| Abstract: | 諾麗 (Morinda citrifolia) 目前已知具有多種功能性，其果實呈強烈後熟現象，果實變軟並散發特殊風味，此過程可能與果膠分解有關。若能促進果膠分解，可望提高果汁產率及促進功能性成份釋放，有助於增強諾麗果汁之品質及縮短發酵時程。本研究分為三部分：第一部分純化諾麗果中果膠甲酯? (Pectin methylesterase, PME) ，並定性其溫度特性。諾麗果泥先以含鹽之緩衝溶液萃取，收集35~75%的硫酸銨沉澱物，再以透析除鹽後經過濾器濃縮，並以陰離子交換管柱去除部分雜質，可得兩種酵素同型體，比活性分別提高1.65倍和14.57倍。使用滴定法 (pH-Stat) 做最適溫度與溫度耐受性之測試，結果顯示諾麗果PME-A最佳活性溫度為60°C，PME-B經70°C加熱5分鐘後仍具有約44%的殘餘活性。第二部份設計以25、35、45、55°C為期一個月之控溫發酵，每週取樣測試產品基本性質與功能性成分變化。初步研究結果指出，諾麗果汁的pH值約3.6，室溫發酵的組別由於微生物生長， 使得pH值和可溶性固形物降低，而高溫發酵組別物理性質相對較穩定。適當提高發酵溫度在初期能提高果汁產率，促進色素生成，提高抗氧化能力；然而過度提高溫度 (45和55°C) 可能因水分蒸散或酵素不安定而造成產率減損。高溫使褐變反應劇烈而色澤釉黑，且易使類黃酮、芸香素等功能性成分受到破壞，造成ACE抑制活性之減損。第三部份對室溫發酵之果汁進行不同殺菌條件之測試，傳統低溫長時殺菌法雖能確保果汁安全，然而其長時間熱處理卻改變果汁品質；使用膜過濾除菌或板式熱交換高溫短時殺菌，對果汁基本性質與功能性成分並無顯著影響，其中又以板式熱交換處理效率較高。總體而言適當提高發酵溫度可促進諾麗果發酵，縮短發酵時間，輔以高溫短時的殺菌方法，可以縮短生產製程。
Noni (Morinda citrifolia) has been known to contain many functional phytochemicals. Noni fruit is climacteric. The fruit will ripe quickly and become soft and juicy. The ripe noni fruit gives strong foul flavor. The changes in texture and flavor during ripening are closely related to activity of its endogenous pectinmethylesterase (PME). Enhancing the PME activity would leads to the increase in fruit juice yield and release of functional phytochemicals and also will shorten the juice production processing and improve the juice quality. This project will focus on three subjects: (1) isolation and characterization of PME from noni juice, (2) production and characterization of noni juice fermented under anaerobic at four different temperature (25, 35, 45 and 55°C), and (3) evaluation the effectiveness of three pasteurization methods (Low Temperature Long Time, LTLT; High Temperature Short Time, HTST; and Ultrafiltration) on the quality of noni juice. First, crude PME was extracted from ripe soft noni fruit with NaCl-Tris buffer, pH 8.0, and precipitated with ammonium sulfate. Precipitate of 35-75% ammonium sulfate was dialyzed and the solution was concentrated with Amicon filter for DEAE column chromatography. Two PME isomers (PME-A and PME-B) were isolated and optimal temperature for PME-A was found to be 60°C. PME-B showed better thermal stability than PME-A. Second, noni juices from different temperature-controlled fermentations were subjected to the measurements of juice-yield, color change, functional phytochemicals and physiological activity. Noni fermented under 35°C gave better juice yield than others at initial fermentation period. Both noni juices from noni fermented under lower temperature, 25 and 35°C, gave better antioxidant activity and lower acidity, probably due to microbial growth. Whereas noni juice from noni fermented under higher temperature, 45 and 55°C, gave lower juice yield, darker in color, less content of phytochemicals, lower ACE inhibitory activity and higher antioxidant activity, probably due to mallard reaction. All three methods selected were found to reduce microorganism effectively and exhibited no significant effectiveness on the content of functional phytochemical and on physiological activity. However, HTST (95°C, 13 sec.) posses the advantage of easy operation and save the pasteurization time over ultrafiltration (0.45 μm) and LTLT (65°C, 24 + 24 hrs) |
