THE MINERAL COMPOSITION OF POTATOES AND ITS INFLUENCE ON THE DARKENING OF TUBERS PULP

Abstract

Potato tubers are one of the most widespread and valuable food products in the world. An important component of their nutrients are minerals. Significant part of them is presented in potatoes in the form of mineral salts that are easily soluble in water. The total quantity of minerals in potato tubers is about 0.4–1.9% of the total weight and includes more than 30 elements. The objects of the study were five varieties of potato tubers that according of the length of the growing season belong to two ripeness groups: medium-early (Satina – control, Red Lady, Mozart) and medium-ripe (Aroza – control, Sifra). The quantitative composition of macro- and microelements (K, Ca, Mg, Na, Al, Fe, Mn, Ni and Cr), content of heavy metals (Cu, Zn, Pb and Cd) was determined and influence of some mineral substances (K, Fe and Cu) on the resistance of raw and cooked potato tubers to different types of darkening was assessed. Mineral substances were determining by corpuscule-emission spectrometry with inductively-linked plasma. Potassium had the highest quantity among macronutrients. Its amount changed from 5860 mg in the Sifra variety to 3740 mg in the Satina. Magnesium content was averaged 200 mg, and calcium ranged from 68 mg in Red Lady to 159 mg in Cifra. The main quantity of microelements was represented by aluminum and iron. The content of heavy metals in potato tubers did not exceed the permissible concentrations, and in some cases it was lower: lead was found in the traces quantities, zinc was almost twice less and copper was in five times lower than the maximum permissible concentration. Direct relationship between the amount of potassium and the degree of darkening of cooked tubers was revealed: if its amount in the tubers increased therefore resistance to darkening of potatoe increased too. It was established that iron and copper can also affecting on the processes of darkening in potato tubers, although a clear relationship between their quantity and the depth of these processes was not found. The reason may be the imperfection of the visual method of detecting of degree of darkening and the possible formation of complex compounds with these minerals, as a result of which they become unavailable for the reaction.