臺灣博碩士論文加值系統

本研究以碳酸鈉 (Na2CO3)溶液萃取仙草葉膠，探討膠濃度(0.3-1.8%)、澱粉種類及濃度(2-4%)對仙草葉膠與澱粉間凝膠作用之影響。仙草膠與澱粉混合之懸浮液以快速黏度測定儀測其黏度，或加熱形成仙草凍後，於動態流變儀上進行頻率掃描及穩剪切測試，或以質地分析儀測其質地，以色差分析儀測其Hunter L、a、b值，經冷凍乾燥固定，以掃描式電子顯微鏡觀察其微細結構。結果發現，澱粉與仙草膠混合系統之黏度比單獨仙草膠或澱粉者高。澱粉與仙草膠濃度及澱粉種類均會影響兩者間交互作用之進行，一般而言混合系統之黏彈性質隨膠或澱粉濃度之增加而增加，所成仙草凍皆呈膠體行為，於所測試頻率範圍內，其儲存模量皆高於耗損模量，然過高濃度之仙草膠若無充足澱粉與之作用，反使黏彈性質下降。仙草凍屬剪稀性，其於冪次模式中之黏稠指數隨膠濃度之增加而增加，流動行為指標則隨濃度增加而下降，比較仙草凍之動剪切及穩剪切結果可知，Cox-Merz理論並不適用於仙草凍系統。三種澱粉中，以小麥或玉米澱粉所成仙草凍硬度較佳，樹薯澱粉較差，可能與其直鏈澱粉含量較低有關。當仙草膠濃度提升，所成仙草凍Hunter L、a、b值下降，但是當膠濃度大於0.9%後則趨於平緩。含樹薯澱粉之仙草凍，其亮度遠較含小麥或玉米澱粉者低，然紅色及黃色值之差異則較不明顯。以較低濃度之仙草膠與不同濃度澱粉所形成之仙草凍，其網狀結構較鬆散零亂，隨著仙草膠濃度之增加，可與加熱糊化之澱粉形成較密且均勻之網狀結構。

Effects of gum concentration (0.3 - 1.8%), starch types (wheat, corn and cassava) and concentration (2-4%) on the gelling behavior of Hsian-tsao (Mesona procumbens Hemsl) leaf gum extracted by sodium carbonate solutions were studied. Steady and dynamic shear rheological measurements, rapid visco analysis, texture profile analysis, color as well as microstucture of the starch/gum mixtures were performed during or after a controlled heating and cooling process. It is found that the starch/gum mixture showed higher rheological/textural properties than starch or gum alone at comparable concentration, indicating significant interactions between starch and Hsian-tsao leaf gum. The gel viscosity as determined by rapid visco analysis, storage modulus as determined by dynamic shear measurement, apparent viscosity as determined by steady shear measurement, as well as firmness as determined by texture profile analysis, of the mixed system increased with increasing gum concentration to a certain extent, then leveled off or decreased with higher gum concentration. The critical gum concentration, which provide an optimum interaction with starch, depended on starch types and increased with increasing starch concentration. The mixed systems showed typical biopolymer gel behavior since their tan delta values were found to be less than one or close to one. In addition, the mixed systems exhibited shear thinning behavior since their apparent viscosity decreased with increasing shear rate. A power law model was used to simulate the flow behavior of the mixed systems. The flow behavior index in the power law model was found to decrease, whereas, the consistency index increase with increasing gum concentration in the mixed systems. A comparison between the steady shear and dynamic shear rheological properties of the mixed system showed that Cox-Merz superposition principle was not suitable for the Hsian-tsao gel system. In general, mixed systems containing wheat or corn starch were brighter than the one containing cassava starch, as indicated by the Hunter''s L values. Scanning electron microscopy observation revealed that a denser and ordered network was formed as the amount of starch and gum increased to a certain extent.