Availability of essential and trace elements in frozen leguminous vegetables prepared for consumption according to the method of pre-freezing processing

The content of ash and P, K, Ca, Mg, Na, Fe, Zn, Mn, Cu, Cr and Ni was determined in broad bean and pea seeds of milk-wax maturity and in French-bean pods. The investigation covered the raw material; blanched and cooked material and frozen products prepared from blanched or cooked vegetables after 12 months of storage at -30 degrees C. Frozen products were prepared for consumption either by cooking or by defrosting and heating in a microwave oven. The smallest general loss of constituents caused by blanching was found in broad bean seeds, while the greatest loss was in French-bean pods. Cooking the same batch of the raw material increased the loss by 0-14%, depending on the species and the analysed element. In 100 g of product, prepared for consumption using the modified method (cooking-freezing-defrosting and heating in a microwave oven), the content of ash was greater by 4-12%; of phosphorus by 2-11%; of potassium by 16-36%; of magnesium by 17-3 1 %; of iron by 7-23%; of zinc by 4-12%; of manganese by 4-16% and of copper by 3-13% compared with products obtained using the traditional method (blanching-freezing-cooking). The recorded level of the remaining elements was not always higher: in the case of calcium the difference varied from -2% to +7%; of sodium from -11% to +24%; of chromium from -14% to +9%; and of nickel from -4% to +54%. (C) 2007 Elsevier Ltd. All rights reserved.