Quality Index Method scheme for whole fresh carapeba (Eucinostomus gula, Quoy & Gaimard, 1824) stored in ice

Abstract

Considering the importance of sensory schemes for the evaluation of the freshness of different fish species, and the fact that carapeba (Eucinostomus gula) is an important commercial marine fish species in Northeastern Brazil, the objective of this study was to evaluate the freshness and shelf life of this fish during 18 days stored in ice. Changes during storage were observed according to the sensory evaluation (Quality Index Method - QIM), physicochemical analyses (pH, total volatile basic nitrogen - TVB-N, and trimethylamine - TMA-N) and microbiological analyses (total mesophilic and psychrotrophic counts). High correlation was found between the Quality Index (QI) and storage time. The microbiological results showed increases in the mesophilic and psychrotrophic counts as from the 9th day of storage. The TVB-N and TMA-N both increased during storage and the pH value increased slowly. The results suggested that the fresh carapeba is acceptable for consumption when kept in ice for up to 10 days.

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Original Article
Campinas, v. 20, e2016088, 2017
http://dx.doi.org/10.1590/1981-6723.8816
ISSN 1981-6723 on-line version
This is an Open Access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited
Quality Index Method scheme for whole fresh carapeba
(Eucinostomus gula, Quoy & Gaimard, 1824) stored in ice
Esquema do Método do Índice de Qualidade para carabepa inteira fresca
(Eucinostomus gula, Quoy & Gaimard, 1824) armazenada em gelo
Abstract
Considering the importance of sensory schemes for the evaluation of the freshness of different fish species, and the
fact that carapeba (Eucinostomus gula) is an important commercial marine fish species in Northeastern Brazil, the objective
of this study was to evaluate the freshness and shelf life of this fish during 18 days stored in ice. Changes during storage were
observed according to the sensory evaluation (Quality Index Method - QIM), physicochemical analyses (pH, total volatile basic
nitrogen - TVB-N, and trimethylamine - TMA-N) and microbiological analyses (total mesophilic and psychrotrophic counts).
High correlation was found between the Quality Index (QI) and storage time. The microbiological results showed increases
in the mesophilic and psychrotrophic counts as from the 9th day of storage. The TVB-N and TMA-N both increased during
storage and the pH value increased slowly. The results suggested that the fresh carapeba is acceptable for consumption
when kept in ice for up to 10 days.
Keywords: Fish; Freshness; Quality; Sensory evaluation.
Resumo
Considerando-se a importância dos esquemas sensoriais para avaliação do frescor das diferentes espécies de
peixes e que a carapeba (Eucinostomus gula) é uma importante espécie comercial de peixe marinho na Região Nordeste
do Brasil, o objetivo deste estudo foi avaliar o frescor e a vida de prateleira desta espécie durante 18 dias de armazenada
em gelo. Alterações durante o armazenamento foram observadas através da avaliação sensorial (Método do Índice de
Qualidade - MIQ), das análises físico-químicas (pH e nitrogênio das bases voláteis totais ‒ N-BVT, e da trimetilamina - N-TMA)
e das análises microbiológicas (contagem total de mesófilos e psicrotróficos). Alta correlação entre o Índice de Qualidade
(IQ) e o tempo de armazenamento foi verificada. Os resultados microbiológicos mostraram um aumento da contagem de
mesófilos e psicrotróficos a partir do nono dia de armazenamento. O N-BVT e o N-TMA aumentaram durante o tempo de
armazenamento, e o pH aumentou lentamente. Os resultados sugerem que o frescor da carapeba permanece aceitável
para consumo pelo resfriamento em gelo até 10 dias.
Palavras-chave: Peixe; Frescor; Qualidade; Avaliação sensorial.
Alex Augusto Gonçalves1*, Karoline Mikaelle de Paiva Soares2
1 Universidade Federal Rural do Semi-Árido (UFERSA), Agricultural Sciences Center (CCA), Laboratory of Seafood Technology and Quality Control
(LAPESC), Mossoró/RN - Brazil
2
Universidade Federal Rural do Semi-Árido (UFERSA), Biological and Health Sciences Center (CCBS), Laboratory of Industrial Biotechnology,
Mossoró/RN - Brazil
*Corresponding Author
Alex Augusto Gonçalves, Universidade Federal Rural do Semi-Árido (UFERSA), Agricultural Sciences Center (CCA), Laboratory of Seafood Technology
and Quality Control (LAPESC), Av. Francisco Mota, 572, Costa e Silva, CEP: 59625-900, Mossoró/RN - Brazil, e-mail: alaugo@ufersa.edu.br,
alaugo@gmail.com
Cite as: Quality Index Method scheme for whole fresh carapeba (Eucinostomus gula, Quoy & Gaimard, 1824) stored in ice. Braz. J. Food Technol.,
v. 20, e2016088, 2017.
Received: July 14, 2016; Accepted: Jan. 13, 2017

