ORIGINAL

Quality Index Method developed for gutted and ungutted red tilapia (Oreochromis ssp)

Esquema del método índice de calidad desarrollado para tilapia roja (Oreochromis ssp) eviscerada y sin eviscerar

Nelson Gutiérrez G,¹* Ph.D, Claudia Amorocho C,¹ Ph.D, Angélica Sandoval A,² Ph.D, Yaneth Ruíz O,¹ M.Sc.

¹Universidad Surcolombiana, Facultad de Ingeniería, Departamento Ingeniería Agrícola, Av. Pastrana Cra. 1 Neiva, Colombia.
²Universidad del Tolima, Facultad de Ingeniería Agronómica, Departamento producción y sanidad vegetal, Barrio Santa Helena, Ibagué Colombia.

*Correspondence: ngutierrezg@usco.edu.co

Received: April 2014; Accepted: November 2014.

ABSTRACT

Objective. To develop a Quality Index Method (QIM) for gutted and ungutted red tilapia from aquaculture ponds. Materials and methods. 40 specimens of gutted red tilapia and 40 ungutted ones were located in foam polyethylene boxes within layers of ice and storage at 4°C. Three fish were randomly sampled on days 0, 3, 5, 8, 11, 14 and 17 for gutted tilapia, and on days 0, 3, 6, 9, 11, 14 and 16 for ungutted tilapia. A sensorial panel of 8 experts was formed to evaluate the product. With three samples each day with average points of the sensorial attributes proposed in the method, the quality index for gutted and ungutted red tilapia was obtained based on the storage time on ice. Results. The Quality Index Method obtained for gutted and ungutted red tilapia showed maximum values of 21 and 29, respectively. It was adjusted in an increasing lineal model with high correlation between the Quality Index and the storage time on ice. Conclusions. The developed model is useful to determine deterioration levels and to define storage and consumption time. For gutted red tilapia the panel rejected the fish after 8 - 11 days of storage whereas the ungutted red tilapia was rejected after 6 - 9 days.

RESUMEN

Objetivo. Desarrollar los esquemas del Método de Índice de Calidad (MIC) para la tilapia roja de piscifactoría eviscerada y sin eviscerar. Materiales y métodos. 40 especímenes de tilapia roja eviscerados y 40 sin eviscerar, fueron ubicados en cajas de polietileno expandido entre capas de hielo y almacenadas a 4°C; se realizaron muestreos los días 0, 3, 5, 8, 11, 14 y 17 para tilapia eviscerada, mientras en la tilapia sin eviscerar los días 0, 3, 6, 9, 11, 14 y 16; se conformó un panel de 8 expertos para la evaluación sensorial de tres ejemplares en cada día de muestreo; con los puntajes promedio de los atributos sensoriales propuestos en el esquema, se obtuvo el índice de calidad para la tilapia roja eviscerada y sin eviscerar en función del tiempo de almacenamiento en hielo. Resultados. Los esquemas del Método índice de Calidad desarrollados para tilapia roja entera eviscerada y sin eviscerar, obtuvieron valores máximos de Índice de Calidad de 21 y 29 puntos respectivamente, ajustados a un modelo lineal creciente con alta correlación entre el Índice de Calidad y el tiempo de almacenamiento en hielo. Conclusiones. Los esquemas del MIC desarrollados son útiles para determinar el nivel de deterioro y definir los tiempos de almacenamiento y consumo. En la tilapia roja eviscerada los panelistas rechazaron el pescado para consumo entre los días 8 y 11 de almacenamiento, mientras que para la tilapia sin eviscerar el producto fue rechazado entre los días 6 y 9 de almacenamiento.

Palabras clave: Evaluación sensorial, frescura, pescado, refrigeración (Fuente: USDA).

INTRODUCTION

In Latin America the production on an industrial scale of species such as salmon, trout and tilapia has seen a notorious increase over the last decade, led by countries such as Brazil, Mexico, Ecuador and Chile. However, the development of aquiculture on a small scale begins to show notable possibilities in the market (1). Over the last two decades in Colombia an important progress has been made in the small to medium scale production of a hybrid tilapia known as red tilapia (Oreochromis ssp) in aquaculture ponds established in reservoirs to generate energy.

However, fish is a highly perishable product and a few hours after death a series of post-mortem reactions occur, among them the auto-degenerative reactions that are enzymatic and microbiological changes (2) that contribute to the detriment of the product (3) by the appearance of undesirable smells, colors and flavors which the final consumer rejects (2,4). These changes are also manifested by the accumulation of organic compounds and microorganisms that can present a hygienic or toxicological risk for the consumer. Nevertheless, the final quality of the fish depends not just on the nature of the species, but also is implicitly related to handling and storage conditions (5,7).

