甘藷（Ipomoea batatas Lam.）之抗氧化研究

Antioxidant activity of sweet potato (Ipomoea batatas Lam.)

杜維耶(Predner Duvivier)

指導教授 ： 謝寶全

國立屏東科技大學/農學院/熱帶農業暨國際合作系所/博士(2009年)

https://doi.org/10.6346/NPUST.2009.00226

摘要

全世界甘藷塊根的年產量超過133億噸，分別為開發中國家第五及世界第七大宗的主要糧食作物。本研究評估並比較三種不同品系的甘藷（Ipomoea batatas Lam.）:台農57、台農66及台農73之抗氧化活性、酚類及類胡蘿蔔素含量與顏色參數，研究主要探討因子有萃取溶劑、不同甘藷品系、不同甘藷部位、乾燥方式、分離方法、貯存溫度及貯存時間的影響。
結果顯示萃取的溶劑中:以乙醇和乙醚萃取所得的平均總酚含量較高，之後依序為丙酮、甲醇、乙酸乙酯、50%乙醇及去離子水；以DPPH法評估抗氧化活性，結果顯示以甲醇、乙醇及丙酮的萃取物平均抗氧化活性較高，依序為乙醚、乙醇水溶液、乙酸乙酯及去離子水。由於以乙醇萃取具有較高的抗氧化效果且相對於丙酮、乙酸乙酯及甲醇，其毒性較低，因此選為進一步之萃取溶劑。在不同品系間，其多酚含量及抗氧化活性含量依序為台農73＞台農66＞台農57；台農66品系則表現出較高含量之類胡蘿蔔素，而台農57 及台農73中的總胡蘿蔔素含量極低，甘藷皮之抗氧化活性及酚含量均高於果肉的部位。
以冷凍乾燥處理的樣品其抗氧化活性及酚類含量平均高於以空氣乾燥處理的樣品。空氣乾燥法包含有日曬、低溫乾燥（25C）及熱風乾燥 ﹙50ºC及75ºC﹚共5種，結果顯示以DPPH、linoleic acid抗氧化系統﹙AOP﹚和ABTS測定後三種不同品系之甘藷其抗氧化活性均明顯下降。抗氧化活性的下降歸因於總酚及總類黃酮含量的下降。而其中台農73之抗氧化活性，在熱風乾燥過程，抗氧化活性、總酚及總類黃酮含量會隨溫度增加而下降。然而台農57 及台農66的抗氧化活性、總酚及總類黃酮含量會隨著乾燥溫度增加及時間減少而增加。由結果顯示食品在乾燥過程中，抗氧化物質及其活性的變化和品系具有相關性，低溫乾燥法不但費時且製程難以放大，而台農73品系，較適合以乾燥處理。
由於此三種抗氧化分析方法之間缺乏相關性，因此利用決定係數（R2）及變異係數（CV）來探討它們之間的最適配合度；結果顯示，這些方法之間因缺乏足夠的證據來指出哪個方法較佔優勢，因此利用單一抗氧化活性指標（single AOA indicator），也稱作抗氧化相關的期望指標（relative desirability index），來評估DPPH、AOP及ABTS之能力，以克服不同方法間缺乏相關性的問題。台農57品系，經冷凍乾燥後其RDI值最高，日曬乾燥最低，相較於多酚及胡蘿蔔素含量，以胡蘿蔔素含量與RDI值有較高的相關性；而台農66品系，經冷凍乾燥後其RDI值最高，日曬乾燥最低。在低溫與熱風乾燥（50 ºC 及75 ºC）時，台農57 及台農66品系，其RDI值會伴隨乾燥溫度增加而降低；台農73品系，以冷凍乾燥法處理其RDI值最高，其次為75C熱風乾燥、日曬乾燥及50C熱風乾燥，以25 ºC處理的樣品其RDI值最低。於台農66及台農73品系，其多酚含量較胡蘿蔔素含量呈現較高的RDI相關性。不同品系之最適乾燥條件，分別為台農73品系: 75 ºC，24 小時、台農57品系及台農66品系，為 25ºC， 10天。
於台農73品系中含有三種主要的酚類化合物；亦即，兒茶素 （catechin）、芸香素（rutin）及沒食子酸（gallic acid），其在萃取物中的含量依序為268.24 mg/kg、67.06 mg/kg 及 25.56 mg/kg。在甘藷不同部位方面，皮的部份以catechin 及 gallic acid含量較高，rutin含量少於果肉的部份，在台農73中主要的抗氧化活性來源為rutin，依序為catechin及 gallic acid。
在貯存試驗方面，樣品貯存在4℃及室溫下其總酚含量並沒有顯著差異，但抗氧化活性以貯存在4℃較室溫為佳；然而，總酚含量和抗氧化活性，均會隨貯存時間增加而下降；甘藷果肉經貯存在室溫9個月及4 ℃貯存10個月其總酚含量會顯著下降，而甘藷皮經貯存在4℃及室溫，11個月總酚含量；甘藷果肉貯存在室溫，5個月及4 ℃，10個月其抗氧化活性均會顯著下降，而甘藷皮經貯存於4℃，11個月其抗氧化活性會顯著下降。
糊化分析方面，結果顯示三種不同品種的尖峰黏度及最終黏度，分別超過495及335 RVU，且尖峰黏度在80 ℃，5分鐘內，由以上結果顯示，三種不同品種的甘藷其萃取殘留物可以應用在原料需要適度高糊化的凝膠食品或其它食品，由本研究的結果中證明將地瓜萃取後的殘留物製成布丁、餅乾及蛋糕是可行的。

