Bol. Inst. Pesca, São Paulo, 44(vol. esp.): 24 - 34, 2017
Doi: 10.20950/1678-2305.2017.24.34
ACID SILAGE OF TUNA VISCERA: PRODUCTION, COMPOSITION, QUALITY AND
DIGESTIBILITY
Jorge Filipe BANZE
1
; Maria Fernanda Oliveira da SILVA
1
; Dariane Beatriz Schoffen ENKE
2
;
Débora Machado FRACALOSSI
1
ABSTRACT
Fish waste processed in the form of silage may constitute an alternative to the use of fishmeal (FM).
In this study the composition and quality of the acid silage produced from tuna viscera (TV) were
characterized and the digestibility of the nutrients of this product was determined for jundia
Rhamdia quelen, using ytrium oxide as an inert marker and a completely randomized design. At the
end of thirty days, 61.74% of the crude protein of TV was solubilized. Acid silage from TV
presented good nutritional composition (high protein, good amino acid profile and essential fatty
acids) and good microbiological quality. Crude protein digestibility was similar (88.52%) for TV
and FM, but dry matter digestibility was higher (P<0.05) for (TV) (92.20%). Tuna silage presented
as a high nutritional quality and nutrient digestibility for jundiá juveniles, R. quelen. Therefore, this
novel ingredient has potential as an alternative protein source in aquafeeds.
Keywords: Fish waste; hydrolysis; protein solubility; Rhamdia quelen
SILAGEM ÁCIDA DE VÍSCERAS DE ATUM: PRODUÇÃO, COMPOSIÇÃO, QUALIDADE
E DIGESTIBILIDADE
RESUMO
Resíduos de pescado processados na forma de silagem podem se constituir em uma alternativa ao
uso de farinha de peixe (FM). Neste estudo caracterizou-se a composição e qualidade da silagem
ácida produzida a partir de vísceras de atum (TV) e determinou-se a digestibilidade dos nutrientes
deste produto para jundiá Rhamdia quelen, utilizando-se o óxido de ítrio como marcador inerte em
delineamento completamente casualizado. Ao final de trinta dias, 61.74% da proteína bruta da TV
estava solubilizada. A silagem ácida de TV apresentou boa composição nutricional (alta proteína,
bom perfil de aminoácidos e de ácidos graxos essenciais) e qualidade microbiológica satisfatória. A
digestibilidade da proteína bruta foi similar (88.52%) para TV e FM, mas a da matéria seca foi maior
(P<0.05) para a TV (92.20%). A silagem de atum apresentou-se como um ingrediente proteico de
alta qualidade nutritiva e digestiva para juvenis de jundiá, R. quelen. Portanto, este novo
ingrediente tem potencial como fonte alternativa de proteína para rações de espécies aquícolas.
Palavras-chave: resíduos de pescado; hidrólise; solubilidade proteica; Rhamdia quelen
Original Article / Artigo Científico: Recebido em 14/11/2016 Aprovado em 05/06/2017
1
Universidade Federal de Santa Catarina (UFSC), Centro de Ciências Agrárias, Departamento de Aquicultura Rod.
Admar Gonzaga, 1346 CEP: 88034-001 Florianópolis SC Brazil. e-mail: banzephillipe@ymail.com;
maria.fos@ufsc.br; debora.fracalossi@ufsc.br (corresponding author)
2
Universidade Estadual Paulista Júlio de Mesquita Filho (UNESP), Campus Experimental de Registro R. Nelson Brihi
Badur, 430 CEP: 11900-000 Registro SP Brazil. e-mail: schoffenke@gmail.com
* Financial support: National Council for Scientific and Technological Development (CNPq) and Ministry of Fisheries and
Aquaculture (MPA) (call nº 42/2012, process nº 406168/2012-1).
Acid silage of tuna viscera: production, composition, quality… 25
Bol. Inst. Pesca, São Paulo, 44(vol. esp.): 24 - 34, 2017
INTRODUCTION
In fish farming, feed costs can vary from 30 to
60% and it may exceed 85% of the total
production costs in intensive systems (SILVA and
ANDERSON, 1995). Fishmeal is traditionally
considered an important protein ingredient in
aquaculture diets because it has high palatability
and excellent source of amino acids, fatty acids,
vitamins and minerals (VALLE et al., 2015),
however the increase in its demand, implies an
increase in its cost. Alternative protein-rich
ingredients with potential to replace fishmeal are
fish waste, which includes by-catch and residues
from fish processing industries, not intended
for human consumption, with potential
environmental and/or health hazzard if discarded
incorrectly. There are techniques for the conservation
of fish residues that allow their processing and
incorporation as an ingredient in animal feed such
as acid, biological or enzymatic silage (ESPE et al.,
1999).
