不同品種甘薯葉乙醇萃取物抗氧化及改善葡萄糖攝入之研究

Abstract

農產品及蔬果中所含之植物化學物質 (phytochemical)，如花青素、類胡蘿蔔素、類黃酮或酚類化合物 (polyphenols)，具有很強的抗氧化能力，可以降低慢性疾病的發生機率，例如心血管疾病、糖尿病、癌症等。甘薯葉富含花青素及多酚類，可被廣泛利用及開發成各種商品。 本研究主要以三個品種的甘薯葉為原材料，針對其冷凍乾燥或40 ℃ 乾燥處理後之 70 % 乙醇萃取物的抗氧化特性加以探討。所用甘薯葉品種包括亞蔬 CN 1927-16、台農64 號及CYY 98-59。抗氧化功能測定包括螯合亞鐵離子、清除 DPPH 自由基與總抗氧化能力。之後再以小鼠肝臟上皮 FL83B 細胞進行細胞毒性 (cell viability) 測試，以確定其安全使用劑量。同時，利用 TNF-α 誘導小鼠肝臟上皮細胞產生胰島素阻抗模式，並以不同品種之甘薯葉萃取物處理前述細胞；評估其對提升葡萄糖攝入能力及改善醣類代謝之效果。 研究結果顯示，總酚含量以台農 64 號 (380.59 mg GAE/g DW)以及 CYY 98-59 (603.09 mg GAE/g DW) 兩個品種的凍乾處理組較高。而在總黃酮類和總花青素類的結果也和總酚含量的測定相近，分別以台農 64 號 (0.30 g 總黃酮類/g DW；0.25 g 總花青素/g DW)以及 CYY 98-59 (0.22 g 總黃酮類/g DW；0.18 g總花青素/g DW) 兩個品種的凍乾處理組較高。在抗氧化特性部份，具有螯合亞鐵離子能力效果最佳的為 CYY 98-59 的40 ℃ 乾燥處理後之 70 % 乙醇萃取物 (EC 50值為3.98 mg/ml)；而台農64 號以及CYY 98-59 兩個品種對DPPH 自由基具有較強的清除活性，EC 50值分別為 4.02 mg/ml 以及4.11 mg/ml。在總抗氧化能力測定的方面，也以台農64 號以及CYY 98-59 兩個品種的凍乾處理組最佳，EC 50值為 7.64 mg/ml 以及8.72 mg/ml。 由細胞試驗結果發現，三種品種甘薯葉之70 % 乙醇萃取物在濃度1 mg/ml 之內對小鼠肝臟上皮細胞均無毒性。胰島素阻抗細胞模式之葡萄糖攝入能力試驗，結果顯示，處理濃度 1 mg/ml 時 ，台農64之40℃乾燥處理組效果最好，與控制組 (TNF-α 處理) 比較可增加 57.72 % 的葡萄糖攝入能力；其次為CYY 98-59 之凍乾處理組及亞蔬 1927-16 之凍乾處理組，分別提升了 46.25 % 和 43.84 %。之後探討不同品種之甘薯葉萃取物對TNF-α 誘導小鼠肝臟上皮細胞之胰島素訊息傳遞蛋白質及葡萄糖轉運蛋白表現量的影響。結果顯示，FL83B 細胞經 20 ng/ml TNF-α 誘導後其 IR、IRS-1 及 GLUT-2 之表現量與正控制組比較之下量並無顯著差異，其明確機轉有待探討。 綜合上述結果，甘薯葉具有抗氧化力將可提供保健食品原料業者之新選擇，並開發出符合市場需求並具保健功效之新產品，藉以提升甘薯葉加工利用多元性，增加甘薯葉之附加價值，提高農民的收益。

Sweet potato leaves have been consumed as a fresh vegetable in many parts of the world. They are rich in vitamin B complex, β-carotene, iron, calcium, zinc, and protein. Recent experiments revealed that sweet potato leaves contain high contents of polyphenolics, namely anthocyanins and phenolic acids, compared with commercial vegetables. This study was aimed to evaluate the antioxidation activities and alleviation of insulin resistance of 70 % ethanol extract of leaves of 3 sweet potato cultivars, TN 64, CYY 98-59 and CN1927. Sweet potato leaves were separated into 2 groups, lyophilized and 40 ℃ air-dried. Afterthat, they were extracted with 70 % ethanol at 25 oC. The antioxidation activities tests include total phenolics assay, α,α-diphenyl- β-picrylhydrazyl (DPPH) scavenging ability, ferrous ion chelating ability and scavenging ability on long-life radical anion ABTS˙+ were performed. The in vitro anti-hyperglycemic activity of the extracts was investigated using glucose uptake test in FL83B mouse hepatocytes. The fluorescent dye 2-(N-(7-nitrobenz-2-oxa-1, 3-diazol-4-yl) amino)-2-deoxyglucose was used to estimate the uptake ability of the cells. The total phenolics of the extracts was determined spectrophotometrically according to the Folin Ciocalteau procedure and ranged from 198.49 to 603.09 mg GAE/g DW. For total flavonoids and total anthocyanins, the values were in the descending order: 0.30 > 0.22 > 0.20 > 0.05 > 0.03 > 0.01 g/g DW which were found in TN 64 > CYY 98-59 > CN 1927-16, respectively. With regard to the results of antioxidation activities of ethanol extracts from leaves of different sweet potato cultivars, the antioxidation activities of lyophilized of 70 % ethanol extract CYY 98-59 and TN 64 were significantly higher than Trolox in ABTS˙+ radical-scavenging activity (p < 0.05), EC 50 values were 8.72 mg/ml and 7.64 mg/ml respectively. The evaluation of ability to chelate ferrous ion showed that 40 ℃ air-drying of 70 % ethanol extract of CYY 98-59 had lower EC 50 value (3.98 mg/ml), on the other hand, lyophilized of 70 % ethanol extract CYY 98-59 and TN 64 had higher scavenging activity on DPPH free radical with EC 50 values at 4.11 mg/ml and 4.02 mg/ml respectively. The cell viability test showed that the ethanol extracts from leaves of different sweet potato cultivars have no cell toxicity in concentration of 1 mg/ml. Results of the glucose uptake test in the insulin resistance cell model indicated that the highest improvement can be achieved by the 40 ℃ air-dried of ethanol extract TN 64 in PBS buffer. Compared with the control group (TNF-α treated group), the ethanol extract could increase the glucose uptake ability by 57.72 %. Next is the lyophilized 70 % ethanol extract of CYY 98-59 and CN 1927-16, the percentage increase of the glucose uptake were 46.25 % and 43.84 % respectively. However, the results did not show that ethanol extracts from leaves of different sweet potato cultivars promote the expressions of insulin receptor substrate-1 (IRS-1), insulin receptor and glucose transporter-2 (GLUT-2). In conclusion, 70 % ethanol extract from sweet potato leaves has potential on physiologic effects as antioxidation and anti-hyperglycemic agents.