關鍵字

甘藷 ； 抗氧化活性 ； 化學組成 ； 乾燥方法 ； 相對期望指標

並列摘要

Sweet potato production and utilization exceeds 133 million tons of tuberous roots annually in the world. It represents the 5th and 7th staple food crop in developing countries and the world, respectively. This study evaluated and compared three sweet potato (Ipomoea batatas Lam.) cultivars: Tainong 57 (TNG57), Tainong 66 (TNG66), and Tainong 73 (TNG73) on the basis of their antioxidant activity (AOA), phenolic and carotenoid contents, and color parameters. The effects of extracting solvent, genotype, part of the root, drying method, fractionation method, storage temperature, and storage duration were tested.
The results showed that on average, ethanol and diethyl ether (DE) extracts exhibited the highest total phenolic contents, followed in descending order by acetone, methanol, ethyl acetate (EA), aqueous ethanol (1:1 v/v) and distilled de-ionized water (ddH2O) extracts. The highest AOA, as evaluated by 1, 1-diphenyl-2-picrylhydrazyl (DPPH) assay, were observed in methanol, ethanol, and acetone extracts, followed in descending order by DE, aqueous ethanol, and EA, and ddH2O extracts. Due to its high effectiveness and its relative lower toxicity compared to acetone, DE and methanol, ethanol was chosen for further extractions. Among the three cultivars, TNG73 had on average the highest phenolic content and AOA, followed by TNG66 and TNG57. TNG66 exhibited the highest carotenoid content, while TNG57 and TNG73 showed low content of total carotenoids. The skin samples had, on average, a higher AOA and phenolic content than the flesh samples.
Freeze-dried samples had on average higher AOA and phenolic content than the air-dried samples. During the air-drying process, including sun-drying, low temperature air drying (LTD) at 25C, hot air drying (HAD) at 50ºC, and HAD at 75ºC, we observed in the three cultivars significant decreases of the AOA, as evaluated by DPPH, anti-oxidative potency in linoleic acid system model (AOP); and 2,2’-Azino-di-[3-ethylbenzothiazoline-6-sulfonate] (ABTS) assays. The decrease of AOA was attributed to a decrease of total phenolics and total flavonoids. The losses of AOA, total phenolics, and total flavonoids decreased with the increase of the drying temperature and the decrease of the drying time of TNG73 during the air-drying process. However, in TNG57 and TNG66, an increase of the losses of AOA, total phenolics, and total flavonoids during the air-drying process was observed with the increase of the drying temperature associated with a decrease of the drying time. These results indicated that changes in antioxidant components and activities during food drying are genotype-dependant, as the trend of variation was different for the three cultivars. As LTD is time consuming and difficult to scale up, TNG73 was therefore the most suitable for being processed by drying.
Low correlations were observed among the three AOA analytical methods. Therefore, their relative goodness of fit was studied using the coefficients of determination (R2) and variation (CV). Based on the results, there was no sufficient evidence to show that one method was better than another. Thus, a single AOA indicator, referred to as AOA relative desirability index (RDI), was computed from the results of DPPH, AOP, and ABTS assays to overcome the problem of lack of correlation among the analytical methods used. For TNG57, the highest RDI value was observed in freeze-dried samples, while the lowest was observed in those treated by sun-drying. Higher correlation of the RDI was observed with carotenoid than with phenolic contents