The nutritional value of fish silage is in its
high protein digestibility due to the high degree of
protein hydrolysis and the presence of essential
amino acids (OETTERER, 1994, JUNIOR and
SALES, 2013). The degree of hydrolysis should be
used as a chemical quality criterion for silage,
because due to autolysis and rancification, the
product quality may be impaired.
Fish silage can be produced from a variety of
raw materials such as heads, bones, viscera, fins,
skins, whole fish or a mixture of different parts of
fish, which may influence the nutritional
composition of the silages produced. Thus, the
production of fish silage with a standard residue
such as tuna viscera becomes interesting, so that
the final nutritional composition does not vary
greatly and the protein content may be relatively
greater than the mineral matter or fat.
Protein hydrolyzate produced exclusively
from sardine viscera (Sardina pilchardus),
improved growth and survival of European sea
bream (Dicentrarchus labrax) when included at 10%
diet (KOTZAMANIS et al., 2007). Similarly, the
replacement of 50% of fishmeal by biological
silage produced from fish viscera provided good
growth performance of the catfish (Heteropneus
fossilis) (MONDAL et al., 2008). Addidtionaly,
good digestibility of the silage produced from
surubin viscera (Pseudoplatystoma sp.) was
reported for Nile tilapia, with values of 83.52,
93.30 and 87.20% for dry matter, crude protein
and ether extract digestibility, respectively
(HISANO et al., 2012).
In Brazil, the skipjack (Katsuwonus pelamis) is
the main species of tuna caught for canning. In
2011, this species capture surpassed 800.000 t
(FAO, 2013), representing more than 95% of the
raw material canned by the Brazilian industry
(GONÇALVES, 2011). Fish waste resulting from
the canning process can be an important raw
material for the production of protein feed
ingredients.
The jundiá, Rhamdia quelen (Siluriformes:
Heptapteridae), is a freshwater catfish, native to
the American continent, present in watersheds
that extend from southeastern Mexico to central
Argentina (FUKUSHIMA and ZANIBONI FILHO,
2009). Jundiá presents good features for intensive
farming in South Brazil, such as easy reproduction,
good tolerance to handling and growth during the
winter months (MEYER and FRACALOSSI, 2004).
Its feeding habit is omnivore with carnivorous
tendencies (FRACALOSSI et al., 2007), which
makes it an interesting model for the study of
alternative protein ingredients. Therefore, this
study aimed to characterize the composition and
quality of the tuna viscera acid silage (TV) and to
determine its nutrient digestibility for jundiá.
MATERIAL E METHODS
Acid silage: preparation, composition, quality and
protein solubility
Tuna residues (K. pelamis), consisting only of
viscera (intestine, stomach, liver, pancreas,
swimming bladder, kidney, spleen, gonads) were
purchased from a fish processing company in the
state of Santa Catarina, Brazil. The viscera were
transported frozen in polyethylene containers for
one hour to the Laboratory of Nutrition of Aquatic
Species (LABNUTRI).
In the laboratory, the raw material remained
at room temperature for thawing (30 min) and
then it was crushed using an electric meat grinder.
Sixty kg of crushed mass were weighed and
26 BANZE et al.
Bol. Inst. Pesca, São Paulo, 44(vol. esp.): 24 - 34, 2017
packed in 200-L polyethylene container with lid.
Subsequently, in order to avoid bacterial growth
and lipid oxidation, 10% acetic acid (w/v) and 2%
butyl hydroxy toluene (BHT) were added. The
crushed mass was stirred once a day, using a
wooden stick (1.5 m), during the first five days
in order to homogenize and promote greater
contact between the acid and the crushed mass
(SEIBEL and SOUZA-SOARES, 2003). During the
30 days of the silage process, the temperature and
pH were monitored daily with a mercury
thermometer and a potentiometer. After 30 days,
the silage was dried in a forced air circulation
oven at 55°C until reaching approximately 15%
humidity, for later use in the preparation of the
experimental diets.
