| Abstract: | 將粗幾丁質以2N HCl及2N NaOH溶液依序除去碳酸鈣及蛋白質製成幾丁質(chitin)，再以濃鹼液(57%，w/v)於高溫下加熱至不同時間以去除乙醯基(acetyl group)，可得20~30、40~50、60~70及80~90 %去乙醯度之幾丁聚醣(chitosan)。進而研究討論於不同去乙醯度之幾丁聚醣、使用濃度(0.5、1.0、1.5及2.0 %)及pH (3.0、4.0、5.0及6.0)下乳化對其乳化能力及乳化安定性之影響。乳化安定性之測試項目包括：乳化液經5℃、室溫、60℃，30 min、100℃，30 min及121℃，30 min處理後存放兩星期；凍結-解凍循環(freeze-thawing cycle)共5次；及黏度、乳滴大小分布。在食品應用方面，將上述不同去乙醯度之幾丁聚醣取代蛋黃製備法式沙拉醬，並比較這些沙拉醬與傳統沙拉醬的官能評估、黏度、安定性及菌的生長問題。 結果發現，在乳化能力方面，80~90 %去乙醯度幾丁聚醣之乳化能力最高，20~30 %去乙醯度者最低，而40~50 %及60~70 %去乙醯度者介在上述兩組中間。幾丁聚醣濃度越高其乳化能力越低，而幾丁聚醣溶液之pH偏於6.0時有較高之乳化能力。 在乳化安定性方面，20~30 %去乙醯度者於pH 3.0及pH 4.0，濃度1.0 %以上乳化，其乳化液經5℃至121℃處理後存放兩星期均無分層現象，若於pH 5.0下乳化則需濃度1.5 %以上，而於pH 6.0下則需提高濃度至2.0 %。40~50 %去乙醯度者，以濃度1.0 %，pH 3.0及pH 4.0下乳化，於100℃之內處理後存放尚為安定，但121℃處理即馬上分層，其於pH 5.0及pH 6.0乳化，除以100℃內處理後存放均為安定外，並於121℃處理後可存放3天方產生分層。60~70 %去乙醯度者，於pH 3.0及pH 4.0，濃度為2.0 %下乳化，其乳化液於100℃內處理後存放均為安定，121℃處理則不宜，於pH 5.0，濃度2.0 %或於pH 6.0濃度1.0 %以上乳化並於121℃內處理後存放兩星期均未分層。此外，80~90 %去乙醯度者更適合偏pH 6.0下乳化，其濃度只要1.0 %以上，121℃內處理後存放均不分層。 在凍結-解凍循環安定性方面，20~30 %去乙醯度組幾乎於每次循環都會有些許油分離情形；40~50 %去乙醯度組表現最差；60~70 %去乙醯度組，使用濃度為2.0 %方為安定；而80~90 %去乙醯度組表現最為安定，其濃度1.5 %以上，凍結-解凍循環5次均無分層。在乳化液之黏度方面，對不同去乙醯度者於適合濃度及pH下乳化，其乳化液較安定者黏度較黏。乳化液之乳滴大小分布情形亦隨著乳化安定性越佳其乳滴直徑0.02 cm內之數量亦越多。此外，幾丁聚醣乳化型態為w/o/w (water-in-oil-in-water)。 此外，在沙拉醬應用方面，由官評結果得知，除了40~50%去乙醯度組及各組呈現澀味為缺點外，其餘去乙醯度組的口感、風味、顏色似乎均略優於傳統組，其總接受性與傳統組為不明顯差異。此外，幾丁聚醣乳化液均比傳統者較安定(不分層)，且雜菌不易生長。
Crude chitin was treated with 2N HCl and 2N NaOH solution to remove calcium carbonate and protein, respectively, to produce chitin. Chitin was treated with concentrated alkali solution (57%, w/v) under high temperature and different intervals to cleave acetyl group and became 20~30、40~50、60~70 and 80~90 % deacetylated chitosans. Emulsifying capacities and stabilities of the chitosans were determined at different deacetylation degree chitosan、concentrations ( 0.5, 1.0, 1.5, and 2.0 % ) and pHs ( 3.0, 4.0, 5.0, and 6.0). The treated items of emulsion stability include: Treating emulsions at 5℃and storing at 5℃for 2 weeks; treating emulsions at room temperature; 60℃, 30 min; 100℃, 30 min; and 121℃, 30 min, and storing at room temperature for 2 weeks; freeze-thawing cycle 5 times; viscosity test and emulsions droplet distribution. To food application, French salad dressing was done by replacing egg yolk with the deacetylated chitosans. The products were compared on the sensory evaluation, viscosity, stability, and microbial growth. Traditional salad dressing was also done as a control. As result, in the aspect of emulsion capacity, 80~90 % deacetylated chitosan had a highest value, 20~30 % deacetylated chtitosan presented lowest, where 40~50 % and 60~70 % deacetylated chitosans were between the 80~90 % and 20~30 % samples. The higher the chitosan concentration, the lower the emulsifying capacity. Chitosan solutions slanted toward pH 6.0 had a higher emulsion capacity. In the aspect of emulsion stability, 20~30 % deacetylated chitosan was emulsified at pH 3.0and pH 4.0, and a concentration above 1.0 %, then appeared no separation after treating at temperature from 5℃to 121℃and storing during 2 weeks . But the emulsion was carried at pH 5.0, or at pH 6.0, a concentration must be above 1.5 %, or at 2.0 %, respectively to keep the stability. For 40~50 % deacetylated chitosan, it was emulsified at a concentration of 1.0 %, pH 3.0 or pH 4.0 then treated at temperatures within 100℃, gave a stable emulsion, but its emulsion immediately separated as treat at 121℃. When it was emulsified at pH 5.0 or pH 6.0, the emulsion separated for 3 days after treating at 121℃. For 60~70 % deacetylated chitosan, its emulsions were all stable at concentration 2.0 %, pH 3.0 or pH 4.0 after treating within 100℃, but separated as treated at 121℃. If the emulsion was carried out at a concentration of 2.0 % and pH 5.0, or at a concentration above 1.0 %, and pH 6.0, then treated within 121℃and stored during 2 weeks, gave no separation. And for 80~90 % deacetylated chitosan, it was emulsified at a concentration above 1.0 % and pH 6.0, then treated within 121℃, gave a stable emulsion during storing 2 weeks. On the freeze-thawing resistance, the emulsion of 20~30 % deacetylated chitosan had some oil leak at every cycle; that of 40~50 % deacetylated chitosan appeared more badly; 60~70 % deacetylated one was stable at a concentration of 2.0 %while 80~90 % deacetylated one was the most stable at a concentration above 1.5 % in 5 freeze- thawing cycles. Most of stable emulsions those were carried out under suitable concentration and pH value, gave a high viscosity and high percentage of small droplet size (less than 0.02cm) distribution. The chitosan emulsion were water-in-oil-in-water type. Salad dressings those were prepared from 20~30 %, 60~70 %, and 80~90 % deacetylated chitosans appeared better mouth-feel, flavor, and color than that of traditional one, and gave a similar score of total acceptability as the latter although they had some astringent taste. Chitosan salad dressings also showed more stable, and less microbial growth than traditional one. |
