Spent coffee grounds as a source of smart biochelates to increase Fe and Zn levels in lettuces

Abstract

Spent coffee grounds (SCG), an ever-increasing food waste whose annual generation is 15 million tons, have the potential to fulfil many different purposes after being recycled. However, though SCG have been used as soil organic amendment, their utilization is limited by their phytotoxic nature. Although SCG favour the assimilation of nutrients by plants, whether or not they could be used as an agronomical bio-fortifying agent has not been investigated yet. Therefore, we carried out an in vitro investigation to analyse the influence of SCG and coffee melanoidins functionalized with Fe and Zn (biochelates) on the agronomic biofortification of lettuce (Lactuca sativa var. longifolia), one of the most consumed edible plants worldwide. Commercial chelates (EDDHA-Fe and EDTA-Zn) and non-functionalized SCG and melanoidins were used as controls. Total Fe and Zn content in lettuces and available Fe and Zn in soil were measured. Functionalized SCG and melanoidins were able to significantly increase both Fe and Zn levels in lettuces. While Fe levels increased around 28–30%, Zn showed a much larger improvement with levels up to 177–416% higher. According to our results, both SCG and coffee melanoidins could be used as agronomical bio-fortifying agents. Additionally, bio-fortified lettuce would provide up to a 16.3% of the Fe recommended daily intake and up to a 6.6% of that of Zn, reflecting positively in human health.