The analyses performed in the acid silage
were: 1) proximate composition (A.O.A.C., 1999);
2) microbiology (BRASIL, 2013); 3) biogenic
amines content by extraction with trichloroacetic
acid (5%) and separation by HPLC (VALE and
GLORIA , 1997); 4) concentration of toxic chemical
elements such as chromium, cadmium, lead and
mercury by mass spectrometry (FLAMENT et al.,
2002), and 5) fatty acid composition by lipid
extraction (FOLCH et al., 1957), followed by
methylation (HARTMAN and LAGO, 1973) and
gas chromatography.
During the ensiling process, the degree of
protein solubilization was also monitored by the
determination of soluble nitrogen. Before the
addition of acetic acid, an aliquot of the ground
raw material was sampled for centesimal analysis
and determination of soluble protein. After the
addition of the acid, silage samples were collected
every two days to determine soluble nitrogen,
which was determined by precipitating the
protein from 1 g of sample with 10 mL of
trichloroacetic acid (40%) and 10 mL of distilled
water (HAARD et al., 1985). After 30 min, the
mixture was filtered using filter paper and the
soluble nitrogen determined in the filtrate by the
Kjeldahl method (N x 6.25).
Digestibility assay
Juveniles of female jundiá were obtained at
the Agricultural Research and Rural Extension
Company (EPAGRI) in Caçador, SC. Fish
handling followed guidelines approved by the
Ethics Committee on Animal Use (CEUA) of the
Federal University of Santa Catarina (UFSC)
(protocol #PP00815). Fish were acclimated for
two weeks to the experimental conditions, in a
closed water recirculation system. After that,
groups of five animals (272.58 ± 20.04 g) were
distributed into nine 200-L cylinder-conical
incubators. Water quality variables, temperature
(27.34 ± 0.66 °C), dissolved oxygen concentration
(6.20 ± 0.57 mg L
-1
), salinity (1.80 ± 0.47 g L
-1
),
pH (6.68 ± 0.32) and electrical conductivity (3.60 ±
0.89 mg L
-1
) were monitored daily with the aid
of a multi-parameter water quality meter. Total
ammonia, nitrite and nitrate were monitored
once a week, using a colorimetric kit (Alfa
Tecnoquímica, Florianópolis, SC), and did not
exceed 0.40 mg L
-1
. Photoperiod was adjusted to
12 h. Water quality remained adequate for jundiá
growth.
During 55 days, the experimental diets were
offered, twice a day (7:00 a.m. and 4:00 p.m.), until
apparent satiation, for three groups of fish.
Digestibility methodology followed that
adopted for channel catfish (KITAGIMA and
FRACALOSSI, 2011). Daily, 1 h after the first
feeding, feces were collected for four hours. Feces
settled in 50-mL tubes coupled to the bottom of
each tank. During the collection period, tubes
remained immersed in ice to avoid microbial
degradation of feces. Fecal collections were
performed twice a day: in the morning (8:00 a.m.
to 12:00 p.m.) and in the afternoon (1:00 p.m. to
5:00 p.m.). After collection, tubes were centrifuged
(1150 x g) for 5 min, the supernatant was
discarded and the fecal matter immediately frozen
to evaluate apparent digestibility of dry matter
and protein.
Experimental diets
To formulate the reference diet of the
digestibility trial, we used the amino acid and
gross energy requirements of jundiá (MEYER
and FRACALOSSI, 2004; MONTES-GIRAO and
FRACALOSSI, 2006). However, the requirement
of another freshwater omnivore, the American
catfish, Ictalurus punctatus (NRC, 2011), were used
for the other nutrients (lipids, vitamins and minerals).
The amino acid profile of the protein-rich
ingredients (fishmeal and tuna silage) was
Acid silage of tuna viscera: production, composition, quality… 27
Bol. Inst. Pesca, São Paulo, 44(vol. esp.): 24 - 34, 2017
analyzed for the correct formulation of the
experimental diets. The aminogram was obtained
by reverse-phase high performance liquid
chromatography (HPLC), with UV detection at
240 nm and quantification by multilevel internal
calibration using aminobutyric acid as an internal
standard (HAGEN et al., 1989).
