Abstract
The sensory characteristics, chemical freshness indicator contents, and microbial counts (total aerobe, psychrotrophic bacteria, H2S-producing bacteria, and Pseudomonas spp.) of whole un-gutted and gutted sea bass stored in ice were compared. Results of this study indicated that the acceptability quality of whole and gutted sea bass as determined by sensorial data is 11 days, respectively. No significant differences (p > 0.05) were found in the level of sensory score between whole and gutted sea bass samples. Total volatile basic nitrogen (TVB-N) values showed no significant increase for whole and gutted sea bass during storage. Trimethylamin (TMA-N) values of whole and gutted sea bass increased very slowly, reaching final values of 3.94 and, 3.38 mg/100g, respectively (day 13). Development of initial decomposition (after 7 days) occurred when bacterial counts were > 4 log CFU/g. Microbial counts showed a significant increase for whole and gutted sea bass during storage. Significant differences (p < 0.05) were found in the microbial counts between whole and gutted sea bass samples. This difference, may be attributed either to gutting procedures, which most probably were the cause of cross-contamination of fish or to the significantly higher fish flesh surface area exposed to environmental microbial contamination in the case of gutted fish.
Keywords:
INTRODUCTION
Seafoods are important sources of nutrients for humans. Proteins and non-protein nitrogenous compounds play an important role in the nutritional value and sensory quality of seafoods. Fish are considered to be among the most perishable foodstuffs; even when held under chilled conditions, the quality quickly deteriorates. Generally, it is desirable to consume fish and shellfish as soon as possible after catching in order to avoid undesirable flavors and loss of quality due to microbial action.[Citation1] The initial quality of seafoods on board is affected by the species characteristics, the seasonal biological changes in the gonads and muscles, the culture conditions, and fishing techniques. The quality preserving effect of chilling seafoods is generally due to the decrease in the rate of undesirable biochemical and chemical reactions, and the retardation of the growth and spoilage activity of microorganisms. The shelf life of chilled fish is affected by the biological properties of the catch, the harvesting conditions and post-harvest treatment, as well as by the standard of hygiene on board and in-shore processing, by the rate of chilling, by the temperature of storage, and by additional treatments.[Citation2, Citation3] Many methods to evaluate fish quality have been suggested and tested. They are conventionally divided into four groups: sensory, physical, chemical, and microbiological.
Sensory methods are the oldest and still the most satisfactory way of grading and assessing the freshness of fish and fish products and one of the most important groups of methods for freshness evaluation in fish research.[Citation4] Sensory assessment has several advantages since it can be fast, reliable, non- destructive, and may require only moderate training and little or no equipment. Characteristic sensory changes occur in the appearance, odor, texture, and taste of fish during deterioration.[Citation5, Citation6] The most commonly used method for quality assessment of whole fish in Europe is the European Union (EU) Freshness Grading (or EU scheme), published in the Council Regulation No. 2406/96.[Citation7] This scheme does not take into account differences between species, because only general parameters for groups of fish are used and each table is valid for several species. Alternative sensory methods, such as the quality index method (QIM), have been suggested where the description of the individual grades is precise, objective, and independent. The Quality Index Method (QIM) is a grading system for estimating the freshness and quality of seafood, which has been demonstrated to be rapid for many fish species. QIM schemes have currently been developed for a number of fish species including: fresh herring, and cod, red fish, Atlantic mackerel, horse mackerel and sardine, brills, Pollock, sole, and sea bream.[Citation8, Citation9] The quality index method is useful essentially because it evaluates those sensory parameters and attributes that change most significantly in each species during degradation processes. The set of characteristic attributes of each parameter is assigned a range of demerit points (≤3) that is in direct proportion to their importance in the deterioration pattern of the species. All attributes score 0 when the fish is very fresh. The sum of the points awarded to each parameter gives a total score, which is the quality index at the time of assessment.[Citation10] In this article, the authors investigated for real and objective sensory characteristic of sea bass two sensory methods (EU and Quality index scheme) utilized by the industry we examined the quality changes of cultured sea bass, ungutted and gutted stored in ice for a period of up to 13 days were determined by sensory, chemical (pH, TVB-N and TMA-N) and microbiological (aerobic, psychrotrophic bacteria, H2S-producing bacteria and Pseudomonas spp.) assessment.
