Effects of Amylomaize Starch on Mineral Metabolism in the Adult Rat: Role of the Microflora

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Abstract
The effects of amylomaize starch on rat mineral metabolism were studied. To elucidate the role of bacterial fermentation, the effects of amylomaize starch were compared in germfree (GF) and conventional (CV) rats. A purified diet, sterilized by irradiation and containing either maize starch (M) or amylomaize starch (A), was fed to the rats. Feed intake was similar in all groups of rats except GF rats fed amylomaize starch ad libitum, whose feed intake was higher. One group of GF rats received amylomaize starch in restricted amounts (pair-fed rats). A balance study of energy, nitrogen and minerals (Ca, P, Mg, Na, K, Fe, Mn, Zn and Cu) was performed. Apparent absorption of Mg, P, Na, K and Zn (expressed as a percentage of the amount ingested) was lower in GF rats fed amylomaize starch than in GF rats fed maize starch. Since feed intake was higher in GF rats fed amylomaize starch ad libitum than in rats fed maize starch, mineral absorption (expressed in milligrams per day) was not reduced in rats fed ad libitum, whereas it was reduced in pair-fed rats. Mineral retention was similar in GF rats fed ad libitum, but was reduced in pair-fed rats. In CV rats fed amylomaize starch, cecal weight and cecal volatile fatty acids concentration were higher than those in CV rats fed maize starch. Apparent absorption of N and P was lower and that of Ca, Mg and Fe was higher in CV rats fed amylomaize starch than in rats fed maize starch. The results for GF rats suggest that amylomaize starch is likely to reduce apparent digestibility of some minerals. However, in CV rats, starch fermentation by the microflora modifies the effect of amylomaize starch on mineral metabolism.