Chemical characterisation and histamine-forming bacteria in salted mullet roe products

Sixteen salted mullet roe products sold in the retail markets in Taiwan were purchased and tested to determine the occurrence of histamine and histamine-forming bacteria. The levels of pH, salt content, water content, total volatile basic nitrogen (TVBN) and aerobic plate count (APC) in all samples ranged from 5.4 to 5.8, 5.1% to 7.2%, 15.4% to 27.3%, 32.0 to 69.6 mg/100 g and <1.0 to 7.1 log CFU/g, respectively. None of these samples contained total coliform and Escherichia coli. The average content of each of the nine biogenic amines in all samples was less than 4 mg/100 g, and only one mullet roe sample had the histamine content (8.18 mg/100 g) greater than the 5.0 mg/100 g allowable limit suggested by the US Food and Drug Administration. Two histamine-producing bacterial strains capable of producing 10.7 ppm and 9.6 ppm of histamine in trypticase soy broth (TSB) supplemented with 1.0% l-histidine (TSBH) were identified as Staphylococcus carnosus by 16S rDNA sequencing with PCR amplification, and they were isolated from the sample with higher histamine content (8.18 mg/100 g).     

Histamine formation by histamine-forming bacteria and yeast in mustard pickle products in Taiwan

The occurrence of histamine, histamine-forming bacteria and yeast were tested in 37 mustard pickle products sold in both retail markets and supermarkets in southern Taiwan. Aerobic plate count (APC), total coliform, and Escherichia coli were also tested for microbiological quality. Salt content, pH value, titratable acidity and sulphite content were determined for quality of mustard pickle products. Only one retail market sample and one supermarket sample had 8.9 and 7.4 mg histamine per 100 g products, although the average content for each of the nine biogenic amines was less than 2 mg/100 g. Ten histamine-forming bacterial strains and 6 histamine-producing yeast strains capable of producing 8.7 to 1260 ppm of histamine in trypticase soy broth (TSB) supplemented with 1% l-histidine (TSBH) were identified as Staphylococcus capitis (four strains),Staphylococcus pasteuri (two strains), Enterobacter cloacae (four strains), Candida glabrata (two strains) and Candida rugosa (four strains). S. capitis, which was previously reported to be halotolerant, was a potent histamine-former, capable of producing more than 1000 ppm of histamine in TSBH in the presence of 0.5–10% NaCl. The numbers of the aerobic plate count (APC) in all samples were below the Taiwanese regulatory level of 5 log CFU/g. None of the samples contained total coliform or E. coli. The values of pH, salt content, titratable acidity and sulphite content in all samples ranged from 3.8% to 5.0%, 2.0% to 10.0%, 0.21% to 1.18% and <2.0–1876 ppm, respectively.     

Histamine formation by histamine-forming bacteria in douchi,a Chinese traditional fermented soybean product

Seven soybean and 19 black bean douchi products sold in the supermarkets in southern Taiwan were purchased and tested to determine the occurrence of histamine and histamine-forming bacteria. The levels of pH, salt content, water content, yeast and mold, and aerobic plate count (APC) in all samples ranged from 4.7 to 5.9, 4.4% to 14.0%, 6.8% to 51.6%, 3.0 to 5.1 log CFU/g, and 5.2 to 9.2 log CFU/g, respectively. None of these samples contained total coliform and Escherichia coli. Although black bean douchi products had an average histamine content of 29.0 mg/100 g, 18 of them had histamine contents greater than 5 mg/100 g, the allowable level set by the US Food and Drug Administration (FDA) for scombroid fish and/or products. In contrast, only four soybean douchi products had histamine levels greater than 5 mg/100 g. Among the black bean samples, four contained histamine at 56.3, 62.1, 80.2 and 80.8 mg/100 g, that are above the 50 mg/100 g hazard action level. Eight histamine-forming bacterial strains, capable of producing 11.7–601 ppm of histamine in trypticase soy broth (TSB) supplemented with 1% l-histidine (TSBH), were identified as Bacillus subtilis (four strains) Staphylococcus pasteuri (one strain) and Staphylocuccus capitis (three strains) by 16S rDNA sequencing with PCR amplification. S. capitis, which was previously reported to be halotolerant, was a potent histamine-former capable of producing more than 500 ppm of histamine in TSBH in the presence of 0.5–10% NaCl.     

