紅龍果肉質莖黏液之萃取與物理化學性質分析

Abstract

紅龍果 (Hylocereus spp.) 屬仙人掌科，為臺灣之重要栽培果樹。仙人掌科植物具肉質莖，其皮層中之黏液細胞富含多醣類黏液物質；已知此類黏液物質於食品、製藥及化妝品等工業上具有應用潛力。紅龍果於栽培過程中需定期對肉質莖進行修剪，因此每年均會產生大量之肉質莖廢棄物，迄今尚無有效之利用方法。本研究之目的為探討自紅龍果肉質莖中萃取黏液物質之方法，研究不同萃取條件對其黏液產率之影響，並分析紅龍果肉質莖黏液物質之化學組成與物理性質。將紅龍果肉質莖分成新鮮狀態、真空乾燥粉末及熱風乾燥粉末三種材料進行萃取試驗。黏液物質之萃取流程為將材料與水於高溫下萃取一定時間，利用棉織布過濾後，以7,500 x g離心20分鐘，取其上清液加入3倍體積之95%乙醇在4℃中置放使黏液物質沉澱，再以12,000 x g離心20分鐘，得到之沉澱物以真空冷凍乾燥製成灰白色黏液物質粉末，量測其重量及總醣含量作為萃取效果之指標。隨溫度上升至80℃三種紅龍果肉質莖材料之黏液萃取產率與總醣含量達到最高，溫度高於80℃會使黏液萃取產率與總醣含量減少。新鮮材料與水之比例為1：1時黏液之萃取不完全，比例為1：2時具最佳萃取效率，再提高水對材料之比例則會造成黏液沉澱不完全而使產率減少。熱風乾燥材料與水比例為1：10時同樣會使黏液之萃取不完全，提高比例為1：20時具最佳萃取效率，再提高水對材料之比例則會造成黏液沉澱不完全而使產率減少。真空乾燥材料與水比例為1：10至1：50皆對其萃取產率沒有影響。新鮮材料萃取1小時之萃取效率低，萃取2小時之效率最佳，提高時間至3小時以上會使多醣降解造成產率下降。乾燥材料萃取0.5小時之萃取效率低，提高萃取時間為1至3小時之萃取產率相近。新鮮材料與水之比例為1：3，在80℃萃取3小時，萃取四次之總產率為1.31%，單次之萃取率為總產率之97.8%；乾燥材料與水之比例為1：30，在80℃下萃取1小時；其中，真空乾燥材料萃取四次之總產率為1.56%，單次之萃取率為總產率之89.7%；熱風乾燥材料萃取四次之總產率為1.03%，單次之萃取率為總產率之68.5%。紅龍果肉質莖黏液物質之總醣含量以新鮮材料最高，真空乾燥材料次之，熱風乾燥材料最低，分別為66.9%、55.9%與42.6%；其蛋白質含量亦以新鮮材料最高，真空乾燥材料次之，熱風乾燥材料最低，分別為1.21%、1.15%與0.56%。熱風乾燥材料之黏液物質之灰份含量為28%，其中鈣及鉀之含量分別為5.7%及3.4%，顯著高於新鮮與真空乾燥材料。熱風乾燥材料之黏液物質之膨潤力於30-90℃下皆高於其他兩種材料之黏液物質，表示灰份中無機物質含量可能與黏液之膨潤力有關。熱風乾燥之紅龍果肉質莖黏液物質以三氟乙酸於120℃水解1小時後，利用高效液相層析系統(HPLC-RI)進行分析，分離條件為 (1) 管柱：Shodex Asahipak NH2P-50 4E，移動相：250 mM磷酸/乙腈 (20/80)，管柱溫度：50℃；(2)管柱：Shodex Sugar SP0810，移動相：去離子水，管柱溫度：80℃；由二種分離條件之結果與標準品相互比對，得知熱風乾燥紅龍果肉質莖黏液物質為異質多醣類，其中含有阿拉伯醣、半乳醣、鼠李醣及一未知單醣；半乳醣、阿拉伯醣與鼠李醣之含量分別為乾重之27.2%、15.2%及2.15%。

