Optimization and Mechanism of Phytochemicals Extraction from Camellia Oleifera Shells Using Novel Biosurfactant Nanobubbles Solution Coupled with Ultrasonication

Camellia oleifera shells are a noteworthy by-product often considered as agricultural waste and discarded rather than efficiently used. The extraction of bioactive compounds from shells using green extraction process can be a better approach for waste valorization. Also, demand for novel and green extraction method is required to avoid organic solvents, high cost, and environmental problems. Nanobubbles (NBs) can be used for extraction purposes due to their high specific area and internal pressure. In this study, a novel method using nanobubbles (NBs) solution coupled with ultrasonication to extract phytochemicals from Camellia Oleifera shells (COSs) was first explored. The characterization was performed to measure the size, zeta potential, and surface tension of NBs stabilized by biosurfactant in this case rhamnolipid (Rh). The produced NBs were of size 100 nm, having a surface tension of 35.26 ± 0.31 mN/m−1. Single-factor experiments were performed to determine the significant variables. The Box–Behnken design optimized the ultrasonic power, ultrasonic time, and surfactant concentration to maximize the phytochemicals extraction. NBs solution coupled with ultrasonication (US) leads to a higher extraction yield of total phenolic (34.42 mg of gallic acid equivalent per gram of dry weight (mg GAE/g DW)) and flavonoid content (23.36 mg of rutin equivalent per gram of dry weight (RE/g DW)), as compared to the conventional extraction method. In addition, in vitro antioxidant activity was also increased in NBs solution and NBs’ solution–US extract compared with the conventional solvent method. The morphological and microstructural changes under NBs solution and ultrasonication were also determined to provide a possible extraction mechanism. The present experiment provides a novel extraction method and an overall green perspective of agro and food waste valorization.