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Effects of high pressure processing (HPP) under 300, 400, 500 and 600 MPa for 5 min on microbiological growth and histamine content of spotted mackerel meats stored at 4 oC were evaluated. It was also found that the L* (lightness), ΔE (color difference), and texture (hardness, cohesiveness and chewiness) of fish meat increased significantly with an increase in pressure, but a* (redness) value decreased. With an increase of pressure, the loads of aerobic plate count (APC), psychrotrophic bacteria count (PBC), H2S-producing bacteria count and coliform in mackerel meat significantly decreased. In addition, HPP significantly delayed the growth of APC and PBC during refrigerated storage for 15 days. Pressure up to 300 MPa significantly inhibited total volatile basic nitrogen (TVBN) and histamine formation, compared to control sample during storage. The results pointed to that the pressurization at least 300 MPa for 5 min on mackerel meat could extend shelf-life during refrigerated storage.

This study aimed to assess the use of the high-hydrostatic-pressure (HHP) method (200–600 MPa, 5 min) for bleaching mustard pickle products as an alternative to the conventional method of sulfite addition. The aerobic plate count (APC) and lactic acid bacteria count (LAB) of the samples decreased with the increase in pressure, and the yeast count decreased to no detectable levels. Next, compared with the control group (no high-pressure treatment) the L* (lightness), W (whiteness), ΔE (color difference), and texture (hardness and chewiness) of the HHP-processed samples, which increased significantly with increasing pressure, while the a* (redness) and b* (yellowness) values decreased slightly. This indicates that HHP processing gave the mustard pickle a harder texture and a brighter white color and appearance. Furthermore, when the mustard pickle was treated with HHP 400 and 600 MPa for 5 min and stored at 25 °C for 60 days, it was found that the APC and LAB counts in the HHP-processed group recovered rapidly and did not differ from those in the control group (the non-HHP treated group) but significantly delayed the growth of yeast, the increase in pH value, and total volatile basic nitrogen (TVBN). The high-throughput sequencing (HTS) analysis revealed that the predominant bacterial genera in the non-HHP-treated mustard pickle were Lactiplantibacillus (74%), Lactilactobacillus (12%), and Levilactobacillus (6%); after 60 days of storage, Companilactobacillus (80%) became dominant. However, after 60 days of storage, Lactiplantibacillus (92%) became dominant in the samples processed at 400 MPa, while Levilactobacillus (52%), Pediococcus (17%), and Lactiplantibacillus (17%) became dominant in the samples processed at 600 MPa. This indicated that the HHP treatment changed the lactic acid bacterial flora of the mustard pickle during the storage period. Overall, it is recommended to treat the mustard pickle with HHP above 400 MPa for 5 min to improve its texture and color and delay the deterioration of quality during storage. Therefore, HHP technology has the potential to be developed as a treatment technique to replace the addition of sulfite.

A second generation and scaled-up equipment, named Aligo-2TM (microwave-assisted induction heating, MAIH) with a sample capacity of approximately 1.0 L was designed and invented by Bottle Top Machinery Co., Ltd., Taiwan. Pre-packaged raw shrimps were heated in a scaled-up system using heating temperatures of 130 °C and 90 °C for 80 to 150 s, and the physicochemical and microbial qualities were evaluated. The total plate count, psychrotrophic bacteria count, and coliform levels decreased as heating time increased, whereas the cooking loss, color (L*, a*, and W) value, and texture increased. When shrimps were heated for the longest time of 120 s at 130 °C or 150 s at 90 °C, they displayed obvious overcooked, shrunken, and dry appearance. To obtain samples that showed a red color, cooked well, and had no microbial count, better heating conditions for the processing of pre-packaged shrimps via the MAIH scale-up system were 130 °C for 100 s or 90 °C for 130 s. This novel and scaled-up MAIH equipment provides shrimp to be cooked after being packed, thereof avoiding the post-contamination problem.

The microwave-assisted induction heating (MAIH) method—an emerging thermal technique—was studied to heat the prepackaged raw hard clam (Meretrix lusoria). The cooking effects on microbial and physiochemical qualities of clam were investigated. After the heating of the clam meat samples, the aerobic plate count (APC), psychrotrophic bacteria count (PBC), and total volatile basic nitrogen (TVBN) levels decreased with increasing heating time, but the shucking ratio, area shrinkage, and texture (hardness, cohesiveness, and chewiness) increased. In addition, the L* (lightness) and W (whiteness) of the clam meat samples increased significantly at the beginning of the heating period, whereas they decreased significantly with extended heating time. However, a* (redness) had the opposite trend. This study found that when clams were heated for more than 120 s at 130 °C or 150 s at 90 °C, they displayed obvious shrinking and a yellow-brown appearance, indicating that they are overcooked. After heating by MAIH for at least 110 s at 130 °C or 130 s at 90 °C, the samples were cooked well and gains a completely shucking, along with no microbial count detected. Therefore, the results indicated that the optimum heating conditions for prepackaged hard clams subjected to an MAIH machine were 130 °C for 110 s or 90 °C for 130 s.

