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Characterization and Storage Stability of Traditional Salted Thunnus albacares and Scomberoides commersonianus

Ismail Al Bulushi*, Mohamed Rahman, Mutamed Ayyash, Mostafa Waly, Mohammed Al Za’abi, Aisha Abushelaib, Jalila Al Hadhrami, Jamila Al kalbani

Department of Food Science and Nutrition, College of Agricultural and Marine Sciences, Sultan Qaboos University, P.O. Box 34, Al Khod, 123, Oman

Abstract: Traditional salted Thunnus albacares and Scomberoides commersonianus processed with a thyme and other additives recipe were microbiologically and physiochemically characterized to evaluate its safety, quality and storage stability at 23 ± 2°C with a reference to the bacterial floral composition and halophilic bacterial floral types and its potential. This study was conducted in two stages. In the first stage, 15 kg of Thunnus albacares and Scomberoides commersonianus each were bought from local markets and characterized, whereas, in the second stage, 20 kg of Scomberoides commersonianus were stored at 23 ± 2°C for 10 weeks and its storage stability was evaluated. Total aerobic mesophilic bacterial and moderate halophilic bacterial counts were log 2.0 ± 0.78 - 2.4 ± 0.44 CFU/g and log 1.8 ± 0.11 - 2.5 ± 0.53 CFU/g. Enterobacteriaceae, Staphylococcus aureus, mesophilic lactic acid bacteria and yeasts and molds counts were < log 1 CFU/g. Vibrio parahaemolyticus was not detected. Bacillus amyloliquefaciens and B. methylotrophicus were the most dominant halophilic bacteria among the flora. Most of the Bacillus species showed antimicrobial, amino decarboxylation and lipolytic activities. Water activity, peroxide value and acid value were 0.79 ± 0.00 - 0.85 ± 0.00, 2.8 ± 1.4 - 5.6 ± 1.4 meq/kg fat and 2.3 ± 0.62 - 3.2 ± 1.1. Tyramine, histamine, cadaverine and putrescine were found in trace amounts. Salted fish product,s characteristics did not change significantly during storage except NaCl content and colour value a. In conclusion, traditional salted Thunnus albacares and Scomberoides commersonianus were found to be microbiologically safe with good quality and storage stability of 10 weeks.

Keywords: traditional salted fish, characteristics, storage stability, halophilic bacteria, safety, quality

Received August 07, 2021; Revised September 10, 2021; Accepted September 22, 2021

Citation: Ismail Al Bulushi, Mohamed Rahman, Mutamed Ayyash, Mostafa Waly, Mohammed Al Za’abi, Aisha Abushelaib, Jalila Al Hadhrami, Jamila Al kalbani, Characterization and Storage Stability of Traditional Salted Thunnus albacares and Scomberoides commersonianus. Journal of Food and Nutrition Research, 9 (9). 484-491. January 2021. doi:10.12691/jfnr-9-9-5

1. Introduction

Traditional salted fish are commonly consumed around the world and mainly in Asia. The basic characteristics of these products were studied in some Asian salted fish such as salted mullet, longtail tuna and queenfish [1,2]. For instance, salted mullet from a Saudi market was found to be loaded with log 3.77 CFU/g of total aerobic bacteria [1]. Chemically, salted long tail, sailfish, queenfish, and kawakawa from Omani markets contained crude proteins 45.66, 25.03, 24.53, and 53.12 g/100 g solids [2]. The main limitations of are, the microbial floral composition was not fully elucidated except certain bacterial species belong to Bacillus and Staphylococcus [1,2]. Moreover, despite the dominancy of certain bacterial species such as B. subtilis, B. licheniformis and B. mycoides [1], the potential of this flora was not studied.

Salted fish characteristics depend on many factors such as types of fish, recipe, salting method, fish handling hygienic conditions, salting, and storage conditions. The effect of some factors on the characteristics of salted fish was studied earlier. For instance, salted freshwater fish; Channa striatus contained more lipids than another salted freshwater fish namely Mystus tengra, and Channa striatus contained more proteins than that was found in Channa punctatus [3,4]. In marine salted fish, palmitic acid was 21.2% in salted mullet and 26.0% in salted sardine [5]. Thunnus albacares (yellowfin tuna) and Scomberoides commersonianus (queenfish) are common salted fish products in some Asian countries such as Oman and UAE, where despite its regular consumption, the composition of the bacterial floral precisely halophilic bacteria was not studied.

