探討分離鴨蛋白鹼性凝膠之穩定性及其應用

Abstract

本研究利用鴨蛋白鹼性凝膠機制，製作類似皮蛋蛋白具彈性之半透明膠體以增加其保存性與利用性，藉此提升鴨蛋白之附加價值與多元應用。近年來研究指出蛋白鹼性凝膠在強鹼持續作用下會導致膠體結構不穩定，因此如何縮短鹼性凝膠時間又能保持蛋白膠體安定性與加工應用性乃本研究之目的。 為建立分離鴨蛋白鹼性凝膠之穩定條件，本試驗首先以不同濃度之氫氧化鈉溶液與鴨蛋白製成凝膠，透過黏度變化來確立膠體形成時間，另外觀察反應時間對於膠體強度之影響，以評估最適氫氧化鈉濃度，結果顯示含0.125 M以下氫氧化鈉之混合蛋白液不易形成凝膠，然而超過0.175 M氫氧化鈉之混合蛋白液，其膠體強度會隨反應時間延長而顯著減弱(p < 0.05)，並產生液化現象。藉由上述試驗篩選出適當氫氧化鈉濃度(0.15 M)，並利用掃描式電子顯微鏡、膠體蛋白質硫醇基與雙硫鍵含量分析，以確認不同反應溫度處理之膠體結構與理化性質差異，結果顯示反應溫度超過25°C能夠顯著提高鴨蛋白凝膠速度(p < 0.05)，但高於35°C時則會導致膠體不穩定甚至液化，再者，經實驗發現膠體形成後保存於15°C以下能有效延緩液化之進程。進一步探討鹼性凝膠於加工食品之應用性，關於第二部分將針對其熱安定性進行評估，採用前述條件製備之膠體，於60-100°C水浴中加熱10分鐘後分析其色澤、安定性與理化特性，其中膠體強度會隨著加熱溫度的提高而顯著下降(p < 0.05)；若與市售皮蛋蛋白進行比較，則發現當膠體經加熱處理後並不會顯著提升游離鹼之濃度，推測膠體受熱後仍可保持膠體穩定性及鹼性成分釋出。因此分離鴨蛋白透過上述試驗條件處理後，能夠快速穩定形成凝膠且經高溫處理後仍具安定性，頗具加工應用之潛力。本研究第三部分將評估鴨蛋白鹼性凝膠應用於肉製品之可行性，由於鴨蛋白鹼性凝膠本身富彈性、水合效果佳且具較高pH值，對於乳化型肉製品之質地與保水性提升應具有正面效果，結果顯示額外添加3%鴨蛋白鹼性凝膠不但可以減少磷酸鹽使用量、提高乳化型肉製品之保水性與彈性(p < 0.05)，並且可以增加產品接受度。 綜上所述，透過本研究建立鹼濃度與溫度條件可將分離鴨蛋白快速製備出膠體穩定、具彈性與熱安定性之鹼性凝膠，除了類似皮蛋蛋白可應用於熱食並可添加於乳化型肉製品，製作出特殊質地與風味之新型態產品，以提高鴨蛋白之利用性。

The alkali treatment is the alternative and practical processing method for creating transparent and elastic protein gels, and it is beneficial to increase added value and usage diversities of separated duck egg white in Taiwan. Recent researches indicated that excess sodium hydroxide (NaOH) causes congealed egg white gel to liquefy. Thus, the purpose of this study was to prepare stable alkali-induced egg white gel efficiently and evaluate its application on meat product. First, the suitable gelation time was determined with different concentrations of NaOH solution mixing with duck egg white. Besides, we investigated the effects of reaction time on gel strength to decide the optimal NaOH concentration. Results indicated that the low-concentration-NaOH environment is unsuitable for gel formation. By contrast, the high-concentration-NaOH one rapidly increased the bloom strength of the duck egg white gel. As a result, 0.15 M NaOH in duck egg white solution was the optimal concentration to form the most stable egg white gels. In this study, reaction as well as storage temperature, rheological properties analysis, bloom strength test, thiol and disulfide bond content, and scanning-electron-microscope (SEM) were assayed. According to current results, it revealed that reaction temperature higher than 25°C could significantly increase the rate of gelation (p <0.05) during the gelation process; however, the temperature higher than 35°C would lead to instability or liquefaction. Moreover, the storage temperature of the gel below 15°C could prevent liquefaction effectively. In the second part of this study, through the thermal stability test, the results showed that the gel strength decrease significantly with the raising heating temperature (p <0.05), but the free alkalinity of prepared duck egg white gel was considerably lower than the commercial preserved egg white. Therefore, it showed that the alkali-induced duck egg white gel could remain stable after heating, which indicates its potential for further processed applications. Alkali-induced duck egg white gel was elastic, high pH value, and superior hydration. The texture and water-holding capacity of emulsified meat products were improved by adding alkaline duck egg white, which attributed to the characteristics as mentioned above. Therefore, it suggested that the optimal added amount is 3% alkaline gel with a 50% phosphate reduction. In conclusion, the optimal NaOH concentration and reaction and storage temperature conditions for prepared stable alkali-induced duck egg white gel were determined, and this product could also improve the taste and water holding capacity of emulsified meat products effectively. Overall, the application of alkaline-induced duck egg white gel on emulsified meat products or other food might be available and promising.