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Braz. J. Food Technol., Campinas, v. 20, e2016088, 2017
Quality Index Method scheme for whole fresh carapeba (Eucinostomus gula, Quoy & Gaimard, 1824) stored in ice
Gonçalves, A. A.; Soares, K. M. P.
1 Introduction
The use of descriptive analyses like the Quality
Index Method (QIM) is currently increasing in the sensory
analysis of marine products (MARTINSDÓTTIR et al., 2001;
GONÇALVES et al., 2015), and in the future is expected
to be the main sensory method for research purposes
(by researchers in laboratories), industries (for more precise
inspection and clear decisions about fish quality) and
possibly also in fish auction markets (MARTINSDÓTTIR et al.,
2001; SVEINSDÓTTIR et al., 2002).
Carapeba or carapicu (
Figure 1
), Eucinostomus
gula (Quoy & Gaimard, 1824) is an important commercial
marine fish species in Northeastern Brazil (SOARES, 2010),
belonging to the family Gerreidae, being characteristic of
tropical and subtropical waters. Considering the commercial
importance of carapeba in Brazil, the demands for quality
and its high perishability, this study aimed to evaluate the
freshness and shelf life of this species when stored on
ice for 18 days.
2 Material and methods
2.1 Fish source
Whole fish were obtained directly from fishermen
(Areia Branca, RN, Brazil), placed immediately into a clean
insulated box containing flaked ice and transported to the
Laboratory of Seafood Technology and Quality Control
(LAPESC). The time elapsed from the catch to the start
of the experiments in the laboratory was no longer than
2 hours. No additives were used on board or after landing.
The fish samples (n = 60) were washed, divided into three
distinct insulated self-draining boxes with flaked ice in layers
(1:1 – fish: ice – 20 fishes per box) and maintained in a
cold room (5 °C). Melted ice from each box was replaced
daily to maintain the proper proportion and suitable cooling
for the fish storage (0±0.1 °C).
2.2 Development of the QIM scheme
Following the guidelines for sensory evaluation
proposed by Martinsdóttir et al. (2001) for fish species,
three people took part in the development and evaluation of
the QIM scheme. All members had previous training in the
development and use of QIM schemes for other seafood
species and attended the standards of research ethics.
They described the day-to-day changes that occurred
during the storage of the carapeba (18 days of storage in
flaked ice) and chose the appropriate parameters (
Table 1
)
for the following experiments. All observations of the fish
were carried out under standardized conditions following
the general guidance for the design of the testing room
and testing conditions described in ISO 8589 (ISO, 2007),
carried out at the baseline (day zero) and at regular 72-hour
intervals (every three days). Photographs of each stage in
the sensory evaluation were taken and used to illustrate
the quality attributes.
2.3 Microbial evaluation
Three samples were taken every 72 hours for total
counts of the mesophilic and psychrotrophic bacteria,
which were carried out according to the Brazilian Official
Analytical Methods (BRASIL, 2003).
2.4 Physicochemical evaluation
Total volatile bases nitrogen (TVB-N) and
trimethylamine nitrogen (TMA-N) were followed using the
LANARA protocol (BRASIL, 1981). The hydrogen potential
(pH) was measured using a digital pH meter (Hayonik
Model FTP905). All analyses were carried out in triplicate
every 72 hours.
2.5 Statistical analyses
The averages were compared using the Analysis of
Variance (ANOVA) and the effects considered significant
(by Tukey’s test) when the p-value ≤ 0.05. The linear equation
(QIM scheme), showing the best fit and the correlation
coefficient (r) between the QI and the storage time in ice,
were evaluated. The uncertainty of the prediction of the
days on ice from the QI was estimated using the partial
least-squares regression (PLS) with full cross-validation.
3 Results and discussion
3.1 QIM scheme
During the storage period, the carapeba showed
gradual and consistent changes for all parameters of the
sensory evaluation (
Figures 2 and 3
). The Quality Index
(QI) was obtained from the sum of the scores and ranged
from 0-19, for which zero or close to zero represented
the best sensory fish quality (freshly caught fish), and
19 completely deteriorated. The QI obtained for each
storage day sample formed a linear relationship with time
(
Figure 2
). A high correlation (r
2
= 0.9786) between the total
QI score (for each storage day) and days in flaked ice was
obtained, with a slope of 1.0349, and its evolution could be
Figure 1. Fresh whole carapeba (Eucinostomus gula, Quoy &
Gaimard, 1824).

