以反應曲面法探討硫酸催化對於微波輔助系統中馬鈴薯澱粉乙醯酯化修飾作用之影響

Abstract

乙醯酯化修飾可降低澱粉糊化溫度及提高澱粉產品的貯藏安定性，以克 服天然澱粉的加工應用限制。本研究以馬鈴薯澱粉做為實驗材料、醋酸酐為反應劑、家用微波爐加熱輔助，探討碘、硫酸、磷酸、硝酸及鹽酸做為催化劑之乙醯酯化反應效能。其中反應效能以硫酸(25%)最高，並且隨催化劑添加量增加而提高。接著進一步利用反應曲面法，以催化劑添加量及微波加熱時間做為反應因子，使用可控溫之微波消化爐，在固定微波溫度為130℃、澱粉脫水葡萄糖單體與醋酸酐莫耳比為1：3下，計算澱粉反應效能及回收率並找出最適化製備條件。以反應曲面法所得到的最適化條件結果，反應效能為硫酸添加量18.3毫莫耳、微波258秒及14.2毫莫耳、微波245秒，回收率為11.6毫莫耳、微波258秒，並以上述最適化條件製備樣品，其取代度依序為1.370、1.029及0.683，再以天然馬鈴薯澱粉為對照組進行後續物化特性分析。澱粉顆粒外觀在經過乙醯酯化修飾後，澱粉偏光十字強度減弱甚至消失，顆粒嚴重崩解形成碎片並聚集成塊。在X-ray繞射圖譜結果，繞射波峰強度減弱，結晶指標顯著從27.47 %下降至5.27 %，表示澱粉結晶區受到破壞。膨潤力與水溶性指標結果，高取代度乙醯酯化澱粉疏水性較高，在75℃下加熱其膨潤力(12.59 g/g)及水溶性指標(12.93 %)顯著低於天然馬鈴薯澱粉(31.15 g/g、38.95 %)。在熱性質分析結果中，經乙醯酯化修飾後其糊化溫度及熱焓值降低。以RVA分析成糊性質結果來看，尖峰黏度顯著自6955cP降低至137cP，澱粉糊安定性增加，回凝傾向降低。HPSEC分子量分佈結果，經過乙醯酯化修飾後分子量顯著下降，以取代度較高組別降解情形較嚴重。最後在FTIR官能基分析中，利用1754 cm-1與1157cm-1內標波峰強度相除之比值與取代度進行迴歸分析，可評估做為取代度快速分析方法之一。

Acetylation can reduce the gelatinization temperature and improve storage stability of starch-contained products, used to overcome the native starch processing application limits. In the present study, potato starch is used as reaction material, acetic anhydride as the reactant, domestic microwave-assisted, to discuss the acetylation reaction efficiency by using iodine, sulfuric acid, phosphoric acid, nitric acid and hydrochloric acid as the esterification catalyst. The reaction efficiency of sulfuric acid is the highest (25%), with the content of catalyst increases. Further use of response surface methodology, it is designed that the content of sulfuric acid catalyst and microwave heating time as dependent factor. Microwave accelerated reaction system with temperature control is used, at a fixed temperature of 130℃ and the mole ratio of starch anhydrous glucose unit (AGU) to acetic anhydride is 1:3. Starch reaction efficiency and recovery as independent responses to identify optimal preparation conditions. In the obtained RSM optimal conditions, when the content of sulfuric acid catalyst added 18.3 mmole, microwave 258 seconds and 14.2mmole, 245 seconds for the highest reaction efficiency, 11.6 mmole, 258 seconds for the highest recovery, which DS is 1.370, 1.029 and 0.683. The optimal acetylated starch samples are for subsequent analysis of physico-chemical properties with native potato starch as blank. After the acetylation, starch granules birefringence intensity is weaken or even disappear, and granules disintegration seriously fragmented. In the X-ray diffraction patterns result, peak intensity is decreased, the crystalline index significantly decreased from 27.47% to 5.27%, which means that the starch crystalline damaged. Swelling power and solubility index results, the hydrophobicity is higher when the high degree of substitution of acetylated starch. When heating at 75 ℃, its swelling power (12.59 g / g) and water solubility index (12.93%) was significantly lower than the native potato starch (31.15 g / g, 38.95%). In the results of thermal properties, the gelatinization temperature and enthalpy decrease after acetylation. It is showed that the peak viscosity (PV) decreased significantly since 6955 cP to 137 cP in RVA pasting profiles, while the stability increased, and the retrogradation tendency of starch paste reduced. In HPSEC molecular weight distribution results, the molecular weight significant decreased after starch acetylation, especially in the higher degree of substitution groups. Finally, in FTIR analysis of the functional groups, the intensity ratio of 1754 cm-1 and 1157cm-1 internal standard peak with the degree of substitution for the regression analysis, which assess a quick analysis method of the degree of substitution.