Marit Espe

Nutrient absorption and growth of Atlantic salmon (Salmo salar L.) fed fish protein concentrate

Absorption of amino acids was studied in Atlantic salmon fed moist diets where 0, 15 and 30% of the fish meal protein was replaced with concentrated fish silage protein prepared from whole minced herring or herring fillet offal (Clupea harengus). Blood samples were withdrawn at 0, 3, 6, 12, 24, 48 and 72 h post-feeding, and plasma-free amino acid concentrations were compared to those of fish deprived of food for 48 h. Fish fed fish protein concentrate showed similar or higher plasma amino acid concentrations than fish fed diets without any added fish protein concentrate. Maximum plasma amino acid concentrations occurred 3–12 h post-feeding, being fastest in fish fed the most soluble protein source. Effects of inclusion levels on growth and nutrient utilisation were studied in two experiments where either 0 to 30% or 0 to 40% of the fish meal protein was replaced with the fish protein concentrates tested. Fish fed diets where less than 15% of the fish meal protein was replaced by fish protein concentrate showed better growth compared to fish fed either none or higher inclusion levels. Protein accretion decreased in fish fed the high inclusion levels, and remained unaffected by lower inclusion levels. Protein synthesis measured as incorporation of labelled lysine was not significantly affected by the fish protein concentrate inclusion. It is assumed that the better growth obtained might be due to a lower protein breakdown.

Enzymatic hydrolysis of by-products from the fish-filleting industry; chemical characterisation and nutritional evaluation.

Fish frames without heads from Atlantic cod and Atlantic salmon were proteolysed with the industrial enzymes neutrase®, alcalase® and pepsin for 1, 15, 30, 45, 60, 90 and 120 min. After 120 min of hydrolysis, salmon treated with alcalase and cod treated with pepsin yielded significantly (p < 0.05) higher protein recoveries (67.6 and 64% respectively) as compared to salmon treated with neutrase or pepsin and cod treated with neutrase or alcalase (53–62%). To minimise bitterness in the fish hydrolysates, kojizyme™ was added after 120 min of pre-hydrolysis with alcalase, and the hydrolysis was run for additional times of 120, 240, 360, 480, 600 and 720 min. Protein recovery did not change significantly during the hydrolysis with kojizyme, but the degree of hydrolysis increased significantly (p < 0.01) in both the cod and salmon hydrolysates. A hydrolysate from cod treated with alcalase (150 min) followed by treatment with kojizyme (510 min) was produced. The final hydrolysate was freeze-dried to a fish protein hydrolysate (FPH) and chemically characterised. The nutritional value of the FPH was established in an experiment with rats. Inclusion of 10% FPH-N showed significantly (p < 0.05) higher nutritional value as compared to rats fed higher inclusion levels of FPH. © 2000 Society of Chemical Industry

Changes in plasma and muscle free amino acids in atlantic salmon (Salmo salar) during absorption of diets containing different amounts of hydrolysed cod muscle protein

1. 1. Atlantic salmon (Salmo salar) were fed three diets of increasingly pre-digested protein for 4 weeks. They were then starved for 2 days, then fed to satiation. 2. 2. Plasma and muscle samples were collected before feeding and 0, 6, 12, 24, 48 and 72 hr after feeding and analysed for free amino acids. 3. 3. Plasma essential free amino acids were significantly higher (P < 0.05) at 6 and 12 hr post-prandial, while the non-essential amino acids were hardly affected. 4. 4. Minor differences were obtained in muscle free amino acids. Maximum concentration was obtained at 24 hr post-prandial in fish fed the control, and at 12 hr post-prandial for both the pre-digested feeds. 5. 5. In both plasma and muscle, total free amino acids were higher in those fed the proteolysed feeds than in those fed the non-proteolysed feed.

Studies on the nitrogen recovery in enzymic hydrolysis of Atlantic salmon (Salmo salar, L.) frames by Protamex™ protease

In three consecutive experiments, frames without heads from Atlantic salmon were hydrolysed by Protamex™ protease. In experiment I (2 4 factorial design) nitrogen recoveries (NR) of 44–76% were obtained, after 120 min of hydrolysis, by systematically varying the hydrolysing parameters, starting pH (5.4–7.7), temperature (36–50 °C), E:S ratio (30–90 AU kg −1 crude protein) and frames–water ratio (0.71–1.21) between low and high levels. The highest levels of E:S ratio (90 AU kg − 1 crude protein), temperature (50 °C) and starting pH (7.7) and the lowest level of frames–water ratio (0.71) resulted in the highest NR (76%). In experiment II, the optimal temperature and starting pH in the hydrolysis with Protamex™ were established at 50–56 °C and 6.5–7.6, respectively. Beyond these temperature and starting pH intervals, the NR tended to decrease. In experiment III, at optimal temperature (50 °C) and starting pH (6.5) conditions and frames–water ratio of 1.2, NR of 43–61% were achieved after 60 min of hydrolysis, by varying the E:S ratios from 10–90 AU kg − 1 crude protein. The highest E:S ratio resulted in the highest NR but running the hydrolysis for a period longer than 60 min resulted in little increase in NR.

