Hai Phong, Vietnam
Hai Phong, Vietnam
Hai Phong, Vietnam
Hai Phong, Vietnam
Hai Phong, Vietnam
Hai Phong, Vietnam
Hai Phong, Vietnam
Introduction. The fisheries industry generates large amounts of fish by-products. Their utilization is one of the relative tasks for fish manufacturers. Hydrolysate from fish by-products is regarded as a valuable bioactive protein source for feed production. In this study, we aimed to optimize hydrolysis conditions for the industrial by-products of catfish. Study objects and methods. We studied the by-products of industrially processed Pangasius hypophthalmus fillet using biochemical methods to find the optimum hydrolysis conditions (enzyme type, enzyme/substrate ratio, temperature, water amount, and time). Then we built a regression model and verified it experimentally. Results and discussion. According to the Box-Behnken design model, the optimum hydrolysis conditions were determined as 10% of water, 0.48% of SEB-Neutral PL enzyme, 57°C temperature, and 6 h duration. We found no significant differences between the modelled and the verified experimental values. The resulting hydrolysate was rich in nitrogen from amino acids, and its other parameters complied with the current national standards. The microbal and sensory attribites satisfied quality requirements as an animal feed supplement. Conclusion. The study results are commercially applicable in feed production, providing a solution for the fisheries industry in byproduct treatment.
Fish, protein, hydrolysate, Pangasius hypophthalmus, catfish, by-products, enzyme
Tra catfish (Pangasius hypophthalmus L.) accounts
for an essential part of Mekong Delta’s and Vietnamese
fisheries’ yield. In 2019, their production area totaled
6600 ha yielding 1.42 million tons, of which 60–70%
were by-products [1–3]. The production expansion
in order to meet the domestic and export demand
has caused a growing concern about the fisheries’
by-product treatment, especially from Pangasius
processing. The Mekong Delta, where Pangasius
production and processing are more developed, needs
economical and environmentally friendly solutions for
large amounts of by-products generated by the local
manufacturing facilities [4]. Recent years have seen an
interest in the utilization of Pangasius by-products to
manufacture value-added products, such as fish powder,
fish skin, and viscera.
Fish powder is the most popular by-product used as
a primary protein supplement for animal feeds. Fish byproducts
are a major source of lipids, native proteins,
and hydrolysates, accounting for 10–20% of the total fish
protein [5, 6]. Presently, most fish powder manufacturers
use the traditional procedure with high pressure and
temperature, resulting in products with a low digestive
and absorptive index.
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Hien B.T.T. et al. Foods and Raw Materials, 2022, vol. 10, no. 1, pp. 19–26
Enzymatic protein hydrolysis of fish by-products
is currently a promising approach to making products
with various applications and high nutritional values [5,
7–10]. Proteases are among common enzymes used
in this process [6]. They hydrolyze protein in fish byproducts
to smaller peptides that usually contain 2–20
amino acids. Fish hydrolysate is a liquid of amino
acids – peptides produced by speeding up fish protein
hydrolysis using proteases under controlled conditions.
When applied in animal feed products, fish hydrolysate
improves the digestion and absorption of proteins, as
well as feed intake, efficiency, and protein utilization
[11–14]. Furthermore, protein hydrolysate enhances
the attractiveness and palatability of the feed, thus
increasing its consumption [15].
There have been several studies in Vietnam on
different aspects of enzymes for hydrolysis of catfish
by-products. Nguyen Cong Ha et al. found that possible
substrate concentrations for an optimal enzyme to
substrate ratio were 108.4 g/L for neutrase, 36.2 g/L
for papain, and 135.8 g/L for bromelain [16]. Nguyen
Thi Thuy et al. investigated Pangasius by-product
hydrolysis using commercialized papain as a protein
source for animal feeds [17]. Dang Minh Hien et al.
also studied papain for application in Bacillus subtilis
cultivation with satisfactory results [18]. Phan Viet
Nam et al. hydrolyzed catfish by-product using a
combination of enzymatic hydrolysis and thermal
treatment, having achieved over 30% hydrolysis, 80%
nitrogen recovery, and a large amount of essential
amino acids [3]. The researchers showed the potential
of catfish by-product treatment with protease enzymes
and possible application of hydrolysates in feed
production. Therefore, an investigation of optimal
hydrolysis conditions is essential for further commercial
application.