The effect of polyethylene packaging (PEP) in air cushion and vacuum packaging (VP) on histamine related to the quality of Japanese Spanish mackerel (JS mackerel) was studied with samples stored at -20, 4, 15, and 25°C. The aerobic plate count (APC), total volatile basic nitrogen (TVBN), and histamine concentrations of the PEP and VP samples stored at 25°C increased as the storage time continued. The PEP and VP samples stored at temperatures below 15°C showed lower levels of APC, TVBN, and histamine, with VP samples having considerably lower levels of APC, TVBN, and histamine than PEP samples. For the frozen JS mackerel stored at -20°C for 2 months and then thawed and stored at 25°C, the VP treatment delayed the increases of TVBN and histamine longer than did the PEP treatment. Thus, the storage of VP JS mackerel at temperatures below 4°C could prevent quality deterioration and extend shelf life.

An incident of foodborne poisoning causing illness in seven victims due to ingestion of fried Japanese Spanish mackerel (JS mackerel; Scomberomorus niphonius) meat occurred in September 2014 in Hualien County, eastern Taiwan. Of the two suspected fish meats, one raw sample contained 3,318 ppm of histamine and one fried sample contained 1,906 ppm of histamine, levels which are greater than the potential hazard action level (500 ppm) in most illness cases. Given the allergy-like symptoms of the victims and the high histamine content in the suspected fish samples, this foodborne poisoning was strongly suspected to be caused by histamine intoxication. In addition, five histamine-producing bacterial strains isolated from suspected raw fish samples, capable of producing 152 to 1,020 ppm of histamine in Trypticase soy broth supplemented with 1.0% l-histidine, were identified as Hafnia alvei (one strain), Enterobacter aerogenes (two strains), Raoultella ornithinolytica (one strain), and Morganella morganii (one strain) by 16S rDNA sequencing with PCR amplification. Moreover, 12 raw fish samples and 39 fried fish samples from retail stores were collected and tested to determine the occurrence of histamine. Two of 12 commercial raw fish samples (16.7%) had histamine levels greater than the U.S. Food and Drug Administration guideline for decomposition of 50 ppm for scombroid fish or product or a combination of both. To our knowledge, this is the first report in Taiwan to demonstrate that the JS mackerel meat products could cause histamine intoxication.

Microwave-assisted induction heating (MAIH) is an emerging alternative technology for shrimp cooking over traditional heating technologies. This study evaluated the effect of the MAIH and boiling in salt solution on the quality and shelf life of prepackaged Pacific white shrimp Litopenaeus vannamei stored at 4 °C in Taiwan. Samples were treated for 80 s at 130 °C or for 100 s at 90 °C with the MAIH technology, and 130 s at 90 °C with boiling in salt solution, respectively. Cooked shrimps were stored 28 days at 4 °C to determine changes in aerobic plate count (APC), psychrotrophic bacteria count (PBC), color, texture, pH, and total volatile basic nitrogen (TVBN). Results showed that the levels of APC and PBC were not detectable (

Microwave-assisted induction heating (MAIH) is a novel heating technology that combines microwave heating in the upper section and induction heating at the bottom. Our previous study demonstrated that optimal cooking in white shrimp can be achieved by MAIH either at 130 °C for 80 s or at 90 °C for 100 s. The objective of this study was to compare the cooking of white shrimp using microwave heating or induction heating alone with that using MAIH under the optimum cooking condition. The following three methods for cooking white shrimp were analyzed: (1) induction heating (IH) at 90 °C for 100 s or at 130 °C for 80 s; (2) microwave heating (MW) at 1300 W and 2450 MHz for 80 or 100 s; and (3) MAIH at 90 °C for 100 s or at 130 °C for 80 s. The results showed that using only induction or microwave heating gave the shrimp an uncooked or undercooked appearance; meanwhile, cold spots and non-uniform temperature distribution were observed in the thermal image of the shrimp. On the contrary, the shrimps processed by MAIH were found to be fully cooked, and a uniform temperature distribution was observed in the corresponding thermal image. Furthermore, no detectable aerobic plate count (APC), psychrophilic bacteria count (PBC), and coliform were found in the shrimp samples processed by MAIH. The color (L*, a*, b*, W, and ΔE), hardness, cohesiveness and chewiness of the samples processed by MAIH were all significantly greater (p Industrial relevance This novel MAIH technology allows shrimp to be heated and pasteurized after being packed, thereby eliminating the post-pollution issue. Therefore, it has a great potential for developing short-time in-package pasteurization processes in food industry.