MATERIALS AND METHODS
Fish Samples and Storage Conditions
Aqua-cultured fresh sea bass, Dicentrarchus labrax were cultivated in net cages in a Turkish fish farm and harvested during the period of June 2004. The fish were slaughtered by immersing in ice-cold water (hypothermia) and delivered to the laboratory (whole) within 12 hours of harvesting, packed in separate insulated polystyrene boxes with ice. Fish was washed once, after landing with running tap water. The fishes were divided into two lots, whole ungutted (A) and gutted (B). Gutting was carried out in the fish processing plant manually. During storage, ice was replenished when necessary. Boxes had perforated bottoms to allow drainage of crushed ice. Boxed fish were stored in refrigerator (+ 4°C). The ice/fish ratio (2:1) was maintained constant throughout the experiment. The mean and standard deviations of the weight and length of the fish studied were 286.7 ± 30.30 g and 27.1 ± 1.07 cm, respectively.
Sensory Assessment of Raw Fish
EU scheme
Five experienced panellists analyzed fish at days 1, 3, 5, 7, 9, 11, and 13, according to EU fish sensory schema for whitefish (6), and for the EU scheme (). The mean points of each panelist were calculated, and the fish were classified according to the following correspondence between points and quality bands: E < 1, 1 ≤ A < 2, 2 ≤ B < 2.7, 2.7 ≥ C points.[Citation10]
Table 1 EU fish sensory scheme.
Quality index method
Quality index method was assessed using the Tasmanian Food Research Unit scheme () with modifications for sea bass.[Citation11] The acceptable shelf life was found to correspond with a demerit score of 20 ± 2.
Table 2 Quality index scheme for sea bass.
Sensory Assessment of Cooked Fish
Quantitative descriptive analysis
The cooked fish using the simplified Torry Sensory Scheme for cooked, white fish.[Citation12] Panellists were asked to score odours, taste and texture of fish using a 0–10 acceptability scale. Scale 10–9 = excellent, 8.9–8 = very good, 7.9–6 = good, 5.9–4 = sufficient, 4 = limit of acceptable, ≤ 3 = unacceptable.
Chemical Analysis
Proximate analyses
Moisture content was determined by drying an accurately weighed sample of minced fish in an oven at 103 ± 2°C for 3 hours.[Citation13] The ash content was obtained by heating the residue for 3 hours at 550°C.[Citation14] The protein contents were assayed by the AOAC method.[Citation15] Total lipid was determined on a 1g sample of the minced fillets using the soxhalet method.[Citation16]
pH
The pH was measured in fish homogenates (5g of fish/5ml distilled water) with a WTW pH Meter (inoLab pH Level 1 model, Weilheim, Germany).[Citation17]
Determination of total volatile basic nitrogen (TVB-N)
Total volatile basic nitrogen was determined according to the Antonacopoulos and Vyncke, method.[Citation18]
Determination of trimethylamin nitrogen (TMA-N)
This was determined by AOAC method.[Citation19] Results were expressed as mg TMA-N/100g muscle.
Microbiological Analysis
Three fish of each batch were randomly chosen. An area of approximately 10 cm2 of the anterior-dorsal region and abdominal cavity of the right side of the fish was swabbed with a sterile swab, previously wetted with sterile Pepton water. Flesh samples (25g) were mixed with 225 ml of pepton water (Merck, Kat No: 107228) diluents in a Stomacher (Stomacher, IUL Instrument, Spain). Further serial dilutions were made in tubes before plating. The media and incubations were: for mesophilic aerobic plate count PCA agar (PCA, Merck, Kat No: 105463), 37°C, 1–2 days; for psychrotrophic bacteria PCA agar (PCA, Merck, Kat No: 105463), 7°C, 10 days;[Citation20] for Pseudomonad's cetrimide agar (Merck, Kat No:105284), 37°C, 2 days;[Citation21] for H2S-producing bacteria (typical of Shewanella putrefaciens) Iron agar (Peptone from casein 5 g; yeast extract 2.5 g; glucose 1 g; agar-agar 14 g, 0.3 g iron III citrate; 0.48 g sodium thiosulfate, 3 g NaCl) 25°C, 2–3 days.[Citation22] Microbiological data were transformed into logarithms of the number of colony forming units (CFU)/g and CFU/cm2.
