Effects of Processing on Antioxidative Properties, Stability of Storage Protein Dioscorin and Quality of Various Yam Cultivars

• Main Authors: Yu-Min Liu, 劉育銘
• Other Authors: Kuo-Wei Lin
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/51580965142274202905

碩士 === 靜宜大學 === 食品營養研究所 === 93 === The total phenol content, antioxidative ability, and the concentration and stability of storage protein dioscorin among different cultivars of Chinese yams followed by various processing treatments were investigated. In addition, the quality of deep-fat fried yam chips during storage was evaluated. Carbohydrates comprised the primary component of all yam cultivars (dry-weight basis). Total phenolic compounds content and DPPH free radical scavenging effect were the highest in Mingchien (MC) and the lowest in Keelung (KL) yam. Following processing, freeze-dried yams of all varieties showed the least decrease in total phenolic compounds and the DPPH radical scavenging effect, while boiling caused the greatest decrease in both. Fraction numbers of dioscorin following purification and gel filtration fell in the range of 15-45, with molecular weight of 32 kDa. Isoelectric point (pI) of dioscorin revealed five distinctive bands with pI of 6.47, 6.34, 4.71, 4.62, and 4.53, respectively. Fresh yams of all varieties contained the highest dioscorin contents comparing with their counterparts. Boiling and deep-fat frying caused severe protein denaturation resulting in loss of dioscorin after purification. Freeze-drying resulted in increase in protein surface hydrophobicity (So); nonetheless, it better attained total phenol content, antioxidative capacity and dioscorin stability of yams comparing with other processing treatments. Moisture content and water activity of deep-fat fried yam chips of all cultivars arose, and the Hunter L, a, b values declined with storage time. The peroxide values of all yam chips increased during the initial stage, then declined with advanced storage. Fracturability of all yam chips decreased, due to the absorption of moisture, with increasing storage time.