Bioavailability of selenium from raw or cured selenomethionine-enriched fillets of Atlantic salmon (Salmo salar) assessed in selenium-deficient rats

The bioavailability of Se from raw and cured selenomethionine-enriched (Se-enriched) salmon fillets was assessed in Se-deficient male albino rats (Mol: Wist). A low-Se Torula yeast feed was supplemented with 0, 50, 100, 150 or 200 microg Se/kg as sodium selenite or as Se from raw or cured Se-enriched salmon. The diets were fed to weanling rats for 10 and 30 d. Bioavailability of Se was assessed by metabolic balance, Se accumulation in femur, muscle, liver and plasma, and induction of Se-dependent glutathione peroxidase (EC 1.11.1.9; GSHpx) in plasma as response parameters. Except for the metabolic balance results, the slope-ratio method was used when calculating Se bioavailability from raw or cured Se-enriched fish fillets (test food) relative to sodium selenite (standard). The data for fractional apparent absorption and fractional retention showed differences (P<0.05) among all three Se sources in the order raw salmon > cured salmon > selenite. At 10 d, Se from raw and cured Se-enriched fish fillets tended to be more bioavailable than selenite. This was supported by the observations for Se accumulation in femur and muscle and induction of GSHpx activity. At 30 d, all response parameters showed a higher bioavailability of Se from raw and cured Se-enriched fish fillets compared with selenite. Differences (P<0.05) in Se accumulation in muscle at 10 and 30d, and differences (P<0.05) in fractional apparent absorption and fractional retention suggested that curing salmon altered the utilisation of Se. The experimental results showed that enrichment of fish fillets with selenomethionine yields fillets with high Se bioavailability.     

Bioavailability of selenium from bovine milk as assessed in subjects with ileostomy

OBJECTIVE: To assess the absorption of dietary selenium in humans, especially of milk selenium. DESIGN:: 1-day meal studies in subjects with ileostomy. SETTING: Hospital outpatient clinics. SUBJECTS: Three subjects in the pilot study and nine subjects in the main study (eight men/ four women). INTERVENTION: Different beverages, 1 l/day, were given in addition to basal diets (soft drink, 1 week; low-fat milk, 3 weeks; fermented low-fat milk, 3 weeks and soft drink, 1 week). Ileostomy effluents were collected during the last 2 days in each of the four periods. RESULTS: On days when the subjects were given 1 l of low-fat milk, the estimated fractional absorption of total dietary selenium was 65.5 (2.3)% (mean (s.d.), n=18), which was similar to the value when fermented low-fat milk was given (64.1 (3.2)%). However, both the calculated amount of milk selenium absorbed (10.9 (2.4) vs 9.4 (1.7) microg selenium) and its fractional absorption (73.3 (16.1) vs 64.1 (11.2)%, n=18) were significantly higher for milk than for fermented milk. CONCLUSIONS: Selenium from milk and other sources is well absorbed in subjects with ileostomy. The real absorption may be even higher than the values shown.     

Bioavailability of selenium from selenium-enriched milk assessed in the artificially reared neonatal pig

There is interest in pre-farm gate fortification of the diet with highly bioavailable selenium (Se) to improve public health, so the aim of the present study was to determine the bioavailabilities of Se from Se-enriched whole milk and milk replacers supplemented with exogenous Se in neonatal pigs. Milk enriched with Se (1070 μg Se/kg dry matter (DM); HSeM) was obtained from cows supplemented with selenised yeast while the control milk diet (135 μg Se/kg DM; LSeM) was made using milk powder from non-supplemented cows. Additional diets were formulated by adding selenised yeast (HSP) or selenate (HSN) to the LSeM diet to give final Se concentrations of 1070 μg Se/kg DM. Neonatal pigs were trained to drink milk and then randomly allocated to their four respective diets and slaughter times (0, 7, 14, 28 and 42 days of feeding). Plasma Se increased over the first 21 days in pigs consuming HSeM, reaching a value over three times higher than the LSeM pigs. Plasma Se concentrations plateaued at 45, 125, 122 and 170 μg/mL for LSeM, HSN, HSP and HSeM pigs, respectively ( P  < 0.001). After 28 days, muscle Se plateaued at 47, 106, 237 and 486 μg/kg for LSeM, HSN, HSP and HSeM pigs, respectively ( P  < 0.001). Colonic selenoprotein P gene expression was greater ( P  = 0.024) in pigs fed HSeM compared with LSeM while the HSP and HSN were intermediate. These data suggest that Se in milk from cows fed selenised yeast is highly bioavailable and may offer a means of delivering supplemental Se to humans.     

