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Thea Morken defended her thesis on November 4th 2011

Ane Gro Siri Skjelfjord

Upgrading plant ingredients in feed for salmonids by thermo­mechanical treatment and acid salt


Abstract from the thesis - PhD thesis 2011:52

Author: Thea Morken


Inclusion of plant ingredients in diets for salmonids is restricted due to low energy con­tents, unbalanced amino acid (AA) composition and presence of antinutritional factors (ANF). The objective of this thesis was to investigate methods for improving the nutri­tional and physical quality of plant ingredients in diets for salmonids by use of thermo­-mechanical treatment and supplemental organic acid salts.

Diets containing plant ingredients derived from soybeans or barley were exposed to thermo-mechanical treatment at different temperatures by (1) expander pretreatment, (2) extrusion and (3) autoclaving, with or without the supplementation of 12 g kg-1 potassium diformate (KDF) or 10.6 g kg-1 sodium diformate (NaDF). Nutritional quality was eva­luated by the content of dietary AA, available lysine and trypsin inhibitor activity (TIA), as well as in vivo apparent digestibility in Atlantic salmon (Salmo salar), rainbow trout (Oncorhynchus mykiss) and mink (Neovison vison). In addition, a two-step in vitro ga­strointestinal model (GIM) was used to assess protein solubility and bioavailability of AA by use of digestive enzymes from Atlantic salmon. Physical quality of extruded diets was evaluated by measuring hardness, expansion ratio, durability and water stability index (WSI).

Expander pretreatment of full-fat soybean meal (FFSBM) at 100 and 120 °C improved (P<0.05) the digestibility of arginine, glutamine and tyrosine in Atlantic salmon. The higher digestibility of expander pretreated FFSBM was confirmed in mink. The improved digestibility of AA in Atlantic salmon and mink by expander pretreatment of FFSBM coincided with the reduction in dietary TIA. Extrusion of diets containing toasted soybean meal (SBM) at 150 °C improved (P<0.05) the digestibility of crude protein (CP) and sev­eral individual AA in Atlantic salmon compared to extrusion at 110 °C. Similar findings were observed for diets containing barley protein concentrate (BPC) when fed to rainbow trout. Extrusion at 141 °C improved (P<0.05) the digestibility of starch, CP, arginine and several dispensable AA, but reduced (P<0.01) the digestibility of phenylalanine compared to extrusion at 110 °C. The improved digestibility of protein and AA in rainbow trout with increasing extrusion temperatures was associated with higher availability of lysine in diets extruded at 141 °C. Heat treatment at 130 °C by autoclaving reduced the dietary AA content (P<0.05), the in vivo digestibility of CP and all individual AA in mink, as well as the in vitro bioavailability of AA (P<0.01) compared to heat treatment at 100 °C. The ad­verse effects of heat treatment at long treatment times on the nutritional quality of diets were also shown by reductions in dietary contents of reactive and available lysine (P<0.001), protein solubility (P<0.01) and increased browning (P<0.001).

Supplementation of KDF to FFSBM and SBM diets did generally not (P>0.1) affect nu­trient digestibility in Atlantic salmon and mink, whereas supplementation of NaDF im­proved (P<0.05) the digestibility of most major nutrients and individual AA in rainbow trout. Addition of NaDF did not (P>0.l) affect the digestibility of CP or individual AA in mink.

Physical quality of the extruded diets was affected by both extrusion temperature and sup­plementation of organic acid salts. Increased pellet expansion was observed in diets with soybeans processed by expander pretreatment and increasing extrusion temperatures, while supplemental KDF reduced pellet expansion. In diets with BPC, increasing extru­sion temperatures improved pellet durability. Addition of NaDF improved the expansion ratio, durability and WSI compared to diets without NaDF.

The improved digestibility of plant proteins in salmonids by thermo-mechanical treatment at increasing temperatures is explained by a reduction in heat-labile ANF concurrent with higher availability of AA, as a result of denaturation and structural unfolding of protein molecules. The negative effects of increasing temperatures in combination with long treatment times in the autoclave on digestibility of CP and AA in mink was explained by a reduction in AA availability. Supplementation of acid salts did not consistently improve the digestibility of plant ingredients in salmonids and did not protect the protein from heat-induced damage during prolonged heat treatment. The lack of consistency remains unclear and requires further investigation. Both increasing temperatures during extrusion and supplementation of acid salts affected the physical quality of the feeds. The improved physical quality by supplemental acid salts indicates increased binding of feed particles.



Oppdatert: 09.11.11
Utskriftsvennlig versjon

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