博士 / 國立臺灣海洋大學 / 食品科學系 / 95 / To survey the hygienic quality and freshness of fresh fish and shellfish, 313 specimens of fish and shellfish were collected from northern Taiwan during the winter and summer seasons for hygienic quality and freshness examinations. It was found that the hygienic quality and freshness of fish and shellfish became worse in summer, especially for clam and mussel. The ratio of unacceptable hygienic quality or freshness of fish and shellfish was the highest in fecal coliform, followed by E. coli and others. The fecal coliform count in products from the traditional markets was the highest, followed by those from supermarkets and fishing ports. Secondary contamination seems to be the most important problem for hygienic quality and freshness of fish and shellfish.
For reducing bacterial contamination, electrolyzed oxidizing (EO) water has been used to reduce microbial population on seafood and platform of fish retailer. The specimens of tilapia were inoculated with Escherichia coli and Vibrio parahaemolyticus, and then soaked into EO water containing 120 mg/L free chlorine for up to 10 min. The EO water achieved additional 0.7 log CFU/cm2 reduction than tap water on E. coli on tilapia after 1 min soaking treatment and additional treatment time did not achieved additional reduction. EO water treatment also reduced Vibrio parahaemolyticus by 1.5 log CFU/cm2 after 5 min treatment and achieved 2.6 log CFU/cm2 reduction after 10 min. The pathogenic bacteria were not detected in EO water after soaking treatment. In addition, the more than 50 mg/L free chlorine of EO water could effectively disinfect the platform of fish retailer in traditional markets and fish markets.
Filter-feeding shellfishes accumulate microorganisms, when they are grown in polluted waters. There are bacterial risks of shellfish in northern Taiwan. The present results showed that EO water could slightly decrease the bacterial count of shell surface of oyster, but could not affect the bacterial count of oyster. Using 50 mg/L free chlorine EO water to the artificial seawater with maintaining the free chlorine concentration of 3 mg/L as the condition of depuration of hard clam, aerobic plate count (APC) reduced 3.36 log CFU/g after 8-hr depuration. After 48-hr depuration, V. parahaemoliticus was decreased to less than 3 MPN/g, and total count was less than 2.40 log CFU/mL in aquaculture water quality after 16 hr. In addition, applying EO water (30 mg/L chlorine) containing 3% NaCl, resulted in reduction of V. parahaemolyticus in oysters by 1.22 log MPN/g after 8 hr. After 48-hr depuration resulted in reductions of aerobic plate count by 3.33 log CFU/g. Elimination of some pathogens in purified hard clams and oysters is significantly affected by the potency of using EO water to the depuration water with maintaining 3 and 30 mg/L free chlorine used, respectively.
In Taiwan, tunas are important fish species because the fish slice (called sashimi) made from tuna is very popular and preferable for Taiwanese people. However, tuna slices are reported to be a significant health risk when consumed raw or lightly cooked. In early period, CO treated tuna was allowed and suppliers could sell it, that looks good enough to eat. But there are many possibilities for contamination during harvest, processing and distribution owing to improper handling and CO treated tuna at 10℃ for 48 hr. CO treatment makes tuna slices appear to be fresh causing consumers showed erroneous judgment to purchase unacceptable hygienic quality of tuna slices. This study was undertaken to investigate the disinfectant efficacy of tuna fillet soaked in EO water for 5 min and followed by CO gas treatment for 48 hr. The results obtained that the more than 50 mg/L chlorine EO water combined with CO gas treatment in tuna fish fillet would be an effective method for enhancing the hygienic quality and freshness for tuna meat and extending refrigerated storage time. Tuna treated with combination of EO water containing 100 mg/L chlorine and CO gas had the lowest APC immediately after treatment and reduced further to below detection limit after 1 month frozen storage at -20℃. The technology can enhance the hygienic quality and freshness for tuna meat and postpone the period of storage.
Moreover, growth inhibition and histamine formation of histamine-forming bacteria by EO water were studied. One milliliter of Enterobacter aerogenes, Klebsiella oxytoca, Morganella morganii or Proteus vulgaris of approximately 109 CFU/mL was transferred in 9 mL of EO water, weak acid hypochlorous water (WAHW) and sterile deionized water (control), and then incubated for 0, 0.5, 1, 5 and 10 min. An exposure time of 5 min reduced the populations of all four pathogens in 30 mg/mL free chlorine concentration of EO water by approximately 8 log CFU/mL, with complete inactivation by 10 min of exposure. An exposure time of 1 min reduced the populations of all four pathogens in the EO water containing 30 mg/L free chlorine by approximately 6-7 log CFU/mL, with complete inactivation by 10 min of exposure. At 1 min of EO water containing 30 mg/L free chlorine had better antibacterial activity than WAHW containing 30 mg/L free chlorine exposure on the histamine-forming bacteria due to extra factors such as the lower pH and higher ORP.
The contaminated tuna fillet surface soaked in EO water for 5 min and then treated with EO water for 5 min again (EO 5+5) showed a significant disinfection better than individually 10 min treatment. EO water containing 100 mg/L free chlorine was the most effective when the contact times were increased to 10+10 min.
In addition, the levels of volatile basic nitrogen (VBN) and histamine were also reduced in tuna fillets by soaked in EO water containing 100 mg/L chlorine for 10+10 min, compared to control group at 4℃ storage. The treatment by immersion in EO water containing 100 mg/L chlorine for 10+10 min reduced E. aerogene by 1.32 log CFU/g when compared to control group at day 0. Histamine content in tuna stored at 4℃ exceeded the 50 mg/Kg tolerance level after 8 days. EO water containing 100 mg/L chlorine for 10+10 min did not completely prevent the high contamination level of histamine-forming bacteria growth and conversion of histidine to histamine in tuna fillet.
The oil-soluble and water-soluble extracts of the treated tuna cubes were checked for mutagenicity using Ames Salmonella typhimurium /microsome mutagenicity assay. No mutagenic activity was detected in the treated tuna samples with EO water toward TA98 or TA100. Negative mutagenic effect was found in case of TA 98 and TA 100 tested strains, with and without S9, when oil-soluble and water-soluble extracts of the treated tuna samples by 100 or 200 mg/L available chlorine of aqueous chlorine and EO water for 10 min. The application of EO water can be fitted in the regulations for hydrochloric acid (HOCl).
These results clearly indicated that EO water has a potential to be used for decontamination of raw seafood and seafood operating areas. The bactericidal effects of 100 mg/L free chlorine EO water to the high contamination of tuna fillet were not enough to reach the sanitation regulation of raw meat in Taiwan. To focus attention on critical control points in HACCP system during the processing of seafood, it is necessary to control the selection of material at beginning and to monitor the store condition and the processing.
| Identifer | oai:union.ndltd.org:TW/095NTOU5253001 |
| Date | January 2007 |
| Creators | Yu-Ru Huang, 黃鈺茹 |
| Contributors | Deng-Fwu Hwang, 黃登福 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | en_US |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 216 |
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