Bioavailability of iron in ground beef and plant protein concentrates

Weanling male Wistar rats were fed a low iron basal diet for 4 weeks. They were then divided into 16 groups according to a randomized block design based on hemoglobin level. During the repletion period of 2 weeks, one group was fed the basal diet. The other fifteen groups received ferrous sulphate, freeze-dried ground beef, ground granular soy product, a 2:1 mixture of beef and the soy product, or rapeseed protein concentrate as iron sources at three levels. All diets were isocaloric and isonitrogenous. The efficiency of iron utilization was calculated on the basis of iron gained in hemoglobin and iron consumed, applying appropriate correction for iron obtained from the ingredients of the basal diet. The relative biological value (RBV) of iron in the test source was calculated as the ratio between the efficiency for the test and the standard source (ferrous sulphate). The RBVs were: freeze-dried ground beef, 0.53; ground soy product, 0.62; 2:1 mixture of beef and soy product, 0.71; rapeseed protein concentrate, 0.55. The low availability of iron in beef containing 60% heme iron indicated that the anemic rat is not a suitable model for normal man, since the absorption of heme iron by man is much higher than that of inorganic or non-heme iron.     

Polybrominated biphenyl congener levels and distribution patterns in raw and cooked beef

The retention and distribution of eight polybrominated biphenyl (PBB) congeners were studied by roasting beef sirloin tip samples to an internal temperature of 65°C, braising and broiling adductor and semimembranosus steaks to an internal temperature of 77°C, broiling ground round and hamburger patties to 77°C, and comparing cooked values with those in the raw. Rounds were obtained from four Holstein cows with known PBB contamination.Significant reductions in PBBs occurred with cooking of all cuts. Roasting sirloin tips reduced the PBBs by 45.7%. Broiling reduced PBBs as follows: Adductor steaks (53.2%), semimembranosus steaks (71.2%), ground beef patties (32.3%) and hamburger patties (31.5%). Braising reduced PBBs in the adductor steaks by 37.2% and in the semimembranosus steaks by 34.9%.The distribution of PBB congeners was also affected by cooking in all cuts except hamburger. The proportion of 2,4,5,2,4,5-hexabromobiphenyl decreased upon cooking but the change in the proportion of 2,3,4,5,2,4,5-heptabromobiphenyl varied with the cut used. Both of these isomers are known to be phenobarbital type inducers. The proportion of 2,4,5,3,4,5-hexabromobiphenyl, which is both a 3-methylcholanthrene and phenobarbital type inducer, increased in the roasted sirloin tip surface and broiled ground round patties.Published as Michigan Agricultural Experiment Station Journal Article Number 9209.     

Selenium from selenium-rich Spirulina is less bioavailable than selenium from sodium selenite and selenomethionine in selenium-deficient rats

The bioavailabilty of selenium (Se) from selenium-rich Spirulina (SeSp) was assessed in Se-deficient rats by measuring tissue Se accumulation and glutathione peroxidase (GSH-Px) activity. For 42 d, rats were subjected to dietary Se depletion by consumption of a Torula yeast (TY)-based diet with no Se; controls were fed the same diet supplemented with 75 microg Se/kg diet as sodium selenite. Se-deficient rats were then repleted with Se (75 microg/kg) by the addition of sodium selenite, selenomethionine (SeMet) or SeSp to the TY basal diet. Selenium speciation in SeSp emphasized the quasi-absence of selenite (2% of total Se); organic Se comprised SeMet (approximately 18%), with the majority present in the form of two selenoproteins (20-30 kDa and 80 kDa). Gross absorption of Se from SeSp was significantly lower than from free SeMet and sodium selenite. SeMet was less effective than sodium selenite in restoring Se concentration in the liver but not in kidney. SeSp was always much less effective. Similarly, Se from SeSp was less effective than the other forms of Se in restoring GSH-Px activity, except in plasma and red blood cells where no differences were noted among the three sources. This was confirmed by measuring the bioavailability of Se by slope-ratio analysis using selenite as the reference form of Se. Although Se from SeSp did not replenish Se concentration and GSH-Px activity in most tissues to the same degree as the other forms of Se, we conclude that it is biologically useful and differently metabolized due to its chemical form.     

Flavor quality of antioxidant-treated, cooked, ground beef patties

The antioxidant tertiary-butylhydroquinone (TBHQ) reduced flavor deterioration and oxidative rancidity in cooked ground beef patties stored up to seven days at refrigerator (2.8 degrees C.) temperatures and up to twenty-one days at freezer (--20.5 degrees C.) temperatures. Freezer conditions maintained flavor quality more effectively than refrigerator temperatures in both TBHQ-treated and untreated samples.     

Bioavailability of selenium from foods

Selenium (Se), an essential nutrient, is needed for activity of several important proteins. Additionally, the consumption of Se in amounts that exceed the Recommended Dietary Allowance (RDA) may protect against prostate and colorectal cancer. Supplemental Se may be acquired through the diet, but Se bioavailability depends on the source. Therefore, dietary advice concerning improvement of Se intake depends on characterization of Se bioavailability from Se-containing food sources.     

