Asparagus (Asparagus officinalis): Processing effect on nutritional and phytochemical composition of spear and hard-stem byproducts

Background: Asparagus (Asparagus officinalis L.), is a well-known vegetable for its unique flavor, texture and presence of many phytochemicals and desirable physiological functions. More than 200 species of asparagus have been identified, of which, Asparagus officinalis is the only species cultivated commercially as a vegetable. Scope and approach : We have comprehensively reviewed the literature on chemical composition and phytochemicals of asparagus, with special attention to phenolic compounds, including rutin as well as saponins, including protodioscin, and diosgenin. The literature on physiology of spear hardening and the utilization of hard-stem byproducts as the source of dietary fiber, and bioactive compounds is also explained. Key findings and conclusions: Asparagus spear and hard-stem byproducts are rich sources of nutritional and phytochemical compounds, the content of which are affected by different factors including asparagus variety, spear part, harvesting season, cultivation method etc. Cold- and MAP-storage are the most widely used processing techniques for fresh keeping of asparagus spear, whereas fermentation, juice production, drying studies have been conducted to some extent. Post-harvest hardening of asparagus spear is inevitable but different methods have been developed to delay such hardening process, such as low-temperature, anaerobic- and dark-condition, along with the control of PAL activity through the application of ammonium sulfate. A large quantity of byproducts (30-50%) generated during production and processing of asparagus, can be converted into various high value products, including bioactive dietary fiber powders, bioactive extracts, mainstream products with these byproducts etc. Therefore, a comprehensive review on botanical, processing and byproduct utilization of asparagus are done in this paper.