The in vitro assessment of the bioavailability of iron in New Zealand beef : a thesis presented in partial fulfillment of the requirements for the degree of Master of Science in Physiology at Massey University, Palmerston North, New Zealand /

Abstract

The bioavailability of iron in New Zealand beef either alone or as part of a 'typical' New Zealand meal was investigated. The solubility of iron and its in vitro absorption by mouse intestinal tissue were used to evaluate iron bioavailability. The solubility of haem and/or non-haem iron in meat (beef longissimus muscle), vegetables and meat-plus-vegetables was investigated. Samples were cooked and then subjected to in vitro gastrointestinal digestion with pepsin followed by a combination of pancreatic enzymes and bile. Cooking at 65°C for 90 minutes reduced the soluble iron concentration in meat by 81% and reduced the haem iron concentration by 27%, which coincided with a 175% increase in non-haem iron concentrations. However, gastrointestinal digestion increased the solubility of iron in cooked meat (333%), vegetables (367%) and meat-plus-vegetables (167%). A proportion (35%) of the haem iron in the meat was broken down by the action of pancreatic enzymes leading to a 46% increase in non-haem iron concentrations, although this was not the case for the meat-plus-vegetables. Validation studies showed that mouse intestinal segments mounted in Ussing chambers maintained integrity and viability, and were responsive to glucose, theophylline and carbachol. Intestinal tissue from iron deficient mice was then used in the Ussing chambers to investigate the absorption of iron from ferrous gluconate and the soluble fractions of meat, vegetables and meat-plus-vegetables after gastrointestinal digestion. Results indicated a trend towards a higher absorption of iron from meat and ferrous gluconate, compared to vegetables and meat-plus-vegetables. However, iron absorption results were difficult to interpret due to the wide variation in the data. This variation was possibly due to errors associated with the sample processing and the analysis of iron, which was by inductively coupled-mass spectroscopy. Overall, the present study showed that before estimations can be made on the bioavailability of food iron, the effects of the cooking and gastrointestinal digestion processes must be considered. Further, the use of in vitro gastrointestinal digestion followed by the use of Ussing chambers to assess intestinal absorption is a potentially valuable system for assessing mineral bioavailability