Histamine and other biogenic amines and histamine-forming bacteria in miso products

Twenty-seven miso products sold in supermarkets and 13 products sold in retail markets were purchased from southern Taiwan, and tested to determine the occurrence of histamine and histamine-forming bacteria. The levels of pH, salt content, and aerobic plate count (APC) in all samples ranged from 5.1 to 5.8, 6.1% to 13.8%, and 2.1 to 9.1 log CFU/g, respectively. Only one of the supermarket miso products contained 100 MPN/g total coliform. None of these samples contained Escherichia coli. Although the average content for each of the nine biogenic amines in all samples was less than 5 mg/100 g, two supermarket samples (22.1 and 11.9 mg/100 g) and one retail market sample had histamine content (10.2 mg/100 g) greater than the 5.0 mg/100 g allowable limit suggested by the US Food and Drug Administration. Eight histamine-producing bacterial strains, capable of producing 10.4–39.4 ppm of histamine in trypticase soy broth (TSB) supplemented with 1.0% l-histidine (TSBH), were identified as Staphylococcus pasteuri (one strain), Bacillus sp. (one strain), B. amyloliquefaciens (two strains), B. subtilis (two strains) and B. megaterium (two strains), by 16S rDNA sequencing with PCR amplification.     

Histamine content and histamine-forming bacteria in dried milkfish (Chanos chanos) products

Thirty-two dried milkfish products sold in five retail markets in southern Taiwan were purchased and tested to determine the occurrence of histamine and histamine-forming bacteria. Except for histamine and cadaverine, the average content of various biogenic amines in tested samples was less than 8.5 mg/100 g. Most of the tested dried milkfish products (78.1%) had histamine levels greater than the FDA guideline of 5 mg/100 g for scombroid fish and/or product, while fourteen of them (43.7%) contained > 50 mg/100 g hazard action level. Thirty histamine-producing bacterial strains, capable of producing 5.4 ppm to 562 ppm of histamine in trypticase soy broth supplemented with 1.0% L-histidine (TSBH), were identified as Enterobacter aerogenes (seven strains), Citrobacter sp. (one strain), Staphylococcusxylosus (ten strains), S. sciuri (one strain), Bacillus thuringiensis (two strains), Citrobacter freundii (five strains), Klebsiella pneumoniae (one strain) and E. cloacae (three strains), by 16S rDNA sequencing with PCR amplification.     

Histamine contents of fermented fish products in Taiwan and isolation of histamine-forming bacteria

Twenty-seven imported fermented fish products from Southeast Asian countries and sold in the supermarkets in Taiwan, including fish sauce, fish paste and shrimp paste, were tested to determine the occurrence of histamine and histamine-forming bacteria. The levels of pH, salt content, total volatile basic nitrogen, trimethylamine, and aerobic plate count in all samples ranged from 4.8% to 6.5%, 16.2% to 45.3%, 51 to 275 mg/100 g, 5.4 to 53.9 mg/100 g and 1.0 to 4.2 log CFU/g, respectively. The average content for each of eight different biogenic amines in all samples was less than 90 ppm, except for histamine which has an average content of 394 ppm in fish sauce, 263 ppm in fish paste, and 382 ppm in shrimp paste. Most of the tested fermented fish products (92.6%) had histamine levels greater than the FDA guideline of 50 ppm, while seven of them (25.9%) contained >500 ppm of histamine. Although Bacillus coagulans and Bacillus megaterium were identified as the two histamine-producing bacteria capable of producing 13.7 and 8.1 ppm of histamine, respectively, in trypticase soy broth broth supplemented with 1.0% l-histidine, they were not determined to be the main contributors to histamine accumulation in these fermented fish products.     

