ALIMET® and DL-methionine solubility in extruded aquatic feeds

trial report summary
ALIMET® and
DL-methionine
solubility in extruded
aquatic feeds.
Background
Traditionally, fish meal has been the most common protein
source used in aquatic feeds due to its optimum amino acid
profile and digestibility. However, due to the reduction in
supply and increase in cost of fishmeal during the last few
years, nutritionists have started to incorporate vegetable-based
protein sources like soybean meal and corn gluten meal in
the diets of aquatic species. However, the amino acid profile
of the vegetable protein sources is not adequate for the high
demands of these commercially grown aquatic species and
synthetic amino acids like lysine and methionine need to
be added to the diet. One of the concerns in the addition of
synthetic amino acids to the aquatic diets is the solubility of
these amino acids and the related potential for water pollution.
Objective
The objective of this study was to determine the solubility of
ALIMET® feed supplement and DL-methionine when included
in extruded aquatic feeds. The type of protein source used in
the aquatic feeds, as well as the floating characteristics and
size of the extruded pellet were also evaluated for solubility for
ALIMET and DL-methionine.
Materials and Methods
ALIMET and DL-methionine were added to six different
extruded aquatic feeds at approximately 0.5 percent. The
six extruded aquatic feeds were selected to represent diets
commonly fed to four commercial aquatic species (catfish,
salmon, shrimp, and trout), differing by floating characteristics
(floating, slow-sinking, and sinking), pellet sizes (2, 3, 6 and 9 mm), and protein sources (soybean meal and
fish meal).
Table 1 describes the comparison made among specific
extruded aquatic feeds to evaluate the effect of protein source,
pellet size and floating characteristics on ALIMET and DLmethionine solubility. The effect of protein source on ALIMET
and DL-methionine solubility was evaluated by comparing
for
Key Findings:
• ALIMET and DL-methionine have very similar solubility in the extruded aquatic feeds evaluated in this
study.
• ALIMET and DL-methionine solubility rate averaged
1.50 percent and 1.43 percent per minute, respectively.
• Several factors impact the solubility of ALIMET and
DL-methionine, including pellet size, fat content of the
pellet, and floating characteristics of the pellet.
solubility between 6 mm pellet-size salmon diet (Diet 3) and
6 mm pellet-size and trout diet (Diet 5). The effect of pellet
size on ALIMET and DL-methionine solubility was evaluated
by comparing solubility among the different pellet sizes
of the salmon diet (Diet 2, 3 and 4). The effect of floating
characteristics of the pellet on ALIMET and DL-methionine
solubility was evaluated by comparing solubility among floating,
slow-sinking and sinking pellets as described in Table 1.
TABLE 1.
Solubility Rate of ALIMET and DL-Methionine
Type of Diet
ALIMET Solubility during First 15 min, %
ALIMET solubility Rate,
%/min
Catfish Diet, 6 mm
23.00
1.53
20.35
1.36
Salmon Diet, 3 mm
30.57
2.04
30.78
2.05
Salmon Diet, 6 mm
10.34
0.69
10.60
0.71
Salmon Diet, 9 mm
9.70
0.65
10.27
0.68
Trout Diet, 6 mm
16.96
1.13
16.88
1.13
Shrimp Diet, 2 mm
44.05
2.94
39.75
2.65
Average
22.44
1.50
21.44
1.43
Solubility during First 15 min. of Incubation, %
Figure 1. of ALIMET and DL-Methionine in
Extruded Aquatic Feeds
Solubility of ALIMET and DL-Methionine over Time
The amount of ALIMET, DL-methionine and soluble protein
released from the pellets increased over time following a
diminishing return curve. The amount of nutrients in solution
increased rapidly during the first 15 minutes of incubation
and slowly during the last 30 minutes of incubation. All diets
showed a similar pattern (Figure 2).
50
45
40
35
30
25
Solubility Rate of ALIMET and DL-Methionine
Pellets are usually consumed quickly after they are offered to
the fish. Therefore, the amount of ALIMET and DL-methionine
released from the pellets during the first 15 minutes will be
the most relevant for practical applications. If ALIMET and
DL-methionine solubility is assumed to be linear during the first
15 minutes of incubation, a solubility rate (% soluble/min) can
be determined. ALIMET and DL-methionine solubility during
the first 15 minutes of incubation averaged 22.44 percent and
21.44 percent, respectively (Table 1). When solubility was
expressed per minute, similar solubility rates were found for
ALIMET and DL-methionine.