Stability of salted fish during storage was limited to few salted fish products. In this connection, Al Asous and Al Harbi [6] found a significant reduction in total mesophilic and psychrotrophic viable counts during ambient and refrigeration storage of salted wild mullet (Valamugil seheli). The stability of oily salted fish such yellowfin tuna at ambient temperature is not clearly known. Therefore, this study aimed to measure the microbiological and physiochemical characteristics of common traditional salted Thunnus albacares (yellowfin tuna) (SYT) and salted Scomberoides commersonianus (talang queenfish) (STQ) to evaluate its safety, quality and storage stability at 23 ± 2°C with a reference to the bacterial flora composition and halophilic bacterial floral types and its potential.

2. Materials and Methods

2.1. Salted Fish Products and Experimental Design

This study targeted two of the main consumed salted fish products in Oman and UAE namely, salted Thunnus albacares (yellowfin tuna) (SYT) and salted Scomberoides commersonianus (talang queenfish) (STQ). These fish were caught by hand line and handled traditionally. Fish were dressed, washed, and mixed with dry salt to the saturation level traditionally. Dried thyme, fresh green pepper, and lemon were added as flavour materials. The exact formula and the recipe of the ingredients usually are not revealed by the producers. The salted fish products were packed in plastic barrels of 20kg and left at 25°C-30°C minimally one month for curing.

This study was conducted in two stages. In the first stage, 15 kg of SYT and 15 kg of STQ were bought from local markets in Oman and UAE in Sep. 2016 to Feb. 2017 after approximately one month of curing. Microbial analyses were conducted immediately after arrival to the laboratory within one hour. In the second stage, 20 kg of STQ was bought from a local market in Oman and brought immediately to the laboratory. This salted fish product was selected precisely due to its e commonly availability in the markets. Salted talang queenfish was stored at ambient temperature (23 ± 2°C, 68% RH) for 10 weeks. At each sampling occasion, 4 samples weighing 500g each were used for the analyses. All analyses were run in 2-4 replicates. Before each analysis, salted fish samples were chopped aseptically.

2.2. Microbial Analyses

2.2.1. Bacterial Enumeration and Identification

Initially, 25g of salted fish was mixed with 225 ml of maximum recovery diluent (Oxoid, UK). After serial dilutions, 0.1 ml of the diluent was used to enumerate the following microorganisms. Total aerobic mesophilic bacteria (TAMB) were incubated aerobically at 35C for 48 ± 2 hr. and enumerated on tryptone soya agar (TSA) (Oxoid, UK) [7]. Moderate halophilic bacteria (MHB) were incubated aerobically at 35C for 72 ± 2 hr. and enumerated on TSA supplemented with 10% sodium chloride (Oxoid, UK) overlaid with 7 ml TSA to recover the injured halophiles [8]. Yeasts and molds were incubated at 25°C for 120 ± 2 hr. and enumerated on potato dextrose agar (Oxoid, UK) [9].

Mesophilic lactic acid bacteria were incubated anaerobically at 30°C for 72 ± 2 hr. and enumerated on De Man, Rogosa and Sharpe agar [10]. Staphylococcus aureus was incubated aerobically at 37°C for 48 ± 2 hr. and enumerated on Baird-Parker agar supplemented with rabbit plasma fibrinogen (Oxoid, UK). Staphylococcus aureus was confirmed using Staphytect plus system (Oxoid, UK) [11]. In Enterobacteriaceae enumeration, 1 ml of the diluent was added to 15 ml of ISO violet red bile glucose agar (Oxoid, UK) and Enterobacteriaceae were enumerated aerobically at 37°C for 24 ± 2 hr. [12].

In Vibrio parahaemolyticus enumeration, 25 g of salted fish was mixed with 225 ml of alkaline saline peptone water (20 g/l of NaCl and peptone equally at a pH of 8.6). The sample was incubated at 41.5°C ± 1°C for 6 ± 2 hr. After that, 1 ml of the bacterial suspension was transferred to another 10 ml of alkaline saline peptone water, and incubated for another 18 h ± 1 h at 41.5°C ± 1°C. Then 0.1 ml the of bacterial suspension was plated on thiosulfate-citrate-bile salts and incubated (Oxoid, UK) at 37°C for 24 ± 2 hr. Blue-green/ yellow colonies were considered as V. parahaemolyticus [13]. Five microbial isolates from each medium were selected randomly using Harrison’s disc for bacterial identification [14]. The isolates were further purified and stored on beads (Abtek, UK) at −80C for further analysis.

