Antithyroid and goitrogenic effects of millet: role of C-glycosylflavones.

Pearl millet [Pennisetum millet (L.) leeke] is the main source of food energy for the rural poor in many areas of the semiarid tropics. Epidemiological evidence suggests that millet may play a role in the genesis of endemic goiter in these areas, and sparse experimental data in rats support this suspicion. This study was undertaken to determine in vivo in rats and in vitro using porcine thyroid slices and a thyroid peroxidase (TPO) assay the goitrogenic and antithyroid effects of millet diets, extracts of millet, and certain pure compounds contained therein. For use in these studies, whole grain millet was progressively dehulled to yield successively four bran and four flour fractions in which direct analyses revealed progressively lower concentrations of C-glycosylflavones. In vivo feeding of bran fraction 1, that richest in C-glycosylflavones, led to a significant increase in thyroid weight and antithyroid effects. Feeding of bran fraction 2, the next richest in C-glycosylflavones, produced similar, but less marked, changes. In vitro studies of 125I metabolism using porcine thyroid slices indicated that extracts of bran fractions 1 and 2 were most potent, producing changes similar to those produced by methimazole (MMI). At a concentration of 60 mumol/L, glucosylvitexin, the major C-glycosylflavone present in millet, had effects comparable to those of 1 mumol/L MMI. Similarly, in studies of porcine TPO, extracts of bran fraction 1 caused pronounced (85%) inhibition of enzyme activity, and progressively less inhibition was induced by extracts of bran fractions 2, 3, and 4. Overall, the TPO-inhibiting activities of the various millet fractions closely correlated with their C-glycosylflavone concentrations. Three C-glycosylflavones present concentrations. Three C-glycosylflavones present in millet, glucosylvitexin, glycosylorientin, and vitexin, also inhibited TPO activity. Thus, in vivo and in vitro studies revealed that millet diets rich in C-glycosylflavones produce goitrogenic and antithyroid effects similar to those of certain other antithyroid agents and small doses of MMI. We conclude that in areas of iodine deficiency in which millet is a major component of the diet, its ingestion may contribute to the genesis of endemic goiter.

Comparison of the effect of cell wall and hull fiber from canola and soybean on the bioavailability for rats of minerals, protein and lipid.

Hull or cell wall material, isolated from canola (Brassica napus cv. Regent) or soybean (Glycine max) or cellulose was added to a basal, semipurified diet at a level of 12% and fed to growing male Wistar rats. The apparent availability of Cu, Fe, Ca, P and protein were lower when the fiber-containing diets were fed compared to the control diet. The availability of Mg was lower when the canola hull (CH) and cellulose (CE) diets were fed, whereas Zn availability was lower when the canola cell wall (CCW) and CE diets were fed, compared to the control diet. Determination of the feed transit time, by using the unabsorbable marker Cr2O3, demonstrated that the CE and soybean cell wall (SCW) diets had the fastest transit rates, followed by the CH, soybean hull (SH), CCW and control diets. Determination of the in vitro binding of the various fibers to metal ions demonstrated that CH was the strongest chelator, whereas CE had the lowest binding affinity for any of the minerals tested. At the termination of the trial, intestinal segments were removed and the in vitro mucosal transport of Cu, Fe, Mn and Zn were compared. The CCW diet consistently demonstrated lower transport for the four minerals, especially in the ileal segment.

The binding of dietary protein by sorghum tannins in the digestive tract of pigs.

The effects of reconstitution of sorghums on dry matter, energy, protein and amino acid digestibilities, and the nature of protein binding by sorghum tannins during digestion were investigated. Grains from a high and a low tannin sorghum were reconstituted by adding 30% (wt/wt) distilled water to the grain and stored at 25 degrees C for 20 days with an acetic-propionic acid mixture added to deter fungal growth. Another lot of grain from the same sources was untreated and used as control. The sorghum grains were then incorporated at an 85% level in diets for a digestibility trial with pigs cannulated at the terminal ileum. The digestibilities of dry matter, protein and amino acids at the terminal ileum were lower than the corresponding values measured over the total digestive tract. Reconstitution improved the digestibilities of dry matter, energy, protein and amino acids in the high but not low tannin sorghum diets. The improvement in digestibility of individual amino acids ranged from 7.5 to 23.5%. The tannin-associated proteins were more hydrophobic than the dietary protein. The results suggest that hydrophobic bonding is important in the formation of tannin-protein complexes in the digestive tract of pigs.

Improvement of the nutritive value of high tannin sorghums for broiler chickens by high moisture storage (reconstitution).

Grains from three high and one low tannin sorghum cultivars were treated as follows: 1) untreated, no water was added, the dry grain had an average moisture content of 8% and 2) the moisture content of the grain was raised by adding 25% (w/w) distilled water to the grain. The treated grain was then stored for 10 or 20 days with a 2% level of acetic-propionic acid mixture (60/40, v/v) added to deter fungal growth. This treated grain was used in diets during a 3-week feeding trial with broiler chickens. High moisture storage (reconstitution) of high tannin sorghums decreased their extractable tannin content. Chickens fed diets containing these treated sorghums had improved weight grains (23 to 83 g) and feed efficiencies compared to birds fed diets containing the untreated grain. Treatment of low tannin sorghum did not improve weight gains. Reconstitution of high but not low tannin sorghums improved protein digestibility (6 to 16%) and dietary metabolizable energy (.1 to .3 kcal/g) for broiler chickens. There was a highly significant cultivar effect on leg scores, but the correlation between dietary tannin content and leg scores was low (r = .10), suggesting that tannin content was not a major factor in leg abnormality incidences shown. The improvement in weight grains, feed efficiencies, and protein digestibilities at 10 and 20 days storage periods was not different (P greater than .05), indicating that the benefits of high moisture storage were already obtained by 10 days.

Improvement of the nutritive value of rye for broiler chickens by gamma irradiation-induced viscosity reduction.

A study was undertaken with chickens to determine the effect of irradiation treatment on the viscosity-inducing properties of polysaccharide components of rye. Three-week body weight, food utilisation, fat retention, and bone ash of chicks were substantially improved by irradiating rye (0 to 10 Mrad) and were maximal at 6 Mrad. Irradiation of the entire diet resulted in no further improvement over irradiating the rye fraction alone. The improved performance coincided with radiation-induced damage to rye polysaccharides, as indicated by reduced viscosity and increased concentrations of reducing sugars.