Halvor Holm

Effects of methionine, cysteine and medium chain triglycerides on nutrient digestibility, absorption of amino acids along the intestinal tract and nutrient retention in Atlantic salmon (Salmo salar L.) under pair-feeding regime.

Abstract Atlantic salmon, kept in seawater (8–11°C), initial weight 180 g, were pair-fed four high energy, low protein diets for 65 days in triplicate. The diets were supplemented isonitrogenously with amino acids: methionine (6.2 g kg −1 ), cysteine (5.0 g kg −1 ) or alanine (3.7 g kg −1 ) (control). In the fourth diet, also supplemented with alanine, medium chain triglycerides (MCT) (100 g kg −1 ) replaced fish oil. Feed intake was estimated and feeding level adjusted based on the difference between delivered and wasted feed. Apparent digestibilities and pancreatic enzyme activities along the intestinal tract were determined from analyses of chyme from different regions and of faeces, using yttrium oxide as the marker. Plasma amino acid concentrations were determined in blood from the caudal vein. Whole fish taken at start and termination of the experiment were used to estimate nitrogen and energy retention. Feed intake in fish fed the MCT-diet determined the feeding level of fish on the other diets. MCT increased digestibilities of protein and starch and increased nitrogen retention from 52% to 66%, while energy retention was significantly reduced. MCT caused accumulation of cysteine in the proximal regions of the post-gastric intestinal tract and increased pancreatic proteolytic activity of the chyme. Methionine supplementation increased fat digestibility. Cysteine increased digestibilities of protein, fat, starch, as well as nitrogen retention. Hence, sulphur amino acids seemed to be the first limiting amino acids and methionine less effective than cysteine in relieving the limitation. Plasma levels of taurine did not, however, indicate any limitation in the capability to convert methionine into cysteine.

Different bioavailability in humans of wheat and fish selenium as measured by blood platelet response to increased dietary Se

The bioavailabilities of selenium (Se) from Se-rich fish species and Se-rich wheat were compared in a study involving 32 healthy volunteers. Initial serum Se values were 109±16 μg/L (mean±SD). For 6 wk, one group (n=11) included Se-rich bread in their diet, bringing daily average intake of Se up to 135±25 μg/d. Another group (n=11) consumed Se-rich fish daily (average Se intake: 115±31 μg/d), whereas the control group (n=10) ate their normal diet, providing 77±25 μg Se/d. Serum Se increased by 17% (P<0.01), and platelet Se increased by 30% (P<0.01) in the wheat group. Although platelet Se decreased by 11% in the fish group, no changes in serum and platelet Se in the fish or control group reached statistical significance. Glutathione peroxidase (EC 1.11.1.9; GSH-Px) activity in serum and platelets did not change during the study, nor did platelet mercury (Hg) content. Since the dietary intake of Hg, arsenium (As), and fatty acids could not satisfactorily explain the lack of response in the fish group, the results are indicative of low bioavailability of fish Se in humans. At present, wheat Se seems to be the most important factor contributing to the body stores of Se in this study population.

Pancreatic proteinases from man, trout, rat, pig, cow, chicken, mink and fox. Enzyme activities and inhibition by soybean and lima bean proteinase inhibitors

1. The specific activities of the trypsins and chymotrypsins, measured with synthetic substrates, varied within one order of magnitude. 2. The trout trypsin and chymotrypsin were 5-15 times as efficient in hydrolyzing casein as the remaining animals. 3. The inhibition of total caseinolytic activity in extracts of pancreatic tissue by SBTI and inhibitors in crude extracts of raw soybeans varied ten-fold. 4. The animals may be ranked as follows according to the sensitivity of the caseinolytic activity to SBTI; trout greater than fox, chicken, greater than pig greater than rat, cow greater than mink greater than man.

Different digestion of caprine whey proteins by human and porcine gastrointestinal enzymes