Determination of histamine and histamine-forming bacteria in tuna dumpling implicated in a food-borne poisoning

An incident of food-borne poisoning causing illness in seven victims, due to ingestion of tuna dumpling, occurred in March 2006, in Chiayi Prefecture, southern Taiwan. The leftovers of the victims’ tuna dumpling and the five other tuna dumpling samples from five other retail stores were collected and tested to determine the occurrence of histamine and histamine-forming bacteria. The levels of pH, salt content, aerobic plate count (APC), total volatile basic nitrogen (TVBN), total coliform (TC) and Escherichia coli in all samples ranged from 6.08 to 6.43, 0.46% to 0.81%, 5.90 to 8.95 log CFU/g, 6.38 to 21.29 mg/100 g, 750 to 8000 most probable number (MPN)/g, and <3 to 1000 MPN/g, respectively. The suspected tuna dumpling contained 160.8 mg/100 g of histamine greater than the hazard action level of 50 mg/100 g set by the US Food and Drug Administration (FDA) for tuna fish. Given the allergy-like symptoms of the victims and the high histamine content in the suspected tuna dumpling, this food-borne poisoning was strongly suspected to be due to histamine intoxication. In addition, although thirteen histamine-producing bacteria strains capable of producing 8.1–19.7 ppm of histamine in trypticase soy broth (TSB) supplemented with 1.0% l-histidine (TSBH), were identified as Enterobacter sp. (three strains), Pantoea agglomerans (two strains), Klebsiella variicola (four strains) and Serratia marcescens (four strains), by 16S rDNA sequencing with PCR amplification, they were not determined to be the main contributors to histamine accumulation in suspected tuna dumpling.     

Histamine production by Enterobacter aerogenes in tuna dumpling stuffing at various storage temperatures

Enterobacter aerogenes was studied for its growth, and promoting the formation of total volatile base nitrogen (TVBN) and histamine in tuna dumpling stuffing stored at various temperatures from −20 °C to 37 °C. The bacterial number rapidly increased in low (2.0 log CFU/g) or high (5.0 log CFU/g) inoculated concentrations at temperature above 15 °C and reached the highest bacterial count at 37 °C. In addition, the low spiked sample stored at 37 °C for 12 h and the high spiked sample stored at 25 and 37 °C for 12 h, formed histamine at above 50 mg/100 g of the potential hazard level in most illness cases. However, bacterial growth was controlled by cold storage of the samples at 4 °C or below, but histamine formation was stopped only by frozen storage. Once the frozen stuffing samples were thawed and stored at 25 °C, histamine started to accumulate rapidly.     

Occurrence of histamine and histamine-forming bacteria in salted mackerel in Taiwan

Thirty-three samples of salted mackerel sold in retail markets and supermarkets in Taiwan were tested to determine the occurrence of histamine and histamine-forming bacteria. The numbers of aerobic plate count (APC) in all samples were below the Taiwanese regulatory level of 6.47 log cfu/g. The levels of pH, salt content, and total coliform in all samples ranged from 5.7 to 6.4, 5.0 to 18.1%, and <3 to 60 most probable number (MPN)/g, respectively. None of these samples contained Escherichia coli. However, eight of the 33 samples (24.2%) had unacceptable levels of total volatile basic nitrogen (TVBN), based on Taiwanese standard for TVBN in seafood products. Although the average content for each of the nine biogenic amines in all samples was less than 3 mg/100 g (30 ppm), two of the 18 samples collected from southern Taiwan contained 70.1 and 120.2 ppm of histamine, which are more than the 50 ppm allowable limit suggested by the US Food and Drug Administration. Of the 40 presumtive histamine-forming bacterial colonies isolated on the differential agar plates for the test samples, 4 strains produced histamine, ranging from 18.3 to 21.0 ppm, in TSBH broth supplemented with 2% L-histidine. These histamine-producing bacteria were identified as Pantoea sp. (2 strains), Pantoea agglomerans (1 strain), and Enterobacter cloacae (1 strain).     