The reference diet was prepared using semi-
purified ingredients such as casein, gelatin,
cellulose and starch. Dry ingredients were
weighed first, mixed (using a bread dough mixer),
then the oils and water were added. The test diets
consisted of 69.9% of the reference diet, 30% of
silage or fishmeal as test ingredients and 0.1% of
the yttrium oxide marker (Table 1). Diets were
prepared by homogenizing the dry ingredients
first and then adding the oils and water. In all
diets the water was added not exceeding 11% of
moisture. Diets were then pelleted (3 mm) and
dried in a forced air circulation oven (55 ºC) for
4 h. After drying, the diets were packed and
stored under refrigeration (4 ºC) until use.
Table 1. Proximal composition of the experimental diets (expressed in dry matter).
Ingredients (g kg
-1
)
Analyzed nutritional composition of experimental diets
Reference
Fishmeal
Silage
Fishmeal
1
0.00
300.00
0.00
Silage
2
0.00
0.00
300.00
Caseine
327.60
229.32
229.32
Gelatine
50.00
35.00
35.00
Starch
390.20
273.14
273.14
Cellulose
80.00
56.00
56.00
Soy oil
20.00
14.00
14.00
Cod liver oil
50.90
35.63
35.63
Vitamin and micro mineral
premix
3
10.00
7.00
7.00
Macro mineral premix
4
37.10
25.97
25.97
Dicalcium phosphate
33.60
23.52
23.52
Yttrium oxide
1.00
0.70
0.70
Butyl-hydroxy-toluene
0.50
0.35
0.35
Nutritional composition (g kg
-1
)
Dry matter
946.80
933.50
819.10
Crude protein
368.60
479.60
463.50
Mineral matter
164.40
156.60
157.10
Ether extract
90.50
72.90
60.10
Gross energy (kcal kg
-1
)
4,349
4,276
4,381
Crude fiber
21.20
20.70
16.10
Yttrium oxide
0.09
0.09
0.09
1
Salmon processing wastemeal (Pesqueira Pacific Star S.A., Chile). Composition (g kg
-1
, wet basis): dry
matter = 870.03 ± 0.81; crude protein = 648.90 ± 0.62; ether extract = 104.00 ± 0.37; mineral matter =
113.40 ± 0.78; crude energy = 4,874 ± 0.38.
2
Acid silage of tuna viscera (intestine, stomach, liver, pancreas,
swimming bladder, kidney, spleen, gonads) (Gomes da Costa (Itajaí, SC, Brazil). Composition (g kg
-1
,
wet
basis): dry matter = 227.80 ± 0.26; crude protein = 669.00 ± 0.97; ethereal extract = 112.10 ± 0.40; ashes =
122.30 ± 0.23; crude energy, kcal kg
-1
= 5,351 ± 0.89.
3
Nutron Alimentos (Toledo, PR, Brazil). Product
composition kg
-1
: 250 mg folic acid; 5,000 mg pantothenic acid; 0.6 g antioxidant; 125 mg biotin; 25 mg
cobalt; 2,000 mg copper; 75,000 mg coline; 13,820 mg iron; 100 mg iodine; 3,750 mg manganese; 5,000 mg
niacin; 75 mg selenium; 1,000,000 UI vitamin (vit.) A; 1,250 mg vit. B
1
; 3,750 mg vit. B
12
; 2,500 mg vit.
B
2
; 1,785 mg vit. B
6
; 42,000 mg vit. C; 500,000 UI vit. D
3
; 20,000 UI vit. E; 35,000 mg vit. K; 17,500 mg
zinc.
4
Composition (g kg
-1
product): dicalcium phosphate = 130; potassium chloride = 120; sodium chloride
= 130; magnesium sulfate = 620.
28 BANZE et al.
Bol. Inst. Pesca, São Paulo, 44(vol. esp.): 24 - 34, 2017
The apparent digestibility coefficients (CDA)
of protein and dry matter were determined using
the equation proposed by CHO and SLINGER
(1979) for the reference diet and the equation
proposed by BUREAU and HUA (2006) for the
tested ingredients:
CDA
diet
(%) = 100 [100 x (%M
diet
/%M
feces
) x
(%Nutrient
feces
/%Nutrient
diet
)];
where: CDA
diet
= apparent digestibility coefficient
of the diet; %M = inert tracer concentration (% in
dry matter) and% N = nutrient content (% in dry
matter).