Bacteria were identified by 16S rRNA gene sequencing according to the protocols followed in an ISO 9001-2005 certified Central Analytical and Applied Research Unit (CAARU), Oman. Briefly, the DNA template was prepared using UltraClean Microbial DNA Isolation Kit (MO BIO, Avantor, USA) and DNeasy PowerSoil Kit (QIAGEN, USA) according to the manufacturer’s instructions. Polymerase chain reactions consisted of 12.5 µl master 2X Promega (Promega Co, USA), 0.5 µl of each of 27F and 1492R primers (Macrogen Co., Korea), 50 ng of DNA template, and the volume was brought to a final volume of 25 µl with PCR water.

PCR mixture was run through 35 cycles using a thermal cycler. The first 5 cycles involved DNA denaturation at 94°C for 30s, primer annealing at 60°C for 30s and extended at 72°C for 4 min. The second 5 cycles involved DNA denaturation at 94°C for 30s, and primer anneals at 55°C for 30s and extension at 72°C for 4 min. The next 25 cycles involved DNA denaturation at 94°C for 30s, and primer anneals at 50°C for 30s and extension at 72°C for 4 min. The reactions were finally held at 4°C. The PCR products were visualized by agarose gel electrophoresis using ethidium bromide staining and purified by QLAQuick PCR Purification Kit Protocol (QLAEN, USA) according to manufacturer’s instructions. Sequencing was conducted according to a protocol followed in CAARU. Sequences were compared with that in the NCBI database using the BLAST algorithm and identity probability was determined following https://dna.macrogen.com/.

2.2.2. Antimicrobial, Amino Acids Decarboxylation, Proteolytic and Lipolytic Potentials

Bacterial antimicrobial activity was evaluated by agar diffusion well assay [15]. Briefly, the isolate was sub-cultured in 10 ml tryptone soya broth (TSB) (Oxoid, UK) and incubated at 32°C for 24 hr. Cell-free Filtrate (CF) was prepared by centrifuging the bacterial suspension in TSB at 10,000×g at 4°C for 20 min. Target bacteria, namely Escherichia coli (ATCC 25922), Staphylococcus aureus (ATCC 25923), and Enterococcus faecalis (ATCC 29212), were obtained from the culture collection at Food Microbiology Laboratory, Sultan Qaboos University, Oman, grown in TSB and concentrated to 10⁸ cell/ml (turbidity is equivalent to McFarland barium sulfate standard 0.5). Antimicrobial activity was determined by spreading 100 µl of the target bacteria on TSA, after drying, 4 wells were filled with 50 µl of the bacterial isolate CF, the plates were incubated at 48 ± 2 hr. at 37°C, and the diameter of the inhibition zone was measured.

Isolates potential to form tyramine, cadaverine, histamine, and putrescine were evaluated by their abilities to decarboxylate tyrosine, lysine, histidine, and ornithine in HD-medium [16] and a protocol followed by Al Bulushi [17]. The HD-medium consisted of 2g/ l peptone (Oxoid, UK), 1g/l lab-lemco powder (Oxoid, UK), 5g/l NaCl (Oxoid, UK), 10g/l of amino acid in question (histidine, lysine, tyrosine, ornithine) (Sigma, USA), 10 ml/l of 0.1% bromocresol green solution (Sigma, USA) and 10 ml/l of 0.2% chlorophenol red solution (Sigma, USA). The medium was adjusted to pH 5.3. 10 ml of HD medium was inoculated with 1 ml of the bacterial isolate CF, sealed with mineral oil and incubated at 30°C for 48 hr. Colour change from green to violet was considered positive for amino acid decarboxylation. The proteolytic and lipolytic activity was evaluated by inoculating 4 wells in gelatin-containing nutrient agar and tween agar 20 respectively with 50 µl of the bacterial isolate CF and measuring the diameter of opaque zones surrounding microbial growth [18].

2.3. Physiochemical Analyses

Proximate composition in terms of water, protein, lipid, and ash contents were determined according to the Association of Official Analytical Chemist methods [19].

2.3.1. Lipid Oxidation

Primary lipid oxidation was assessed by acid value (AV) and peroxide value (PV) according to AOCS and others [20,21,22]. Briefly, 3 g of dried sample was mixed with 50 ml of neutralized isopropanol and titrated with 0.1N potassium hydroxide in the presence of phenolphthalein. The acid value was calculated according to the following formula:

Where, N is the normality of KOH and S is the sample weight.