In April 2017, an outbreak of histamine fish poisoning causing illness in nine victims associated with consumption of milkfish surimi products (fish ball) occurred in Kaohsiung City, southern Taiwan. Of the two suspected frozen milkfish surimi samples, one sample contained 91.06 mg/100 g of histamine, levels that are greater than the potential hazard action level (50 mg/100 g) in most illness cases. Moreover, 28 frozen milkfish surimi samples from retail stores were collected and tested to determine the occurrence of histamine. One (3.6%) of 28 commercial surimi samples had histamine levels greater than the U.S. Food and Drug Administration (FDA) guideline for decomposition of 5 mg/100 g for scombroid fish and/or products. Thirteen histamine-producing bacterial strains isolated from suspected and commercial surimi samples were identified as prolific histamine formers, able to produce 98.4 to 121.8 mg/100 mL of histamine in Trypticase soy broth supplemented with 1.0% l-histidine. In addition, milkfish surimi was inoculated with Raoultella ornithinolytica at 5.0 log CFU/g and stored at 4, 15, 25, and 37°C to investigate bacterial growth and formation of histamine. The histamine contents quickly increased to more than 50 mg/100 g in samples stored at 37 and 25°C within 12 and 24 h, respectively, as well those stored at 15°C within 96 h. To our knowledge, this is the first report in Taiwan to demonstrate that milkfish surimi products could cause histamine intoxication. HIGHLIGHTS

Forty-one cod steaks, fifteen escolar steaks, and fifteen salted escolar roe products sold in Taiwan market were purchased and tested to determine the biogenic amine, histamine-forming bacteria, and identification of fish species. The levels of pH value, salt content, Aw, TVBN and APC in all samples ranged from 5.3 to 7.0, 0.7 to 5.6%, 0.80 to 0.99, 0.8 to 59.9 mg/100 g and 2.5 to 7.3 log CFU/g, respectively. None of these samples contained coliform bacteria and Escherichia coli . The average content of histamine in all samples was less than 5 mg/100 g US Food and Drug Administration guideline value. Nine histamine-forming bacterial strains isolated from cod, escolar, and salted escolar roe samples produced 2.0–62.3 ppm of histamine in trypticase soy broth (TSB) supplemented with 1.0% l -histidine (TSBH). Assay of DNA direct sequence and polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) revealed that mislabeling rate of 41 cod steaks was 31.6% (13/41). Among them, 7 samples (17%) and 6 samples (14.6%) were identified as Ruvettus pretiosus (oilfish) and Reinhardtius hippoglossoides (Greenland halibut), respectively. In addition, most of escolar steaks and salted escolar roe products were identified as Lepidocybium flavobrunneum (escolar), while other samples were identified as R. pretiosus .

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.

Fifty-seven salted seafood products sold in the fishing village stores in Taiwan, including salted fish product, salted mollusc product and salted shrimp product, were tested to determine the occurrence of histamine and histamine-forming bacteria. Although the average content of each of nine different biogenic amines in all samples was less than 5.0 mg/100 g, 10.5% (6/57) of tested samples had the histamine content greater than the 5.0 mg/100 g allowable limit suggested by the US Food and Drug Administration. One histamine-producing bacterial strain, capable of producing 78.5 ppm of histamine in trypticase soy broth supplemented with 1.0% l -histidine (TSBH), was identified as Bacillus megaterium. The B. megaterium isolate was a halotolerant bacterium which grew well to an elevated NaCl concentration of 15% in TSBH medium. Besides, it had a consistent ability to produce >300 ppm of histamine at 10% NaCl concentration in TSBH medium after 72 h.

Twenty fish meats and 21 environmental surface samples obtained from a Hazard Analysis Critical Control Points (HACCP) fish processing factory and two non-HACCP fish processing factories in Pingtung, southern Taiwan were tested to determine the hygienic quality and histamine-forming bacteria. The levels of aerobic plate count (APC), total volatile basic nitrogen and total coliform in fish samples obtained from the HACCP factory were significantly lower than those of fish samples obtained from the two non-HACCP factories. The average content of the eight biogenic amines in HACCP fish samples was less than 1.0 mg/100 g, while that in non-HACCP fish samples was less than 1.5 mg/100 g. In environmental surface samples, the average levels of ATP bioluminescence and APC (swabbing method) of HACCP processing factory were significantly ( P l -histidine (TSBH), belonged to Enterobacteriaceae (thirteen strains) and Staphylococcus spp. (two strains).