This study assessed optimal conditions for Pangasius
hydrolysis, such as the type of enzyme, enzyme/
substrate ratio, temperature, time, and the amount of
water added by analyzing total nitrogen and amino
acids. As a result, we identified the initial conditions to
produce hydrolysates from Pangasius by-products for
the animal feed industry.
STUDY OBJECTS AND METHODS
Study objects. This study featured the by-products
of industrially processed Pangasius c atfish ( Pangasius
hypophthalmus L.) fillet.
Materials. Pangasius by-products, including
heads, bones, and fins (Fig. 1), were collected from the
processing factory of the Travel Investment and Seafood
Development Corporation (Trisedco, Vietnam). They
were minced into small pieces of 3–5 mm and stored
at –20°C until use.
The enzymes were obtained from ICFood Vietnam,
including bromelain (active pH 5.5–7.0, 55–60°C,
500 IU/g), papain (pH 4.5–8.5, 60–70°C, 500 IU/g),
protease (pH 4.5–8.5, 50–60°C, 500 IU/g), and
SEB-Neutral PL (pH 5.5–7.5, 35–60°C, 750 IU/g). They
are commercial enzymes commonly used in animal feed
production.
Optimal hydrolysis conditions. The materials were
defrosted, mixed with 20% water, and heated to 55°C
before adding enzymes. Hydrolysis was performed in
a pilot-scale hydrolysis equipment with a capacity of
80 kg/batch. It was terminated by heating to 85–90°C in
10 min.
After hydrolysis reactions, the mixtures were filtered
and analyzed for total nitrogen (Naa). The optimal
hydrolysis conditions were obtained by optimizing a
single condition at a time in consecutive order. The
resulting condition in the previous experiments was used
as a constant condition in the later experiments. The
protein recovery efficiency was evaluated using the ratio
of nitrogen amino acid (Naa) to total nitrogen (Nts) in the
hydrolysates.
Evaluating the chemical composition of the
materials. We analyzed such parameters as crude
protein, moisture content, lipid, ash, TVB-N, and total
aerobic microorganisms.
Choosing the enzyme. We assessed four enzymes,
namely protease, bromelain, papain, and SEB-Neutral
PL. Hydrolysis reactions were performed with the
enzyme/substrate (E/S) ratio of 0.3%, temperature
of 55°C, and 20% water added in 5 h. The hydrolyzed
products were then analyzed for total protein and Naa to
choose the most effective enzyme. The chosen enzyme
was used in the later experiments.
Figure 1 Pangasius by-products used as study objects
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Hien B.T.T. et al. Foods and Raw Materials, 2022, vol. 10, no. 1, pp. 19–26
Choosing the optimal enzyme/substrate ratio. Seven
enzyme/substrate ratios, namely 0.0, 0.1, 0.2, 0.3, 0.4,
0.5, and 0.6%, were analyzed during hydrolysis. The
hydrolysis reactions were performed at a temperature
of 55°C, with 20% of water added in 5 h. The chosen
enzyme/substrate ratio was then used in the later
experiments.
Choosing the optimal temperature. Five
temperatures (45, 50, 55, 60, and 65°C) were assessed.
The hydrolysis was performed with the optimal
enzyme and enzyme/substrate ratio from the previous
experiments and with 20% water added in 5 h.
Choosing the optimal amount of added water. Water
in amounts of 0, 5, 10, 15, 20, 25, and 30% was used
for hydrolysis under the optimal conditions chosen from
the previous experiments in 5 h. The products were then
analyzed to choose the optimal ratio of water required
for hydrolysis.
Choosing the optimal hydrolysis time. Hydrolyses
with the optimal conditions from the previous
experiments were performed in five different periods,
from 3 to 7 h. The products were then analyzed to
choose the optimal reaction time.