Bioavailability to rats of selenium in various tuna and wheat products

Bioavailability of selenium (Se) in tuna and wheat at various stages of processing was studied in rats. The protein source of the rat diets was torula yeast with Se supplied by either raw, precooked or canned tuna, or whole wheat flour, whole wheat bread or bran. Sodium selenite was used as the standard. Each Se source was fed at three levels: 0.05, 0.10 and 0.15 ppm. By using increase in glutathione peroxidase (GSH-Px) activity in liver, kidney and whole blood as an indicator of bioavailability, no differences were found among the three tuna products or among the three wheat products tested. However, significantly lower GSH-Px activity was found in the combined tuna groups as compared to the combined wheat groups, suggesting that selenium in wheat was more available than that in tuna. There was a significant increase in the liver Se content of rats fed all levels of Se in canned tuna and in kidney, blood and muscle Se of rats fed 0.10 and 0.15 ppm Se in canned tuna in comparison to the tissue Se content in rats fed these same levels of Se in raw or precooked tuna. Since this did not correspond with an increase in GSH-Px activity it was concluded that it did not represent increased bioavailability of canned tuna. Thus, food processing does not appear to affect Se availability, but Se appears to be more available in wheat than tuna.     

Effects of feeding cooked ground beef on plasma lipid and apolipoprotein concentrations in male turkeys

Two experiments with male turkeys were designed to study the effects of eating cooked ground beef on plasma lipid and lipoprotein levels. In both experiments, cooked ground beef from forage-finished cattle (F-Bf) and grain-finished cattle (G-Bf) were added at an average of 28.1 and 34.5 g of beef per 100 g of ration in order to provide 40% of the protein requirement. The experimental diets formulated to be isocaloric and isonitrogenous were: 1) basal diet (negative control) in which soybean meal and corn oil served as protein and fat sources, respectively; 2) basal plus crystalline cholesterol (positive control) incorporated at 1 and 2% of the diet in trials 1 and 2, respectively; 3) basal plus F-Bf; 4) basal plus G-Bf. The polyunsaturated to saturated fat ratio averaged 3.45 for diets 1 and 2 and 0.17 for diets 3 and 4, respectively. At 16 weeks, consumption of diets 3 and 4 elevated (P less than 0.05) plasma triglyceride levels and phospholipid levels (trial 1). In trial 2, only diet 4 elevated (P less than 0.05) plasma phospholipid levels. In both trials, the beef diets did not significantly elevate plasma cholesterol and high density lipoprotein (HDL) cholesterol levels above the basal diet. However, the major apoprotein in the HDL fraction, apolipoprotein A-I (apoA-I), was increased (P less than 0.05) in the plasma of male turkeys fed the G-Bf diet in both trials and F-Bf diet in trial 1. Plasma apolipoprotein B (apoB), primarily found in low density lipoproteins (LDL), was increased (P less than 0.05) in one of the two trials by the inclusion of beef in the diet. There were no significant differences in plasma cholesterol, HDL-cholesterol, apoA-I and apoB levels between the types of beef (F-Bf vs. G-Bf).     

Effect of intermittent supplementation with selenate on selenium status of rats fed selenium-deficient diet

To examine the selenium (Se) status of rats intermittently supplemented with Se, we measured tissue Se contents and glutathione peroxidase (GPx) activities in rats fed a Se-deficient diet intermittently supplemented with selenate. In experiment 1, four groups of male 4-wk-old Wistar rats were fed a Torula yeast-based Se-deficient diet (Se content, < 0.01 microg/g) for 28 d. During the experimental period, the diet of each group was supplemented with sodium selenate (0.17 microg Se/g) for 0, 1, 2 or 7 d/wk. The tissue Se contents and GPx activities both increased gradually with an increase in frequency of the selenate supplementation, and significant linear regressions were observed between the frequency and these Se indices. In particular, the correlation coefficient in the liver and plasma indices was nearly equal to a value of 1.0. In experiment 2, three groups of rats were fed the Se-deficient basal diet for 28 d. Among these, one group was daily supplemented with sodium selenate to the Se-deficient diet at a level of 0.17 microg Se/g, and another group was intermittently supplemented with the selenate at a level of 1.19 microg Se/g for 1 d/wk. The tissue Se contents and GPx activities both were increased by the selenate supplementation and no significant difference was observed between daily and weekly supplementation in the Se indices except in erythrocyte Se. These results indicate that Se status in the growth period is dependent on total Se intake in this period and that weekly intermittent supplementation with Se can maintain adequate Se status.     