Different investigators and institutes in the fishing industry have developed methods to evaluate the freshness of fish, based on postmortem changes associated with sensorial, physicochemical and microbiological changes (4,8). Included in these is appearance, smell, taste and texture, which have been establishes as the principle attributes of freshness (9, 10), and that is why the sensorial method is considered the most reliable to determine freshness of fish in relation to the physicochemical and microbiological methods (10,11).

Sensorial evaluation is considered an important method to evaluate freshness (6) and quality (12), commonly used by control organisms in different countries to determine that fish complies with quality standards established by the fishing industry as part of quality control and by buyers to assure that the products meets their expectations (13).

This characteristic has made, for instance, in the European legislation has established the use of such analysis, followed by a chemical or microbiological one, always when the sensorial evaluation determines it, in order to eliminate doubts about the product (2,14). In Colombia, the activities of inspection, surveillance and control of fishing products, in particular fish, mollusks and fresh crustaceans, are regulated by means of Resolution 122 of 2012 (15) and are exclusively based on chemical and microbiological tests. Within those sensorial methods, different classification systems have been developed that are applicable to specific situations or to a limited number of fish species or products without having one particular defined method (11).

Over several years the Quality Index Method (QIM) has been used as a reference method in the European Union to determine the quality of sliced fish. The QIM is based on an objective evaluation of certain attributes of raw fish during storage on ice (12,13,16). This evaluation should be done by trained personnel with clear and defined guidelines keeping in mind different attributes, such as the eyes, gills and scales, allowing accurate judgment about the product. The QIM has been catalogued as a precise and objective method, not destructive, quick, easy to apply and specific (17,18,19). In the QIM each one of the analyzed attributes is qualified with a point system from 0 to 3, where zero represents the greatest indications of freshness and three determines the greatest indication of deterioration (13,17,18). Points for each one of the analyzed attributes are added to give a total sensorial score for the day it is evaluated on; this way the Quality Index is achieved.

Due to the fact that higher scoring is given the longer the product is stored (18), the quality index is lineally increased (13,18,20) and therefore is frequently used to predict the remaining storage time on ice (12,18,21), which is useful for fish merchants to determine how much time it is acceptable to keep the product on the market (2). This method has been implemented to establish the degree of freshness in species such as: gilt-headed bream (Sparus aurata) (17,22, 23), red sea bream (Pagellus bogaraveo) (18), sardine (Sardinops sagax), (16), cod (Gadus morhua) (20), herring (Clupea harengus L.) (21), common octopus (Octopus vulgaris) (19), common cuttlefish (Sepia officinalis) (24), and red mullet (Mullus barbatus) (25), among others.

The objective of this investigation was to develop IQM model for gutted and ungutted red tilapia relating to the storage time on ice, and implicitly to study sensorial changes with results applicable both to the industrial sector as well as for regulatory entities of this food and agriculture product.

MATERIALS AND METHODS

Sampling and storage conditions. A total of 80 samples of commercial sized fish (380-420 g) were acquired from aquaculture ponds in the Betania reservoir, located in the south west of the department of Huila, 35 km from Neiva, where the greater amount of tilapia for the national and international market is produced. 40 fish with scales were gutted at the collection site, packed in expanded polystyrene boxes with ice, alternating layers of fish with layers of ice in a 1:1 proportion. Once packed, they were taken to the laboratory within an hour after acquiring them, and the polystyrene boxes were stored in refrigeration at a temperature that oscillated between 0 and 4°C. Another 40 specimens were transported without gutting in the same conditions as the gutted fish. To analyze the gutted tilapia, sampling was done at 0, 3, 5, 8, 11, 14 and 17 days according to the methodology suggested by Simat et al (17), while the ungutted tilapia was sampled on days 0, 3, 6, 9, 11, 14 y 16.

Sensorial model. A group of 8 expert panelists made up of academics, investigators and businessmen in the fishing sector were trained to do a sensorial evaluation by means of the Quality Index Method (QIM). An initial model for whole red tilapia was planned according to the one proposed by Martinsdóttir et al (13) for redfish due to its morphologic similarity to tilapia.

In gutted red tilapia, the aspects to evaluate through a developed model were: appearance (skin, blood in the gills, firmness), eyes (cornea, form, pupil), gills (color, smell, mucous) and meat (color and structure). Among others, the aspects for ungutted tilapia to evaluate were appearance (scales, blood in gills, firmness, belly), eyes (cornea, form, pupil), gills (color, smell, mucous) and meat (color and structure) and entrails (appearance, firmness and consistency).

The panelists evaluated each one of the established sensorial attributes on a scale of demerits from zero to three points, and judgments emitted for each evaluator were centralized in an numeral measurement. With the sum of the average scores of the sensorial attributes that were part of the QIM, a quality index was obtained for gutted and ungutted red tilapia (Oreochromis ssp) based on storage time on ice.

Statistical analysis. Data obtained from the value table as suggested by Sykes et al (26) were subjected to a lineal regressive analysis with a correlation between the quality index and the storage time on ice with a confidence level of 95%.