Optimizing the hydrolysis procedure. A Box-
Behnken design was used to investigate the effect of
three factors: A – hydrolysis time, B – enzyme/substrate
ratio, and C – temperature on the Naa/Nts ratio [19].
An optimal scenario was obtained, and a verification
experiment with the optimum conditions was performed
in the lab.
Analysis methods. The following Vietnamese
standards (abbreviated TCVN) were used to analyze
the chemical quality parameters in this study: TCVN
3705:1990 for crude protein; TCVN 3708:1990 for amino
acid nitrogen; TCVN 3700:1990 for water amount;
TCVN 9215:2012 for vaporized acid-base; TCVN
3706:1990 for ammonia nitrogen; and TCVN 5165:1990/
TCVN 4884:2005 for total aerobic microorganisms.
Data analysis. Each experiment was done in
triplicate, each time with three samples, and the results
were averaged. The data were processed and charted in
MS Excel 2007 and model analysis was performed in
Design Expert (version 10).
RESULTS AND DISCUSSION
Materials’ quality. The quality of the by-products
used for hydrolysate production was evaluated through
chemical and microbiological parameters, as shown in
Table 1.
The materials’ crude protein and moisture contents
were 12.76 and 59.27%, respectively, similar to other
research in Vietnam [20]. TVB-N, a freshness quality
indicator, was 13.45 mg/100 g, which was much better
than the best quality limit of 25 mg/100 g. Although the
total microorganism count was 1.13×105, a large number
relating to long storage before use, the TVB-N result
indicated that the materials were still fresh and did not
contain any spoilage compounds that could adversely
affect the quality of hydrolysates [21].
Optimal hydrolysis conditions. Choosing the
hydrolysis enzyme. The Naa/Nts ratios obtained from the
hydrolysis with four enzymes under study are shown
in Fig. 2.
Under the same hydrolysis conditions, SEB-neutral
PL resulted in the highest Naa amount (36.12 ± 0.31%),
equivalent to 1.4 times from bromelain hydrolysis and
1.3 times from protease or papain. The SEB-neutral PL
enzyme was chosen to be used in the later experiments
in this study.
Choosing the enzyme/substrate ratio. The effect
of the enzyme/substrate ratios on the Naa/Nts ratio is
presented in Fig. 3.
Table 1 Chemical and microbiological parameters
of the materials
Parameters Results
Crude protein, % 12.76 ± 0.48
Moisture, % 59.27 ± 0.33
Lipids, % 21.19 ± 0.32
Ash, % 7.02 ± 0.24
TVB-N, mg/100 g 13.45 ± 0.37
pH 6.41 ± 0.17
Nitrogen from amino acid, % 0.07 ± 0.0028
Total aerobic microorganism, CFU/g 1.13 ± 0.18×105
Figure 2 Proteases effect on Naa/Nts ratio Figure 3 Enzyme/substrate ratio vs. Naa/Nts ratio
10
15
20
25
30
35
40
Protease Bromelin Papain SEB-Neutral
PL
Naa/Nts ratio, %
Enzyme protease
10
15
20
25
30
35
40
45
50
0 0,1 0,2 0,3 0,4 0,5 0,6
Naa/Nts ratio, %
E/S ratio, %
20
25
30
35
40
45
50
Naa/Nts ratio, %
30
35
40
45
50
Naa/Nts ratio, %
10
15
20
25
30
35
40
Protease Bromelin Papain SEB-Neutral
PL
Naa/Nts ratio, %
Enzyme protease
10
15
20
25
30
35
40
45
50
0 0,1 0,2 0,3 0,4 0,5 0,6
Naa/Nts ratio, %
E/S ratio, %
25
30
35
40
45
50
Naa/Nts ratio, %
30
35
40
45
50
Naa/Nts ratio, %
22
Hien B.T.T. et al. Foods and Raw Materials, 2022, vol. 10, no. 1, pp. 19–26
The lowest Naa/Nts ratio demonstrated the reaction
without enzyme (14.96 ± 0.38%), and the highest was
from 0.6% enzyme added (45.22 ± 0.32%), though the
ratios of 0.4 and 0.5% were not much different from
0.6%. The enzyme/substrate range of 0.3–0.5% was
chosen for further analysis, and the enzyme/substrate
ratio of 0.4% was chosen for the later experiments.
