Effect of heating treatments on the antioxidative properties of purple yam

• Main Authors: Ji-Yin Chiou, 邱致穎
• Other Authors: none
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/61329225195238489350

碩士 === 靜宜大學 === 食品營養研究所 === 91 === The purpose of this study was to investigate the effect of different heating treatment on the antioxidant activity of ethanolic extracts of purple yam (D. alata L. var. purpurea). The results showed that 50 % ethanolic extracts of purple yam had the highest antioxidant activity. The lowest antioxidant activity was observed in the 95 % ethanolic extracts of the purple yam. When the solution of purple yam reached to 70 mg/ml, the ethanolic extracts of purple yam showed the similar scavenging power of DPPH（?? diphenyl -β -picrylhydrazyl）radical with BHA（butylated hydroxyanisole）, up to 80 %, under the different heating temperature (70 – 100 ℃). The scavenging power of DPPH radical of ethanolic extracts of purple yam decreased with increasing of heating time (10 - 40 min). The same phenomenon was observed in reducing power of ethanolic extract of purple yam. Comparing with three commercial products ( BHA, ascorbic acid, ?tocopherol ), the ethanolic extracts of purple yam existed relatively high chelating power of ferrous ion. Moreover, the ferrous ion chelating power increased with the increase of heating time in ethanolic extracts of purple yam. Anthocyanin and total phenol of ethanolic extracts of purple yam were decreased with increasing of extracting temperature and time. Comparing the effect of deep-frying and steam-cooking treatments on the antioxidant activity, the ethanolic extracts of purple yam from deep-frying showed the higher scavenging power of DPPH radical and chelating power of ferrous ion than steam-cooking treatment. The reducing power of ethanolic extract of purple yam from both treatment showed decreasing initially then increasing with extent of treatment time. Compare fresh and treatment samples by using above three methods, the higher antioxidant activity than treated samples. This evidence proved that both deep-frying and steam-cooking would decline the antioxidant power of extracts of purple yam. In the comparison of deep-frying and steam-cooking treatment on the phenolic compounds, the results showed that high quercetin content was found in the initial period of treatment. However, the content of quercetin decreased with increasing time, there are no significant change in the content of rutin, narigin and naringenin. The results were demonstrated that higher temperature and shorter time of heating treatment would obtain more antioxidant compounds. Moreover, deep-frying treatment exhibited more antioxidant power than steam-cooking treatment.