Effects of UV-B Radiation on Oxalate Content of Silver Beet Leaves

Silver beet (<em>Beta vulgaricus </em>var. <em>cicla</em>) a common vegetable in New Zealand is known to contain high levels of oxalates in the leaves. Silver beet plants were grown in afield trial under glass and perspex sheets which filtered sunlight reaching the plants. After eight weeks of growth, the plants were harvested and the total, soluble and insoluble oxalate content of the leaves of the plants grown under the two filter treatments and a no-frame control were measured. Perspex allowed the transmission of UV-A, UV-B and photosynthetically active radiation (PAR), whereas glass excluded UV-B radiation. No significant differences between the perspex treatment and the no-frame control were observed when the data was compared on a wet matter (WM) or dry matter (DM) basis Shielding the growing plants with glass significantly reduced the total oxalate and soluble oxalates to 83 and 84% respectively when compared to the perspexand no-frame treatments.

Oxalate Content of Stir Fried Silver Beet Leaves (Beta Vulgaris Var. Cicla) with and without Additions of Yoghurt

Total and soluble oxalic acids were extracted and analysed by HPLC chromatography following Asian cooking methods, which involved soaking, boiling and stir frying of silver beet (<em>Beta vulgaris </em>var. cicla) leaves. Autumn-grown silver beet leaves contained 1658 ± 114 mg/100 g dry matter (DM) of total oxalates, 954 ± 49 mg/100 g DM of soluble oxalates and 704 ± 98 mg/ 100 g DM insoluble oxalates. Soaking and boiling before stir frying reduced the soluble oxalate contents to a mean of 455 mg/100 g DM. Addition of standard or low fat yoghurt following the pre-treatments of soaking, boiling, stir frying and soaking, boiling and stir frying further reduced the soluble oxalate content to a mean of 190.8 ± 49.8 and 227.5. ± 47.0, respectively, for the standard and low fat yoghurt mixes.