Texture profile analyses in tench (Tinca tinca L., 1758) from extensive and intensive culture

The aim of the study was to evaluate the differences in texture profile of tench flesh. Texture profile analyses in tench, two years old, (Tinca tinca L.) was investigated using instrumental texture profile method, focused on hardness, springiness, cohesiveness, gumminess and chewiness performed with Texture Analyser TA.XTPlus. One group of fish was raised extensively in natural earth pond conditions; the other group was intensively cultured in a recirculation system, feeding on a commercial diet for 7 months. Twelve fish (6 females and 6 males) from each group were used for analyses. Flesh of male tench in both groups was harder, more gummy and chewy, compared to female. Springiness was lower in tench male from intensive culture and cohesiveness lower in females from both groups. The result of texture analysis in the extensive culture group was 16.01 N for hardness and 0.72, 0.66, 10.73 and 7.69 for springiness, cohesiveness, gumminess and chewiness, respectively. In the intensive culture group it was 15.16 N for hardness and 0.59, 0.52, 8.06 and 4.96 for springiness, cohesiveness, gumminess and chewiness, respectively. The results proved that the flesh of fish raised extensively is harder, springier, more cohesive and more gummy, and thus more appealing to consumers. This is the first similar study of texture profile of tench. Cohesiveness, hardness, muscle, springiness, flesh quality Textural quality is primarily a sensory attribute that is quantified in foods by several instrumental methods. According to Bourne and Szczesniak (2003) and Cardoso et al. (2009), texture profile analysis (TPA) is a resulting force-generated time curve used to quantify a number of textural properties that correlate well with the results from sensory evaluation. Post mortem textural changes are caused directly or indirectly by physicochemical changes in myofibrillar proteins (Křížek et al. 2011) and changes in extracellular structure such as the loss of fibre compaction and the increase of extracellular space between fibres (Ingolfsdóttir 1997; Popelka et al. 2012). Muscle texture is also affected by other variables such as fish rearing, seasonality and methods of capture, handling and processing (Johnston et al. 2000; Periago et al. 2005). The main quality indicators for fresh fish are fat, colour, texture and freshness. Other indices commonly cited are white stripes (connective tissue), bloodstains, marbling and melanin. Double compression used in the instrumental procedure enables performing TPA as a plot of force-time curves (Rahman 2006). Other terms describing texture are firmness, stiffness and the yield point (Vácha et al. 2007). Many attempts have been made to correlate physical measurements with sensory evaluation of texture (Johansen et al. 1991; Chamberlain et al. 1993). Reproducibility of texture measurements is affected by the sampling technique due to heterogeneity of the fillets (Nesvadba et al. 2004). Therefore, it is difficult to find a representative average sample in fish and measurements of textural properties may depend on the location within the fillet. Some authors recommend raw fish to be tested in the form of a fillet or a part of a fillet (Stejskal et al. 2011). The aim of the ACTA VET. BRNO 2013, 82: 421–425; doi:10.2754/avb201382040421 Address for correspondence: František Vácha University of South Bohemia Faculty of Fisheries and Protection of Waters, Institute of Aquaculture Husova tř. 458/102, 370 05 České Budějovice, Czech Republic Phone: +420 387 774 649 E-mail: fvacha@frov.jcu.cz http://actavet.vfu.cz/ study was to evaluate the differences in texture profile of tench flesh under two different ways of fish rearing and determine the effect of sex. Materials and Method