RESULTS

QIM model for gutted red tilapia. Results of the sensorial evaluation done by the panel of experts for each one of the evaluated parameters provided the model of the quality index method for gutted red tilapia, and sensorial attributes were included that presented a notorious evolution during storage time. This way the developed model in the end had 4 quality parameters and 11 sensorial attributes, and the maximum total score was 21 points (Table 1).

In analysis done through the QIM model for gutted tilapia, the evolution of sensorial attributes such as “firmness” in the quality parameter, “appearance”, the “form” in the “eye” parameter, “color” in the “gill” parameter and “structure” in the “meat” parameter were those that best reflected deterioration of the product's quality by showing a gradual evolution that increased during the 17 days of storage on ice (Figure 1).

With the total sum of the average score from the 11 sensorial attributes composed in the QIM model (Table 1), the quality index for gutted red tilapia (Oreochromis ssp) was obtained based on the storage time on ice (Figure 2).

The parameters that were included in the quality index model (Table 1) were useful to establish the detriment to the quality of gutted red tilapia during storage on ice and showed a high positive correlation (R2=0.98; p≤0.01) that shows its utility in determining the evolution of the loss of freshness in the fish. As can be seen in figure 2, the quality index increases as storage on ice advances, and reaches a maximum detriment value of 21 points on day 17.

QIM framework for ungutted red tilapia. The sensorial evaluation done by the panel of experts for each one of the parameters evaluated determined the quality index method model for ungutted red tilapia (Table 2). The developed model had 5 quality parameters and 14 sensorial attributes, with a total maximum assigned score of 29 points of demerit.

In the case of ungutted tilapia, the evolution of the sensorial attributes “firmness” in the quality parameter “appearance”, “form” in the “eye” parameter, “color” in the “gills” parameter, “structure” in the “meat” parameter and “consistency” in the quality parameter “entrails”, were those that best reflected the changes in the product by presented a growing gradual evolution during 16 days of storage on ice (Figure 3).

With the total sum of average scores of the 14 sensorial attributes that make up the QIM model, the Quality Index for ungutted Red Tilapia (Oreochromis ssp) based on storage time on ice (Figure 4).

Just like with the gutted tilapia, the quality index obtained increased lineally regarding storage time on ice; finding a high positive correlation, adjusting the lineal model adequately (R2=0.9794; p≤0.01), for which the parameters that were included in the quality index model (Table 2) were useful to establish the evolution of the loss of freshness in the fish. As can be seen in Figure 4, the quality index increased with storage time on ice, reaching a maximum demerit value of 29 points at day 16.

DISCUSSION

In gutted tilapia, results obtained are similar to those found by Nielsen and Hyldig (21), who determined the shelf life of herring as being 8-14 days when the fish is caught in winter and 3-8 days when caught in autumn; similarly, Méndez (27) found the shelf life of fresh and unfrozen gilt-head bream to be 7 days, which matches the microbiological count obtained.

Additionally, following the recommendation of the group evaluator, the acceptation level of the product can be determined based on sensorial evaluation. Based on this, it is clear that QIM becomes a tool to aid any person with short training to decide on the deterioration level of red tilapia according to the analysis of attributes described in the model for storage conditions on ice as evaluated here.

The quality model index developed by evaluating the deterioration of gutted and ungutted red tilapia showed a gradual growing evolution, similar to the model developed for other species of fish (18-20, 28); additionally, in the two cases evaluated, the relation between the quality index and storage time were adjusted to a lineal model with high correlation values.

Other studies show reports in the case of sweet water species such as the hybrid tambacu or chacmoto (Colossoma macropomum x Piaractus mesopotamicus). In this case, QIM scores between 0 and 26 were reported with 5 quality parameters and 10 sensorial ones (29) and the pacu (Piaractus mesopotamicus) that is found in rivers to the south of the continent, although in this case QIM scores were reported between 0 and 32, with 9 quality parameters and 15 sensorial attributes (30).

In the same way, the quality index values obtained based on storage time on ice resulted in the same order as those cited in other studies (18), reaching a maximum demerit value of 21 points on day 17 with gutted red tilapia and 29 points on day 16 with ungutted red tilapia.

In addition to determining the loss of freshness based on storage time, the QIM allows the indirect establishment of criteria to reject the product when needed for consumption or later transportation and processing. With the results of this study a maximum limit is proposed for consumption between 8 and 11 days of storage in gutted red tilapia and ungutted red tilapia, the product was rejected by the panelists between 6 and 9 days of storage.

For future investigations, it is proposed to compare the results of the evaluation of deterioration obtained by sensorial analysis, with results of the loss of freshness obtained with useful methods such as Torrymetro (18).

Acknowledgements

To the Universidad del Tolima for partial financing of this project (project: 290213).

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