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 °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 17–31%; 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%.