Histamine level and species identification of billfish meats implicated in two food-borne poisonings

Two incidents of food-borne poisonings, causing illness in 59 and 43 victims due to ingestion of billfish meats, occurred in May 2004, in Pingtung, southern Taiwan and in December 2004, Taichung, central Taiwan, respectively. One fried billfish fillet and five frozen billfish fillet samples collected, respectively, from the suspected restaurants in Pingtung and Taichung, respectively, were tested to determine the histamine levels and identify fish species. Analyses of histamine showed that the suspected billfish samples in two food poisonings contained more than 150 mg/100 g of histamine, which is higher than the hazard action level of 50 mg/100 g. Judging from the allergy-like symptoms of the victims and the high histamine levels in the suspected billfish samples, both food-borne poisonings were strongly suspected to be caused by histamine intoxication. A polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method was used to identify the species of the suspected billfish samples in both food poisonings. The 348 bp amplified fragment of the mitochondrial cytochrome b gene by PCR was digested with BsaJI, Cac8I and HpaII enzymes to distinguish the species of the suspected billfish samples. Consequently, the species of Pingtung and Taichung billfish samples implicated in food poisonings were identified as Makaira nigricans and Xiphias gladius, respectively.     

An amperometric biosensor for the rapid assessment of histamine level in tiger prawn (Penaeus monodon) spoilage

Histamine could accumulate in seafood when bacteria spoilage commenced and caused histamine poisoning without altering the fish normal appearance and odor. Therefore, a histamine biosensor using immobilized enzyme diamine oxidase (DAO) has been developed for the rapid monitoring of the histamine levels in tiger prawn (Penaeus monodon). The histamine biosensor had a response time of <1 min and optimum pH of operation was 7.4 with reproducibility and repeatability (n = 5) of 4.87% and 5.26% relative standard deviations (RSD) respectively. Recoveries ranging from 93.11% to 100.58% were obtained for histamine spiked at levels from 5 to 20 ppm. The variation in histamine levels of some tiger prawn samples after a 5-h exposure at temperature of 30 °C ± 2 were studied using the histamine biosensor and the results were comparable to histamine levels determined by an HPLC method. The two methods showed a linear correlation with R² = 0.9612 (Y = 0.9164x + 5.58). The limit of detection was 0.65 ppm of histamine, which is below the indicator level of 50 ppm established by USA FDA. The reusable biosensor is simple and can be used for direct histamine determination without further sample pretreatment, and is suitable for the routine analysis of histamine in tiger prawns to monitor spoilage.     

Histamine production by bacilli bacteria, acetic bacteria and yeast isolated from fruit wines

Eleven red wines imported from foreign country and 40 domestic fruit wines, including 15 red wines, 4 white wines, 7 plum wines, and 14 other fruit wines, sold in the supermarkets in Taiwan were purchased and tested to determine the occurrence of biogenic amines and histamine-forming bacteria. The levels of pH, total soluble solids (TSS), titratable acidity (TA), reducing sugar (RS), total sugar (TS), sulphites, methanol (milligram per liter of pure ethanol), ethanol and Pb in all samples ranged from 3.0 to 4.1, 6.8 to 24.4 °Brix, 0.3 to 1.7 g/100 mL, 0.2 to 17.6 g/100 mL, 1.6 to 28.4 g/100 mL, <2 to 260.5 mg/L, <1 to 2559 mg/L, 5.0 to 15.6 g/100 mL and <1 to 46.2 μg/L, respectively. The levels of TSS, TA, RS, and TS in plum wine samples were significantly higher than those of the other wines samples, whereas the pH value in plum wine samples was lower than that of the other wines samples. The average content for each of the nine biogenic amines in all samples was less than 5.2 mg/L. However, higher levels of histamine and spermine were detected in domestic fruit wine samples than the imported red wine samples. Five histamine-forming isolates isolated from domestic red wine and jackfruit wine, capable of producing 13.0 mg/L to 69.1 mg/L of histamine in trypticase soy broth (TSB) supplemented with 2 g/100 mL l-histidine (TSBH) or MRS broth supplemented with 2 g/100 mL l-histidine (MRSH), were identified as Bacillus pumilus (one strain), Bacillus sp. (two strains) and Acetobacter pasteurianus (one strain) by 16S rDNA sequencing with PCR amplification, and Zygoascus hellenicus var. hellenicus (one strain) by internal transcribed spacer sequencing with PCR amplification. To our knowledge, this is the first report to demonstrate the occurrence of histamine-forming bacilli bacteria, acetic bacteria and yeast in fruit wine.     