Fish silage prepared from different cooked and uncooked raw materials : Chemical changes during storage at different temperatures

Four silage types were prepared from raw and cooked whole herring, whole mackerel, by-products from the filleting-line of cod and saithe, and from the viscera of cod. Each silage type was stored at 4, 20 and 50°C for 48 days. The raw materials were analysed fresh and after 2, 4, 8, 16, 32 and 48 days of storage. Dry matter, crude protein and total fat were not affected by the different storage temperatures or the length of the storage period. Neither was there any change in amino acid contents. Chemical composition in different silage types reflected the amounts in the raw materials used for silage production. Hydrolysis, on the other hand, varied with the type of raw material used for silage production as well as with the temperature under which the silages were stored. Cooked raw materials did not show any change in hydrolysis during storage. © 1999 Society of Chemical Industry

Do Atlantic salmon (Salmo salar) utilize mixtures of free amino acids to the same extent as intact protein sources for muscle protein synthesis

Pre-smolt Atlantic salmon (Salmo salar) averaging 30 g body weight were fed diets in which a mixture of free amino acids replaced 0, 10, 20, 30 and 40% of the intact protein source. Plasma free amino acids and the content of RNA, DNA and protein synthesis were analysed in white trunk muscle to determine to what extent free amino acids could replace intact protein in the feed without reducing the protein synthesis. Increased inclusions of dietary free amino acids led to increased weight gains, higher concentrations of plasma free amino acids and better utilization of the feed protein for synthetic purposes. Inclusions of about 20–30% free amino acids seemed to be optimal to secure high protein synthesis within muscle tissue. Higher or lower levels resulted in a reduction in protein synthesis.

Atlantic salmon (Salmo salar, L) as raw material for the smoking industry. II: Effect of different smoking methods on losses of nutrients and on the oxidation of lipids

The changes in total fat content, fatty acid composition, tocopherol, ascorbic acid, pH and oxidation were analysed in Atlantic salmon (Salmo salar, L.) in response to either cold smoking (20 or 30 C) or electrostatic smoking. Both fresh and frozen fillets were dry-salted before smoking. The fish smoked were the lean ocean-ranched salmon caught off Iceland in June 1998 and farmed Norwegian salmon, slaughtered in either November 1998 or April 1999, differing in fresh fillet fat content from 84 to 169 g.kg 1 wet weight. The fresh material used in smoking significantly affected the smoking loss of nutritive components in the fillets. The leaner the fish the higher percentile loss in fillet fat. Ascorbic acid decreased about 80 percent from the fresh value, independent of smoking temperature (20 or 30 C). The fish that were dry-salted and electrostatically smoked only lost about 10 percent of the fresh ascorbic acid content, independent of the type of raw material used, indicating a conserving effect on ascorbic acid by the electrostatic process. Also, the electrostatically smoked fish showed a smaller drop in fillet pH than cold-smoked fillets, while tocopherol was little affected by the smoking methods tested. # 2002 Elsevier Science Ltd. All rights reserved.

ABSORPTION AND INCORPORATION OF DIETARY FREE AND PROTEIN BOUND (U14C)-LYSINE IN ATLANTIC COD (GADUS MORHUA)

Atlantic cod (Gadus morhua) were fed (U-14C) lysine in an amino acid diet and (U-14C) lysine bound into an intact protein to study the retention and metabolism of lysine. Fish fed the amino acid diet showed both earlier and higher maximum isotope activity in plasma as compared with fish fed the intact protein diet. Despite the lower values in plasma, the fish fed the intact protein diet showed the greatest retention of lysine in muscle tissue. Fish fed intact protein diet showed a maximum incorporation of 38.4% of the fed isotope into muscle at 24–48 hr postprandially. Those fed the amino acid diet reached a maximum level at 24 hr postprandially with isotope incorporation of 30.4%. Incorporation into the myosin heavy chain was higher in cod fed the intact protein diet as compared with those fed the amino acid diet. The metabolism of lysine into fat was low.

Autolysed fish silage as a feed ingredient for atlantic salmon (Salmo Salar)

Abstract 1. 1. Fish silage made from saithe stored for 2 and 5 months was compared to raw minced saithe as a replacement for parts of the dietary feed protein for Atlantic salmon (Salmo salar). 2. 2. Weight gain and feed utilization were better in the fish fed the silage stored for 2 months and the raw mince than fish fed the silage stored for 5 months. These fish also showed somewhat better protein utilization. 3. 3. Those fish fed the most hydrolysed feed nitrogen, stored less fat in carcass and fillets, resulting in higher amounts of protein.

Intestinal absorption of amino acids in fish: kinetics and interaction of the in vitro uptake of l-methionine in Atlantic salmon (Salmo salar L.)

Abstract The kinetics and interaction of the in vitro uptake of l -methionine were studied in the mid-intestine in Atlantic salmon by the everted sleeve method. The uptake kinetics of l -methionine alone was measured, and also how l -methionine interacted with other dietary amino acids when present in physiological concentration within the incubation medium. Knowledge of how the uptake of l -methionine is affected by other amino acids at physiological concentrations in the gut is important as methionine is considered to be the first limiting amino acid in many proteins used in fish feeds. The carrier-mediated uptake of l -methionine showed a maximum rate of transport ( V max ) of 0.12 nmol mg −1 min −1 and the apparent affinity value ( K t ) was estimated to be 3.0 mM l -methionine. The permeability coefficient ( P ) for the nonsaturable uptake was estimated to be 0.017 nmol mg −1 min −1 mM −1 . These in vitro experiments might indicate that an efficient uptake of l -methionine in a physiological mixture of all amino acids depends on a certain concentration of l -methionine in the incubation solution (2.5 mM), as methionine uptake was inhibited at lower concentrations. At higher l -methionine concentrations (10–25 mM), the uptake of l -methionine when present alone was not different from the uptake of l -methionine measured in a mixture of all amino acids. However, when the other neutral amino acids were omitted from the incubation medium, a reduced uptake of 10 and 25 mM l -methionine was found.