20
15
10
5
0
fish
Cat
n
n
mo
mo
Sal mm Sal mm
3
6
n
mo
Sal mm
9
t
u
Tro
imp
Shr
e
rag
Ave
Diets
 ALIMET
 DL-methionine
Figure 2. Solubility of ALIMET, DLMethionine and Protein over Time
across All Diets
Factors Affecting the Solubility of ALIMET and DL-Methionine
0.15
50
45
40
35
30
25
20
15
10
5
0
0.10
0.05
Protein Solubility, %
Solubility, %
DL-Methionine Solubility DL-Methionine Solubility Rate,
during First 15 min, %
%/min
0
0
10
20
30
40
Incubation Time, min
50
60
 ALIMET Solubility  Soluble Protein  DL-Methionine Solubility
Results
ALIMET and DL-Methionine Solubility across All Extruded
Aquatic Feeds
Within each extruded aquatic feed, no differences were found
in the amount of ALIMET or DL-methionine released from the
pellet. It appears that in extruded aquatic feeds, DL-methionine
and ALIMET have similar solubility (Figure 1).
1. Type of Protein Source Used in the Extruded Aquatic Pellets
The effect of type of protein used in the diet (fish meal vs.
soybean meal) on nutrient solubility was evaluated. ALIMET
and DL-methionine solubility in trout pellets (45% soybean
meal and 12% fish meal) was compared to solubility in salmon
pellets (45% fish meal and 12% soybean meal) within the
same pellet size. It was found that nutrients solubility in salmon
pellets was lower than in trout pellets, suggesting that fish
meal could reduce nutrients solubility (Figure 3). However,
when all diets were evaluated, a positive correlation was
found between levels of fat in the diet and ALIMET and DLmethionine solubility during the first 15 minutes of incubation
(Table 2, Figure 4). This correlation suggests that the higher
content of fat in fish meal might reduce ALIMET and DLmethionine solubility.
TABLE 2.
Correlation between ALIMET and DL-Methionine Solubility during the First 15 Minutes and Dietary Content
of the Diets
Type of Diet
ALIMET Solubility during First 15 min, %
DL-Methionine Solubility
during First 15 min, %
Dietary Fat,
%
Fish Meal,Soybean Meal,
%
%
Catfish Diet, 6 mm
23.00
20.35
32.04
5.2
5
30
Salmon Diet, 3 mm
30.57
30.78
38.49
25.44
45
12
Salmon Diet, 6 mm
10.34
10.60
38.49
25.44
45
12
Salmon Diet, 9 mm
9.7
10.27
38.49
25.44
45
12
Trout Diet, 6 mm
16.96
16.88
37.54
14.98
12
45
Shrimp Diet, 2 mm
44.05
39.75
38.72
3.08
15
43.5
35
Figure 3. Effect of Type of Protein in
the Diet on ALIMET and DL-Methionine
Solubility
30
Solubility, %
CP in Diet,
%
25
20
15
10
5
0
Trout,
ALIMET
Trout,
DL-methionine
Salmon,
ALIMET
Salmon,
DL-methionine
the extruder conditions. Floating and slow-sinking pellets are
obtained by preconditioning the feed with high steam and
temperature prior and at the mid-point of the extruder. The
combination of steam and temperature gelatinizes the starch
of the feed, reducing the density of the pellet and the solubility
of the nutrient. The sinking pellets have less steam and
temperature during preconditioning and extrusion, resulting
in higher dense pellet (Table 3). ALIMET and DL-methionine
solubility in the sinking pellets (shrimp diet) was the highest of
all diets. However, the pellet size of the shrimp diet was also
the smallest (2 mm). In general, the more expanded the feed
is, the lower the nutrient solubility and, therefore, ALIMET and
DL-methionine solubility (Figure 8 and 9).
