芒果汁飲料熱處理後果汁分層現象之理化特性

Abstract

芒果汁飲料屬於果肉系的混濁果汁，不溶性固形物的含量很高，是構成芒果汁飲料特有風味與口感的主要因素。芒果原汁在製成稀釋果汁後，很容易發生果肉分層的現象。本論文採用台南縣六甲鄉農會所生產之冷凍愛文芒果原汁為實驗原料，探討造成芒果原汁稀釋後加熱生成果肉分層的原因，並以不同均質條件處理稀釋後之芒果汁，以分析芒果汁飲料中的顆粒粒徑分布與水溶性果膠含量對果汁混濁穩定性之影響。 20%芒果汁在經過不同條件熱處理後，以95℃/30sec出現最顯著的果肉上浮情形，可見高溫加熱會促使稀釋芒果汁分層變得較不穩定。分析熱處理後各分層的組成分，以水溶性果膠在果清與果肉分層之間的含量差異最大，果肉的水溶性果膠含量明顯高於果清，因此推測水溶性果膠為影響稀釋芒果汁混濁安定性的最主要因子。 隨著均質處理時間的增長，稀釋芒果汁的粒徑分布會逐漸向小顆粒方向移動。均質時間對於粒徑小於34.58μm以下顆粒所佔體積百分比有成正比的趨勢，在此範圍的顆粒中，加熱前後的40%芒果汁經長時間（10min）均質而增加的幅度平均約1.67%，而20%芒果汁則約為1.39%左右，因此40%芒果汁受到均質時間長短的影響較20%芒果汁來得大。40%芒果汁在均質2分鐘以上，果汁顆粒粒徑明顯的較20%芒果汁相同均質條件下來得小。 40%芒果汁在均質0~3分鐘內水溶性果膠即大量釋出，有明顯的均質效應，3分鐘之後增加趨勢則趨緩。20%芒果汁在均質0~3分鐘內水溶性果膠無明顯增加，不具有均質效應，均質3分鐘之後水溶性果膠釋出量明顯增加。因此，20%芒果汁在均質3分鐘時，果汁顆粒受到均質的切割效應已趨近平衡，故3分鐘之後的均質處理，較類似在進行攪拌的動作，而將果肉顆粒中的水溶性果膠大量溶出。 稀釋芒果汁之不可溶性固形物結合水溶性果膠量對混濁穩定性有很大的影響。不可溶性固形物所結合的果膠量越少，表示游離的果膠量越多，有助於維持果汁的混濁安定性。20%芒果汁在均質10分鐘以上，不可溶性固形物結合果膠量始有顯著降低的情形，而40%芒果汁在均質2分鐘後不可溶性固形物結合果膠量即有顯著下降，均質5分鐘之後亦有顯著降低，因此低濃度果汁（20%）的均質時間必須較高濃度果汁（40%）長，才能有效的改善混濁安定性。 在相同均質條件下，20%及40%芒果汁經加熱（95℃，30秒）並以超高速離心（9500×g，30分鐘）後，果清之水溶性果膠含量均有增加的情形，可知熱處理可促使水溶性果膠釋出。隨著均質時間的增長，發現長時間均質（10分鐘）較短時間均質（2分鐘）更能使游離的水溶性果膠增加，並可顯著降低不可溶性固形物結合果膠量，因此可明顯提高稀釋芒果汁的混濁穩定性。

Mango juice drink is typical cloudy juice. The high content of fruit pulp contributes to the special flavor and taste of mango juice products. However, the sedimentation often occurred in processed dilute mango juice drink during storage. The objectives of this study are to investigate the factors resulting in the sedimentation of mango juice drink, and to analyze the effect of homogenization treatments and solid particle distribution on the cloud stability of the dilute mango juice drink. Having analyzed chemical constituent of three pulp separation layers formed in dilute mango juice drinks after 95oC heating for 30sec, the soluble pectin content in each layer shows great difference. Pulp layer contains significantly higher soluble pectin than the serum layer. The results indicate soluble pectin may play an important role in the cloud stability of the dilute mango juice drink. The volume of smaller particle size in mango juice drink tends to increase with the extension of homogenization (1000rpm) time, especially for the particle diameter smaller than 34.58μm. The average increases of percent volume for the particle size below 34.58μm in 20% and 40% mango juice drinks are 1.39% and 1.67%, respectively. Homogenization has greater effect on particle size reduction in 40% mango juice drink than in 20% mango juice drink. Homogenization of 40% mango juice drink within 3min, the soluble pectin content increased rapidly in the serum. In contrast, soluble pectin content in the serum of 20% mango juice drink began to increase after homogenization for more than 3min. The later result may due to the stirring effect rather than homogenization. The dissociation of soluble pectin from insoluble solid/soluble pectin complex plays an important role in the increase of cloud stability in mango juice drink. Homogenization of 40% mango juice drink for 2min significantly increased the soluble pectin in the serum. For 20% mango juice drink, it took more than 5min homogenization to start increasing soluble pectin content in the serum. Thermal treatment of mango juice drinks at 95oC for 30sec also resulted in the increase of free soluble pectin. The better cloud stability of 20% mango juice drink with longer homogenization time in shelf-life study suggests that free soluble pectin content is the key factor to the cloud stability in mango juice drink.