Sensory,microbiological and chemical assessment of the freshness of red mullet (Mullus barbatus) and goldband goatfish (Upeneus moluccensis) during storage in ice

The shelf life of red mullet and goldband goatfish during ice storage were studied in terms of sensory, microbiological and chemical changes. The sensory acceptability limit was 8 days for goldband goatfish (Upeneus moluccensis) and 11 days for red mullet (Mullus barbatus) stored in ice. The TVC level was correlated with sensory assessment. The TVC exceeded 7 log cfu g⁻¹ after 8 days for goldband goatfish, and 11 days for red mullet. At the end of storage period, pH, TVB-N, TBA, FFA and PV for red mullet were 7.84, 47.19 mg/100 g, 0.69 mg MA kg⁻¹, 1.17% oleic acid and 1.58 meq O₂/kg and for goldband goatfish they were 7.53, 43.97 mg/100 g, 0.74 mg MA kg⁻¹, 1.62% oleic acid and 1.68 meq O₂/kg, respectively. In red mullet, agmatine, serotonin, histamine and dopamine became the dominant amines, reaching 7.30, 5.97, 2.52 and 2.31 mg/100 g, respectively. Also the dominant amines for goldband goatfish were 4.37, 3.88, 3.38 and 2.00 mg/100 g for histamine, agmatine, dopamine and putrescine, respectively.     

Proteinase-producing halophilic lactic acid bacteria isolated from fish sauce fermentation and their ability to produce volatile compounds

Halophilic lactic acid bacteria were isolated from fish sauce mashes fermented at 1 to 12 months. Seven out of sixty-four isolates were selected according to their proteolytic activity and growth at 25% NaCl for characterization and investigation of volatile compound production. All selected isolates were Gram-positive cocci with pairs/tetrads and grew at 0-25% NaCl, pH 4.5-9.0. Results of 16S rRNA gene sequence analysis showed 99% homology to Tetragenococcus halophilus ATCC 33315. The restriction fragment length polymorphism (RFLP) patterns of all isolates were also similar to those of T. halophilus ATCC 33315. These isolates were, thus, identified as T. halophilus. All isolates hydrolyzed fish protein in the medium containing 25% NaCl. Intracellular aminopeptidase of 7 isolates exhibited the highest activity of 2.85-3.67 U/ml toward Ala-p-nitroanilide (Ala-pNA). T.halophilus strains MS33 and M11 showed the highest alanyl aminopeptidase activity (P < 0.05), and produced histamine in mGYP broth containing 5 and 25% NaCl in the level of 6.62-22.55 and 13.14-20.39 mg/100 ml, respectively. Predominant volatile compounds of fish broth containing 25% NaCl inoculated with T. halophilus MS33 and MRC5-5-2 were 1-propanol, 2-methylpropanal, and benzaldehyde, corresponding to major volatile compounds in fish sauce. T.halophilus appeared to play an important role in volatile compound formation during fish sauce fermentation.     

Characterisation of histamine-producing bacteria from farmed blackspot seabream (Pagellus bogaraveo) and turbot (Psetta maxima)

Turbot (Psetta maxima) and blackspot seabream (Pagellus bogaraveo) represent two of the most important emerging farmed fish species in European countries. However, no information of the presence and development of histamine-producing bacteria on them has been reported so far. Accordingly, the aim of this study was to isolate and identify the main histamine-producing bacteria in farmed turbot and blackspot seabream. For this study, 24 isolates (12 from turbot and 12 from blackspot seabream) were preliminarily selected on Niven medium. Two of these isolates were confirmed as prolific histamine producers by HPLC. Thus, Pseudomonas fragi (isolated from turbot) and Pseudomonas syringae (isolated from blackspot seabream) were able to produce 272 ± 69 ppm and 173 ± 45 ppm of histamine in vitro, respectively, after incubation at 30 °C/24 h. While turbot fillets proved to be quite resistant to histamine formation at temperatures below 10 °C, blackspot seabream fillets inoculated with P. syringae and the prolific histamine former Morganella morganii accumulated 696 ± 84 and 760 ± 59 ppm histamine, respectively, under such conditions. Genetic identification based on 16S rRNA sequencing was performed in parallel with the investigation of characteristic mass spectral profiles of the isolates by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS). The MALDI-TOF MS analyses provided species-specific fingerprints, which allow rapid identification and classification of the isolates. Six genus-specific mass peaks in the range of 2218-4434 m/z were shared by both strains. Bacterial identification was achieved by the identification of six species-specific mass peaks in the ranges of 2534-7183 m/z and 2536-9113 m/z for P. fragi and P. syringae, respectively.     

