Mechanisms, Capabilities, Limitations, and Economic Stability Outlook for Extracting Phenolics from Agro-byproducts Using Emerging Thermal Extraction Technologies and Their Combinative Effects

The agro-food industries produce substantial waste that has an adverse effect on the ecosystem. Nevertheless, these byproducts have abundant polyphenols with various bioactivities. Although conventional extractions (CE) are used for extraction, they require a long extraction time and more solvents, affecting product quality. Hence, this article reviewed emerging thermal extraction technologies (subcritical water, supercritical fluid, microwave, high pressurized liquid extraction, etc.) and their combinative effects (for instance, integrated subcritical-microwave, integrated supercritical fluid-hot-pressurized liquid extraction) that have been applied to extract polyphenols from agro-byproducts in the last 5 years. The fundamental mechanisms, their applications, shortcomings, and future investigations on augmenting these technologies are presented. The review showed that integrating cutting-edge technology could facilitate the development of more polyphenol extraction from agro-byproducts as there are many benefits, including increased extractability, reduced impurities, preserved thermosensitive compounds, and consume low energy. Hence, it is proposed that the next 5 years should explore combined novel thermal extraction technologies. The techno-economic analysis must be considered to fully investigate the implementation of these technologies in the polyphenol extraction from byproducts. Finally, waste valorization can inspire creativity and agro-business creation, particularly when integrated with food industry 4.0.