50
Figure 4. Effect of Fat Content in the
Diet on ALIMET and DL-Methionine
Solubility
60
ALIMET Solubility, %
Solubility during First 15 Min.
of Incubation, %
 5 min  15 min  30 min  60 min
40
30
Figure 5. Effect of Pellet Size on ALIMET
Solubility in Salmon Diets
50
40
30
20
10
20
0 0
10
10
0
20
30
40
Incubation Time, min
50
60
 9 mm Pellet  6 mm Pellet  3 mm Pellet
0
5
10
15
20
25
30
Fat Content in Diet, %
2. Pellet Size of the Extruded Aquatic Pellets
As the fish grow, the size of the pellet fed to the fish also
increases. In order to evaluate the effect of pellet size on
nutrient digestibility, three sizes of pellets (3, 6 and 9 mm)
were chosen within a diet. It was found that as the pellet size
increased, the solubility of the nutrients decreased, probably
due to the increase in the surface area of the pellet (Figure
5 and 6). When all diets were evaluated a similar inverse
correlation was found between pellet size and solubility during
the first 15 minutes of incubation (Figure 7).
3. Floating Characteristics of the Extruded Aquatic Feeds
The different floating characteristics (floating, slow-sinking
and sinking) of the aquatic diets are achieved by changing
DL-Methionine Solubility,
%
ALIMET  DL-Methionine
60
Figure 6. Effect of Pellet Size on DL-Methionine Solubility in Salmon Diets
50
40
30
20
10
0 0
10
20
30
40
50
Incubation Time, min
 9 mm Pellet  6 mm Pellet  3 mm Pellet
60
TABLE 3.
Effect of Floating Characteristics of Pellet on ALIMET and DL-Methionine Solubility
Type of Diet
Floating ALIMET Solubility
DL-Methionine Solubility
Characteristics during First 15 min, %
during First 15 min, %
Preconditioning Preconditioning
Steam Flow, kg/h Temperature, C°
Steam in
Extruder, kg/h
Salmon Diet, 3 mm Slow-sinking
30.57
30.78
50
93
9
Salmon Diet, 6 mm Slow-sinking
10.34
10.60
35
89
11
Salmon Diet, 9 mm Slow-sinking
9.7
10.27
40
93
6
Trout Diet, 6 mm Slow-sinking
16.96
16.88
34
78
6
Catfish Diet, 6 mm Floating
23.00
20.35
52
92
13
Shrimp Diet, 2 mm Sinking
44.05
39.75
20
64
0
Conclusion
• Several factors can influence ALIMET and DL-methionine
solubility
Figure 8. Effect of Pellet Floating
Characteristics on ALIMET Solubility
90
80
ALIMET Solubility, %
• ALIMET and DL-methionine have very similar solubility
in the extruded aquatic feeds evaluated in this study.
ALIMET and DL-methionine solubility during the first
15 minutes of incubation averaged 22.44 percent and
21.44 percent, respectively. ALIMET and DL-methionine
solubility rate averaged 1.50 percent and 1.43 percent per
minute, respectively.
70
60
50
40
30
20
• Pellet size: The smaller the pellet the higher the solubility
of ALIMET and DL-methionine
10
00
• Fat content of the pellet: The higher the fat content of the diet, the lower the solubility of ALIMET and DL-methionine
10
20
30
40
50
60
Incubation Time, min
 Floating, Catfish
 Slow-Sinking, Trout
Slow-Sinking, Salmon
• Floating characteristics of the pellet: The process of
expanding the feed to achieve floating and slow-sinking
pellet characteristics reduces ALIMET and DL-methionine
solubility
Sinking, Shrimp
Figure 9. Effect of Pellet Floating
Characteristics on DL-Methionine Solubility
90
50
Figure 7. Effect of Pellet Size on ALIMET
and DL-Methionine Solubility across All
Diets
40
30
ALIMET Solubility, %
Solubility during First 15
Min. of Incubation, %
80
70
60
50
40
30
20
20
10
10
0 0
2
4
6
Pellet Size, mm
8
10
ALIMET  DL-Methionine
00
10
20
30
40
50
60
Incubation Time, min
 Floating, Catfish
Slow-Sinking, Salmon
 Slow-Sinking, Trout
Sinking, Shrimp
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