Toxic compounds in essential oils of coriander, caraway and basil active against stored rice pests

Essential oils, distilled from seeds of Coriander sativum and Carum carvii and from leaves of five different varieties of Ocimum basilicum, were fractionated by column chromatography and tested in the laboratory for volatile toxicity against three stored rice pests (Sitophilus oryzae, Rhyzopertha dominica and Cryptolestes pusillus). The active fractions were analyzed by GC-MS. Coriander contained linalool (1617 ppm of the oil) as the main product active against the three pests. Camphor-rich fractions (over 400 ppm) were very toxic to R. dominica and C. pusillus. The caraway profile included carvone and limonene as expected but (E)-anethole, generally regarded as a minor product in the essential oil of this species, was also a major component, being present at 365 ppm. Carvone was the most effective (972 ppm) monoterpenoid against S. oryzae. In addition, (E)-anethole at 880 ppm was toxic to R. dominica while vapors of limonene (1416 ppm) and fenchone-rich (554 ppm) fractions killed adults of C. pusillus only. Three major essential oil profiles were present in the five varieties of O. basilicum analyzed: methyl eugenol/estragole, estragole and estragole/linalool chemotypes. The abundance of components had a strong influence on the outcome of the bioassays. Fractions, where combinations of products occurred with or without other minor compounds, were often more toxic than any one compound alone.     

The effect of sodium reduction with and without potassium chloride on the survival of Listeria monocytogenes in Cheddar cheese

Sodium chloride (NaCl) in cheese contributes to flavor and texture directly and by its effect on microbial and enzymatic activity. The salt-to-moisture ratio (S/M) is used to gauge if conditions for producing good-quality cheese have been met. Reductions in salt that deviate from the ideal S/M range could result in changing culture acidification profiles during cheese making. Lactococcus lactis ssp. lactis or Lc. lactis ssp. cremoris are both used as cultures in Cheddar cheese manufacture, but Lc. lactis ssp. lactis has a higher salt and pH tolerance than Lc. lactis ssp. cremoris. Both salt and pH are used to control growth and survival of Listeria monocytogenes and salts such as KCl are commonly used to replace the effects of NaCl in food when NaCl is reduced. The objectives of this project were to determine the effects of sodium reduction, KCl use, and the subspecies of Lc. lactis used on L. monocytogenes survival in stirred-curd Cheddar cheese. Cheese was manufactured with either Lc. lactis ssp. lactis or Lc. lactis ssp. cremoris. At the salting step, curd was divided and salted with a concentration targeted to produce a final cheese with 600 mg of sodium/100 g (control), 25% reduced sodium (450 mg of sodium/100 g; both with and without KCl), and low sodium (53% sodium reduction or 280 mg of sodium/100 g; both with and without KCl). Potassium chloride was added on a molar equivalent to the NaCl it replaced to maintain an equivalent S/M. Cheese was inoculated with a 5-strain cocktail of L. monocytogenes at different times during aging to simulate postprocessing contamination, and counts were monitored over 27 or 50 d, depending on incubation temperature (12 or 5°C, respectively). In cheese inoculated with 4 log₁₀ cfu of L. monocytogenes/g 2 wk after manufacture, viable counts declined by more than 3 log₁₀ cfu/g in all treatments over 60 d. When inoculated with 5 log₁₀ cfu/g at 3 mo of cheese age, L. monocytogenes counts in Cheddar cheese were also reduced during storage, but by less than 1.5 log₁₀ cfu/g after 50 d. However, cheese with a 50% reduction in sodium without KCl had higher counts than full-sodium cheese at the end of 50 d of incubation at 4°C when inoculated at 3 mo. When inoculated at 8 mo postmanufacture, this trend was only observed in 50% reduced sodium with KCl, for cheese manufactured with both cultures. This enhanced survival for 50% reduced-sodium cheese was not seen when a higher incubation temperature (12°C) was used when cheese was inoculated at 3 mo of age and monitored for 27 d (no difference in treatments was observed at this incubation temperature). In the event of postprocessing contamination during later stages of ripening, L. monocytogenes was capable of survival in Cheddar cheese regardless of which culture was used, whether or not sodium had been reduced by as much as 50% from standard concentrations, or if KCl had been added to maintain the effective S/M of full-sodium Cheddar cheese.     