For PV determination, 0.5 g of dried sample was mixed with 25 ml of acetic acid: chloroform (3:2). Then, 1 ml of saturated potassium iodide and 30 ml of distilled water was added, and the liberated iodine was titrated with 0.01 N sodium thiosulfate in the presence of 1 ml of freshly prepared 1% starch until the disappearance of the blue color. Peroxide value was calculated as meq/kg fat according to the following formula:

Where, A is the titration value for the sample, B is the titration value for the blank, and S is the weight of the sample.

2.3.2. Biogenic Amines

Histamine, cadaverine, putrescine, and tyramine were quantified according to Tsai et al [23]. Five grams of ground dried salted fish was mixed with 20 ml chilled 6% trichloroacetic (TCA) (Sigma, USA) in a high-speed homogenizer (Black and Decker, USA) for 3 min. The mixture was centrifuged at 10,000g for 10 min at 4C and filtered through Whatman No. 2 filter paper (Sigma, USA), and the filtrates were brought to a final volume of 50 ml with TCA and stored at -50C until used. HPLC with a Lichrospher100 RP-18 reversed-phase column (5 lm, 125·4.6 mm, E. Merck, Damstadt, Germany) was used to determine the biogenic amines content. The gradient elution program was started with 50/50 (methanol: water) at a low rate of 0.8 ml/min for the 5 min then followed by a linear increase to 85/15 (methanol: water) at the same flow rate for 6.5 min. The latter protocol was held for another 5 min then decreased to 50/50 (0.8 ml/min) for the last 2 min. The standards consisted of putrescine dihydrochloride (Put), cadaverine dihydrochloride (Cad), histamine dihydrochloride (His) and tyramine dihydrochloride (Tym) (Sigma, Germany). Putrescine (91.5 mg), Cad (85.7 mg), His (82.8 mg) and Tym (63.2 mg) were prepared in 50 ml of 0.1 M HCl and used as the standard stock solution (each at 1.0 mg/ml). Before injection to HPLC, the sample and standards were derivatized and the biogenic amines contents were determined according to Tsai et al [23].

2.3.3. Sodium Chloride Content

Sodium chloride content was determined according to Egan et al [22]. Briefly, 5 g of salted fish was mixed with 10 ml of distilled water, 25 ml of standard sliver nitrate solution and 30 ml of concentrated nitric acid. The mixture was boiled for about 10 min. After cooling, 50 ml of distilled water was added and the excess of silver nitrate was titrated with 0.1N potassium thiocyanate in the presence of 5 ml of ferric alum indicator. Sodium chloride was calculated according to the following formula:

Where, B titration value used in blank, S titration value used in sample, N normality of potassium thiocyanate and W is the weight of the sample.

2.3.4. Colour

The colour of salted fish was measured using a colour meter, Minolta Chroma meter (Model CR-310, Japan) using a method followed by Rahman et al [20]. Briefly, the equipment was calibrated with a white standard calibration plate according to the manufacturer instructions. Five salted fish fillets were placed on a flat surface separately, the tip of measuring head was pointed on the sample and the colour measurement was done. Five readings for each value from each sample were recorded. The results were expressed in Hunter as L, a, and b values, where L is lightness or darkness (black L = 0; white L = 100), a the intensity of red color, and b is the intensity of yellow colour.

3. Statistical Analyses

Bacterial counts are reported as log10 CFU/g. A one-way ANOVA test was used to evaluate the effect of ambient storage on the parameters. This test was conducted in Minitab release 14 software (Minitab Inc., USA), and a level p < 0.05 was considered statistically significant. Each sample was run minimally in 2 replicates.

4. Results and Discussion

4.1. Chemical Characteristics

Salted yellowfin tuna contained water, lipid, protein and ash as 47.0 ± 2.6, 3.0 ± 1.6, 25.5 ± 2.1 and 38.6 ± 3.4 g/100 g dry fish, respectively, whereas STQ contained 49.2 ± 3.8, 2.0 ± 0.87, 25.8 ± 1.8 and 40.4 ± 4.0 g/100 g dry fish, respectively (Table 1). Water activity was 0.85 ± 0.00 and 0.79 ± 0.00 in SYT and STQ, respectively (Table 1). Lipid primary oxidation assessed by PV and AV were found 5.6 ± 1.4 meq/kg fat and 3.2 ± 1.1 respectively in SYT and 2.8 ± 1.4 meq/kg fat and 2.3 ± 0.62 respectively in STQ (Table 1). Talang queenfish was salted at 021.2 ± 0.52 % level. Colour in terms of L, a and b values were found 033.4 ± 4.4, 9.0 ± 1.6 and 014.3 ± 2.6, respectively in SYT and 45.1 ± 2.9, 10.1 ± 0.73 and 19.1 ± 1.7, respectively in STQ (Table 1). In the case of STQ when stored at ambient conditions, most of the microbial, physiochemical characteristics did not change significantly (P > 0.05), while salt content and colour a-value showed significant increase (P < 0.05) during the 10 weeks of storage (Table 4).