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Braz. J. Food Technol., Campinas, v. 20, e2016088, 2017
Quality Index Method scheme for whole fresh carapeba (Eucinostomus gula, Quoy & Gaimard, 1824) stored in ice
Gonçalves, A. A.; Soares, K. M. P.
expressed by the equation (QI = 1.0349 x days +1.5825).
When applied to the data, the PLS model indicated that
the regression model proposed had a mean square of
errors (MSE) of approximately 1.8 days (1.755) based
on the average QI scores of six samples per storage day
(
Figure 2
), and the measured and predicted values were
statistically similar. Since the QI is the sum of nine values
of the parameter, the measurement error can be assumed
Table 1. Quality Index Method (QIM) scheme for carapeba, Eucinostomus gula.
QUALITY PARAMETER DESCRIPTION SCORE
Appearance
Skin
Bright, iridescent 0 ⬜
Loss of brightness, colors more opaque 1 ⬜
Opaque 2 ⬜
Stiffness
In rigor 0 ⬜
Flexible, elastic 1 ⬜
Soft 2 ⬜
Smell
Fresh, reminding of seawater 0 ⬜
Not of seawater, but fresh and specific 1 ⬜
Neutral or slightly acid 2 ⬜
Strong (acid), rancid, putrid 0 ⬜
Eyes
Eyeball transparency
Clear 0 ⬜
Slightly opaque 1 ⬜
Milky, opaque 2 ⬜
Pupil
Slightly Brownish, well-delineated 0 ⬜
Misty, loss of design 1 ⬜
Grey, no design 2 ⬜
Form
Bulging, convex 0 ⬜
Flat 1 ⬜
Concave, sunken 2 ⬜
Gills
Color
Bright red 0 ⬜
Less colored, becoming discolored 1 ⬜
Discolored 2 ⬜
Smell
Fresh, like seawater 0 ⬜
Neutral 1 ⬜
Acid, rancid 2 ⬜
Form
Full 0 ⬜
Slightly deformed 1 ⬜
Deformed 2 ⬜
QUALITY INDEX TOTAL 0-19
Figure 2. Quality Index (QI) for carapeba (N = 6) stored in flaked ice. PLS Regression modelling of the 19 demerit points of the
QIM scheme for carapeba stored in flaked ice using full cross-validation: measured vs. predicted Y values. Average QI for each
storage day based on an assessment of six carapeba used to predict the storage time in days.

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Braz. J. Food Technol., Campinas, v. 20, e2016088, 2017
Quality Index Method scheme for whole fresh carapeba (Eucinostomus gula, Quoy & Gaimard, 1824) stored in ice
Gonçalves, A. A.; Soares, K. M. P.
to be normally distributed, and the prediction considered
as t-distributed. The 95% confidence interval (estimated by
MSE x t (df = 39) = 1.755 x 2.021 = 3.55) may therefore be
estimated as approximately 3.6 days. One can therefore
assume that the QI based on the average scores of three
samples evaluated per storage day could predict the
storage time with an accuracy of ± 1.7 days. A similar
correlation was obtained by several authors but the slope
was different from the slope observed for other fish species
(SVEINSDÓTTIR et al., 2002, 2003; BONILLA et al., 2007),
probably due to the biological variation between species
and/or to the difference in scores used for the attributes.
One of the possible uses of the QIM values, apart
from the estimation of the storage time in ice, is to obtain
the remaining shelf-life estimation (SVEINSDÓTTIR et al.,
2002, 2003; BORGES et al., 2013, 2014; CYPRIAN et al.,
2013; LÓPEZ-GARCÍA et al., 2014; ANDRADE et al.,
2015; GONÇALVES et al., 2015), by applying the tables
to samples of unknown storage time and subtracting the
number of days already spent in ice from the total, up
to rejection. These estimations, however, must take into
account that in the particular case of carapeba (captured
by artisan fisherman), the shorter storage time (10 days) up
to rejection (or shelf-life) means all the degradation phases
are consequently considerably shorter. It was assumed
in the Quality Index Method that the scores for all quality
attributes increased with storage time in ice, which is in
accordance with the studies of Sveinsdóttir et al. (2003).
This was indeed observed, but to a different extent for
the different quality attributes, where, with the attribution
of demerit points for each separate sensory parameter, it
was possible to observe that some carapeba parameters
showed early variation (
Figure 3
).
During the later stages, the sensory attributes
changed and the odor was described as sour and finally
as rotten (day 15). The sour and rotten odors may have
originated from short chain fatty acids, alcohols, sulfur
compounds and amines generated by microbial activity
(SVEINSDÓTTIR et al., 2003), which corroborate with the
increase in microorganisms and the TVB-N and TMA-N
Figure 3. General appearance of the skin, gills, and eyes of fresh carapeba and after 18 days of storage in flaked ice.