Choosing the hydrolysis temperature. Figure 4 shows
the effect of hydrolysis temperatures on Naa/Nts ratios.
The results showed that the higher the temperature,
the better the hydrolysis performance till it reached
optimum at 55°C. The effective ratio went down as the
temperature increased beyond that. Thus, 55°C was
chosen for use in later experiments, and the range of 55–
60°C was used in the optimal analysis.
Choosing the amount of added water. The amount
of added water influences the enzyme’s dispersal
and contact with substrates. As we can see in Fig. 5,
hydrolysis performance increased steeply when the
water amount went up from 0 to 10%. Then it slowed
down considerably with water increasing from 10
onward to 30%, suggesting an equivalent efficiency.
To economically use other substances in the hydrolysis
reaction, we chose 10% added water to use in later
experiments.
Choosing the hydrolysis time. The samples were
hydrolyzed in 3, 4, 5, 6, and 7 h under the conditions
from the previous experiments (0.4% SEB-neutral
PL, 55°C, and 10% added water). The hydrolysis
performance increased sharply from 34.44 ± 0.34% (3 h)
to 43.90 ± 0.26% (5 h), then slowing down and reaching
highest at 44.65 ± 0.30% (7 h). The difference between
the samples hydrolyzed in 6 and 7 h was not statistically
significant (P > 0.05). Although nitrogen solubility
Figure 4 Hydrolysis temperature vs. Naa/Nts ratio
Figure 5 Effect of water amount on Naa/Nts ratio
Figure 6 Effect of hydrolysis time on Naa/Nts ratio
Table 2 ANOVA results
Factors Sum of square Degrees of freedom Mean square F ratio P-value (P < 0.05)
Model 390.41 9 43.38 155.85 < 0.0001 significant
A 116.13 1 116.13 417.24 < 0.0001
B 24.12 1 24.12 86.65 0.0002
C 70.27 1 70.27 252.47 < 0.0001
AB 4.82 1 4.82 17.31 0.0088
AC 5.45 1 5.45 19.59 0.0069
BC 4.67 1 4.67 16.76 0.0094
A² 58.95 1 58.95 211.81 < 0.0001
B² 112.44 1 112.44 403.98 < 0.0001
C² 12.68 1 12.68 45.57 0.0011
Residual 1.39 5 0.2783
Lack of fit 1.18 3 0.3934 3.72 0.2190 insignificant
Standard deviation 0.2115 2 0.1057
R2: 0.9964 Expected R²: 0.9506
A – Enzyme/substrate ratio, B – Temperature, and C – Hydrolysis duration
10
15
20
Protease Bromelin Papain SEB-Neutral
PL
Naa/Enzyme protease
10
15
20
25
0 0,1 0,2 0,3 0,4 0,5 0,6
Naa/E/S ratio, %
15
20
25
30
35
40
45
50
45 50 55 60 65
Naa/Nts ratio, %
Temperature, oC
25
30
35
40
45
50
0 5 10 15 20 25 30
Naa/Nts ratio, %
Water added, %
30
32
34
36
38
40
42
44
46
3 4 5 6 7
Naa/Nts ratio, %
Time, hour
10
15
Protease Bromelin Papain SEB-Neutral
PL
Enzyme protease
10
15
20
0 0,1 0,2 0,3 0,4 0,5 0,6
E/S ratio, %
15
20
25
30
35
40
45
50
45 50 55 60 65
Naa/Nts ratio, %
Temperature, oC
25
30
35
40
45
50
0 5 10 15 20 25 30
Naa/Nts ratio, %
Water added, %
30
32
34
36
38
40
42
44
46
3 4 5 6 7
Naa/Nts ratio, %
Time, hour
10
15
20
25
30
35
