UV-B對採收後土肉桂葉子黃酮類化合物含量之影響

Abstract

土肉桂（Cinnamomum osmophloeum Kaneh.）為臺灣重要之經濟樹種，其葉子之黃酮類化合物具有抗氧化、抗發炎、人類乳癌腫瘤細胞毒殺及降低血糖等生物活性。本研究以UV-B照射採收後之土肉桂葉子，探討UV-B照射能量、照射持續時間及照射環境溫度等不同條件，對其黃酮類化合物含量之影響，並進一步分析不同照射條件對抽出物抗氧化能力之影響。結果顯示，土肉桂葉子以UV-B照射能量3.68 Wm-2、照射持續時間6 h及照射溫度25℃為最佳處理條件，能使乙醇抽出物中主要10種Kaempferol醣苷之總含量由62.89 ± 2.04 mg/g（94.48 ± 3.14 μmol/g）增加至78.09 ± 2.29 mg/g（116.22 ± 3.51 μmol/g），並且能增加抽出物抑制脂質過氧化之能力，其中含量增加較多者為經過2次醯基化且UV-B吸收能力較強之化合物7 – 10（平均增加5.7倍）。因此，土肉桂受到UV-B照射後，葉子能藉由增加黃酮類化合物來抑制脂質細胞膜損傷，並且藉由醯基化之黃酮類化合物吸收UV-B能量，降低植物受UV-B照射之影響。 此外，本研究亦探討土肉桂葉齡對UV-B照射促進其黃酮類化合物生合成之影響，尋找最適合採收之時期。結果顯示葉子抽芽後8 – 9 w為UV-B照射提升黃酮類化合物含量效率最佳之採收葉齡，照射後每片葉子之乙醇抽出物能得到3.47 ± 0.05 mg of RE及0.70 ± 0.05 mg of QE。綜合不同照射條件之結果，本研究利用多元迴歸模型，以3種UV-B照射變因（照射能量、照射時間及照射溫度）設計出總黃酮類化合物含量增幅之預測模型，供未來土肉桂葉子UV-B處理上，能同時選擇對其適合之條件，亦能達到有效提高黃酮類化合物產量之目的，增加土肉桂葉子的醫療保健及經濟價值，更能提供其他樹種利用之參考。

Cinnamomum osmophloeum Kaneh. is an important indigenous tree species in Taiwan. Flavonoids in leaves of C. osmophloeum were proved to have antioxidant activity, anti-inflammatory activity, cytotoxic activity against human breast adenocarcinoma cell, and hypoglycemic effect. In this study, we treated leaf of C. osmophloeum with UV-B irradiation in various conditions about irradiation intensity, irradiation time, and irradiation temperature after harvest, and discussed the changes of flavonoids contents. In addition, the influence of UV-B irradiation on the antioxidant activity of leaf extract was also examined. As a result, UV-B irradiation at 25℃ at an intensity of 3.68 Wm-2 for 6 h was the best post-treatment for mature leaf of C. osmophloeum, which resulted in an increase in the total contents of 10 major flavonoids in ethanolic extract from 62.89 ± 2.04 mg/g (94.48 ± 3.14 μmol/g) to 78.09 ± 2.29 mg/g (116.22 ± 3.51 μmol/g), of which acylated flavonol glycosides 7 – 10 were increased the most average about 5.7-fold. Furthermore, the lipid peroxidation inhibition of leaf extract was also enhanced by UV-B irradiation. Therefore, when C. osmophloeum leaf was irradiated with UV-B, the lipid peroxidation inhibition was enhanced to avoid the damage of cell membrane. At the same time, the contents of acylated flavonol glycosides were increased to absorb the intensity of UV-B irradiation. In addition, the influence of leaf age of C. osmophloeum on induced flavonoid biosynthesis by UV-B was also discussed to find the best harvest time. The results showed that 8 – 9 w after sprouting was the best harvest time which was the most efficiency to gain the flavonoids by using UV-B as the post-treatment, and each leaf can gain 3.47 ± 0.05 mg of RE and 0.70 ± 0.05 mg of QE after UV-B irradiation. According to the results of different irradiation conditions, we constructed a multiple regression model to calculate the increment of total flavonoid contents from independent variables of three UV-B treatments (intensity, time, and temperature). This model can be used to forecast the increment of total flavonoid contents in leaf of C. osmophloeum with the different conditions of UV-B treatments, and helps to find the more efficient UV-B treatments in different cases to increase flavonoids. This forecast model may supply a well instance for the other tree species in the future.