Impact of trona-aided boiling on the phytochemical constituents and beneficial micronutrients of lima bean (Phaseolus lunatus L.)

The influence of boiling lima bean, using trona solution, on its phytochemical constituents and selected micronutrients was investigated. Lima bean was initially boiled for 3 h using 0.1, 0.2, 0.3, 0.4 and 0.5% trona solution, respectively at ratio 1:5 (bean/trona solution). The boiled lima bean was subsequently dried in an oven at 55°C for 12 h after which it was subjected to various analyses. Maximum reduction of phytochemicals such as trypsin inhibitor activity (74.1%), haemagglutinin (98%), tannin (68.6%), phytic acid (39.6%), and cyanogenic glycoside (73.8%) was obtained at 0.5% boiling with trona-solution. The reduction profile for the B-vitamins includes thiamine (0.58 to 0.13 mg/100 g), riboflavin (0.37 to 0.21 mg/100 g), niacin (0.97 to 0.28 mg/100 g) and pyridoxine (0.41 to 0.11 mg/100 g). Boiling lima bean in trona solution led to significant decrease (p<0.05) in the concentration of calcium, magnesium and phosphorus while mineral concentration enhancement was observed with potassium, sodium and iron. Maximum in vitro protein and starch digestibilities of 88.6% and 51.9 mg/g, respectively were obtained for 0.5% trona solution boiling of lima bean. Trona usage in the boiling of lima bean therefore served as a beneficial step in the utilization of the legume.   Key words: Lima bean, trona, boiling, phytochemicals, micronutrients.