Nutritional Assessment of Magnesium from Raw and Processed Chickpea (Cicer arietinum L.) in Growing Rats Teresa Nestares, Gloria Urbano, Magdalena Lo ´pez-Frı ´as,* and Mercedes Barrionuevo Department of Physiology, School of Pharmacy, Campus of Cartuja, and Institute of Nutrition and Food Technology, University of Granada, E-18071 Granada, Spain We studied the effect of different processing methods (dry heating, soaking in distilled water, acidic solution, or basic solution, and soaking + cooking) on the nutritive utilization of magnesium from chickpeas (Cicer arietinum L.) in growing rats. We also investigated the effects of processing on several seed components that affect magnesium utilization. Chemical and biological methods were used for nutritional determinations. Although a large amount of the magnesium from raw chickpeas was absorbed (3.92 ( 0.36 mg/rat/day), the digestive utilization of magnesium (apparent digestibility coefficient) from unprocessed chickpeas was low. Processing led to an overall decrease in magnesium absorption and digestive utilization, because of modifications in certain components (e.g., fiber) of the legume. Under our experimental conditions feeding with raw or processed chickpeas led to elevated urinary excretion of magnesium (4.22 ( 0.37 mg/rat/day) in comparison with that found in growing rats fed a standard diet (1.11 ( 0.09 mg/rat/day). This increase resulted in a negative metabolic balance of this element. However, muscle and bone concentrations of magnesium were not affected by any of the experimental diets. Keywords: Chickpea; fecal excretion; fiber; magnesium; nutritive utilization; processing techniques INTRODUCTION The fundamental role of magnesium in various physi- ological processes in humans and animals has been described in detail in several reviews of this cation. Nevertheless, this information has apparently not been sufficiently disseminated; therefore dietary intake in the general public is often deficient (Hazell, 1985; Wester, 1987; Moreiras et al., 1990). Many studies have noted the relationship between dietary magnesium deficiency and the incidence of certain diseases (including athero- sclerosis); the links between intake and disease are especially worrisome in children (Aikawa, 1978; Hazell, 1985; Wester, 1987). Recent investigations (Moreu et al., 1995; Ferna ´ ndez et al., 1997; Nestares et al., 1997) have shown that legumes can be a good source not only of protein but also of minerals. After soybean, chickpea (Cicer arieti- num L.) is the legume that contains the greatest amounts of magnesium; this species constitutes a major source of magnesium in the Mediterranean diet (Mataix et al., 1995). The mean amounts of this mineral do not differ significantly between known varieties of chickpea (desi and kabuli). This is in contrast to the findings for fiber (Jambunathan and Singh, 1981; Rossi et al., 1984) or in crops grown in different locations, a factor known to influence protein content (Singh et al., 1983). Other components of chickpeas such as protein, fiber, vitamin D, phytic acid, and other minerals affect the nutritive utilization of magnesium directly or indirectly, however (Wester, 1987; Brink et al., 1991; Torre et al., 1991). These factors, like the amount of magnesium in chickpeas, are modified by processing (Meiners et al., 1976; Khan et al., 1988; Vidal and Frı ´as, 1991; Attia et al., 1994; Nestares et al., 1996), and notable differences in how these nutrients change have been reported (Singh, 1985; Vidal and Frı ´as, 1991). Because chickpeas must be processed for human consumption, information on the relationships between these changes may help in determining optimum methods for preparing this legume. This study investigated the effects of commonly used processing methods on the composition and nutritive utilization of magnesium from chickpeas and sought to identify the main factors that modify these parameters. Chickpeas are the most commonly consumed legume in Spain (Varela et al., 1995), and the processing methods tested here were chosen to reproduce, as closely as possible, different cooking methods used in the home. Dry heating was tested because chickpea flour is used in a number of dishes and in dietary foods. We also tested the effects of simmering with or without prior soaking in water alone, water with bicarbonate (baking soda), or water with citric acid (lemon juice). MATERIALS AND METHODS Samples and Processing Techniques. Raw, dried chick- peas (R) (Cicer arietinum L.) were grown in Andalusia (southern Spain). The seeds were subjected to seven different treatments: H ) dry heating, S ) soaking in distilled water, SA ) soaking in acidic medium, SB ) soaking in basic medium, SC ) S + cooking, SAC ) SA + cooking, and SBC ) SB + cooking. Raw chickpeas were dry heated under pressure at 120 °C, 1 atm, for 15 min. In processes S, SA, and SB, raw seeds were soaked at room temperature for 9 h in distilled water (pH ) 5.3), citric acid solution (0.1%, pH ) 2.6), or sodium bicarbon- ate solution (0.07%, pH ) 8.4), respectively. The seed-to- solution ratio was 1:3 (wt/vol). The soaking liquid was drained off, and the seeds were blended and lyophilized. Soaked chickpeas were cooked (SC, SAC, SBC) by boiling in distilled water for 35 min, at a seed-to-water ratio of 1:6.67 (wt/vol). The cooking water was drained off, and the seeds were blended and lyophilized. Analytical Techniques. Water content was determined by oven-drying at 105 ( 1 °C until a constant weight was obtained. Ash was measured by calcination at 500 °C to a * Author to whom correspondence should be ad- dressed (tel, +34-58-243879; fax, +34-58-243879; e-mail, nestares@platon.ugr.es). 3138 J. Agric. Food Chem. 1997, 45, 3138-3142 S0021-8561(96)00828-X CCC: $14.00 © 1997 American Chemical Society