Yellowfin tuna and talang queenfish normally contained water from 77-69 g/100 g fish [24,25]. Water content of salted fish products reduced water by osmosis phenomenon. The low water content, e.g., 47 and 49 g/100 g fish in could reduce the juiciness of the products when reconstituted. Ash content of 38% and 40% in SYT and STQ respectively should be expected as the products were salted at a high level; thus rapid penetration of salt to the products was quite possible. Low contents of 3 % (i.e. SYT) and 2 % (i.e. STQ) lipids provided reasonable storage stability in terms of lipid oxidation as evidenced from the low PV and AV (Table 1) Lipid oxidation in term of rancidity can be noticed at PV more than 10 meq/kg [22]. The lipid stability could be further attributed to the antioxidant potential of some additives, such as thyme as previously reported [26,27].

Table 1. Physiochemical characteristics and biogenic amines content in salted fish products

Table 2. Microbial counts in salted fish products

Water activity of 0.85 and 0.79 in SYT and STQ, respectively could provide potential growth of microorganisms, especially for Gram-positive bacteria, yeasts and molds [28]. However, this factor did not support the growth of most microorganisms in the presence of other inhibitors, such as salt (i.e. 20%) and other food additives, such as spices (Table 2 and Table 4). In the current study, water activity of STQ was close to the dried fish available in the Omani market [2]. Significant salt content increased in STQ during storage could be attributed to the high water evaporation rate. Red-halophilic bacteria were found to cause the redness of the salted fish during the ambient storage [29], therefore, the significant increase in colour value a during the storage of STQ could be attributed to the growth of halophilic bacteria. This group of bacteria however, was not enumerated in the current study.

4.2. Biogenic Amines Contents

Low biogenic amines content in the salted fish products could be attributed mainly to the two factors; sodium chloride and biogenic amines degradation activity of some types of bacteria. Sodium chloride was found to inhibit the main biogenic amines producers, such as Morganilla morganii and Proteus vulgaris, which were unable to produce biogenic amines, such as histamine at sodium chloride concentration ≥10% [30]. Another possible reason for the trace amount of biogenic amines in the current study could be attributed to the biogenic amines degradation activity of certain halophilic bacteria. In fact, halophilic bacteria, such as Bacillus amyloliquefaciens , B. subtilis and B. polymyxa which were found in the current study were found to degrade histamine, cadaverine and putrescine [25,31].

4.3. Microbial Characteristics and Its Potential

4.3.1. Microbial Floral Counts

Total aerobic mesophilic bacterial and MHB counts were found to be log 2.0 ± 0.78 CFU/g and log 1.8 ± 0.11 CFU/g in SYT, respectively and in STQ, the counts of TAMB and MHB were found to be log 2.4 ± 0.44 CFU/g and 2.5 ± 0.53 CFU/g respectively (Table 2). Enterobacteriaceae, S. aureus, mesophilic lactic acid bacteria and yeasts and molds counts were less than 1 log CFU/g in both products. Vibrio parahaemolyticus was not detected in both products. Neither TAMB nor MHB did change insignificantly (P > 0.05) during the storage (Table 4).

Aerobic mesophilic bacterial count in both salted fish products indicated that both products maintained good microbial quality during handling and curing compared with log 5 CFU/g [32]. Although, traditional processing conditions could be expected to increase microbial loads in the products, the inhibitory effects of low water activity, salt and spices contributed to maintain microbial load. In fact, the antimicrobial effect of some spices, such as green pepper was reported earlier [33,34].

The current study could be the initial study to investigate MHB quantitatively and qualitatively in the salted fish products, which could provide an indication of the safety and quality of salted fish products in the Arabian Gulf region. Low MHB count in the current study could be attributed to inhibitory effect provided by additives, such as lemon. For example, Alfonzo et al [35] did not observe halophilic bacterial growth in salted sardines due to the presence of essential oil from lemon. Moderate halophilic bacterial count stability in the current study agreed with the study presented by Silvina et al [36]. The low incidence of Enterobacteriaceae and S. aureus in the current study could be attributed to the effects of initially fish environment and secondly to the inhibitory effects of salting and added thyme. Indeed, the effect of fish environment could be explained by a high incidence of Enterobacteriaceae such as E. coli, Citrobacter sp., Enteriobacter sp. and Klebsiella sp. in freshwater fish, such as Tilapia nilotica Linn, whereas incidence of Enterobacteriacea in marine fish such as these used in the current study showed low level [37].

