Comparison of some additives used in the preparation of freeze-dried lemon juice candidate reference materials

The stability, storage, and distribution of certified reference materials which consist of liquid or frozen fruit juices is rather problematic. As a better alternative a stable orange juice powder has been obtained by freeze-drying to a moisture content below 0.4%. However, freeze-drying lemon juices resulted in unstable materials which collapsed into lumps after standing some weeks in brown bottles under argon. An additive was sought which can be used to obtain stable lemon juice powders without influence on important analytical parameters as amino acids, sugars, organic acids, minerals and flavanone glycosides. The additives pectin, hydroxy ethylcellulose, and hydroxypropyl methylcellulose were examined. Powders containing pectin quickly showed a loss of structure (collapse) and resulted in non-acceptable changes in amino acids, sugars or minerals compared to the original lemon juice. The addition of up to 3% hydroxypropyl methylcellulose seemed more promising, although some minor changes in the sugar and sodium concentration occurred.