| Summary: | 碩士 === 國立海洋大學 === 食品科學系碩士在職專班 === 90 === ABSTRACT
The release of free ClO2 by acidification of sodium chlorite (activation of ClO2) depends greatly on the type of GRAS acids employed, the ionic strength of the acid, the reaction time and temperature. The release of free ClO2 using lactic acid reaches a maximal level in 3 hours when pH is 2.0, while it takes 5 hours to reach the same maximal activation at pH 2.5. Citric acid, on the other hand, takes 36 hours to release similar concentration of free ClO2 as lactic acid does at pH 2.5. Acidic meta- polyphosphate salts show increasing level of ClO2 activation within a 48-hour time period. Therefore, the activation of ClO2 is partially determined by the resulting pH value or the amount of acids added. In general, the lower the pH value is, the faster the free ClO2 will be released.
The reaction temperature will change the releasing rate of free ClO2. Activation of ClO2 by lactic acid at 60oC shows no residual free ClO2 in the solution at 24 hours after the addition of acid, while citric acid, at the similar condition, gives only 67% reduction of free ClO2 as compared to the initial level of free ClO2. Acidic metapolyphosphate salts is more inert to the temperature changes where, at 60oC, 14% and 34% reduction are respectively observed at 24 and 48 hours. The unique nature of acidic metapolyphosphate salts will extend the functionality and application of ClO2.
Neutralization of acid-activated ClO2 by sodium bicarbonate to a pH between 6.5 and 7.0 will result in a 21-25% reduction of free ClO2 level as compared to the control without neutralization. Additional reduction in free ClO2 concentration (50-60%) occurs at 12 hours after the neutralization suggesting that neutralization of activated ClO2 will result in a reduction of free ClO2 concentration. Therefore, neutralized ClO2 is not suitable for long-term antimicrobial application.
Application of ClO2 in Japanese seabass and cobia fillets shows that ClO2 is significantly effective in reducing the bacteria counts. Regardless of the addition of acids, the higher concentration of total or free ClO2 will give a better antimicrobial activity. Since the acidified or activated ClO2 is generally more effective than the stabilized ClO2 (no acid added), higher concentration of stabilized ClO2 is needed to reach a similar antimicrobial activity as a lower concentration of activated ClO2.
The ClO2-treated fish fillet shows a significant lower total plate count (TPC) than the non-treated control when stored at 6oC for 3 days, while treatment with 100 ppm acidified ClO2 gives a lowest TPC count among all tested concentrations after a 7-day storage period. The fish fillets treated separately with either 20 ppm acidified ClO2 or 100 ppm of stabilized ClO2 do not show significantly reduced TPC counts. However, the combination of the above two ClO2 concentrations synergistically enhances the antimicrobial activity of ClO2 and its effectiveness in long-term storage. The combination of acidified and stabilized ClO2 provides a new application direction for ClO2 and greatly improves the disadvantage of ClO2 in its duration of antimicrobial activity. The ClO2, at the concentrations including 200 ppm stabilized ClO2, 100 ppm acidified ClO2 and the combination of 100 ppm stabilized and 20 ppm acidified ClO2, will maintain the coliforms counts in fish fillets in compliance with the hygiene standards for seafood sashimi(raw fish) even after 7-day storage at 6oC. Therefore, regardless of the sanitary status of the seafood, processing with optimal concentration of ClO2 will significantly and effectively reduce coliforms counts and greatly reduce the risk of food poisoning.
ClO2 can be applied in almost all types of fishery products to improve the safety of the seafood and comply with the standards in hygiene and quality. The proper use of ClO2 will greatly enhance its antimicrobial activity, appreciate the quality of the treated seafood, extend the shelf-life and increase the economical efficacy.
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