Statistical Analysis
Results are expressed as mean standard deviation. Data were subjected to analyses of variance (ANOVA). Tukey's Honestly Significant Difference test procedure was used to test for differences between mean at the 5% significance level. Correlation coefficients between sensory score and microbial counts—chemical and microbial results were determined by Pearson test. Statistical analyses of data were calculated by Microsoft, Excel XP 2003.[Citation23]
RESULTS AND DISCUSSION
Proximate composition of fresh sea bass is shown in . These results expected, similar to those reprinted by Kyrana and Lougovois[Citation24] for sea bass (76.72% moisture, 4.81% fat, 1.23% ash). Proximate composition values (17.99% Protein, 6.53% Fat, 74.74% Water and 1.53% Ash) were reported by Grigorakis et al.[Citation25] and Karl und Meyer[Citation26] for gilthead sea bream. The chemical composition of fishes is affected by species, catching region, season, age of fish, and other environmental conditions.[Citation27, Citation28]
Table 3 Proximate composition of Sea bass.
shows the changes in sensory attributes of fish stored in ice. Excellent and very good grades (E and A) were scored during the first 7 days storage for ungutted and during the first 9 days for gutted fish. Moderate grades (B) were obtained between days 7 and 11 of storage for whole fish, and after day 9 for gutted samples. Unfit for sale raw fish samples (C) were obtained after 11 days of storage for whole and gutted raw sea bass samples. The pattern of increase in the demerit score from day 1 to day 13, for whole and gutted sea bass in ice storage conditions, is shown in . The rate of increase of demerit points is fairly linear with storage time in the two groups. No significant differences (p > 0.05) were found in the level of demerit points between sea bass held in whole and in gutted samples. The observed shelf-life of whole and gutted sea bass was found to be 9 days (demerit score: 19.96–19.12) for fish stored in ice. Panelists' acceptability scores for odor and taste of whole ungutted and gutted sea bass decreased significantly (p < 0.05) with time of storage. The limit of acceptability of odour and taste was reached after 11 days for the ungutted and gutted sea bass. This may be attributed to the fact that the majority of bacterial metabolic products, which contribute to the sensory deterioration, are volatile and are assessed more objectionably by odor.[Citation29] Acceptability scores for sensory analyses of whole ungutted and gutted sea bass evaluated by the panelists were not statistically significant (p > 0.05).
Table 4 Changes in sensory analyses of whole ungutted (A), gutted (B) sea bass stored in ice.
The shelf life of redfish stored in ice was found to be 12 days.[Citation30] In a previous study, the shelf life of whole ungutted sea bream stored in ice was found to be 17–18 days at 2 ± 2°C[Citation11] Lougovois et al.[Citation31] reported that whole sea bream stored in ice was still acceptable after 15 days. The storage life of whole, iced sea bream evaluated by sensory assessment of the raw fish has been reported to be 15–17 days.[Citation7, [Citation32] Poli et al.Citation33] reported that the limit of acceptability for ungutted sea bass was 10 days. Karl et al.[Citation12] investigated the influence of gutting on the fish quality during storage on ice in tench (Tinca tinca). These authors found no differences between gutted and ungutted fish during 12 days of storage on ice. Papadopoulus et al.[Citation29] found the shelf life of whole ungutted and gutted sea bass stored in ice by the acceptability sensory scores and microbiological data is 13 and 8 days, respectively. Taliadourou et al.[Citation34] determined the shelf life, fish using acceptability, sensory, and microbiological data. They found a shelf life of 8–9 days and 12–13 days for filleted sea bass and ungutted sea bass, respectively. Chytiri et al.,[Citation35] indicated that the shelf life of whole and filleted trout stored in ice were 15–16 and 10–12 days, respectively. Paleologos et al.,[Citation36] reported unacceptable quality for whole sea bass, gutted sea bass and filleted sea bass, after 13, 11, and 9 days, respectively. The shelf life of fish is affected by the initial microbial load of the fish and storage temperature. Results of this study indicate that the shelf life of whole ungutted and gutted sea bass stored in ice as determined by the sensory scores is 11 days, respectively.