Pitaya (Hylocereus spp.), belonging to the Cactus family, is an important fruit crop in Taiwan. The succulent stem of Cactus contains mucilage cells which are rich in mucilage. There are reports suggests that cactus mucilage may have potential applications in food, pharmaceutical, and cosmetic industries. Each year, periodical pruning of Pitaya plants resulted in huge amounts of succulent stem left in the field as agricultural waste. Currently, effective ways of utilization of these wastes do not exist. The aim of this research was to study the methods of extraction of mucilage from pitaya succulent stem. To investigate the effects of different extraction conditions on the yield of mucilage, and to analyze the chemical compositions and physical properties of mucilage extracted from pitaya succulent stem. In this study, three forms of Pitaya succulent stems starting material were prepared: fresh stems, vacuum-dried powder and hot-air-dried powder. The general process of mucilage extraction was as follows: Starting material was mixed with water and extracted at high temperature for a given time; after filtration through cheese cloth and centrifuged at 7,500 x g for 20 min, the supernatant was precipitated by adding 3 volumes of 95% ethanol and stored at 4℃.The precipitates was centrifuged at 12,000 x g for 20 min to form pellet, which was freeze-dried to give the final gray-white crude mucilage powder. The final weight (to calculate the yield of extraction) and total sugar content of the powder was used as the efficiency of purification. With the extraction temperature increased to 80℃, the yield of extraction and total sugar contents reached its maximum for all three starting material. Further elevation in the temperature resulted in less yield and lower total sugar content. When the fresh stem to water ratio was 1:1, the extraction was incomplete and when the ratio was 1:2, the best extraction efficiency was obtained. Further increase in the ratio of water to fresh stem would affect the process of mucilage precipitation and lowered the yield. When the hot-air-dried powder to water ratio was 1:10, the extraction was incomplete; when the ratio was 1:20, the best extraction efficiency was obtained. Further increase in the ratio of water to fresh stem would also affect the process of mucilage precipitation and lowered the yield. For vacuum-dried powder, changing the material to water ratio from 1:10 to 1:50 did not affect the yield very much. For fresh stems, extraction for 1 hour was not enough and the best result was obtained by extraction for 2 hours. Increase extraction time to 3 hours or more resulted in degradation of mucilage polysaccharide and hence lower the yield. For fresh stems, when the material to water ratio was 1:3 and extracted at 80℃ for 3 hours, the total yield was 1.31% of fresh weight after 4 cycles of extraction, and the extraction percentage of the first cycle was 97.8%. For hot-air-dried powder, when the material to water ratio was 1:30 and extracted at 80℃ for 1 hours, the total yield was 1.56% of fresh weight after 4 cycles of extraction, and the extraction percentage of the first cycle was 89.7%. For vacuum-dried powder at the same conditions, the total yield was 1.03% of fresh weight after 4 cycles of extraction, and the extraction percentage of the first cycle was 68.5%. The total sugar content of mucilage was highest in mucilage extracted from fresh material, followed by vacuum-dried material, and is lowest in hot-air-dried material, the value were 66.9%, 55.9% and 42.6% respectively. The protein content of mucilage was also highest in mucilage extracted from fresh material, followed by vacuum-dried material, and is lowest in hot-dried material, the value were 1.21%, 1.15% and 0.56% respectively. The ash content of mucilage extracted from hot-air-dried material was 28%, which contain 5.7% calcium and 3.4% potassium. All these value were significantly higher than the mucilage extracted from fresh and vacuum-dried material. The value of mucilage swelling power extracted from hot-air-dried material at 30-90℃ were all higher than other two material extracted mucilage. This phenomenon suggested that there might be a positive correlation between the ash and mineral content and the swelling power of mucilage. Mucilage extracted from hot-air-dried pitaya succulent stem was hydrolyzed for 1 hr. at 120℃ with trifluoroacetic acid (TFA) and analyzed by HPLC-RI system with the following two separation condition: (1) column: Shodex Asahipak NH2P-50 4E, mobile phase: 250 mM phosphoric acid/acetonitrile (20/80), column temperature: 50℃; (2) column: Shodex Sugar SP0810, mobile phase: deionized water, column temperature :80℃. Comparison between the separation results of the two column system and sugar standards showed that the mucilage of hot-air-dried powder was a hetero-polysaccharide and composed of arabinose, galactose, rhamnose and another unknown monosaccharide. The content of arabinose, galactose, rhamnose were 15.2%, 27.2%, and 2.15% d.w. respectively.