Thirty-four tuna candy products sold in retail markets and supermarkets in Taiwan were purchased and tested to determine the biogenic amine, histamine-forming bacteria, and adulteration of bonito meat. The levels of pH value, water activity (Aw), water content, total volatile basic nitrogen (TVBN), aerobic plate count (APC) and total coliform (TC) in all samples ranged from 5.3 to 6.1, 0.47 to 0.65, 7.37% to 17.32%, 12.1 to 54.6 mg/100 g, l -histidine (TSBH) after incubation at 35 °C for 24 h. Assay of multiplex polymerase chain reaction (PCR) revealed that adulteration rate of bonito meat was 26.5% (9/34) in tuna candy samples. Tuna species in tuna candy samples was identified as Thunnus albacares for 29 samples (85.3%), Thunnus alalunga for four samples (11.8%) and Thunnus obesus for one sample (2.9%) by polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP).

Paralytic toxicity was detected by tetrodotoxin (TTX) bioassay in 41 specimens of four species of coral reef crabs collected from Kenting National Park, southern Taiwan from January 2003 to March 2004. The frequency of toxicity in Zosimus aeneus, Xanthias lividus, Actaeodes tomentosus (Xanthidae family) and Camposcia retusa (Majidae family) specimens was 93.3%, 100%, 46.7% and 66.7%, respectively. The average toxicity of crab specimens was 483 ± 225 (mean ± SD) mouse units (MU) for Z. aeneus, 51 ± 32 MU for X. lividus, 6 ± 5 MU for A. tomentosus, and 18 ± 11 MU for C. retusa. Each toxin of four species of crabs was extracted with acidic methanol, cleansed using a C18 solid-phase extraction column, filtered through a microcentrifuge filter and analyzed by HPLC, LC-MS and GC-MS. The toxins of Z. aeneus and X. lividus contained TTX (90%) and a small amount of gonyautoxins (10%), whereas those of A. tomentosus and C. retusa all mainly contained TTX, but no paralytic shellfish poison. Except for Z. aeneus and X. lividus, two species A. tomentosus and C. retusa were first recorded as toxic in Taiwan.

The effects of salt concentrations (0-15.0%) and drying methods on the quality of dried milkfish were studied. The results showed that the levels of aerobic plate counts, total coliform, water activity, moisture contents, total volatile basic nitrogen (TVBN) and thiobarbituric acid (TBA) of the dried milkfish samples prepared with the same drying method decreased with increased salt concentrations. The samples prepared with the cold-air drying method had better quality in term of lower TVBN and TBA values than those of samples prepared with other drying methods. The histamine contents in all samples, except two, prepared with various salt concentrations by different drying methods were less than 1.9 mg/100 g. Two unsalted samples prepared with hot-air drying at 35 °C and sun drying methods were found to contain histamine at levels of 249.7 and 67.4 mg/100 g, respectively, which were higher than the potential hazard level of 50 mg/100 g.

Histamine is the main causative agent of scombroid poisoning. However, unlike scombroid fish, histamine poisoning due to consumption of flying fish has never been reported. In this study, the white muscle of flying fish had high levels of free histidine at approximately 423.9 mg/100 g, and was inoculated with Staphylococcus xylosus Q2 isolated from dried flying fish at 5.0 log CFU/g and stored at −20 to 35°C to investigate histamine-related quality. The histamine contents quickly increased to higher than 50 mg/100 g in samples stored at 25 and 35°C within 12 h as well as stored at 15°C within 48 h. However, bacterial growth and histamine formation were controlled by cold storage of the samples at 4°C or below. Once the frozen flying fish samples stored at −20°C for 2 months were thawed and stored at 25°C after 24 h, histamine started to accumulate rapidly (>50 mg/100 g of fish). Therefore, flying fish muscle was a good substrate for histamine formation by bacterial histidine decarboxylation at elevated temperatures (>15°C) when it is contaminated with S. xylosus. In conclusion, since the improperly contaminated flying fish muscle with S. xylosus could lead to production of hazardous levels of histamine over time when stored at temperatures >15°C, the flying fish should be stored below 4 °C or below to control proliferation of S. xylosus, and TVBN and histamine production.