Quality assessment of wild European eel (Anguilla anguilla) stored in ice

The quality assessment of wild European eel (Anguilla anguilla) stored in ice and in boxes without ice (3 ± 1 °C) was investigated by the sensory analysis, levels of nucleotide breakdown products and biogenic amines for up to 19 days. Sensory analysis was assessed using the Tasmanian Food Research Unit Scheme. K and related values (K_i, G, P, H and F_r) were used as freshness indicators. Linear regressions (r²) obtained from K, K_i, G, P, H and F_r were 0.95, 0.96, 0.83, 0.96, 0.99 and 0.96, respectively, for eel stored in ice whereas, for eel kept in boxes without ice, the values were 0.86, 0.86, 0.96, 0.91, 0.98 and 0.86, respectively. When eel stored in ice and in boxes without ice were considered at the limit of acceptability by assessors at ∼12–14 days and ∼5–7 days, respectively, the average K, K_i and P values were ∼70–85%, H values were ∼60% and F_r values were ∼10% for both storage conditions. The level of histamine exceeded the legal limit (5 mg/100 g fish) in eel stored without ice after 6–7 days and, in ice, after 13–14 days of storage, at which time eels were rejected by the sensory panel. The concentrations of biogenic amines were higher in eel stored in boxes without ice than in eel kept in ice. The levels of histamine in the muscle of eel kept in boxes without ice and in ice increased to the maximum levels of 17.9 mg/100 g on day 12 and 12.6 mg/100 g on day 19, respectively.     

Histamine levels in seventeen species of fresh and processed South African seafood

Histamine levels were determined in fresh and processed seafood from a representative range of 10 outlets after several incidents of scombroid seafood poisoning occurred. Species included seventeen fresh and processed scombroid- and non-scombroid fish, marine mollusks and crustaceans. Histamine levels in fresh seafood were generally low (0–9 ppm) with the exception of one sample of snoek (scombroid fish; >50 ppm) and one sample of yellowtail (non-scombroid fish; >50 ppm). Both species are rich in free histidine (1.5–5.3 ppb), a precursor of histamine. Processed seafood had, in general, low histamine concentrations (0–3 ppm) with the exception of fish meal (76 ppm), salted herring (47 ppm), one sample of smoked snoek (>50 ppm) and dried tuna (8000 ppm). In total, 5 of 80 examined samples (6%) contained histamine concentrations above the legal limit of 50 ppm. Experimental formation of histamine was demonstrated to be strongly temperature- and time-dependent. Samples were not contaminated with Vibrio spp., Pseudomonas spp., Klebsiellas spp. or Enterobacteria.     

Organic acids,antioxidant capacity,phenolic content and lipid characterisation of Georgia-grown underutilized fruit crops

Four underutilized Georgia-grown fruit crops, namely loquat (Eriobotrya japonica), mayhaw (Crataegus sp.), fig (Ficus carica), and pawpaw (Asimina triloba), and their leaves were analysed for total polyphenols by Folin–Ciocalteau method, and antioxidant capacity by ferric-reducing antioxidant power (FRAP) and Trolox-equivalent antioxidant capacity (TEAC) assays. Organic acids and phenolic compounds were identified by RP-HPLC. For lipid profile, fruits were separated into two fractions – seed and fruit (i.e., without seed); lipid was extracted using the Folch method and analysed for fatty acids, phytosterols, tocopherols, and phospholipids. The major organic acid identified in all samples was malic acid (177–1918 mg/100 g FW). The predominant phenolic acids in all the fruits were gallic (1.5–6.4 mg/100 g FW) and ellagic (0.2–33.8 mg/100 g FW), and the most abundant flavonoid was catechin (12.2–37.8 mg/100 g FW). Total lipid content varied from 0.1% in mayhaw fruit to 21.5% in pawpaw seed. Linoleic acid was the predominant fatty acid in all of the samples (28.2–55.7%).