The objective of the present study was twofold: first to compare the degradation patterns of caprine whey proteins digested with either human digestive juices (gastric or duodenal) or commercial porcine enzymes (pepsin or pancreatic enzymes) and second to observe the effect of gastric pH on digestion. An in vitro two-step assay was performed at 37 degrees C to simulate digestion in the stomach (pH 2, 4 or 6) and the duodenum (pH 8). The whey proteins were degraded more efficiently by porcine pepsin than by human gastric juice at all pH values. Irrespective of the enzyme source, gastric digestion at pH 2 followed by duodenal digestion resulted in the most efficient degradation. Lactoferrin, serum albumin and the Ig heavy chains were highly degraded with less than 6 % remaining after digestion. About 15, 56 and 50 % Ig light chains, beta-lactoglobulin (beta-LG) and alpha-lactalbumin remained intact, respectively, when digested with porcine enzymes compared with 25, 74 and 81 % with human digestive juices. For comparison, purified bovine beta-LG was digested and the peptide profiles obtained were compared with those of the caprine beta-LG in the digested whey. The bovine beta-LG seemed to be more extensively cleaved than the caprine beta-LG in the whey. Commercial enzymes appear to digest whey proteins more efficiently compared with human digestive juices when used at similar enzyme activities. This could lead to conflicting results when comparing human in vivo protein digestion with digestion using purified enzymes of non-human species. Consequently the use of human digestive juices might be preferred.

Lipid digestibility and metabolism in Atlantic salmon (Salmo salar) fed medium-chain triglycerides

Abstract Atlantic salmon with an average initial weight of 180 g were fed either a control diet containing 25% fish oil or a diet with 15% fish oil and 10% of an oil based on medium-chain fatty acid triglycerides (MCTs). The fish were kept in tanks supplied with saltwater for 65 days. The fish group with the lowest feed intake determined feeding level in the remaining groups. Exchanging 1/3 of the dietary fat with a MCT oil affected fatty acid digestibility and lipid metabolism. The medium-chain fatty acids (MCFAs) were highly digestible, 99.6% for 8:0 and 96.7% for 10:0, and were absorbed mainly in the pyloric region. However, MCT seemed to reduce pyloric absorption of other fatty acids. In the pyloric region, only 5.4% of 22:6 n −3 was absorbed in fish fed MCT, whereas 32.0% of this fatty acid was absorbed in fish fed the control diet. Fat percentage in muscle was reduced from 6.1% in controls to 4.4% in MCT fed fish. Dietary MCTs were found to increase the percentage of C18:1 fatty acids in the liver and reduce mitochondrial β-oxidation of C16:0 in this organ.

Identification of lactoferrin peptides generated by digestion with human gastrointestinal enzymes

Lactoferrin (LF) is a protein present in milk and other body fluids that plays important biological roles. As part of a diet, LF must survive gastrointestinal conditions or create bioactive fragments to exert its effects. The degradation of LF and formation of bioactive peptides is highly dependent on individual variation in intraluminal composition. The present study was designed to compare the degradation and peptide formation of bovine LF (bLF) following in vitro digestion under different simulated intraluminal conditions. Human gastrointestinal (GI) juices were used in a 2-step model digestion to mimic degradation in the stomach and duodenum. To account for variation in the buffering capacity of different lactoferrin-containing foods, gastric pH was adjusted either slowly or rapidly to 2.5 or 4.0. The results were compared with in vivo digestion of bLF performed in 2 volunteers. High concentration of GI juices and fast pH reduction to 2.5 resulted in complete degradation in the gastric step. More LF resisted gastric digestion when pH was slowly reduced to 2.5 or 4.0. Several peptides were identified; however, few matched with previously reported peptides from studies using nonhuman enzymes. Surprisingly, no bovine lactoferricin, f(17-41), was identified during in vitro or in vivo digestion under the intraluminal conditions used. The diversity of enzymes in human GI juices seems to affect the hydrolysis of bLF, generating different peptide fragments compared with those obtained when using only one or a few proteases of animal origin. Multiple sequence analysis of the identified peptides indicated a motif consisting of proline and neighboring hydrophobic residues that could restrict proteolytic processing. Further structure analysis showed that almost all proteolytic cutting sites were located on the surface and mainly on the nonglycosylated half of lactoferrin. Digestion of bLF by human enzymes may generate different peptides from those found when lactoferrin is digested by nonhuman enzymes. The degradation of LF in the GI tract should be taken into consideration when health effects are proposed, because LF has now been approved by the European Food Safety Authority as a dietary supplement in food products.

