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題名 | 鮮乳與還原乳之乳清蛋白分光光度性研究=Studies on Spectrophotometric Properties of Whey Protein in Pasteurized and Reconstituted Milk |
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作者 | 吳安邦; 阮文惠; 鄭慧文; 林慶文; 陳朝洋; Wu, An-bang; Juan, Wen-hui; Cheng, Hui-wen; Lin, Chin-wen; Chen, Chau-yang; |
期刊 | 食品科學 |
出版日期 | 19970400 |
卷期 | 24:2 1997.04[民86.04] |
頁次 | 頁178-185 |
分類號 | 473.7 |
語文 | chi |
關鍵詞 | 牛乳; 乳清蛋白; 呈色法; Folin法; Milk; Whey protein; Colorimetry; Folin method; |
中文摘要 | 將牛乳樣品加入0.3N醋酸溶液至pH4.2時,所得上層液即為乳清蛋白質。本研究以 紫外光λ max 280 nm 測得的乳清蛋白吸光係數:生乳為 410 ± 33;鮮乳為 242 ± 28; 還原乳為 172 ± 16。乳清蛋白溶液以 0.125 N NaOH 滴定之,還原乳與空白試驗組均為有 明顯的中和點、β - 乳球蛋白次之、鮮乳組則不明顯。由此酸 - 鹼滴定結果顯示還原乳中 乳清蛋白已失去緩衝性。就牛乳分光光度特性而言,從吸光度 A278 與 A294 之差異性可換 算出鮮乳及還原乳中乳清蛋白質酪胺酸與色胺酸濃度比 (CTyr/CTry) 分別為 1.527、 1.74 。 亦即在一固定色胺酸濃度下,鮮乳中含較多酪胺酸,是還原乳的 1.301 倍。以三種呈色 法:Folin、Biuret 與 Coomassie 法測定牛乳乳清蛋白含量, 由檢量線斜率求得鮮乳╱還 原乳吸光係數比值:Folin 法 = 1.947:Coomassie 法:1.663、Biuret 法:1.205。 可見 Folin 法靈敏度最大,最適用於區分鮮乳中摻入還原乳的含量。 |
英文摘要 | By adding 0.3 N acetic acid solution to a milk sample and adjusting the pH to 4.2, the supernatant obtained was whey protein solution. In this study, the absorptivity of the whey protein solution at λ max280 nm was determined: raw cow milk =410 ± 33; pasteurized milk =242 ± 28; reconstituted milk=172 ± 16. When the whey protein solution of the milk samples was titrated with 0.125N NaOH solution, the reconstituted milk and blank group showed definite stoichiometric points; β -lactoglobulin group not very obvious; pasteurized milk not at all. The results of the acid-base titrations clearly showed that the whey protein in the reconstituted milk had lost its buffer action. Based on the spectrophotometric properties of milk, the differences of A278-A294 were related to the concentration ratios of tyrosine/tryptophan; CTyr/CTry=1.527 for pasteurized milk; 1.174 for reconstituted milk. That is, when the concentration of tryptophan was set constant, the pasteurized milk contained more tyrosine-1.301 times moer than did the reconstituted milk. By applying three colorimetric methods, the Folin, Biuret and Coomassie methods, to determine the content of the whey protein in milk, the slope (absorptivity) ratios of the calibration curves for pasteurized milk/reconstituted milk were:1.947 (Folin method);1.663 (Coomassie method); 1.205 (Biuret method). These results clearly showed that the Folin method had the greatest sensitivity among the three; it is the best choice for determination of the quantity of reconstituted milk blended in to pasteurized milk. |
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