The changes in pH, TVB-N, and TMA-N for whole ungutted and gutted sea bass during the 13 day storage period in ice are shown in . pH value ranged from 6.46 to 6.64 for whole ungutted and from 6.55 to 6.67, for gutted sea bass respectively, during the 13 day storage period. Values of pH were not significantly different (p > 0.05) during the entire period of storage. pH increases are in agreement with the findings of[Citation24, Citation29, Citation34, Citation37] for sea bass and sea bream stored in ice. The pH of live fish muscle is close to the value 6.5–7. Post mortem pH can vary from 6.0 to 7.1 depending on season, species and other factors.[Citation38] The pH level reached 6.76 for the group A and 6.87 for group B by day 11 of storage. According to the literature, the pH is about 6.0–6.5 for fresh fish, and it increases during storage. The limit of acceptability is usually 6.8–7.0.[Citation28]
Table 5 Changes in pH, TVB-N, and TMA-N of whole ungutted (A), gutted (B) sea bass stored in ice.
Total volatile nitrogen content (TVB-N) of fish is indicator of the raw material freshness.[Citation39] The TVB-N content ranged from 17.66 mg/100 g to 14.14 mg/100 g flesh for whole ungutted and from 16.10 mg/100 g-15.74 mg/100 g for gutted samples, respectively, during the 13 days period of storage in ice. According to the table, TVB-N values fluctuated for whole ungutted sea bass during storage reaching a value of 16.55 mg/100 g (day 11) whereas for gutted fish 18.10 mg/100 g was recorded. Changes in TVB-N in ice stored samples, ungutted and gutted, showed a slight decrease and increase in the after 3 days of storage, probably as a result of the washing of nitrogen compounds from the sea bass by ice in this period. Similar results were found by Huidobro et al.,[Citation40] for sea bream stored in liquid ice. TVB-N values showed significant fluctuation for all fish samples as a function of storage period indicating that TVB-N is a poor indicator of fish freshness, as also proposed by.[Citation29, Citation32, Citation37] A TVB-N level of about 25 mg/100 g flesh could be regarded as the limit of acceptability for iced European sea bass.[Citation24, Citation41, Citation42]
TMA-N is formed from bacterial use of TMAO; a naturally occurring osmoregulating substance found in most marine fish species can reach high concentrations.[Citation43] The quantity and presence of TMAO depends on the species which size, sex, station of year, etc.[Citation27] It is reduced to trimethylamine (TMA-N) by spoilage bacteria giving rise to the characteristic pungent smell of iced fish and TMA-N is therefore an indicator of spoilage.[Citation44] Initial TMA-N values of whole ungutted and gutted sea bass (groups A and B) samples were 0.71 and 0.68 mg/100 g, respectively. After 13 day storage, TMA-N values 3.94 mg/100 g and 3.98 mg/100 g were reached for whole samples and ungutted samples reached this content (3.38 mg/100 g) after 13 days of ice storage, respectively. The concentrations of TMA-N in numerous fatty fish never reached the limit of 5 mg TMA-N/100 g, although the rejection limit in fish flesh is usually 5–10 mg TMA-N/100 g.[Citation45] The level of TMA-N was typically around 0.07 mg/100 g in ice stored whole fish (sea bass) rejected by sensory panels.[Citation29] Similarly, low TMA-N values have been reported for whole fresh sea bass and sea bream.[Citation32, Citation37] In some fish that do not contain TMAO or where spoilage is due to a non-TMAO reducing flora, a slow rise in TVB-N is seen during storage, probably resulting from the deamination of amino-acids.[Citation46] Authors such as Kyrana and Lougovois[Citation24] attributed these low levels of TVB-N to the relatively low pH values, and the composition of the microbial flora encountered during the trial. The optimum pH for the activity of the bacterial TMAO-reducing enzymes has been reported to be 7.2–7.4. With respect to the microbial flora, it has been reported[Citation47] that a population of 108–109 colony forming unit (cfu)/g of Shewanella putrefaciens is considered crucial for TMA-N production and thus for TVB-N levels. In European sea bass, Pseudomonas spp., which can be the dominant bacterial spoilage organisms in warm waters, does not reduce TMAO so that spoilage can occur with little or no TMA-N production. Different authors establish the importance of Pseudomonas spp. as flora of the deterioration and their competition with Shewanella putrefaciens.[Citation48] In this study H2S- producing bacteria counts reached at the end storage were 6.07 log cfu/cm2 (skin), 5.17 log cfu/cm2 (Abdominal cavity), 5.60 log cfu/g (flesh) for ungutted sea bass, 6.24 log cfu/cm2 (skin), 5.78 log cfu /cm2 (Abdominal cavity), 5.56 log cfu/g (flesh) for gutted sea bass, respectively. Thus, TMA-N is not a particularly useful indicator of sea bass freshness. A highly significant correlation was found between TMA-N and H2S- producing bacteria counts ().
