Cradle to grave: The multifaceted soapnut-an update on the applications of Sapindus spp

Soapnuts and other saponin-rich plant materials are known for their phytochemistry and pharmacology. After a gap of two decades, there has been a sudden spate in research on soapnuts with experiments on a wide range of applications. The present review compiles these different aspects of research to explore the possibility of creating a circular economy around soapnut. We are looking at the study from the cradle-to-grave approach. Of the twelve soapnut species present globally, this paper focuses on three- Sapindus mukorossi, S. trifoliatus syn laurifolia, and S. emarginatus. The saponin content varies among the three species, making it difficult to ascertain the critical micelle concentration (CMC), an important functional aspect. Recent research in applications includes surfactants in industry, laundry, bioremediation, biopesticide, poultry feed supplement, biodiesel, biochar, and pharmacology. As an alternative to laundry detergent, soapnut works best at CMC. The ecological services of the tree are restricted to terrestrial ecosystems, while the fruit is toxic to aquatic animals. More research is needed to establish the permissible limits for soapnut saponins in wastewater and their biodegradability before soapnuts can be accepted as a bio-based surfactant. Nevertheless, research indicates that it will be beneficial to propagate soapnuts as a sustainable supplement to petroleum-based surfactants and fuels. With many by-products from soapnuts, it is possible to attain zero wastage. Propagation techniques, including natural regeneration, selective crop breeding, vegetative propagation, and tissue culture, have been explored to promote high-quality crops. Planting the appropriate variety of soapnuts could provide a sustainable agroforestry crop that is resilient to climate change. • Reviews soapnuts as sources of natural surfactant for bioremediation, crude oil recovery, cleaning action and pest control. • Identifies a range of other uses including biodiesel, biochar, pharmacy and animal husbandry, with scope for agroforestry. • Alerts against the pitfall of toxicity, if released unchecked into aquatic ecosystems. • Suggests a cradle-to-grave approach to prepare soapnut-based products to meet Sustainable DevelopmentGoals.