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Braz. J. Food Technol., Campinas, v. 20, e2016088, 2017
Quality Index Method scheme for whole fresh carapeba (Eucinostomus gula, Quoy & Gaimard, 1824) stored in ice
Gonçalves, A. A.; Soares, K. M. P.
values as from the 10
th
day of storage. The QIM tables are
only the first step in implementation of the QIM system.
All the sensory parameters/attributes were considered to
be useful to distinguish the freshness of carapeba, and
also these parameters were connected with the microbial
and physicochemical results to define rejection (end of
the shelf life).
3.2 Microbiological and physicochemical evaluations
The low total counts found in the early days of
storage were due to the flesh of newly caught fish being
sterile, since the immune system of fish prevents the
bacteria from growing (SVEINSDÓTTIR et al., 2002).
However, when the fish dies, the immune system collapses
and consequently, during storage, bacteria invade the
flesh. The total counts of mesophilic aerobic bacteria in
the fish flesh increased with storage time, ranging from
1.81 x 103 CFU g-1 (SD = 0.34) to 1.92 x 106 CFU g-1
(SD = 56.57) on the 18th day, showing a significant increase
mainly from the 15th day (3.8 x 105 CFU g-1 – SD = 0.14) of
storage in ice. The psychrotrophic bacteria showed visible
colonies as from the 6
th
day of storage with scores ranging
from 0 to 3.0 x 106 CFU g-1 and with a significant increase
as from the 12th day. The total counts of psychrotrophic
bacteria showed an initial absence followed by an average
of 1.31 x 10
3
CFU g
-1
(SD = 0.08 – 6
th
day), and increasing
to 3.05 x 105 CFU g-1 (SD = 63.64) on the 12th day and
2.97 x 106 CFU g-1 (SD = 63.64) on the 18th day. Similar
values for the total counts of mesophilic bacteria at the
beginning of the experiment (2.14 x 103 CFU g-1) were
found by Baixas-Nogueras et al. (2003), but between the
8th -10th day they exceeded the legal limit of 1 x 106 CFU g-1.
Fish are notorious for spoiling rapidly even when stored
under chilled conditions. The measurement of freshness
is therefore an important part of the quality assurance of
chill-stored fish, and though sensory methods are generally
considered to be the most appropriate for measuring the
freshness of fish, there is a role for non-sensory methods
(HOWGATE, 2010a).
The carapeba flesh had an initial average pH value
of 6.16±0.03 and such a value was maintained up to the
6
th
day of storage. Between the 6
th
and 15
th
days there was
an increase up to 6.51±0.04, and on the 18th day, the pH
attained 6.96±0.01 (
Figure 2
). The TVB-N increased day by
day as from the 6
th
day of storage, but only on the 12
th
day
did the TVB-N reach values of 30.43±2.11 mg 100 g
-1
, which
is close to the limit of acceptability of 30 to 35 mg 100g-1
(HOWGATE, 2010a), and on the last day (18) the TVB-N
values reached 31.93±1.64 mg 100g
-1
. The TVB-N
content of typical marine demersal fish at the limit of
acceptability as a result of spoilage is around 30 mg
nitrogen 100 g-1 of flesh. Along with the TVB-N values,
the TMA-N is the most useful index for spoilage in fresh
seafood (HOWGATE, 2010a,b), and, in general, they are
considered unreliable for the measurement of spoilage
during the first 10 days of the chilled storage of several fish
species (ÓLAFSDÓTTIR et al., 1997). Although the TVB-N
values of all the samples increased throughout the storage
period, the TMA-N increased in smaller proportions, i.e.,
ranging from 1.23±0.05 (1st day) to 5.92±0.53 mg N 100 g-1
(18th day). The determination of these compounds at
the time of sensory rejection appears to be adequate to
evaluate the spoilage level of fish. In the present work,
a significant formation of these volatile compounds was
observed. This TVB-N analysis is often used as an index
of assessing the shelf life and storage quality of seafood
products. The spoilage pattern of fresh seafood generally
shows an increase in TVB-N concentration, which closely
parallels the bacterial population (HOWGATE, 2010a,b).
4 Conclusions
The Quality Index Method showed high linear correlation
between the QI and storage time in ice (QI = 1.0349 x days
in ice + 1.5825; r2 = 0.9786), making it possible to predict
when the fish flesh can be considered fresh and acceptable
for consumption, i.e., carapeba can be considered fresh
up to the 7th day when stored in ice, and acceptable up to
the 10th day, based on the microbiological counts, TVB-N,
TMA-N and sensory evaluations.
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