Table 6 Correlation coefficients between sensory score, volatile amine, and microbial counts in whole and gutted sea bass.
The changes in the micro flora of aqua cultured sea bass during storage in ice are shown in , , and . Psychrotrophic bacteria counts for all samples increased with increasing time of ice storage (p < 0.05). Initial total viable counts for whole ungutted and gutted sea bass were 2.5 log cfu/g, respectively. Psychrotrophic bacteria counts reached 6 log cfu/cm2 (skin) for whole ungutted and for gutted sea bass, respectively, after 9 days of storage. Initial mesophilic counts were low for whole ungutted and gutted fish sampling periods, respectively, with final counts of 4.90 log cfu/cm2 (skin), 4.32 log cfu/cm2 (abdominal cavity), 4.93 log cfu/g (flesh), and 5.10 log cfu/cm2 (skin), 4.52 log cfu/cm2 (abdominal cavity), 5.84 log cfu/g (flesh). The Pseudomonas spp. counts of fresh fishes were 2.48 log cfu/cm2 (skin and abdominal cavity), 2.48 log cfu/g (flesh) and remained constant during storage for ungutted sea bass samples. The Pseudomonas spp. count of gutted sea bass increased during storage to reaching after 11 days 3.80 log cfu/cm2 (skin) and 3.69 log cfu/ cm2 (abdominal cavity) and 3.48 log cfu/g (flesh). The quality of fresh fish is a major concern to industry and consumers. Like marine fish, freshwater fish are extremely perishable food commodities. Deterioration of fish mainly occurs as a result of bacteriological activity leading to loss of quality and subsequent spoilage. Bacterial spoilage and thus microbiological analyses of refrigerated fish under aerobic storage conditions focus on Gram- negative psychrotrophic organisms such as Pseudomonas, Aeromonas, Shewanella and Flavabacterium spp.[Citation34, Citation46] Pseudomonas and H2S-producing bacteria have been reported to be the specific spoilage bacteria in fish from temperature and tropical waters[Citation49] and in fresh Mediterranean fish.[Citation35] Statistical analysis showed significant differences were found only for the microbiological analyses between the whole and gutted groups (p < 0.05). Correlation coefficients between microbial counts and sensory results are shown . In this study, bacterial populations of gutted fish were higher than those obtained for whole ungutted fish samples throughout the entire period of storage in ice. This may be attributed either to gutting procedures, which most probably were the cause of cross-contamination of fish or to the significantly higher fish flesh surface area exposed to environmental microbial contamination in the case of the gutted fish.
Table 7 Changes in H2S-producing bacteria of whole ungutted (A), gutted (B) sea bass stored in ice.
Table 8 Changes in Psychrotrophic bacteria of whole ungutted (A), gutted (B) sea bass stored in ice.
Table 9 Changes in aerobic mesophilic count of whole ungutted (A), gutted (B) sea bass stored in ice.
Table 10 Changes in Pseudomonas spp. of whole ungutted (A), gutted (B) sea bass stored in ice.
