Household Food Processing Strategies to Improve Iron and Zinc Bioavailability in Ethiopian Dishes Based on Chickpea (Cicer arietinum L.) and Dry Bean (Phaseolus vulgaris L.)

Abstract

Pulses are major constituents of the human diet. Dry bean and chickpea, commonly grown in Ethiopia, are among the pulses that serve as important sources of energy and nutrients, particularly protein, minerals and folate. However, pulses also contain anti-nutrients which bind minerals, mainly iron and zinc, rendering them less bioavailable or unavailable for absorption. These anti-nutrient contents of pulses are a particular problem in Ethiopia, where the population consumes a plant-based diet and a large percentage of young children and women are affected by micronutrient deficiencies. The nutrient and anti-nutrient contents of raw, cooked, soaked-cooked, germinated-cooked and fermented dry bean (Hawassa Dume, Nasir and Red Wolaita) and chickpea (Habru, Mastewal and Local) varieties grown in Ethiopia were determined with the hypothesis that the iron and zinc bioavailability can be enhanced through processing methods applicable at household scale. In addition, the effect of soaking and germination on cooking time and the acceptability of dishes prepared from dry bean and chickpea were determined. Ferritin formation in the Caco-2 cell intestinal absorption model was used as a proxy for iron bioavailability. Fermentation of dry bean and chickpea flours significantly reduced the contents of anti-nutrients (phytate, tannin and polyphenols), as well as the phytate:iron molar ratio compared to unfermented samples. For most dry bean and chickpea samples, germination-cooking yielded superior results in terms of reducing cooking time, phytate, tannin, and phytate:iron and phytate:zinc molar ratios compared to cooking and soaking-cooking. Polyphenol contents were lower for soaking-cooking than for germination-cooking. With a few exceptions, the scores for sensory attributes of bean-based and chickpea-based dishes prepared from soaked or germinated samples were not significantly different than those of dishes prepared from untreated bean and chickpea. Among the unprocessed dry bean and chickpea varieties, there was significantly higher ferritin formation (better iron bioavailability) in Caco-2 cells exposed to Habru compared to the other samples of dry bean and chickpea varieties used in the study. Overall, soaking (18 h)-cooking resulted in higher ferritin formation for the dry bean samples. On the other hand, soaked (12 h)-cooked and germinated (72 h)-cooked in Habru, soaked (12 and 18 h)-cooked and germinated (72 h)-cooked in Local and germinated (72 h)-cooked in Mastewal chickpea resulted in higher ferritin formation compared to samples cooked without pre-treatment. Fermentation for 72 h was effective in increasing ferritin formation in all dry bean samples, but not in chickpea samples, with the exception of Habru. Although the expected improvements due to the reduced anti-nutrient contents were not confirmed by high ferritin formation in Caco-2 cells or by lowering molar ratios below critical values in all samples, soaking-cooking, germination-cooking and fermentation will still be effective with regards to lowering the total anti-nutrient contents.