Concentrations of vitamin D3 and 25-hydroxyvitamin D3 in raw and cooked New Zealand beef and lamb

Meat from four lamb cuts and four beef cuts was assayed for vitamin D3 and 25-hydroxyvitamin D3 (25OHD3) before and after cooking. Vitamin D3 was measured by HPLC, while 25OHD3 was assayed using a radioimmunoassay method developed for blood plasma. Concentrations of both these compounds tended to increase with cooking for most cuts, but retention levels were often less than 100%. Positive relationships between fat percentage and vitamin D3 were shown before and after cooking, but not for 25OHD3. For lamb, the highest levels of vitamin D3 were in the shoulder chop both before and after cooking, while levels were lowest in the rack muscle. Similar cut differences were shown for 25OHD3 concentrations. For beef there were no significant differences between the cuts for vitamin D3, but concentrations of 25OHD3 were lower in the striploin before and after cooking, Vitamin D3 levels tended to be higher in beef cuts than in lamb cuts, but the opposite held for 25OHD3. Concentrations of vitamin D3 were similar to those in other reports, but the 25OHD3 levels were at the high end of reported ranges. With 25OHD3 being more potent than vitamin D3, it is concluded that meat can make a useful contribution of this vitamin to the human diet.     

Bioavailability of iron in cooked egg yolk for maintenance of hemoglobin levels in growing rats

The relative biological value (RBV) of iron in egg yolk was compared with that of iron in ferrous sulfate in prophylactic assays with weanling rats. Egg yolk cooked by one of three different methods was used in each experiment: (1) yolk of eggs boiled in the shell, lyophilized, and mixed with other dry diet ingredients; (2) pasteurized yolk and other diet components steamed with 8 liters of water per kilogram of diet; and (3) pasteurized yolk and other diet ingredients baked with 0.5 liters of water per kilogram of diet. Diets containing three levels of egg yolk and four levels of ferrous sulfate were fed to different groups of rats for 1, 2, and 3 weeks. Response of dietary iron was calculated as the regression of hemoglobin iron gain on iron intake and the nutritional quality of egg iron relative to that of ferrous sulfate iron was evaluated by slope-ratio analysis. RBV was 61, 64, and 90%, respectively, for iron of egg yolk cooked by the three methods. The presence of ascorbic acid during heat treatment of the diets significantly increased RBV of yolk iron from 64 to 92% in experiment 2, and increased it to a value equivalent to that of ferrous sulfate in experiment 3.     

Altered arachidonic acid metabolism in platelets and aortas from selenium-deficient rats

Selenium (Se) deficiency results in decreased activity of the seleno-enzyme, glutathione peroxidase (GSHPx), an intracellular scavenger of hydroperoxides which may thereby influence the activity of various enzymes of arachidonic acid (20:4) metabolism in platelets and aortic tissue from rats. In vitro studies, performed with platelets isolated by gel-filtration, demonstrated that platelets from selenium-deficient (−Se) rats aggregated to a significantly greater extent when stimulated by ADP and collagen than those from selenium-supplemented (+Se) rats. Platelets from the −Se rats also produced more thromboxane B₂ (TXB₂) when stimulated by collagen than did those from +Se rats. In aortic tissue from −Se rats, a significant depression in the generation of prostacyclin (PGI₂)-like material was demonstrated compared to the tissue from +Se rats. Type of dietary fat and age of the animals also influenced the production of PGI₂-like activity in aortas from both +Se and −Se rats. Our results suggest that an imbalance in the production of two 20:4 metabolites — proaggregatory TXA₂ and antiaggregatory PGI₂ — could occur in response to certain physiological stresses when GSHPx activity is reduced by a selenium-deficient diet.     

tert-butyl hydroperoxide-induced hemolysis of alpha-tocopherol-decreased erythrocytes from selenium-deficient and selenium-adequate rats

The protective function of alpha-tocopherol, glutathione (GSH), and glutathione peroxidase (GSH-Px) from tert-butyl hydroperoxide (t-BuOOH)-induced hemolysis was studied with the erythrocytes from male Wistar rats fed selenium (Se)-adequate or -deficient diet for 3 months. By the preincubation with a water-soluble radical initiator, 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH), at 10 mM for 6 h at 37 degrees C, alpha-tocopherol levels of the erythrocytes were decreased to 40% of the original level, that is, to the level insufficient for supporting the normal functions of the erythrocytes. With the Se-deficient cells, the hemolysis proceeded rapidly irrespective of the presence or absence of GSH in the incubation medium, and irrespective of the presence or absence of AAPH in the preincubation medium. Contrarily, GSH suppressed the hemolysis of Se-adequate cells which were preincubated with and without AAPH. These results are consistent with the notion that Se serves as the prime, important defense mechanism in the t-BuOOH-induced hemolysis through the activity of GSH-Px. Either alpha-tocopherol or GSH by itself, or both by themselves, may not play so significant a role as Se does in suppressing the hemolysis.