Textural quality is primarily a sensory attribute that is quantified in foods by several instrumental methods.According to Bourne and Szczesniak (2003) and Cardoso et al. (2009), texture profile analysis (TPA) is a resulting force-generated time curve used to quantify a number of textural properties that correlate well with the results from sensory evaluation.
Post mortem textural changes are caused directly or indirectly by physicochemical changes in myofibrillar proteins (Křížek et al. 2011) and changes in extracellular structure such as the loss of fibre compaction and the increase of extracellular space between fibres (Ingolfsdóttir 1997;Popelka et al. 2012).Muscle texture is also affected by other variables such as fish rearing, seasonality and methods of capture, handling and processing (Johnston et al. 2000;Periago et al. 2005).The main quality indicators for fresh fish are fat, colour, texture and freshness.Other indices commonly cited are white stripes (connective tissue), bloodstains, marbling and melanin.Double compression used in the instrumental procedure enables performing TPA as a plot of force-time curves (Rahman 2006).Other terms describing texture are firmness, stiffness and the yield point (Vácha et al. 2007).Many attempts have been made to correlate physical measurements with sensory evaluation of texture (Johansen et al. 1991;Chamberlain et al. 1993).Reproducibility of texture measurements is affected by the sampling technique due to heterogeneity of the fillets (Nesvadba et al. 2004).Therefore, it is difficult to find a representative average sample in fish and measurements of textural properties may depend on the location within the fillet.Some authors recommend raw fish to be tested in the form of a fillet or a part of a fillet (Stejskal et al. 2011).The aim of the study was to evaluate the differences in texture profile of tench flesh under two different ways of fish rearing and determine the effect of sex.

Fish and diets
There were two groups of fish used in this study.Fish in the group of extensive culture (EC) were initially pre-reared in a flow-through earth pond.Fish were raised in polyculture with common carp; stocking density for common carp was 500 pcs•ha -1 and for tench 400 pcs•ha -1 .Natural production was 220 kg•ha -1 .Oxygen concentration was from 6 to 8 mg O 2 •l -1 without the use of aerator.The pH level ranged from 6.8 to 7.5.No supplemental feeding was used.
Fish in the group of intensive culture (IC) were progressively trained to accept the formulated feed.The fish were held in fibreglass tanks connected to a recirculation system.Fish had been well adapted to the experimental diets and environment for more than seven months, as they were previously used in growth trials, during which they were fed the same diets and kept under the same conditions as in the present study.The rearing system consisted of tanks (600 litres of usable volume), mechanical drum filter and three percolating filters.Water temperature was stabilized at 23.3 ± 0.5 °C, monitored by a thermometer Testo 106, range -50 to + 275 °C (Testo Ltd., Czech Republic).The water was oxygenated by oxygen diffusers.The oxygen concentration at the inflow did not fall below 8.0 mg O 2 •l -1 .The total ammonia nitrogen concentration at the inflow and outflow did not exceed 0.29 and 0.68 mg TAN•l -1 , respectively.The water pH level ranged from 6.85 to 7.14 and it was monitored using a pH Tester 20, range 1.00 to 14.00 (Chromservis Ltd., Czech Republic).The water flow rate was kept constant during the experiment.Fish of this group were fed a commercial diet consisting of 92% dry matter, 26% protein, 5.3% fat, 2.7% fiber and 4% ash, determined following the Czech reference methods.
For the trial, the fish size between groups was well balanced with a live weight of 150 ± 20 g, total body length was 200 ± 20 mm, body height was 45 ± 10 mm.The fish were killed, gutted and filleted.For further texture analyses, one hour after killing specific parts of fillet were determined by the position above the lateral line towards the cranial body part in an identical manner (Fig. 1).

Texture analyses
The texture of tench flesh was characterised by the instrumental method texture profile analysis (TPA) for hardness, springiness, cohesiveness, gumminess and chewiness.Samples of raw skinned fillets 24 mm in diameter were prepared from every tench and stored on ice until analysis.Texture profile analysis was conducted using a Texture Analyser TA.XTPlus (Stable Micro Systems, Godalming, England) with a load cell of 50 kg at a stable temperature of 17 °C.For texture measurement a compression plate suitable for fish fillets was used.This instrument provides a rigid framework for tension, compression cycling and texture tests to generate true 3-dimensional product analysis of force, distance and time.