Protease Bromelin Papain SEB-Neutral
PL
Naa/Nts ratio, %
Enzyme protease
10
15
20
25
30
35
40
45
0 Naa/Nts ratio, %
15
20
25
30
35
40
45
50
45 50 55 60 65
Naa/Nts ratio, %
Temperature, oC
25
30
35
40
45
50
0 Naa/Nts ratio, %
30
32
34
36
38
40
42
44
46
3 4 5 6 7
Naa/Nts ratio, %
Time, hour
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Hien B.T.T. et al. Foods and Raw Materials, 2022, vol. 10, no. 1, pp. 19–26
Figure 7 Factors relative influences on the dependent variable in the statistical model: (a) Influences of E/S ratio and duration;
(b) Influences of temperature and E/S ratio; (c) Influences temperature and duration
Naa/Nts, %
C: Duration, h
A: E/S ratio, %
6.0
5.5
5.0
4.5
4.0
0.30 0.35 0.40 0.45 0.50
34
36
38
40
42
44
46
3
38
Design-Expert® Software
Factor Coding: Actual
Naa/Nts, %
Design points above predicted value
Design points below predicted value
29.56 45.47
X1 = А: Е/S ratio
X2 = C: Duration
Actual Factor
B: Temperature = 55
C: Dur ation, h
50
45
40
35
30
25
6.0
5.5
5.0 4.5
4.0 0.35 0.40 0.45 0.50
0.30
Design·Expert® Software
Factor Coding: Actual
Naa/Nts, %
Design points above predicted value
Design points below predicted value
29.56 45.47
X1 = А: Е/S ratio
X2 = B: Temperature
Actual Factor
C: Duration = 5
A: E/S ratio, %
0.30 0.35 0.40 0.45 0.50
60
58
56
54
52
50
B: Temperature, °C
35
40
35
3
Naa/Nts, %
B: Temperature, °C
50
45
40
35
30
25
60
Naa/Nts, %
56
52 50 0.30
0.40
0.45
0.50
0.35
54
58
6.0
5.5
5.0
4.5
4.0
B: Temperature, °C
50 52 54 56 58
Design·Expert® Software
Factor Coding: Actual
Naa/Nts, %
Design points above predicted value
Design points below predicted value
29.56 45.47
X1 = B: Temperature
X2 = C: Duration
Actual Factor
А: Е/S ratio = 0.4
B: Temperature, °C
50
45
40
35
30
25
6.0
C: Duration, h
5.0
4.0 50 52
54 56 58 60
4.5
5.5
C: Duration, h
60
45
35 40
3
Naa/Nts, %
a
b
c
A: E/S ratio, %
A: E/S ratio, %
Naa/NtsN , % aa/Nts, %
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Hien B.T.T. et al. Foods and Raw Materials, 2022, vol. 10, no. 1, pp. 19–26
increases with time in enzyme hydrolysis, after a
certain period, the formation of hydrolysis products
and the reduction of peptide bonds during hydrolysis
inhibit enzyme activities and decrease hydrolysis
rate [22, 23]. Therefore, the effective range of duration
was determined to be from 4 to 6 h.
Optimizing Pangasius by-product hydrolysis with
Seb-Neutral PL enzyme. We studied the influence of
different variables on the outcome of hydrolysis by
performing Box-Behnken Designs in Design-Expert. In
particular, we used the following factors: A – enzyme/
substrate ratio (0.3–0.4–0.5%); B – Temperature
(50–55–60°C); and C – Hydrolysis duration (4–5–6 h).
The ANOVA results are presented in Table 2.
The model was significant with the F ratio of 155.85
(P < 0 .000) a nd t he l ack o f fi t o f 3 .72 ( P = 0 .2190).