CDA
test
ingredient
(%) = CDA
test
ingredient
+ [(CDA
test
diet
CDA
reference diet
) x (0.7 x D
reference diet
)/(0.3 x D
ingredient
)];
where: D
reference diet
= % Nutrient in reference diet,
D
ingredient
=% of nutrient in test ingredient.
Statistical analysis
Digestibility data showed normality and
homoscedasticity and were submitted to t-Student
test to determine the differences between
apparent digestibility coefficients of dry matter
and crude protein. The level of significance
adopted was 5%. Statistical analyzes were
performed using the STATISTICA program,
version 7.0 (StatSoft, Inc., 2004).
RESULTS
Proximal composition of tuna viscera silage
The protein hydrolysis period was 30 days,
with an average temperature of 28.0 ± 1.30 °C; pH
4.18 ± 0.12, within the standard for acid silage
production. Both the raw material and the silage
produced presented crude protein values suitable
for use as a protein ingredient in fish diets
(Table 2). During the silage process, the contents
of dry matter, ether extract and ashes registered a
slight reduction but crude protein remained
unchanged.
Table 2. Proximal composition, expressed as dry
matter, of the raw material and acid silage
produced after 30 days. Means and standard
deviation of three replicates.
Raw material
1
Silage
244.60 ± 0.05
227.80 ± 0.26
669.43 ± 0.92
669.40 ± 0.97
129.50 ± 0.33
112.10 ± 0.40
128.10 ± 0.19
122.30 ± 0.23
1
Tuna viscera (intestine, stomach, liver, pancreas,
swimming bladder, kidney, spleen, gonads) acquired at
Gomes da Costa (Itajaí, SC, Brazil).
Silage microbiological quality
Microbiological analyzes of the raw material
and silage at 30 days showed absence of
contaminating microbiological agents (Table 3).
Contamination of silage by toxic chemical elements
The silage presented the following profile of
toxic chemical elements: chromium 2.60 ± 0.02
mg kg
-1
, cadmium 4.25 ± 0.03 mg kg
-1
, lead 0.25 ±
0.01 mg kg
-1
, and mercury 0.53 ± 0.08 mg kg
-1
.
Amino acid profile of silage and fishmeal
The silage presented a profile of essential and
non-essential amino acids numerically superior to
that of fishmeal for all amino acids, except for
glycine (Table 4).
Table 3. Microbiological analysis of the raw material (tuna viscera) and silage.
Analysis
Raw material
Silage
Staphylococcus coagulase positive¹ (CFU g
-1
)
< 1.0 x10
< 1.0 x10
Thermotolerant coliforms
2
(45ºC) (CFU g
-1
)
< 1.0 x10
< 1.0 x10
Salmonella spp.
Ausência em 25 g
Ausência em 25 g
1
Analysis performed in triplicate;
2
Analysis performed in duplicate;
3
CFU = Colony-forming units.
Concentration of biogenic amines
During the production process of acid silage
from tuna viscera, the concentration of biogenic
amines increased (Table 5), with the exception of
putrescine and spermidine, whose concentration
decreased.
Acid silage of tuna viscera: production, composition, quality… 29
Bol. Inst. Pesca, São Paulo, 44(vol. esp.): 24 - 34, 2017
Table 4. Aminogram of the protein ingredients used in the manufacture of the diets for the digestibility
experiment.
Aminoacids (g 100
-1
)
Silage
Fishmeal
Essentials
Histidine
2.11
1.24
Arginine
8.04
3.71
Threonine
5.02
2.29
Valine
1.87
0.99
Methionine
2.89
1.47
Lysine
3.70
3.32
Isoleucine
4.24
2.36
Leucine
6.12
3.75
Phenylalanine
4.08
2.55
Non essentials
Alanine
5.30
4.40
Proline
3.62
3.42
Tyrosine
5.75
5.05
Serine
5.12
3.40
Glyicine
5.08
6.20
Aspartic acid
7.10
5.72
Glutamic acid
14.60
10.70
Cistine
3.64
1.87
Table 5. Concentration of biogenic amines in the raw material (tuna viscera) and silage.