Gobantes et al[Citation50] have accepted the marketable aerobic plate count (APC) level as 106–107 cfu/g and the APC limit of spoilage as 107–108 cfu/g. The fish industry generally considers spoilage to occur when the APC reaches 106–107 cfu/g.[Citation51] Aerobic bacteria of two Series reached 106 in skin after 11 days of storage. Spanish regulations for fresh and refrigerated fish establish the microbial limit of acceptability at 105 cfu/g for psychrotrophic bacteria.[Citation52] This data reached skin and flesh of whole and gutted sea bream respectively after 9 and 11 days of storage. Rehbein et al.[Citation30] reported that mesophilic aerobic counts showed a slight increase for redfish during storage, reaching a value of 104 cfu/g (day 12), when the fish reached the borderline of saleability (sensory score > 4) the bacterial count did not exceed 106cfu/g. Eifert et al.[Citation53] reported hybrid striped bass fillets stored at 4°C, did not reach 107cfu/g until 12 days. Kyrana und Lougovois[Citation24] reported for sea bass after 1 day ice storage mesophilic counts of 3log cfu/g, H2S-producing bacteria counts of 1.5 log cfu/g muscle with a maximum of 7 log cfu /g mesophilic count, 5 log cfu /g H2S-producing bacteria counts after 14–15 days; this increment was associated with off-odors and flavors for cooked fish as well as rancidity odors in gills. Lougovois et al.[Citation31] reported that the amount of mesophilic count and H2S-producing bacteria in sea bream flesh at the time of rejection (15 days) in ice was 6.3 log cfu/g and 5 log cfu/g. This is in agreement with the conclusions made by the literature data. Seafood freshness is affected by conditions and length of storage before processing. From the time of catching, fish undergo changes brought about by the action of the enzymes of the fish (autolysis), and also from the action of bacteria present on the surface of the fish and in the gut. The rate at which raw material spoils depends on the species of fish, storage time and temperature and, degree of microbiological contamination.[Citation54] Papadopoulos et al.[Citation29] reported mesophilic counts for whole ungutted and gutted sea bass 5.3 log cfu/g-7.5 log cfu/g after 9 days of storage. H2S-producing bacteria count were similar 7 log cfu/g in ungutted sea bass and 6.6 log cfu/g in gutted sea bass samples. Chytiri et al.[Citation35] found initial mesophilic viable counts of whole and filleted rainbow trout 2.5 log cfu/cm2 and 3.8 log cfu/ cm2. This count reached 7 log cfu/cm2 after 18 days of storage for whole trout and after 10 days for filleted samples. Taliadourou et al.,[Citation34] reported mesophilic aerobic count of 5.5 log cfu/f-7.5 log cfu/g for whole- filleted sea bass in ice after 9 days, respectively. This is in agreement with the conclusions made by Papadopoulos et al.,[Citation29] Taliadourou et al.,[Citation34] and Chytiti et al.[Citation35] data. Quality changes and shelf life of whole ungutted and gutted aquacultured sea bass stored in ice were monitored by sensory evaluation, chemical and microbiological analyses. Results of this study indicate that shelf life of whole and gutted sea bass stored in ice determined by the overall acceptability sensory scores and microbiological data is 11 days, respectively. The presence of high microbial count in gutted sea bass samples may be related to the number of bacteria originating from cross- contamination of fish during the gutting procedures.
CONCLUSION
Quality changes and shelf life of whole ungutted and gutted aquacultured sea bass stored in ice were monitored by sensory evaluation, chemical, and microbiological analyses. Results of this study indicate that shelf life of whole and gutted sea bass stored in ice determined by the overall acceptability sensory scores and microbiological data is 11 days, respectively. The presence of high microbial count in gutted sea bass samples may be related to the number of bacteria originating from cross-contamination of fish during the gutting procedures.
ACKNOWLEDGMENTS
This study was supported by the Research Fund of the University of Istanbul (Project No: Number UDP–384/260804 and BYP–313/11122003).
Notes
a: no significant(p > 0.05)between two Group.
b: significant(p < 0.05) between two Group.
2. Gasnell, M.; Milne, D.; Blaha, F.; Wright, K.; Cumming, A. Identify Characteristics of Quality and Describe Seafood Spoilage Factors and how Seafood Spoilage is controlled. A Learning Resource for Unit Standards: Wellington, 5316, 5328, and 15884; 2000
6. EC Regulation. Council Regulation N 2406/96 of 26 November 1996 laying down common marketing standards for certain fishery products (OJ L 334, 23.12.1996, 1996; 1–15
41. 95/149/EG. Entscheidung der Kommission vom 8. März 1995 über TVB- Grenzewerte für bestimmte Kategorien von Fischereierzeugnissen und die anzuwenden Analysemethoden. Amtsblatt nr. L 097 vom 29/04/1995, pp. 0084–0087
Related Research Data
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