The variables AB, AC, BC, A2, B2, and C2 all had
P < 0.05 and therefore were significant and included
in the regression formula. The model to determine the
relationship between the dependent variable Naa/Nts and
enzyme/substrate ratio, temperature, and duration, as
well as their interactions, was presented in the following
formula:
y = a + b1·A + b2·B + b3·C + b12·AB + b13·AC +
+ b23·BC + b1
2·A2 + b2
2·B2 + b3
2·C2
Naa/Nts ratio = 43.79 + 3.81·A + 1.74·B + 2.96·C +
+ 1.10·AB + 1.17·AC – 1.08·BC – 4.00·A2 –
– 5.52·B2 – 1.85·C2 (1)
In formula (1), b1, b2, and b3 were positive, showing
that the hydrolysis performance (Naa/Nts) was directly
proportional to the analyzed factors: enzyme/substrate
ratio, temperature, and duration. ǀb1ǀ<ǀb3ǀ<ǀb2ǀ suggested
that the enzyme/substrate ratio had a more substantial
influence on the performance of the hydrolysis reaction
than the other factors. The coefficients b1
2, b2
2, and b3
2
were negative, suggesting that the graphs were parabolic
faces with concave surfaces facing downwards and
having extreme points. The coefficients b12 and b13
were positive, showing a positive interaction between
temperature and time, with the enzyme/substrate ratio
increasing hydrolysis performance. At the same time,
b23 was negative, indicating that the interaction between
temperature and time was inversely proportional to
the Naa/Nts ratio. This could be explained by the nature
of enzyme reactions, where high temperature and
prolonged duration might cause unstable enzymes and
reduce enzyme hydrolysis activities. The effects of these
factors on the Naa/Nts ratio were graphically presented
in Fig. 7.
Based on the Box–Behnken design model, the
optimum hydrolysis conditions (enzyme/substrate
ratio = 0 .48%, t emperature = 5 6.52°C, a nd d uration =
5.77 h) was chosen to conduct a laboratory experiment.
The results of the laboratory experiment in comparison
with the predicted values are shown in Table 3.
There were no significant differences between
the predicted and experimental values. Therefore, we
proposed the following optimum hydrolysis conditions
for Pangasius by-products: 10% added water, 0.48%
SEB-Neutral PL enzyme, 57°C, and 6 h.
Product quality. The results of the hydrolysate
quality evaluation are presented in Table 4.
The resulting Pangasius hydrolysate was a highquality
source of nutrition with 12.41 g/L nitrogen from
amino acids, accounting for 46.08% of total nitrogen
(26.94 g/L). Its other parameters fully complied with
the current national standard QCVN 01-190:2020/
BNNPTNT, making it suitable for use as a supplement
to animal feed to improve its amino acid content and
aroma.
CONCLUSION
We investigated the initial hydrolysis conditions to
produce hydrolysates from Pangasius hypophthalmus L.
by-products. The regression model prediction and
laboratory verification determined the following
optimum hydrolysis conditions: 10% water amount,
0.48% SEB-Neutral PL enzyme, 57°C temperature,
and 6 h hydrolysis time. The hydrolysates yielded from
the proposed hydrolysis procedure satisfied the quality
requirements for animal feed supplements and complied
with the national standard QCVN 01-190: 2020/
BNNPTNT. Thus, our study results were commercially
applicable for feed production and provided a solution
for by-product treatment in the fisheries.
CONTRIBUTION
B.T.T. Hien designed the study concept. P.T. Diem
developed the methodology. L.A. Tung, T.T. Huong,
Table 3 Predicted vs. experimental results
Value Enzyme/
substrate
ratio, %
Temperature,
°C
Duration,
h
Naa/Nts
ratio, %
Predicted 0.48 56.52 5.77 46.25
Experimental 0.48 57 6 46.08 ± 0.31
Table 4 Quality parameters of the resulting hydrolysate
Parameters Results
Total nitrogen, g/L 26.94 ± 0.16
Nitrogen from amino acid, g/l 12.41 ± 0.08
Naa/Nts ratio, % 46.08 ± 0.31
TVB-N, mg/100 g 42.73 ± 0.63
Lipid, % 2.6 ± 0.02
Escherichia coli Not detected in 1 g
Salmonella Not detected in 25 g
Sensory
Color: deep brown
Smell: aroma characteristic of fish protein hydrolysates,
no off-aroma.
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and N.H. Hoang performed the validation experiment.
N.H. Hoang and N.K. Bat conducted formal analysis.
N.V. Nghia and B.T.T. Hien drafted, reviewed, and
edited the manuscript. All the authors were involved in
the investigation, as well as read and agreed to the final
version of the manuscript.
CONFLICT OF INTEREST
The authors declare that there is no conflict of
interest.
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