In vitro studies of the digestion of caprine whey proteins by human gastric and duodenal juice and the effects on selected microorganisms

The in vitro digestion of caprine whey proteins was investigated by a two-step degradation assay, using human gastric juice (HGJ) at pH 2.5 and human duodenal juice (HDJ) at pH 7.5. Different protein and peptide profiles were observed after the first (HGJ) and second (HDJ) enzymatic degradation. The minor whey proteins serum albumin, lactoferrin and Ig were rapidly degraded by HGJ, while alpha-lactalbumin (alpha-LA) and beta-lactoglobulin (beta-LG) were more resistant and survived both 30 and 45 min of the enzymatic treatment. Further digestion with HDJ still showed intact beta-LG, and the main part of alpha-LA also remained unchanged. The protein degradation by HGJ and HDJ was also compared with treatment by commercial enzymes, by using pepsin at pH 2.5, and a mixture of trypsin and chymotrypsin at pH 7.5. The two methods resulted in different caprine protein and peptide profiles. The digests after treatment with HGJ and HDJ were screened for antibacterial effects on some selected microorganisms, Escherichia coli, Bacillus cereus, Lactobacillus rhamnosus GG and Streptococcus mutans. Active growing cells of E. coli were inhibited by the digestion products from caprine whey obtained after treatment with HGJ and HDJ. Cells of B. cereus were inhibited only by whey proteins obtained after reaction with HGJ, while the products after further degradation with HDJ demonstrated no significant effect. Screenings performed on cells of Lb. rhamnosus GG and S. mutans all showed no signs of inhibition.

Supplementation with wheat selenium induces a dose-dependent response in serum and urine of a Se-replete population

In spite of a rather modest dietary intake of selenium (80 micrograms/10 MJ), Norwegian serum Se levels are among the highest in Europe. As part of an ongoing study of Se bioavailability, effects of different doses of wheat Se were investigated in eighteen healthy, Norwegian women. The participants were given Se-rich bread providing 100, 200 and 300 micrograms Se daily for 6 weeks. About 50% of the Se intake was excreted in the urine by week 6, compared with 67% before the intervention started. Serum Se increased by 20, 37 and 53 micrograms/l respectively, in the three group (P less than 0.001). The blood response and renal clearance results compare well with data obtained from less Se-replete populations, and support the hypothesis that selenomethionine from the diet is incorporated into a non-specific amino acid pool. Our study indicates that the intake of wheat Se is the main determinant of blood Se levels in Norway.

Protein metabolism in rats with ventromedial hypothalamic lesions

Abstract The finding that destruction of the ventromedial area of hypothalamus in rats results in obesity has been correlated to the hyperphagia possessed by these animals. Recently, however, obesity has been demonstrated even on restricted food intakes, which indicates that changes in carbohydrate and protein metabolism may have taken place as well. To study the latter, nitrogen balance experiments were combined with carcass analyses. Bilateral lesions in the ventromedial hypothalamic area (VMH) in growing rats are shown to cause increased protein catabolism and/or decreased protein synthesis. Nitrogen balance studies reveal that the lesion affects the protein metabolism within 24 hr. Increased food consumption, due to hyperphagia, renders only a transitory positive effect on protein deposition possible. Carcass analyses, confirming the balance data, also demonstrate an altered lipid metabolism. Animals receiving normal or sub-normal amounts of food accumulate more lipids than their increase in body weight, and, in agreement with this, a loss of body water and protein is found. In animals allowed to overeat, more than 80% of their weight gain is accounted for by lipids. Evidence is reported for a normal protein digestion in lesioned animals, and it is suggested that the increased nitrogen excretion is due to an impaired amino acid utilization.

Fish arsenic may influence human blood arsenic, selenium, and T4:T3 ratio

The effects of an arsenic-rich fish diet and selenium (Se) supplementation on blood arsenic (As), Se, and thyroid hormones were studied in 32 women divided into four equal groups. Groups 1 and 4 received 400 µg Se-methionine daily, group 2 received 400 µg selenite daily, and group 3 received placebo tablets for 15 wk. In addition, groups 1–3 increased their fish intake, eating at least three fish dinners weekly. Mean blood Se concentrations (initially 1.68 ± 0.24 µmol/L) increased twofold in the Se-methionine groups (p < 0.0001) and by 32% in the selenite group (p < 0.01). Group means of blood As concentrations increased by 63% (p < 0.01), 50% (p < 0.01), 106% (p < 0.01), and 29% (p < 0.05) in the four groups, respectively. Analyzed As intake from duplicate portions of consumed fish correlated with final blood As concentrations (r=0.85, p < 0.001, n=32). In the group not receiving Se, there was a positive correlation between final blood As concentrations and plasma T4 : T3 ratio (r=0.80, p < 0.02, n=8). Initially, blood As concentrations correlated negatively with both T3 and T4 in plasma, but this correlation disappeared upon Se supplementation. The results demonstrate that increased intake of fish may influence blood As concentrations and that circulating thyroid hormones may be influenced by Se-As interactions.