Compression plate
A compression plate of 75 mm diameter was selected.Penetration depth of 5 mm into the fillet was selected as the maximum distance which could be applied without breaking the muscle fibres and affecting the muscle structure by disrupting it and leaving a mark on the fillet.Double compression was applied to construct the TPA variables.Then the plate was pressed on the fillet a second time and TPA was obtained by analyzing the forcetime curve (Bourne 1982).The plate was pressed down onto the fillet at a speed of 2 mm•s -1 until the fillet was compressed to 50% of its original thickness.Samples were allowed to rebound for 15 s with the compression plate just contacting the surface.Data collection and calculations (hardness, springiness, cohesiveness, gumminess Position of sample extraction for texture profile analysis (TPA) Fig. 1.Illustrative location for sampling in texture profile analysis in the tench body and chewiness) were carried out using the Texture Expert program, version 1.11 (Stable Micro Systems Ltd., Godalming, England).Hardness was defined as the maximum force detected during first compression, expressed in N. Springiness was defined as the ratio of the time or distance from the start of the second area to the second probe reversal over the distance, or the time between the start of the first area and the first probe reversal (Alvarez et al. 2002).Cohesiveness was measured as the ratio of the positive force during the second compression to the positive force during the first compression (Alvarez et al. 2002).Gumminess was defined as the product of hardness × cohesiveness.Chewiness was defined as hardness × cohesiveness × springiness.Cohesiveness, gumminess, springiness and chewiness are dimensionless.

Statistical analysis
The TPA effect was determined using one-way ANOVA by analysis of variance and Tukey's mean test (P < 0.05).The software used was StatSoft, Inc. ( 2001), STATISTICA CZ, version 6. Student's t-test was applied in order to test for the differences between extensive and intensive culture.

Results
Difference of texture quality (hardness, springiness, cohesiveness, gumminess and chewiness) was studied between fish from extensive and intensive culture.The results of texture analyses in fish from the extensive group were 16.01 ± 1.91 N, 0.72 ± 0.52, 0.66 ± 0.01, 10.73 ± 1.44 and 7.69 ± 0.85 for mean hardness, mean springiness, mean cohesiveness, mean gumminess and mean chewiness, respectively.The results of texture analysis in fish from the intensive group were 15.16 ± 4.56 N, 0.59 ± 0.06, 0.52 ± 0.04, 8.06 ± 1.91 and 4.96 ± 1.73 for mean hardness, mean springiness, mean cohesiveness, mean gumminess and mean chewiness, respectively.Significant difference (P < 0.05) between groups (EC/IC) was found for hardness, springiness and gumminess; and significant difference (P < 0.01) for cohesiveness and chewiness.The results of texture analysis proved, that the flesh of fish from EC group fed natural food was harder (Fig. 2), springier, more cohesive, gummier and chewier compared to IC group.
Flesh of male tench in both groups was harder, more gummy and chewy, compared to female.Springiness was lower in male tench from intensive culture and cohesiveness lower in females from both groups (Table 1).

Discussion
The experiment proved that the texture of tench flesh can be influenced both by the method of fish culture (extensive, intensive) and by the sex of the fish, as partly mentioned in allometric analysis published by Jobling (2001).The results also confirmed an important factor in quality assessment of the texture profile; namely myosin, as stated in Ingolfsdóttir (1997), which may influence the hardness level in extensively cultured fish.
Texture quality measurement expressed in particular curves as mentioned by Bourne and Szczesniak (2003) and Cardoso et al. (2009), is used in sensory evaluation and correlates well with the gained data in differences of type of fish culture.
Similar indications were found by the procedure from Rahman (2006) and Bourne (1982), using a double compression technique to perform texture profile analysis in forcetime curves.The technique of measurement is an important factor in fish texture evaluation because of heterogeneity of the fillets, mentioned especially for freshwater fish species as common carp, tench, perch and others by several authors, e.g.Reid and Durance (1992), Nesvadba et al. (2004).
Thus, the experimental protocols already developed can also help in finding more detailed procedure and solutions in the development of fish processing.Texture profile analyses of the tench tend to commercial use where the data can be used in several ways of products development to be incorporated into new fish products.It has a substantial effect on the desirable storage period of frozen fish maintained in proper conditions during their shelf life as mentioned in Rahman (2006).
As the available literature does not refer to particular characteristics included in the analysis of texture profile, this study contributes to more complex investigation into the subject of freshwater fish texture.

Fig. 2 .
Fig.2.Statistical evaluation of hardness (in N) in tench fillets depending on type of fish culture and sex.ICF -intensive culture female, ECF -extensive culture female, ICM -intensive culture male, ECM -extensive culture male.Data are expressed as mean ± standard deviation.

Table 1 .
Data are expressed as mean ± standard deviation.Values in the same row with different superscripts are significant at P < 0.05, (n = 6) Texture profile analyses in tench fillets depending on type of fish culture and sex.