Mineral Content Assessment and Bioavailability in Amaranth Leaves Cooked in Water and Steamed with Four Types of Piper Nigrum

Leafy green vegetables such as amaranth constitute an important source of minerals that can help filling certain deficiencies. However, minerals bioavailability is hindered by antinutritional factors and cooking process induces their losses by leaching and by heat destruction. There is therefore a need to improve their bioavailability during cooking. For this, amaranth leaves were cooked and steamed with four types of peppers ( Piper nigrum ) during 10, 20 and 30 minutes. Minerals, antinutritional factors and minerals’ bioavailability were determined. The results revealed that. However, in steamed and water-cooked amaranth leaves with black pepper for 10 minutes calcium (21.8 - 23.39%), magnesium (24.19 - 25.16%), phosphorus (22.32 - 23.20%), potassium (20.56 - 20.92%), sodium (22.70 - 23.51%) and iron (13.02 - 13.48%) losses were reduced compared to cooking without pepper. Moreover, at the same time and with the same cooking process, phytate/mineral ratios (0.35-0.43 Ca; 0.09-0.10 Mg; 0.06-0.08 K), oxalate/mineral ratios (0.62-0.64 Ca; 0.14-0.15 Mg; 0.11-0.12 K) and Ca/P (0.32-0.42) ratio were lower than the thresholds showing that calcium, phosphorus, magnesium and potassium are bioavailable. But, the high phytate/iron ratio (0.73-1.14) indicate a reduction in iron bioavailability. From 10 to 30 minutes of steam cooking, the mineral contents (mg/100 g) of amaranth leaves cooked with peppers decreased from 80.00 ± 0.04 to 58.20 ± 0.19 for calcium, from 337.19 ± 0.99 to 237.02 ± 0.64 for magnesium, from 194.10 ± 0.28 to 141.51 ± 1.20 for phosphorus, from 429.39 ± 0.49 to 331.75 ± 0.46 for potassium, from 209.03 ± 0.54 to 152.28 ± 0.49 for sodium and from 42.20 ± 0.17 to 28.21 ± 0.08 for iron; against respectively 62.90 ± 0.05 to 50.70 ± 0.08, 246.36 ± 0.20 to 205.97 ± 0.08, 145.02 ± 0.61 to 115.47 ± 0.44, 333.24 ± 0.13 to 262.67 ± 0.26, 156.72 ± 0.19 to 111.43 ± 0.07 and 33.69 ± 0.08 to 24.10 ± 0.12 mg/100 g for leaves cooked without peppers. Steaming amaranth leaves for 10 minutes with black or red pepper better preserve minerals and improve their bioavailability.