Changes in Oxalate, Nitrate, and Lutein Contents in Whole and Cut Spinach Boiled with Different Additives

The purpose of this study was to optimize the processing and cooking conditions to retain lutein and reduce the concentrations of oxalate and nitrate in spinach. We investigated the effects of preliminary processing, particularly cutting size and the inclusion of different additives, on changes of oxalate, nitrate, and lutein concentrations in cooked spinach. The results of this study indicated that a combination of boiling in water (100 °C for 2 min) and a 1-cm cutting size resulted in maximal removal of oxalic acid and nitrate ion (72% and 58%, respectively) and maximal retention of lutein (79%) in spinach. Although the inclusion of some adjuvants had significant effects on the concentrations of oxalic acid, nitrate ions and/or lutein at certain concentrations, these effects were not concentration-dependent. We conclude that the addition of various compounds during boiling may not consistently promote either the removal of oxalate and nitrate or lutein retention.