Research progress of ultra-high pressure on the extraction of plant active substances

There are various sources of plant-active substances with biological activities, such as antioxidant, antibacterial, immunomodulatory, and anti-inflammatory. It is very necessary to rapidly, efficiently, and environmentally friendly extract these active substances in the food, medicine, and cosmetics industries. Among them, ultra-high pressure (UHP) with high hydrostatic pressure (HHP) has been widely applied in food non-thermal processing and extraction in recent years. The UHP can be expected to extract the plant active substances for the higher extraction yield and lower extraction time, compared with the traditional solid-liquid extraction. This review aims to introduce the development of UHP in food processing, in order to extract the flavonoids, polyphenols, polysaccharides, and saponins. The principles, processes, and applications were also covered to extract the various active substances, such as flavonoids, polyphenols, polysaccharides, and saponins. The assisted UHP extraction included the three stages: pressure boost, holding, and relief stage, which determined the extraction performance of UHP. Since the UHP tended to destroy the raw tissues, cell walls, cell membranes, and organelles, the solvents were penetrated into tissue cells to dissolve the soluble components for the high mass transfer and the release rate of cell contents. UHP processing included raw material pretreatment, sample treatment, UHP extraction, separation, and purification. The efficiency of UHP extraction depended on the operating conditions. The solvent, pressure level, and extraction temperature were the three most important parameters of the performance of UHP extraction. Furthermore, the UHP extraction was still an effective way to extract polysaccharides, although there were some effects on the structure and biological activity of polysaccharides. Compared with the traditional heat reflux extraction, the UHP extraction was carried out at room temperature or lower temperature, in order to reduce the impact of heat. The simple, rapid, and efficient UHP extraction effectively shortened the extraction time to improve the biological activity for energy saving. A huge market prospect and development potential were found in the UHP-assisted extraction. Previous studies were focused mainly on the extraction optimization and mechanism. Only a relatively few studies explored the performance of antioxidant, antibacterial, and biological activities in the active substances after UHP extraction. And even fewer studies were focused on in vivo antioxidant activities. Many challenges also remained in the UHP application to extract the active substances, such as the imperfect theoretical basis of UHP extraction and high equipment cost. It is necessary to explore the synergistic extraction of UHP combined with other extraction methods. The safer, larger volume and lower cost of UHP equipment can be developed to explore the influence of UHP extraction on the biological activity and antioxidant effect of active substances, particularly the mechanisms behind them. The finding can be expected to promote the wide application and sustainable development of UHP extraction in various fields.