Mineral composition of boiled, green leafy vegetables found in Hawaiʻi and iron bioavailability using the in-vitro digestion/Caco-2 cell method
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2012-08
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University of Hawaii at Manoa
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Abstract
There is an increasing trend toward a more vegetarian diet. The 2010 Dietary Guidelines promote healthier eating patterns by recommending increased consumption of fruits and vegetables. They specifically advocate for the increased consumption of green leafy vegetables (GLV), which are associated with reduced risk of chronic disease, low in calories, and can contribute adequate amounts of folate, magnesium, potassium, dietary fiber, vitamins A, C, and K, nutrients typically under-consumed in the U.S. However, iron deficiency is the most prevalent micronutrient deficiency in the world and plant-based diets low in iron content and low in iron bioavailability are major contributors. Therefore, research is needed to identify plant-based foods with both high iron content and good iron bioavailability. Green leafy vegetables are purportedly good sources of iron. This study objective was to evaluate the mineral content and iron bioavailability of ten green leafy vegetables consumed by many ethnic groups in Hawaii. These included: chrysanthemum, sweet potato leaf, ung choy, watercress, amaranth leaf, bitter melon leaf, edible hibiscus, kale, moringa, and taro leaf. Produce was purchased from local markets or obtained from local growers and prepared by boiling for typical preparation times. Produce was then drained, homogenized using stainless steel equipment, and freeze-dried. Samples were sent to the LSU Agricultural Center and analyzed using inductively coupled plasma-emission spectroscopy. Mineral contents were compared with Daily Values (DV) per 85 g reference amount (RA). Bitter melon leaf met the DV definition of good (10% of DV per RA for calcium, copper, iron, magnesium, and manganese. Four additional vegetables would be ranked as good or excellent (20% of DV per RA) in calcium (amaranth leaf, edible hibiscus, moringa, and taro leaf). Only bitter melon and amaranth were good in magnesium. Copper and manganese were good in most produce. The four highest iron containing GLV (amaranth, bitter melon, edible chrysanthemum, and moringa) were further screened for iron bioavailability using the in-vitro digestion/Caco-2 cell system. Beef and spinach were used as reference foods. All foods were subjected to in-vitro gastric and intestinal digestions followed by application to monolayers of human intestinal (Caco-2) cells to assess iron bioavailability. In experiment 1, all samples were normalized to 67 μM Fe in the digests to compare absorption efficiency. In experiment 2, equal amounts of sample (0.5 g dry matter) were digested. Results showed that spinach and moringa had the highest efficiency of iron absorption, while amaranth and bitter melon had the lowest efficiency. However, iron bioavailability per recommended 85 g serving amount (RA) was the same among all GLV and spinach. Beef had 50% higher bioavailability per RA compared to all plant foods. We conclude that while there are differences in iron content and efficiency of iron absorption among these selected plant foods, the amount of iron absorbed from a serving of all of these GLV is equal to that from a serving of spinach. Further investigation is warranted to find other local, plant-based foods with greater potential to provide adequate iron. Our results present new information on mineral content and iron bioavailability of Hawaiian-grown boiled produce. This data could be used to improve local and national databases and in turn improve the nutritional quality of the diet.
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Iron, Caco-2 cell method, in-vitro digestion
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Theses for the degree of Master of Science (University of Hawaii at Manoa). Nutritional Sciences.
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