4.3.2. Microbial Floral and Halophilic Bacterial Flora Composition

Seven genera and 26 species belonging to Psychrobacter, Bacillus, Pseudomonas, Enterobacter, Staphylococcus, Corynascus and Amesia were found in the dried fish (Figure 1). Most of these microbial genera were isolated from TSA with 10% sodium chloride. This was the initial study to explore the diversity of the microbial floral in the traditional salted fish products in the Arabian Gulf [1,2]. Among MHB, Bacillus sp. dominated the microbial flora by 12 species with the most frequent B. amyloliquefaciens and B. methylotrophicus. Bacillus sp. The dominance could be expected as this genus was found in sea environment [38]. It species such as B. amyloliquefaciens was isolated from different foods, such as salted sardines, dry cured sausages and silage [39]. The second most frequent B. methylotrophicus was also isolated from soil and cassava-based products [40]. To our best knowledge, the current study was the initial study to report the incidence of B. methylotrophicus in the salted fish. None of the found Bacillus strains in this study was previously reported to be associated with food poisoning outbreaks.

4.3.3. Halophilic Bacterial Potential

Different halophilic Bacillus species showed good antimicrobial, amino acids decarboxylation, lipolytic and proteolytic activities potential (Table 3). For instance, B. amyloliquefaciens showed remarkable antimicrobial activity against Enterococcus faecalis, S. aureus and E. coli, decarboxylation of tyrosine, lysine, histidine and ornithine and lipolytic activity. The antimicrobial activity of B. amyloliquefaciens found in this current study was similar as observed in different strains of B. amyloliquefaciens against wide ranges of pathogens such as Staphylococcus aureus and Escherichia coli [41,42,43].

Moreover, lipolytic activity of this specie agreed with the different strains of B. amyloliquefaciens such as SA26, SA35, SA37, SA39 and SA43 [44]. Bacillus siamensis showed similar potential to that of B. amyloliquefaciens. In addition, absence and low incidence of pathogens such as Enterobacteriaceae, S. aureus and Vibrio parahaemolyticus could be attributed to antimicrobial activity of certain Bacillus species, such as B. amyloliquefaciens and B. siamensis.

Figure 1. Microbial diversity and frequency in salted fish products

Table 3. Antimicrobial, amino acid decarboxylation, lipolytic and proteolytic activities of moderate halophilic Bacillus sp. isolated from salted fish products

Table 4. Changes in microbial and physiochemical characteristics of salted talang queenfish during ambient storage

5. Conclusion

Salted yellowfin tuna and STQ loaded with 1 to 3 log CFU/g of total and halophilic bacteria. Enterobacteriaceae, S. aureus, mesophilic lactic acid bacteria, yeasts and molds. However, Vibrio parahaemolyticus did not observe. All chemical parameters, such as lipids and biogenic amines were found in low levels. High diversity in the bacterial floral composition was found with 26 bacterial species. Halophilic bacterial flora analysis revealed the dominancy of Bacillus sp. with the most frequent species of B. amyloliquefaciens and B. methylotrophicus. These showed antimicrobial activity against En. faecalis, S. aureus and E. coli, decarboxylation of tyrosine, lysine, histidine and ornithine, and lipolytic potential. Most of the STQ characteristics showed storage stability for 10 weeks. Low total bacterial, Enterbacteriaceae and S. aureus counts, absence of V. parahaemolyticus and traced biogenic amines contents ensured the safety and good microbial quality of salted fish. However, salted yellowfin tuna and STQ need to be studied more to ensure its safety from the chemical hazards such as nitrosamines and heavily metals. In addition, maximum shelf-life needs to be studied. This is the initial study to analyze the composition of halophilic bacterial flora in SYT and STQ and document the incidence of B. methylotrophicus in salted fish.

Acknowledgements

SQU-UAEU Joint fund (CL\SQU-UAE\15\03) for finance support and Central Analytical and Applied Research Unit for technical assistance in bacterial identification.

Conflicts of Interest

The authors declare that there are no conflicts of interests.

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