In vitro calcium bioavailability of vegetables, legumes and seeds

Plant foods high in calcium were collected from representative markets in Bangkok. The purpose of this research was to study the bioavailability of calcium in plant sources and the presence of some in situ calcium inhibitory factors. Single composite samples from each market were prepared as commonly consumed and analyzed for in vitro calcium bioavailability (by equilibrium dialysis after simulated gastric digestion method) and for dietary fiber, phytate and oxalate. Compared to milk powder, which contains 25 mg calcium/100 g, five out of 11 vegetables had higher calcium dialysability (25%). High levels of dialysable calcium (20-39%) were found in kale, celery, collard, pak-chee-lao (Anethum graveolens L.), Chinese cabbage and soybean sprouts. These vegetables contained low levels of dietary fiber, phytate and oxalate. Medium levels of dialysable calcium (11-18%) were found in Indian mulberry and sesbania leaves, both of which had medium levels of oxalate (290-580 mg/100 g). Medium levels of dialyzable calcium were also found in young and mature cooked soybean seeds, both of which had low levels of oxalate and medium levels of phytate (290-400 mg/100 g). Pak-paw (Polygonum odoratum Lour.), amaranth, wild betal and white and black sesame seeds contained low dialysable calcium (2-7%) with high level of oxalate (680-2620 mg/100 g). Sesame seeds also contained high levels of dietary fiber and phytate. The presence of inhibitory factors, especially oxalate, at high or medium levels could limit the calcium bioavailability of plant foods. (C) 2004 Elsevier Ltd. All rights reserved.