Production of flavonol quercetin and fructooligosaccharides from onion (Allium cepa L.) waste: An environmental life cycle approach

摘要

Onion (Allium cepa L.) is a worldwide culinary ingredient and the second most important vegetable crop. Hence, the amount of onion solid waste (OSW) is really abundant and constitutes an environmental problem due to its pungent odour and the proliferated growth of phytopathogens. However, the content of flavonol quercetin and fructooligosaccharides (FOS) makes it a potentially recoverable residue. The aim of this study is to incorporate a biorefinery approach, developing a full-scale plant for the valorization of OSW into quercetin and FOS, under a circular economy perspective and, in parallel, to evaluate the environmental profile of this alternative according to a Life Cycle Assessment perspective. To do so, inventory data are obtained from modelled processes at large scale. A mass-based allocation approach is established as baseline, although a sensitivity assessment is further developed considering the influence of the different variables on the results obtained. The results identify that the sections responsible for the extraction of quercetin and FOS, based on the use of ethanol as an extractive agent, have significant environmental burdens. Consequently, the use of this solvent is responsible for a high environmental load due to its background production processes, reaching contributing ratios of up to 30% and 50% in some categories for the extraction of quercetin and FOS, respectively. In addition, the consumption of electricity in the different stages of the process is also responsible for high environmental loads (up to 93% for flavonol quercetin and 86% for FOS) due to its dependence on fossil fuels. Therefore, improvement alternatives should be studied (e.g. microwave and ultrasound-assisted extractions) to significantly reduce impacts on the environmental profile.