碩士 / 國立高雄海洋科技大學 / 水產食品科學研究所 / 93 / The conditions of pretreatments with alkali reagent were conducted to investigate its effect on the quality improvement of gelatin extracted from tilapia skin using acetic acid or phosphoric acid. Acetic acid extraction of gelatin was taken after tilapia skin was soaked in 0.1 NaOH solution for 1 h and sufficiently washed, then divided to three groups and extracted at 50℃ for 1 h, 60℃ for 30 min and 70℃ for 25 min respectively. The effect of temperature on the extractability and the jelly strength (JS) of gelatin extract were comparatively studied. The result showed the similar extractability of gelatin extracted at 50 and 60℃, which was higher than that at 70℃. Besides, the best JS was found in that of 50℃, even as converted to JS per g of nitrogen (JS/N). As fish skin was pretreated with Ca(OH)2 suspension (0.8 g/L), or 0.1 N NaOH solution, and subsequently extracted with acetic acid at 50℃ for 1 h, the latter (NaOH-A50) yielded the gelatin with the better quality then the former (Ca(OH)2-A50) in appearance, turbidity, bloom value, as well as JS, JS/N, and higher melting point. Both the alkali pretreatments could improve the quality of gelatin in comparison with that of non-pretreatment (Control-A50).
In this study, 4% phosphoric acid solution was also used to extract tilapia skin gelatin. After the soaking in 0.1 N NaOH solution for 1 h, sufficiently washing, the skin was soaked in phosphoric acid solution, and then extracted with water at 50℃ for 1 h (NaOH-P50). The alkali pretreatment could produce the gelatin with superior quality to that without treated (Control-P50) in appearance, turbidity, JS, JS/N ratio, bloom value, and higher viscosity as well as melting point.
To sum up the results, bloom value of NaOH-P50 gelatin was the highest, and which decreased in the order of NaOH-A50, Control-P50, Ca(OH)2-A50 and Control-A50. In accord with the results, higher content of high molecular weight proteins, ranged from 100 kDa to 200 kDa, was identified with SDS-PAGE patterns in NaOH-A50, Ca(OH)2-A50, and NaOH-P50 gelatins. NaOH-A50, Control-A50 and Control-P50 gelatins were similar in the composition of amino acid components.
At last part of this study, effect of conditions of NaOH pretreatment on gelatin quality was investigated. Using 0.1 N NaOH solution, and treating time was set as 1, 3, or 5 h, gelatin was extracted with acetic acid solution at 50℃ for 1 h, it was found the 5 h NaOH treated sample yielded the best JS and JS/N ratio of gelatin, however, prolonging the pretreatment time led to the increasing of nitrogen content losing thus decreasing the extracting ratio. As skin was soaked in 0.05 N, 0.1 N, 0.2 N, or 0.3 N NaOH solution for 1 h, and gelatin was extracted with acetic acid solution at 50℃ for 1 h, the best result of JS and JS/N was found in that of 0.2 N. The concentration of NaOH as 0.3 N would significantly cause the decreasing of extraction ratio.
In conclusion, appropriately alkali pretreatment of tilapia skin with NaOH could improve the quality of gelatin extracted. It might be elucidated through that the gelatin contained the high amount of protein with molecular weight more than 100 k dalton.
| Identifer | oai:union.ndltd.org:TW/093NKIMT084007 |
| Date | January 2005 |
| Creators | Wan-Chun Huang, 黃婉君 |
| Contributors | Chau-Jen Chow, 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 | 95 |
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