Biogenic amines (mg 100 g
-1
)
Raw Matter
Silage
Putrescine
12.90
9.71
Cadaverine a
57.69
77.97
Histamine
0.74
1.30
Tyramine
28.47
36.59
Agmatine
88.33
90.38
Spermidine
88.08
76.56
Phenylethynamine
1.53
2.03
Tryptamine
nd
1
nd
1
Not detected; detection limit 0.4 mg kg
-1
.
Composition of silage fatty acids
The fatty acid composition of the silage
produced showed that fatty acid concentrations of
the n-3 series were higher than those of the n-6
series.
Fatty acid composition (% lipid fraction) of silage from
tuna viscera
The fatty acid composition of the produced
tuna silage showed that the content of the n-3 fatty
acid series, Eicosapentanoid and Docosahexanenoic,
were 6.07 ± 0.05% and 21.72 ± 0.70%, respectively.
The n-6 polyunsaturated fatty acids, Linoleic and
Arachidonic were 3.19 ± 0.1% and 3.04 ± 0.73%,
respectively.
Protein solubility of silage
The protein hydrolysis period for obtaining
the silage was 30 days, with the mean temperature
of 28 ± 1.30 °C and mean pH of 4.18 ± 0.12, within
the standard for the production of acid silage. The
soluble protein increased until the 23
rd
day,
reaching a plateau from there until day 30
th
.
During the silage process, the acid hydrolysis
increased the protein solubility from 32.38% to
30 BANZE et al.
Bol. Inst. Pesca, São Paulo, 44(vol. esp.): 24 - 34, 2017
41.33%, corresponding to 48.37% and 61.74% of
the crude protein, respectively. The final product
was in a pasty liquid form, due to the continuous
protein hydrolysis, potentiated by the enzymes
present in the viscera.
Digestibility assay
Protein digestibility was similar between
silage and fishmeal protein ingredients. As for dry
matter, silage was more digestible than fishmeal
(P<0.05) (Table 6).
Table 6. Apparent protein and dry matter digestibility coefficients of tuna viscera silage and fish residue
meal for jundiá (Rhamdia quelen).
Test ingredient
Apparent digestibility coefficient (%)
Protein
Dry Matter
Silage
88.12 ± 0.58
a
92.20 ± 3.50
a
Fishmeal
88.92 ± 1.98
a
83.84 ± 2.80
b
a,b
Means followed by the same letter in the same column do not
differ from one another by the t-student test (P>0.05).
DISCUSSION
Crude protein constituted the largest fraction
of the silage produced, since we used a
standardized residue (viscera), devoid of bones,
fins or heads. According to SILVA et al. (2013), the
presence of heads and fins in the raw material
contribute to a decrease in protein and an increase
in mineral content. When compared to other
silages of fish residues (ABIMORAD et al., 2009;
ARRUDA et al., 2009; SILVA et al., 2013), where
the mineral matter ranged from 17.3 to 43.60%,
our acid silage of tuna viscera presented low
content of mineral matter. This is a positive
aspect, considering that excess mineral matter is
undesirable in fish diets (SILVA et al., 2013).
However, silage high humidity should be
considered when preparing large quantities of fish
feeds commercially.
Microbiological analyzes did not indicate
significant growth of microorganisms in the raw
material nor in the silage produced, which shows
the good quality of the tuna viscera used. The
absence of microorganisms in the silage also
reflects the important role of acetic acid in
preventing the proliferation of microorganisms
during the process.
Biogenic amines are formed by the
decarboxylation of amino acids (for example:
histidine in histamine, lysine in cadaverine,
arginine in putrescine, tyrosine in tyramine)
(RICQUE-MARIE et al., 1998). A number of factors
may affect biogenic amine concentrations, both
abiotic (post-capture management, refrigeration
system and temperature) and biotic (genetics, sex,
physiological state and tissue type of the residue)
(SILVA et al., 2013). During the silage production
process of this study, the concentration of biogenic
amines increased, with the exception of putrescine
and spermidine. This increase may be related to
the ambient temperature (28.0 ± 1.3 °C), which
was high during the ensiling process. However,
the levels of putrescine, cadaverine and histamine
found in this study are lower than those found in
other studies (COWEY and CHO, 1992; MENDOZA
et al., 1997; FAIRGRIEVE et al., 1994). Studies
monitoring the concentration of biogenic amines
in silage production for feeding fish are scarce.