of TNG57. For TNG66, freeze-dried samples showed the highest RDI, followed by sun-dried ones. In LTD, HAD at 50ºC, and HAD at 75ºC, the RDI decreased with the increase of the drying temperature for both TNG57 and TNG66. For TNG73, the highest RDI was observed in freeze-drying, followed by HAD at 75C, then sun-drying, and then HAD at 50C. The samples dried at 25ºC showed the lowest RDI. Both for TNG66 and TNG73, higher correlation of the RDI was observed with phenolic than carotenoid contents. The best air-drying conditions were at 75ºC for 24 h for TNG73, and at 25C for 10 days for TNG57 and TNG66.
Three major phenolic compounds, namely, catechin, rutin, and gallic acid were identified in TNG73. Catechin (268.24 mg/kg dry matter) was the highest, followed by rutin (67.06 mg/kg dry matter), and then gallic acid (25.56 mg/kg dry matter), respectively. Comparing with the flesh samples, the skin exhibited higher contents of catechin and gallic acid, but had lower content of rutin. Rutin was the major contributor to the AOA of TNG73, followed by catechin, and gallic acid.
In a storage test, the samples stored at room temperature and 4ºC did not show significant difference in the total phenolic content, but the AOA was on average lower at room temperature than at 4ºC. Both the AOA and total phenolics exhibited a general trend of decrease during the storage. The decrease of the total phenolics of the flesh samples was significant after nine-month storage at room temperature and 10 months at 4ºC. For the skin samples, the decrease of total phenolics was significant after 11-month storage both at room temperature and 4ºC. The decrease of the AOA of the flesh samples was significant after five-month storage at room temperature and 10-moonth storage at 4ºC. For the skin samples, the decrease of AOA was significant after 11-month storage both at room temperature and at 4ºC.
Results of a pasting profile analysis showed that the peak and final viscosity of the starches isolated from all three cultivars exceeded 495 and 335 RVU, respectively, with a peak viscosity time shorter than 5 min around 80ºC. These results showed that the solid extraction residue of the three cultivars could be processed as gel foods and other food items that require moderate to high gelatinization ability of the raw material. Sweet potato-based puddings, cookies, and cakes prepared in this study supported our findings of the suitability and usefulness of the starches contained in the residue of sweet potato after extraction of antioxidants.

並列關鍵字

sweet potato ； relative desirability index ； drying methods ； chemical compositions ； antioxidant activity

參考文獻

Huang, D.-J., C.-D. Lin, H.-J. Chen, and Y.-H. Lin (2004) Antioxidant and antiproliferative activities of sweet potato (Ipomea batatas [L.] Lam.) ‘Tainong 57’ contituents. Bot. Bull. Acad. Sinica. 45:179-186.

Afanas, E. V., A. I. Dorozhka, A. V. Brodskii, V. A. Kostyuk, and A. I. Potapovitch (1989) Chelating and free radical scavenging mechanisms of inhibitory action of rutin and quercetin in lipid peroxidation. Biochem. Pharmacol. 38(11):1763-1769.

Ansari, N. M., L. Houlihan, B. Hussain, and A. Pieroni (2005) Antioxidant activity of five vegetables traditionally consumed by South-Asian migrants in Bradford, Yorkshire, UK. Phytother. Res. 19: 907–911.

AOAC (1970) Official methods of analysis of the association of analytical chemists (11th edn.). AOAC, Washington, D.C., USA. pp. 1015 pp.

AOAC (2000) Official methods of analysis of the association of analytical chemists (17th edn.). Association of Analytical Communities, Gaithersburg, MD, USA.