (CUA) were prepared from pomelo fruitlets. The results showed that cellulose CUA had higher yield and purity with higher crystallinity and smaller particle size than those of CAA or CA (p < 0.05). Specifically, the yield of CUA was 82.75% higher than that of CAA, and purity was increased by 26.42%. Additionally, water- and oil-holding capacities of CUA were superior to those of CAA or CA, increasing by 13–23% and 10–18%, respectively. The improvement of water- and oil-holding capacities were highly related to its smaller particle size with increased surface area. The results suggested that ultrasonic assisted alkaline hydrogen peroxide hydrolysis is a promising and efficient method to prepare high-purity cellulose from pomelo fruitlets, and this cellulose is expected to be a food stabilizer and pharmaceutical additive.

Curcumin (Cur), a polyphenol with excellent antioxidant and anti-inflammatory properties, is widely used in aquaculture. However, its low water solubility limits bioavailability. This study first investigated the effects of a highly water-soluble and bioavailable valine-curcumin (Val-Cur) on growth performance, antioxidant capacity, inflammatory factor expression and gut microbiota in juvenile largemouth bass. A total of 450 healthy largemouth bass (initial weight 12.00 ± 0.45 g per fish) were randomly divided into six groups: the basal diet group (CK), the group supplemented with 60 mg/kg of curcumin (Cur), and groups that were fed with 15, 30, 60, and 120 mg/kg of Val-Cur. Each group had three replicates (25 fish per replicate). After 8 weeks, compared with both the CK and Cur groups, 30–60 mg/kg Val-Cur displayed significantly increased growth rates, specific growth rates, and protein conversion efficiency, and significantly decreased the feed conversion ratio. Quadratic regression analysis indicated that the optimal supplementation level was approximately 51.62 mg/kg Val-Cur. The Cur and Val-Cur between 30 and 60 mg/kg groups also displayed significantly improved serum biochemical indicators (↑HDL-C, ALB, LZM, CAT and SOD, and ↓MDA). These groups also promoted the expression of intestinal anti-inflammatory factors (TGF-β1 and IL-10) and physical barrier genes (Claudin1, Occludin and Claudin4). In terms of regulating the intestinal microbiota, both Cur and Val-Cur significantly reduced the bacterial diversity (↓Sobs, Chao1 and PD indices) and increased the evenness of bacterial distribution (↑Simpson, Shannon and Pielou indices). In addition, the abundance of some potential pathogens (e.g., Plesiomonas, Plesiomonas shigelloides, and Pseudomonas fluorescens) significantly decreased, while the abundance of beneficial bacteria (e.g., Faecalibaculum, Faecalibaculum rodentium and Lactobacillus murinus) significantly increased. Pearson’s correlation analysis showed that the increase in the abundance of beneficial bacteria was positively correlated with improvement in growth performance, serum biochemical and antioxidant capacity indicators. In summary, Val-Cur exerted superior biological effects at lower dietary inclusion levels than Cur. This study laid a theoretical foundation for elucidating the mechanism of Val-Cur in improving fish immunity and promoting the application of water-soluble curcumin in aquaculture.