|Abstract: ||本研究以黑眼豆為原料，製成豆漿，利用等電點沉澱法（pH4.5）除去蛋白質，而將乳清部分以噴霧乾燥法製成粉末後，探討黑眼豆乳清粉末的起泡特性及其相關的理化性質。乳清粉末的成分含有2.6%的皂素，27%的酸可溶性蛋白質與34.5%的醣類。黑眼豆豆漿與乳清的起泡力分別為580與813%，泡沫安定性(t1/2)則分別為28與11.5分鐘。當乳清的pH值在4.5與7時，在泡沫特性上則無差異。在乳清粉末的起泡特性方面，不同乾燥方法對起泡力影響較小，而泡沫安定性(t1/2)方面，則凍結乾燥組為6.2分鐘，噴霧乾燥組為10.6分鐘。乳清粉末中添加多糖類三仙膠與鹿角菜膠(濃度0-0.3%)時，起泡力由790%分別下降至663%與700%，然而泡沫安定性(t1/2)由10.6分鐘增加至大於100分鐘。當調整食鹽濃度由0至1.5%時，對起泡力及泡沫安定性(t1/2)的影響不大。而當添加蔗糖濃度0-20%時，起泡力由790%下降至716%，泡沫安定性(t1/2)由11.2分鐘增加至22.8分鐘。 市售商業皂素quillaja，當濃度由0.1增至1%時，泡沫安定性(t1/2)由10分鐘增加至40分鐘，而食鹽的添加(濃度0-1.5%)則會使泡沫安定性(t1/2)由10分鐘下降至6.1分鐘。在quillaja溶液中添加黑眼豆分離蛋白質0-4%時，則使泡沫安定性(t1/2)由40分鐘增加至120分鐘。不同來源的商業皂素(quillaja和soybean)與乳清粉末比較，起泡力分別為997、1050與790%，泡沫安定性(t1/2)則分別為40、5及10.6分鐘。 將黑眼豆乳清粉末溶液經由薄膜過濾後，以膠體過濾法進行劃分，在蛋白質部份可得5個主要劃分區，分子量分別為>80000, 21466, 16050, 10375及<3000 Da。主要部分的分子量在3000 Da以下，而醣類分子量則分布在3000 Da以下的部分。 在乳化特性方面，商業皂素(quillaja和soybean)、乳清粉末及黑眼豆分離蛋白質之乳化活性分別為60.8、56.6、55.3及54.0%；乳化安定性為59.9、58.7、68及60%，彼此間並無顯著差異。|
In this study, cowpea was used as raw material to prepare cowpea milk, then the protein was removed by isoelectric point method at pH 4.5 to produce a whey. The whey powder was prepared by spray drying. The foaming and physicochemical properties of whey powder from cowpea were investigated. The whey powder contained 27% of acid soluble protein, 34.5% of carbohydrate and 2.6% of saponin, respectively. Foaming ability of cowpea milk and whey were 580 and 813%, and foaming stability (t1/2) were 28 and 11.5 mins, respectively. There were no difference in the foaming properties between pH 4.5 and pH 7.0 of whey sample. The foaming stability (t1/2) of whey powder prepared by spray drying and freeze drying were 6.2 and 10.6 mins, respectively. The addition of xanthan gum and κ-carrageenan (Conc. 0-0.3%) in the whey solution, the foaming ability was lowered from 790 to 663 and 700%, respectively, but the foaming stability (t1/2) increased from 10.6 to 100 mins. There were no effect on foaming ability and stability as NaCl was added from 0 to 1.5%. Foaming ability decreased from 790 to 716%, foaming stability (t1/2) increased from 11.2 to 22.8 mins as sugar was added from 0 to 20%. The foaming stability (t1/2) of commercial quillaja, increased from 10 to 40 mins as concentration increased from 0.1 to 1%, but foaming stability (t1/2) decreased to 6.1 mins as NaCl was added from 0 to 1.5%. The addition of isolate cowpea protein in the quillaja solution at concentration of 0 to 4%, the foaming stability (t1/2) increased from 40 to 120 mins. Comparison of commercial saponin from quillaja and soybean, and cowpea whey, the foaming ability were 997, 1050 and 790%, and the foaming stability (t1/2) were 40, 5 and 10.6 mins, respectively. After ultrafiltration, the solution of cowpea whey was fractionated by Gel permeation Chromatography. In protein profiles, 5 fractions were seperated which molecular weight distribution were >80,000, 21,466, 16,050, 10,375 and <3000 Da, respectively. The main substance’s molecular weight was below 3,000 Da in protein and carbohydrate moieties. The emulsifying activity of commercial saponin (quillaja and soybean), whey powder and isolated cowpea protein were 60.8, 56.6, 55.3 and 54.0%, respectively. The emulsion stability of those sample were 59.9, 58.7, 68.0 and 60.0%, respectively, and no significant difference was found.