In the natural aquatic environment, fish are
subject to contamination by heavy metals. The
amount of heavy metals in fish varies depending
where fish are raised but fish viscera can
concentrate these metals (GONÇALVES, 2011).
The levels of heavy metals found in fish silage,
except for lead and mercury, are above the
maximum tolerated by ANVISA in predatory fish
(chromium 0.10 mg kg
-1
, cadmium 1.0 mg kg
-1
,
lead 2.0 mg kg
-1
and mercury 1.0 mg kg
-1
) for
human consumption (BRASIL, 1998). This is a
negative aspect regarding the use of silage of tuna
viscera, which would probably be attenuated
with the removal of liver from raw material,
since toxic substances ingested tend to accumulate
in this organ for detoxification (GONÇALVES,
2011). Specific studies on the toxicity of the metals
present in the silage of fish tuna viscera are
required.
Acid silage of tuna viscera: production, composition, quality… 31
Bol. Inst. Pesca, São Paulo, 44(vol. esp.): 24 - 34, 2017
Protein solubilization by enzymatic action is
high, especially when the raw material of ensilage
is constituted by viscera (RAA and GILDBERG,
1982), as is the case of the present study.
However, partially hydrolyzed silage has a higher
nutritional value than fully-hydrolyzed silage
(STONE et al., 1989; VIANA et al., 1996). Studies
report the manipulation of protein hydrolysis of
silages so that the degree of protein solubilization
is monitored. In this process, after the mass is
liquefied, the acid hydrolysis process is
interrupted (MENDOZA et al., 2001; LIANG et al.,
2006; DELCROIX et al., 2014; VALLE et al., 2015)
and the enzymes are inactivated by increasing the
temperature. Thus, it is ensured that the proteins
are no longer hydrolyzed and that the integrity of
the peptides and free amino acids produced is
maintained. In the present study, although there
was no temperature control, protein hydrolysis
was not complete in thirty days. This means that
the conditions adopted in the present study were
adequate for ensiling the tuna viscera.
Fish readily accepted the experimental diets,
suggesting that the inclusion of tuna viscera silage
did not affect diet palatability. The apparent
digestion coefficient (ADC) of the tuna viscera
silage protein was similar to the ADC of the fish
waste meal protein. Lower ADCs protein values
(84.08 and 85.11%) were reported for Indian carp
(Labeo rohita), when fed fish residue silages,
produced with formic and sulfuric acids,
respectively (HOSSAIN et al., 1997). Similarly, the
protein ADCs of biological silage of tilapia residue
varied from 79.4 to 87.2% for African catfish
(Clarias gariepinus) (FAGBENRO and JAUNCEY,
1995). The higher values of protein digestibility
found in this study may be related to the raw
material used for silage production. Tuna viscera
constitutes a standardized residue, different from
that used in other studies, whose raw material
included heads, bones and other fish components,
which can generate silages with varied nutritional
composition, influencing nutrient digestibility.
However, the protein digestibility of the acid
silage of tuna viscera was lower than that found
for acid fish silage (ADC = 96.7%), when fed to
Nile tilapia (PIMENTA et al., 2008), which may be
related to the long digestive tract of tilapia,
favorable to the best utilization of nutrients.
On the other hand, the high dry matter
digestibility of the silage when compared to that
recorded for fishmeal is probably due to the acid
hydrolysis. High apparent digestibility of dry
matter (95.5%) of acid silage for Nile tilapia
was also reported by PIMENTA et al. (2008).
CONCLUSION
The acid silage of tuna viscera has good
nutritional composition (high protein, good amino
acid and essential fatty acid profile), good
microbiological quality and a protein solubility
of 61.74%. Tuna viscera silage also has high
protein and dry matter digestibilities for jundiá
juveniles. Therefore, this novel ingredient has
potential as an alternative protein source in
aquafeeds.
ACKNOWLEDGEMENTS
To the National Council for Scientific and
Technological Development (CNPq) and the
Ministry of Fisheries and Aquaculture (MPA)
for funding the study (call 42/2012, process
406168/2012-1). Also, to CNPq, for fellowships
awarded to the first and last authors.
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