碩士 / 國立高雄海洋科技大學 / 水產食品科學研究所 / 94 / Chlorine dioxide (ClO2) has been used in the seafood disinfection recently, while the ozonated water is often used to reduce bacteria count in the processing of raw fish fillet for Sashimi use. In the case of frozen tuna fish block, there is no antimicrobial procedure during the processing. In order to improve the hygience and quality of raw tuna fish, ClO2 and ozone (O3) were used to treat tuna steak, and their effects on microorganism control and quality of tuna flesh were investigated.
Commercial stabilized ClO2 solution can be changed into available ClO2 by the addition of lactic acid. The absorption spectrum from 340 to 440 nm near UV range can be used to distinguish whether the ClO2 solution is activated or not. Three methods, measurements with direct absorbance, chlorophenol red (CPR) titration, or phenylarsine oxide (PAO) titration, were used to determine the concentration of available ClO2. All of them showed high correlation coefficients with the concentration of ClO2 (R2 in order to 0.9995, 0.9998 and 0.9983). The results obtained by direct absorbance and CPR titration were similar, and showed better sensitivity than PAO titration.
The 5,000 ppm of ClO2 was activated with various level of lactic acid (88%), ranged from 0 to 10% for final solution volume. These solutions were diluted to 50 ppm of total ClO2 with deionized water and then subjected to determine the concentration of available ClO2. The absorption spectra of various ratio of lactic acid to activate ClO2 solution, remained unchanged within 60 h at 4ºC. As adding 0~6% of lactic acid to activate ClO2, higher content of available ClO2 were obtained with the increase of lactic acid addition (p<0.05). The concentration of available ClO2 maintained approximately at 20 ppm when 6~10% of lactic acid was added.
After the addition of 6% lactic acid, the concentration of available ClO2 set for 36 h was 16.2% higher than that set for 14 h. When activated ClO2 solution was adjusted to neutral pH or higher with Na2CO3, and then diluted to 1,000 ppm of total ClO2, the concentration of available ClO2 approximately reduced 19~37%. The higher pH value adjusted, the lower concentration of available ClO2 obtained.
As tuna steaks were soaked in 10~50 ppm available ClO2 solutions for 30~150 sec, the available ClO2 almost decomposed. However, the concentration of total ClO2 reduced slightly and maintained at the range of 72~88% of the initial concentration.
Tuna steaks were inoculated with E. coli ranged of 104~105 CFU/g and then subjected to soak in 10~50 ppm available ClO2 solutions for 0~150 sec. As a result, 30 sec exposure of tuna steak caused the reduction of 0.39~0.43 and 0.38~0.44 logs in number of aerobic plate count (APC) and Escherichia coli (EC), respectively. As further soaking for 150 sec, the change of APC was not significantly (p>0.05). Using 50 ppm to soak resulted in the darker of the appearance of tuna steaks and surface myoglobin turned brown obviously (p<0.05). The levels of TBARS by lipid oxidation were higher than those with 10 or 20 ppm ClO2. Therefore, to avoid the change of color of tuna fish that will lose commodity value, the soaking time shorter than 30 sec and the concentration of available ClO2 lower than 20 ppm were recommended.
Antimicrobial treatments of tuna steak with 10 ppm available ClO2 for 30 sec or saturated ozonated water for 30 sec were carried out as follows: soaking 10 ppm available ClO2 solution once (10C), soaking in ozonated water once (O3), soaking in 10C twice (10C/10C), soaking in O3 twice (O3/O3), soaking in 10C and O3 once each (10C/O3). The results showed that the treatments with 10C or O3 single soaking reduced 56~61% and 58~65% of APC and EC, respectively, for tuna steaks inoculated with E. coli previously. The multiple treatments reduced 74~80% and 61~89% of APC and EC, respectively. In the case of tuna steak without inoculation, after 10C or O3 single soaking, these treatments caused reduction of 75~80%, 72~82 and 71~83% of APC, EC and TC, respectively. And multiple treatments reduced 81~84%, 87~91% and 76~87% of APC, EC and TC, respectively. It showed that the multiple treatments were better than single treatments.
After the treatment with 10C/10C, the color of tuna steak changed significantly (p<0.05). The ratio of 630 nm/580 nm of the surface myoglobin showed that tuna steak treated by 10C/10C had lower oxymyoglobin than other treatments. However, there is no significant difference in metmyoglobin formation ratio from the superficial portion (2 mm) of tuna steak (p>0.05) between 10C/10C and control. These results suggested that the oxidation of myoglobin was limited at the surface. The level of TBARS of all treatments were not significantly different (p>0.05), except those with 10C/10C and 10C/O3 showed higher content than control (p<0.05). In comparison with the single treatment of ClO2 or O3, multiple treatments would reduce bacteria more effective, yielded the less change in surface color and lipid oxidation. With the consideration of microorganism control and quality of tuna steak, antimicrobial treatments with 10C/O3 seems to be a better condition than others.
| Identifer | oai:union.ndltd.org:TW/094NKIMT084002 |
| Date | January 2006 |
| Creators | Tzeng Wan-Ning, 曾琬甯 |
| Contributors | Chow Chau-Jen, 周照仁 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 72 |
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