本實驗探討新鮮(FS)、冷凍乾燥(FD)與熱風乾燥(HD)對菱角殼其總酚類含量和抗氧化力影響之評估；此抗氧化力測定方法包含DPPH自由基清除能力、還原力與銅離子螯合力，且與抗氧化劑α-tocopherol和BHT之抗氧化力進行比較。實驗結果顯示，經甲醇萃取後之菱角殼的總酚含量為5.21-8.59g GAE/100g，其中以FS萃取物具有最高總酚含量為8.59g GAE/100g。由前述結果發現菱角殼萃取物之抗氧化效力與其濃度具有高度相關性。本實驗劑量反應顯示在達到閾值之前，DPPH自由基清除能力與甲醇萃取物濃度具有正相關性。當FS萃取物的濃度在0.2mg/mL時，DPPH自由基清除能力可達79.3%，相較於其他組別的劑量，HD 為1.5mg/mL，FD為1.8mg/mL和BHT為1.3mg/mL；其他抗氧化力測定方面，在濃度0-1.0mg/mL時，FS萃取物的還原力相較於HD和FD萃取物與BHT和α-tocopherol具有顯著性的效果；在濃度2.0mg/mL時達到閾值；三種菱角殼甲醇萃取物之螯合力，最高為28%。FS萃取物之K值和總酚類物質含量較高，但IC50值較低於其他組別。由結果得知新鮮菱角殼(FS)萃取物相較於BHT於食品應用上具有重要的抗氧化特性。

This study was conducted to compare the total phenolics content and antioxidant activity of extracts from fresh (FS), freeze-dried (FD) and hot air-dried (HD) water caltrop hulls. The antioxidant properties, including 2,2-diphenyl-1-picrylhydrazyl (DPPH) free-radical scavenging activity, reducing power, and cupric ion chelating ability were evaluated along with alpha-tocopherol and butylated hydroxytoluene (BHT) in this study. The results showed that total phenolics content of methanolic extracts ranged from 5.21-8.59 g GAE/100 g, and the extracts of FS exhibited a substantial total phenolics content (8.59 g GAE/100 g) compared with other dried samples. It was found that the antioxidative effect of water caltrop hulls was strongly concentration dependent. The dose response study indicated that before reaching a threshold level, there was a positive correlation between DPPH free-radical scavenging ability and concentration of methanolic extracts. At the point where the scavenging ability of DPPH free-radical was 79.3%, the dose of the methanolic extracts was 0.2 mg/mL for FS, 1.5 mg/mL for HD, 1.8 mg/mL for FD, and 1.3 mg/mL for BHT. The chelating ability of three different water caltrop hull extracts reached a threshold level of only 28% at a dose of 2 mg/mL. The total phenolics contents were higher, but IC50 was lower in FS extracts than in other antioxidants. Compared with other treatments with antioxidants, the reducing power of FS extracts was found to be significantly more pronounced than that of HD and FD extracts, BHT and ct-tocopherol, at dose ranges of 0-1.0 mg/mL. This finding demonstrated that FS extracts is comparable to BHT in terms of its antioxidant properties in food application.