NMR and Food Chemistry - Rhubarb

Many gardeners here in Canada are currently harvesting their rhubarb to make pies and other desserts.  Like cranberries, rhubarb is very sour due to the presence of organic acids.  The leaves of the rhubarb plant contain so much oxalic acid that they are toxic.  The stalks of the plant contain less oxalic acid and are not toxic (although I would argue that they taste awful).  Oxalic acid is used in many cleaning products, so if you are like me and hate the taste of rhubarb, you can still make use of it as a cleaning agent.  If you have a very dirty stainless steel pot, you can clean it by simply stewing rhubarb in it.  The figure below shows the ¹H and ¹³C NMR spectra of an aqueous extract of rhubarb stocks.  The major constituents are organic acids with smaller quantities of sugars.  Some of the ¹³C signals from oxalic, malic and citric acids are labelled.