Eight laboratories participated In a collaborative study to estimate precision of a standardized rat assay for determining true protein digestibility In selected animal, fish, and cereal products. Each of 7 test protein sources (casein, tuna fish, macaroni/cheese, pea protein concentrate, rolled oats, pinto beans, and nonfat dried milk) was fed as the sole source of protein at a 10% protein level in mixed diets. Each diet was fed to 2 replicate groups of 4 rats each for a 4-day acclimation period and a 5-day balance period. Mean digestibilities ranged from 98.6% for casein to 72.6% for pinto beans. Repeatability standard deviations ranged from 0.5 to 2.0%; the mean relative standard deviation for repeatability was 0.9% (range 0.5-2.8%). Reproducibility standard deviations ranged from 1.2 to 3.2%, and the mean relative standard deviation for reproducibility was 2.4% (range 1.3- 4.4%). The method has been approved interim official first action for determining true protein digestibility In foods and ingredients
The influence of dietary lutein, with and without moderate amounts of vitamin C (VC) or vitamin E (VE), on biomarkers of oxidative stress was examined in rats. Nine groups of immature Zucker obese (fa/fa) and lean female rats (8/group) consumed ad libitum for 8 wk the AIN-93G diet (Control) to which was added either dl-alpha-tocopherol acetate (VE) at 0.60 mg/kg or ascorbic acid (VC) at 0.75 mg/kg diet. Each of these diets contained lutein oil (FloraGlo) at 0.5 (Lut0.5) or 1.0 (Lut1.0) mg/kg diet. Weight gain, food efficiency and relative liver weight were higher in obese than in lean rats. Although liver malondialdehyde (MDA) concentrations were significantly higher in obese than in lean rats, levels were significantly lower in obese rats fed VE, VE-Lut and VC-Lut0.5 compared with other obese groups. The accumulation of alpha-tocopherol in liver was 6- and 3-times greater in the VE and VE-Lut1.0 groups, respectively, compared with the obese and lean control groups. Lutein reduced the activity of superoxide dismutase (SOD) in obese rats, independent of VC or VE, and raised the activity of glutathione peroxidase to higher levels in lean rats when combined with VC. Plasma insulin levels were dramatically higher in obese compared with lean rats, but significantly lower in obese rats fed VC-Lut0.5, VE-Lut1.0 and Lut1.0 compared with the Control group. These results suggest that lutein independently reduces the activity of SOD and alters more biomarkers of oxidative stress when combined with vitamin C than with vitamin E, and that vitamin E reduces liver lipid peroxidation in obese rats when the accumulation of liver alpha-tocopherol is very high.
The effects of ingesting the alga Spirulina maxima on the storage and utilization of vitamins A and E were investigated by feeding diets containing 0, 2.7, 10.7, 18.7 and 26.7% S. maxima to male rats for 6 wk. All diets contained 18% protein, which was contributed by S. maxima or by casein or by a mixture of them. Growth results indicated that rats did not utilize the diets containing S. maxima as well as the casein control diet (0% S. maxima) when levels were 10.7% or more of the diet. The ingestion of S. maxima caused a significant increase in dry matter and chloroform-extractable crude fat in the feces. A low level of 2.7% S. maxima caused a significant reduction in plasma, liver and heart alpha-tocopherol levels. The concentrations of alpha-tocopherol in these tissues showed a marked decline with 10.7% S. maxima in the diet, followed by a lesser decline at higher levels. Liver retinoid levels of rats increased when S. maxima was added to the diet, suggesting conversion of the naturally occurring carotenoids in S. maxima to vitamin A. However, the plasma levels of retinol decreased when S. maxima was fed at 10.7% or more. These data demonstrate that S. maxima can significantly alter the storage and utilization of vitamins A and E.
Male Holtzman rats (78 g) were fed semipurified 16% protein diets for 8 weeks using a food grade soy protein concentrate as the protein source. The basal diet (A) contained added DL-methionine (0.26%) and adequate amounts of vitamins A (14,535 IU/kg as retinyl acetate) and E (60 IU/kg as DL-alpha-tocopheryl acetate) and all other required nutrients. Experimental diets included: (B) basal plus 600 IU of vitamin E/kg; (C) basal plus 6,000 IU of vitamin E/kg; (D) basal plus 2.9 X 10(6) IU of vitamin A/kg; (E) basal plus 2.9 X 10(6) IU of vitamin A plus 600 IU of vitamin E/kg; and (F) basal plus 2.9 X 10(6) IU of vitamin A plus 6,000 IU of vitamin E/kg. Both vitamin A and vitamin E had a significant (P less than 0.05) effect on growth. There was an increase in growth with vitamin E intake and a decrease in growth with vitamin A intake. The net result of these two effects was that the groups fed both vitamins tended to be quite close in mean values to the group fed only the basal diet. Vitamin A significantly (P less than 0.05) increased relative weights of spleen and testes; vitamin E reduced that effect. Vitamin E also significantly (P less than 0.05) reduced relative adrenal weight whereas vitamin A significantly increased it. The two effects tend to cancel each other in the sense that the group fed both vitamins had an average relative adrenal weight quite close to that of the group fed only the basal diet. However, vitamin A still had an effect even when 6,000 IU of vitamin E was fed. The interaction effect of the two vitamins was significant (P less than 0.05) for plasma total protein and liver vitamin A. There was an increase in liver vitamin A with increasing levels of vitamin E in the diet. Blood urea nitrogen and plasma cholesterol were unchanged. A significant interaction of vitamins A and E was found to effect plasma total protein, liver vitamin A, and relative weight of spleen and testes.
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