Spent coffee grounds improve the nutritional value in minerals of lettuce (Lactuca sativa L.) and are an ecological alternative to inorganic fertilizers

Abstract

The concentrations of several essential and toxic mineral elements of five groups of lettuces (non-cultivated, cultivated with low or high percentages of spent coffee grounds-SCG, without SCG and with NPK) were compared. The influence of adding increasing amounts of SCG in an in vitro assay with a crop soil from Vega of Granada (Spain) was studied. Lettuces with SCG had a higher level of most essential elements (Fe, Co, V, Mn and Zn) as well as some toxic elements (As, Pb and Al), without exceeding the limits established for these elements. Furthermore, blocking of Cd absorption from soil was observed. The direct relations between nutrient absorption and toxic elements and the presence of SCG could be related with minerals chelation by some SCG components, such as melanoidins. In conclusion, the addition of SCG produces lettuces with a higher nutritional value.